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350 Uneven Cranking, Won't Stay Running After Break In

1929 Views 32 Replies 9 Participants Last post by  evilWS6
Before I start rambling..
Rebuild specs:

350 4 bolt main bored .030 over
10:1 CR
Stock Cast Crank turned .010
SCAT Forged 5.7" I-beam Rods
Sealed Power Flat Top Pistons w/ 4 valve reliefs
Vortec 906 Iron Heads
.016 Steel Shim Head Gaskets
Jones Cam's Hydraulic Flat Tappet: 110LSA 224/232 @ .050, .501"/.504" with 1.52 rockers
Cloyes Heavy Duty Double Roller Timing Set (set to advanced keyway while degreeing cam)
Melling 10552 HV Oil Pump
Holley 4160 600cfm Vac. Secondary Carb
Edelbrock Performer RPM Vortec Intake
Stock GM HEI Distributor
NGK TR55 Plugs
Factory replacement Taylor wires
High Torque Mini Starter
Rotating assembly was balanced during rebuild

Well fellas, I'm currently stumped. I just recently rebuilt my 350, and broke it in a few days ago.. used PennGrade break in oil. Break in went pretty well.. I set distributor in at 14* before starting it. It started right up, bounced around a little for a few seconds, then smoothed out as I raised the RPM's. I varied the engine speed between 2000-2500 for 20 minutes. After 20 minutes, I started to back the engine speed down. I eventually got to the point where I could no longer unscrew my curb idle screw any further. I snapped the throttle a few times, but it didn't come down. I pushed the throttle lever forward a little to make sure it wasn't the cable, when suddenly the idle dropped, I heard a clack, and it shut off. I started it again, heard clacking, and shut it right off. After removing the valve covers, I found that my #3, 5, and 6 intake rockers were loose. They weren't making a single sound until I pushed the throttle blade forward and the car died. I started turning the engine over by hand to readjust these valves.

I turned the engine over by hand while watching the corresponding cylinder's exhaust valve. Once the exhaust valve started to open, I adjusted the intake valve, and gave it 1/2 turn past zero lash. I did this for all 3 that loosened up. Then, like a complete idiot, I forgot to take the breaker bar and socket off of the crank pulley, and blipped the ignition. I heard the breaker bar rotate clockwise, hit my frame rail, and then fall to the ground. I went and double checked that the crank bolt didn't loosen up, shook my head at myself and then started the car up. It was running terribly. The engine was bouncing and running very rough, and it wouldn't stay running unless I held the throttle open. The second I let go, it would die. Now I noticed that while cranking, it was "galloping" rather than a steady crank. You could hear it crank fast, then slow, fast, then slow. Before adjusting the timing, I marked the distributor cap location so I could go back to my starting point. I tried advancing it further - didn't help. Tried retarding it a bit, didn't help. Eventually I got it to where it would at least stay running well enough that I could pull it in the garage. Out of curiosity, I checked where the timing was at this point, and it was somewhere near the 30's at idle with the vacuum advance plugged! I retarded the timing, and it shut off. Lined up with my original reference mark on the distributor cap, it wouldn't stay running again. Before taking a break, I pulled my plugs - they were black, sooty and fouled. Smelled like gas.

Today I went back to the garage and swapped another working carb onto the engine. I installed brand new plugs, and relashed every single valve. I jiggled the pushrod up and down until I felt zero play, and this time, I gave them each 1/4 turn. Rotated the engine until I saw the exhaust valve open, and fully close - right on TDC on my timing tape. Rotated it one more revolution to TDC. Adjusted my distributor to line the #1 terminal up with the rotor, as close as I could get it. Turned the key, it fired up and died. Held the throttle open a little, turned the key again, and it's struggling to start. Keeps firing off but dying. I tried adjusting the timing a little, but once again it didn't help much. Try giving it more throttle, backfires out the carb. It still has that "gallop" present while cranking. I checked my plug wires numerous times, and aside from them currently being a little messy and strung about, they are in the right positions. Verified that I have 12.4 volts at the ignition wire at the distributor, and 10.4 volts while cranking. I removed the distributor cap, and it was spotless inside. No signs of arcing. I couldn't find any noticeable rips or tears in my wires either. I cranked it again with the ignition disabled, and it sounded exactly the same.

I am completely stumped at this point. I keep asking myself if I wiped the cam, but it made it entirely through break in with zero issues, and no valve noise until the RPM's dropped and it died out. I was hoping my initial valve adjustment wasn't consistent, and maybe those few were just a little loose. But why didn't they make any noise until the engine died out when I closed the carb? The other thing I'm wondering is.. when I hit the ingition with the breaker bar still on the crank bolt, did it hit the frame and jump timing? The bolt didn't loosen, so either it fell right off, or something else had to give. I double checked my timing chain slack, and it only moves 2 degrees before turning the rotor if I turn it counter clockwise.

At this point, the only things I haven't really checked are my ignition coil, ignition module, and my timing set. I've also yet to drain the oil to check for metal particles. Either way, it sounds like the valve event timing and ignition timing is not occurring when it should, or something happened with my compression. I'm not sure, this is my 3rd engine rebuild and I am stumped and defeated at this point. Any help would be greatly appreciated, and if you read ALL of that, thank you - lol!

Here are 2 videos. The first shows what it currently sounds like while cranking, and the second is after 20 minutes of break in when I started to back the idle down. You can hear that it's running nice and smooth during this time.



Cam card:



Any guidance is much appreciated. Thank you
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30 degrees of advance without vacuum connected seems like a lot for this cam.

Clacking noise isn’t good, one has to wonder why rockers came loose. Choices could be the nut wasn’t locked down, pistons hit open valves, Vortec heads weren't clearance enough for the valve lift colliding retainer to guide seal or guide itself, lobes and or lifters going away.

Up and down idle can be a carb or ignition timing issue.

Black fouled plugs is usually a fueling issue of too much but backfiring through the intake is mostly a sign of a lean mixture, then again not getting to operated temp snd staying there a while can cause this as well.

You said the cam is advanced if so by how much?

A Holley 600 vac secondary Holley is going to want a lot of throttle opening to get enough air to idle, this is going to get into the transition circuit so it will be running along with the idle circuit which is going to mess up the idle and transition to main metering in fact the open throttles might also trigger the mains making for an extremely rich idle.

Lots of things to check out unfortunately.

Bogie
 

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Sounds like you covered the basics. Assuming it's mechanical sound, Next, put a timing light on every wire and make sure it's firing on all those. If you have headers you can spit on the primary tubes and note if any are colder than the others. A spray bottle or similar works as well. Your very next step is a leak down test. A compression test is okay at this point, a leak down would be better. The next thing I'd look at is the dist gear roll pin and ensure it didn't shear.
 

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Are the heads machined for screw in rockers? That cam is too big for press fit rocker arms studs and will pull those out by the pressure on the pushrods. Are the springs beehive? Beehive springs help vortec heads. check for bent valves, bent pushrods, and bent connecting rods, check for marks on piston tops, Check valve to piston clearance, check valve tubes clearance and valve seal at the seat or leak down test. The engine likes too much advance i wonder why? The holley needs modified with a new circuit created with a calibrated jet size installed as a transitional circuit that basically isn't there from factory. Hardened oil pump driveshaft?
 

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Discussion Starter · #6 ·
what brand lifters?
check compression on a few cylinders.
Johnson lifters. Gotta buy a compression tester, I'm long overdue.

30 degrees of advance without vacuum connected seems like a lot for this cam.

Clacking noise isn’t good, one has to wonder why rockers came loose. Choices could be the nut wasn’t locked down, pistons hit open valves, Vortec heads weren't clearance enough for the valve lift colliding retainer to guide seal or guide itself, lobes and or lifters going away.

Up and down idle can be a carb or ignition timing issue.

Black fouled plugs is usually a fueling issue of too much but backfiring through the intake is mostly a sign of a lean mixture, then again not getting to operated temp snd staying there a while can cause this as well.

You said the cam is advanced if so by how much?

A Holley 600 vac secondary Holley is going to want a lot of throttle opening to get enough air to idle, this is going to get into the transition circuit so it will be running along with the idle circuit which is going to mess up the idle and transition to main metering in fact the open throttles might also trigger the mains making for an extremely rich idle.

Lots of things to check out unfortunately.

Bogie
Hey Bogie. Yeah, I was surprised to see that after fiddling with the distributor just to get it to stay idling, that it was around 30 degrees initial.

I was hoping that those 3 valves loosened up from not being locked down, but I did the EOIC method while the engine was on the stand, turned them about 1/4 turn, tightened the poly locks, and gave them another 1/4 turn. I wish it were that easy, but I somehow doubt it unfortunately. The Vortec heads are stock. I installed Comp Cams 787-16 retainers with LS6 springs, which were supposed to provide enough valve guide to retainer clearance. I don't have my build sheet here with me, but I remember having quite a bit of piston to valve clearance at max lift.

I swapped to another carb to hopefully rule out a carb issue, but it's pretty much the same and won't run. It's the same fuel pump that's been on the car for years, and I don't have a fuel pressure gauge. The only things I haven't checked ignition wise are the coil and module, which I replaced a year ago.

I rebuilt this engine twice in the last year, because I thought I wiped the last cam. It would run and idle well, could even drive it around. But if I got on it, it would backfire through the carb. Come to think of it, one of the rockers kept loosening up on me then too. Thought it was because I wiped the cam. Now that I'm on another cam and the issues seem to be the same but worse, I'm questioning the heads now. Maybe I didn't even actually wipe that last cam. That setup was loading up my plugs at idle as well.

I currently have a Holley 670 double pumper on it, but like i said, can't get it running, so.. not sure if it's better. What carb would you recommend for this setup?

It's just really strange that break in went fine, no noises during break in or while lowering the idle, and then suddenly clacking. I'm really questioning this top end now.

Sounds like you covered the basics. Assuming it's mechanical sound, Next, put a timing light on every wire and make sure it's firing on all those. If you have headers you can spit on the primary tubes and note if any are colder than the others. A spray bottle or similar works as well. Your very next step is a leak down test. A compression test is okay at this point, a leak down would be better. The next thing I'd look at is the dist gear roll pin and ensure it didn't shear.
Good idea on the timing light. I was considering throwing a spark tester on each of them too. I'll have to (finally) buy a compression tester. A leak down tester would be good to have too. I was questioning the distributor itself as well. It's been in the car for 20+ years. Worked just fine before the rebuild though.
 

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Discussion Starter · #7 ·
Are the heads machined for screw in rockers? That cam is too big for press fit rocker arms studs and will pull those out by the pressure on the pushrods. Are the springs beehive? Beehive springs help vortec heads. check for bent valves, bent pushrods, and bent connecting rods, check for marks on piston tops, Check valve to piston clearance, check valve tubes clearance and valve seal at the seat or leak down test. The engine likes too much advance i wonder why? The holley needs modified with a new circuit created with a calibrated jet size installed as a transitional circuit that basically isn't there from factory. Hardened oil pump driveshaft?
They are completely stock Vortec heads with comp cams 787-16 retainers (supposed to provide ample valve guide to retainer clearance) and LS6 beehive springs. Still has press in studs. Matter of fact, I should lay a straight edge across the top of them and make sure they didn't start to come out. I was told they'd be fine, but.. who knows. As I said above, I checked piston to valve clearance while the engine was on the stand, using lightweight checking springs and a dial indicator. Got each valve to max lift, zeroed the indicator and pressed the valve down until it hit the piston. I don't have the number on hand but I remember it being plenty. Yes, matching hardened oil pump driveshaft. What carb do you recommend for this setup?

Checking for bent pushrods is easy enough, as well as marks on the pistons.. would just need an inspection camera. Bent rods and valves on the other hand, not as easy I would guess. Would have to take them out, correct?
 

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They won't be fine sorry to say it. They pull out with any camshaft over .450" lift. You have .510" lift. You need to press them back in and pin em or tack freakin weld them in so they won't pull out. Or you can get the tool that lets you shave the bosses down and drill and tap them for screw in studs yourself or with help from someone that knows how to do them correctly so they don't get messed up. You have done some great work and its looking good you shall get all this worked out don't worry. The 670 holley should work awesome. i always recommend modifying the Holley for part throttle cruise and fuel economy and tuning the carb for Wide Open Throttle. There is a great video on this on you tube by: Unity Motorsports Garage. This explains the idle and part throttle circuit and additional jet that should be added in to complete a holley carburetor's functionality.
 

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Discussion Starter · #9 ·
They won't be fine sorry to say it. They pull out with any camshaft over .450" lift. You have .510" lift. You need to press them back in and pin em or tack freakin weld them in so they won't pull out. Or you can get the tool that lets you shave the bosses down and drill and tap them for screw in studs yourself or with help from someone that knows how to do them correctly so they don't get messed up. You have done some great work and its looking good you shall get all this worked out don't worry. The 670 holley should work awesome. i always recommend modifying the Holley for part throttle cruise and fuel economy and tuning the carb for Wide Open Throttle. There is a great video on this on you tube by: Unity Motorsports Garage. This explains the idle and part throttle circuit and additional jet that should be added in to complete a holley carburetor's functionality.
You have no idea how much I needed to hear that LOL! I am exhausted over this engine.

I have a compression and leak down tester on the way. We'll see. Maybe I should've just bought a nice pair of heads instead of going with junkyard Vortec's. At this point, as long as my bottom end and block are fine, I'll be happy.. If I need to pull the engine again, I'm screwed. I need to move this car ASAP!

Thanks for the tip on the carb. I'm eyeing a Holley carb tuning book.

What causes a bent valve? Contact with the piston/overheating?
 

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I have had Comp lifters that had to be adjusted to zero preload to keep from holding the valves open, not had the issue with Johnson.
when you have the valve cover off see if the oil is sparkly, or drain it and check with a magnet. the studs will be at different heights if they are being pulled out. anything over about 330 pounds over the nose can be a problem for press in studs. are you sure you don't have a big vacuum leak?
 

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Discussion Starter · #11 ·
I have had Comp lifters that had to be adjusted to zero preload to keep from holding the valves open, not had the issue with Johnson.
when you have the valve cover off see if the oil is sparkly, or drain it and check with a magnet. the studs will be at different heights if they are being pulled out. anything over about 330 pounds over the nose can be a problem for press in studs. are you sure you don't have a big vacuum leak?
I had the lifters adjusted to zero lash plus half a turn on the engine stand. That’s how they were when I broke it in, before this problem started.. so I think something else is going on here. It’s obviously completely possible I wiped this cam too, but I don’t think that’s the case for some reason. I’ll have to take a closer look at the oil.

As for a vacuum leak, I think the only thing it could be at this point would be the intake manifold. The only vacuum lines running to the carb are: brake booster at rear of carb, pcv at front of carb, trans vacuum modulator at front of carb, and distributor vacuum advance on the side ported vacuum. Everything is hooked up tight. If I could actually get it to stay running I would check each hose and spray some carb cleaner around everything to double check. I’m not sure where else one could be, especially one that got significantly worse after the break in procedure was finished.
 

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I had the lifters adjusted to zero lash plus half a turn on the engine stand. That’s how they were when I broke it in, before this problem started.. so I think something else is going on here. It’s obviously completely possible I wiped this cam too, but I don’t think that’s the case for some reason. I’ll have to take a closer look at the oil.

As for a vacuum leak, I think the only thing it could be at this point would be the intake manifold. The only vacuum lines running to the carb are: brake booster at rear of carb, pcv at front of carb, trans vacuum modulator at front of carb, and distributor vacuum advance on the side ported vacuum. Everything is hooked up tight. If I could actually get it to stay running I would check each hose and spray some carb cleaner around everything to double check. I’m not sure where else one could be, especially one that got significantly worse after the break in procedure was finished.
if you check compression and it's low, adjust the valves to zero preload, or even a few thousandths lash. if it's still low, back the valves off and put Aire pressure in the cylinder and see where it's going. if a valve stuck in the guide it might tag the piston and be bent but that is not a common event for an engine not under load.
 

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Did you cut open your oil filter ? Did look at the break in oil in the sunlight ? Did you use a moly paste on the cam lobes & lifters ? Did you put a straightedge across the tops of the rocker studs ? Did you check the lobe lift with a dial indicator ?
 

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Discussion Starter · #15 ·
if you check compression and it's low, adjust the valves to zero preload, or even a few thousandths lash. if it's still low, back the valves off and put Aire pressure in the cylinder and see where it's going. if a valve stuck in the guide it might tag the piston and be bent but that is not a common event for an engine not under load.
Will do. I have a compression tester and leakdown tester on the way. Should be here in a couple days.

Did you cut open your oil filter ? Did look at the break in oil in the sunlight ? Did you use a moly paste on the cam lobes & lifters ? Did you put a straightedge across the tops of the rocker studs ? Did you check the lobe lift with a dial indicator ?
I did not drain the break in oil or cut open the filter yet. I used Penngrade green assembly lube on the cam and lifters as instructed by the cam grinder. I will check the studs. I did not check the lift yet.

For checking the lift, do I position the dial indicator tip on the rocker, above the pushrod?

This is terrible news. I hope you get ot sorted.
Me too! Thank you.

Also, for anyone wondering, this is the cam card:



While degreeing the cam, I had it on the zero keyway, and the valve events were a few degrees off. I switched to the advanced (triangle) keyway, and they were on the money. I kept it on that keyway.
 

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So I just went out to the garage to check a couple things. Distributor cap, rotor, and coil all look/tested fine. I was rotating the engine by hand to make sure the distributor was lined up properly, and I noticed something...

I was cranking it over by hand with the distributor cap and the valve covers off, watching the rotor and the rockers. I had all the spark plugs in. It was (of course) a bit more difficult to turn. I was able to hear the air hiss as I rotated the crank - building compression I assume? Sounded like it was in the crankcase. Then I got to a point in the rotation where the engine turned much more easily, and I heard no air. I kept rotating it around, same thing happened every time right around the same spot - near the #3 firing position when looking at the rotor. I then observed the #5 rockers at this time - exhaust opened, closed, then intake open and closed during this area of "easier rotation." What's interesting is that the rockers that loosened up for #3, #6, and #5. All of which are in succession in the 18436572 firing order. I wonder what could have happened that affected all 3, one after the other.

Anyway, if the air/hiss sound is in fact just compression being built while I turn the engine, there is definitely an area where compression isn't being built. I guess I'll confirm with the testers when I get them.
 

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Hopefully after you find out your issue soon. As far as you wanting to know will your carbs work, the answer is yes to both of them but they both would need to be modified in order to get the proper tune on the idle circuit and adjusted to your camshaft. The 650 double pumper would be on the way richer side as it is out of the box. The primary metering block has a .031 to .033 idle feed restrictor size and the rear metering block has around a .039 idle feed restrictor size. This was on a Holley 4777-7 stamped on the main body.

On the number after the dash mark for example the -7, the higher the number after that the more newer the carb is as Holley makes tweaks to there carbs over time and 90 percent of the time is very minor. The 650 double pumper out of the box is setup for more racy motors and big cams and may or may not be too rich for your engine starting off wise but is in the starting ball field but it will still have to be tweaked some to get best possible tune you can get.

The Holley 600 vacuum secondary is a lot leaner out of the box and for mild engines with small camshafts and near stock or rv cam type of deals. Once you get into anything a lot more aggressive after that with cams around [email protected] duration and lower vacuum readings of 17 inches or less then it will always be too lean and will make you end up having the primary idle set open way too much to get a usable idle and too much opening on the transfer slot and cause your idle mixture screw to either not work well or not work at all.

The 600 vacuum secondary comes with .028 idle feed restrictor size in the primary metering block and the secondary metering plate has a .031 idle feed restrictor size. You would have to replace the secondary metering plate with a metering block. It would have to be changed I guarantee it as I use that exact carb on my build and I modified mine to work with whatever I throw it at on my small block builds.

Before you would go going to do these mods I will recommend that you get a Holley tuning book I listed below. It gives great detail on the different circuits on the holley carbs and how they work and stuff and will give you a better idea on tuning them for the best tune you can get.

Now the mods you can do is you will need a 61-80 drill bit gauge set with a pin vice and you can get them off ebay for pretty cheap and less then $20 bucks if you look good. It comes with tiny sized drill bits you will use to make custom sized idle feed restrictors for your carb. Then the next thing you will need is a good drill bit gauge set of different sizes drill bits to carefully drill out the pressed in idle feed restrictors in the metering blocks.

After that you use a 6-32 tap and then tap the holes left over where the pressed in idle feed restrictors were in the metering blocks. Then you would have to get some 6-32 x 3/16 brass allen set screws from Mcmaster.com as they have them for pretty cheap in boxes of 25 and 50 count and you would use your drill bit pin vice set to make them the size restroctors your carb would need to get the proper and best idle circuit calibration.

There is a bit more detail on doing the tuning with that mod but this is where you would start at.The thing is the idle feed restrictors are way more sensitive to change versus the idle air bleeds and in 95 percent of the time, I only had to change the idle feed restrictors out and not have to touch the idle air bleeds to get a spot on tune. Idle air bleed changes are more for the finest tweak and final overall tune but usually a wide band O2 is needed to really get the effect of what is going on when doing air bleeds.

It takes only a .001 change in idle feed restritor size to get a double digit percentage change in the mixture going through the ifr going up or down in size and its recommended to do a .002 change at a time up or down as needed. On air bleeds you have to have a .004 change and its sometimes not even noticed by feel or performance of it being changed and outside of using a wide band gauge it takes a lot of trial and error to mess with them to get the finest setting on those.


That will give you the best idle and off idle tune your carb needs and the best mileage on the transition circuit. I get all my carb stuff needed from allcarbs.com and they are good on prices on things and they have the secondary metering block you would need for your 600 vacuum secondary if you were to want to run it instead of your double pumper.

I took my stock 600 vacuum secoondary holley and modified my metering blocks for adjustable feed restritors using the brass allen set screws and also my idle air bleeds as well and then got a seconary metering block and center hung fuel bowls and installed down leg boosters and added a quick fuel adjustable pod. I have had it on several builds and it runs like a charm once tuned in.

Here is the Holley book I recommend.

 

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It's unlikely to be a bent valve but instead a bent push rod. Valves tend to be stronger than pushrods.
What I'd do, awhile you wait for parts, I'd pull the valve covers, pull the plugs, put your straight edge across the studs, looking for any too high, do the same across the valve tips, put your DI on the valve retainers and spin the engine by hand looking for a substantial difference in DI readings.
I wouldn't worry about .005ish but something like .030ish is an indicator of something.
Note what you find including the easy to turn spot. Also take a look at the convertor bolts and flex plate bolts for witness marks to looseness or the bolt heads hitting something. Then pull the pushrods and look for any bent ones. Roll them on a table or chuck them up in a drill and it'll be obvious.
Note what you find.
Then [email protected] it all and when the tools arrive, do a leak down. A leak down will tell you everything a compression tester will plus more so no need to do both although a compression tester is somewhat faster to do. Just be mindful a compression test is effected by the battery and starter cranking speeds. It's a comparison check against the other cylinders.
Note any cylinders that aren't like the others. Some small variance is fine, big ones aren't. Once all this is done, you've checked everything mechanical and so you can then look at the ignition first, then the carb.
 

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Discussion Starter · #19 ·
Welp, here's the oil filter:






Some oil on my finger. You can see some small metal particles:




What do you guys think?

Hopefully after you find out your issue soon. As far as you wanting to know will your carbs work, the answer is yes to both of them but they both would need to be modified in order to get the proper tune on the idle circuit and adjusted to your camshaft. The 650 double pumper would be on the way richer side as it is out of the box. The primary metering block has a .031 to .033 idle feed restrictor size and the rear metering block has around a .039 idle feed restrictor size. This was on a Holley 4777-7 stamped on the main body.

On the number after the dash mark for example the -7, the higher the number after that the more newer the carb is as Holley makes tweaks to there carbs over time and 90 percent of the time is very minor. The 650 double pumper out of the box is setup for more racy motors and big cams and may or may not be too rich for your engine starting off wise but is in the starting ball field but it will still have to be tweaked some to get best possible tune you can get.

The Holley 600 vacuum secondary is a lot leaner out of the box and for mild engines with small camshafts and near stock or rv cam type of deals. Once you get into anything a lot more aggressive after that with cams around [email protected] duration and lower vacuum readings of 17 inches or less then it will always be too lean and will make you end up having the primary idle set open way too much to get a usable idle and too much opening on the transfer slot and cause your idle mixture screw to either not work well or not work at all.

The 600 vacuum secondary comes with .028 idle feed restrictor size in the primary metering block and the secondary metering plate has a .031 idle feed restrictor size. You would have to replace the secondary metering plate with a metering block. It would have to be changed I guarantee it as I use that exact carb on my build and I modified mine to work with whatever I throw it at on my small block builds.

Before you would go going to do these mods I will recommend that you get a Holley tuning book I listed below. It gives great detail on the different circuits on the holley carbs and how they work and stuff and will give you a better idea on tuning them for the best tune you can get.

Now the mods you can do is you will need a 61-80 drill bit gauge set with a pin vice and you can get them off ebay for pretty cheap and less then $20 bucks if you look good. It comes with tiny sized drill bits you will use to make custom sized idle feed restrictors for your carb. Then the next thing you will need is a good drill bit gauge set of different sizes drill bits to carefully drill out the pressed in idle feed restrictors in the metering blocks.

After that you use a 6-32 tap and then tap the holes left over where the pressed in idle feed restrictors were in the metering blocks. Then you would have to get some 6-32 x 3/16 brass allen set screws from Mcmaster.com as they have them for pretty cheap in boxes of 25 and 50 count and you would use your drill bit pin vice set to make them the size restroctors your carb would need to get the proper and best idle circuit calibration.

There is a bit more detail on doing the tuning with that mod but this is where you would start at.The thing is the idle feed restrictors are way more sensitive to change versus the idle air bleeds and in 95 percent of the time, I only had to change the idle feed restrictors out and not have to touch the idle air bleeds to get a spot on tune. Idle air bleed changes are more for the finest tweak and final overall tune but usually a wide band O2 is needed to really get the effect of what is going on when doing air bleeds.

It takes only a .001 change in idle feed restritor size to get a double digit percentage change in the mixture going through the ifr going up or down in size and its recommended to do a .002 change at a time up or down as needed. On air bleeds you have to have a .004 change and its sometimes not even noticed by feel or performance of it being changed and outside of using a wide band gauge it takes a lot of trial and error to mess with them to get the finest setting on those.


That will give you the best idle and off idle tune your carb needs and the best mileage on the transition circuit. I get all my carb stuff needed from allcarbs.com and they are good on prices on things and they have the secondary metering block you would need for your 600 vacuum secondary if you were to want to run it instead of your double pumper.

I took my stock 600 vacuum secoondary holley and modified my metering blocks for adjustable feed restritors using the brass allen set screws and also my idle air bleeds as well and then got a seconary metering block and center hung fuel bowls and installed down leg boosters and added a quick fuel adjustable pod. I have had it on several builds and it runs like a charm once tuned in.

Here is the Holley book I recommend.

That's the exact book I've been keeping my eye on. Thank you for all the info, it's much appreciated. I know basic carb tuning stuff, but beyond that I don't have much experience. What you described with the 600 vac secondary carb is exactly what was happening with this new setup. Last year (when I wiped the other cam) It was fouling up the plugs in no time just sitting there idling. Adjusted my floats and **** several times and couldn't tune it out. Guess what you explained is why.

It's unlikely to be a bent valve but instead a bent push rod. Valves tend to be stronger than pushrods.
What I'd do, awhile you wait for parts, I'd pull the valve covers, pull the plugs, put your straight edge across the studs, looking for any too high, do the same across the valve tips, put your DI on the valve retainers and spin the engine by hand looking for a substantial difference in DI readings.
I wouldn't worry about .005ish but something like .030ish is an indicator of something.
Note what you find including the easy to turn spot. Also take a look at the convertor bolts and flex plate bolts for witness marks to looseness or the bolt heads hitting something. Then pull the pushrods and look for any bent ones. Roll them on a table or chuck them up in a drill and it'll be obvious.
Note what you find.
Then [email protected] it all and when the tools arrive, do a leak down. A leak down will tell you everything a compression tester will plus more so no need to do both although a compression tester is somewhat faster to do. Just be mindful a compression test is effected by the battery and starter cranking speeds. It's a comparison check against the other cylinders.
Note any cylinders that aren't like the others. Some small variance is fine, big ones aren't. Once all this is done, you've checked everything mechanical and so you can then look at the ignition first, then the carb.
Sounds like a plan. The testers should be here tomorrow. I'll report back with my findings as I go along.
 
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