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Old 03-26-2009, 06:33 PM
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350/305? timing backfire/carb-what do I check next

Sorry that This is so long. I dont know enough to know what is relevant...

Hi. I am new to all of this. I have been reading automotive books and scanning the internet to figure out what the He## I am doing. Ive had my 1960 chevy truck for a few months now.

Went to visit dear old mom. The idle was fast.. neighbor said - "let me adjust your timing" .. this is when everything went wrong.. Now that I have driven an hour to get home.. Ive noticed:
Truck backfiring through carb.

I decide to try to learn to fix it myself.

A friend said to get a vacuum gauge -"it can diagnose a myriad of things" and that I could set the timing by
getting the highest vacuum from carb idle air/fuel screws then adjust the distributor for highest steady vacuum - the drop it back a bit.
listen for pinging.. - too advanced
sluggish - too retarded
I tried all kinds of combination's - Still backfiring.
I found out later that I shouldnt have turned the "idle speed screw" to get a steady vacuum... I was getting a vacuum of 17


I went out and bought a timing light, tach

I have a 1960 chevy truck - the engine says its a 350 but I could swear the guy said it was a 305. I can't figure out what the numbers on passenger side engine pad mean:
(im0826 4vp). The websites that have serial numbers listed dont have an i in them..

So. I followed directions for a chevy 350. 10 deg BTDC -still backfiring
Checked for highest vacuum/fuel air/timing combo.. still backfiring
I couldn't get the vacuum to stay steady unless I cranked idle speed screw
the vacuum chart said - if needle steadies at higher rpm then : air /fuel or timing problem..

I have a Holley 80457-7 600 CFM Four Barrel Vacuum Secondary. I followed their directions for setting curb idle screw.

With in all of this messing around I think I see a pattern. As I adjust the carb's (with vacuum hose plugged) the engine speed increases and the timing changes.
I have to retard the rotor cap ..


I think its missing.
I check for spark. Some spark plugs are weaker than others.. I replaced HEI distributor cap and rotor. The auto shop didnt have a matching coil - I dont know if this matters..? I put on old coil.
Changed spark plugs. Noticed two plugs 7 and 4 were ?? cant tell if 2 plugs are oil fouled -carbon fouled - splashed fouled -or ash fowled.
Couldnt figure out how to make spark plug wires. I wasnt strong enough to get the wire to fit into the boot. Returned them. Bought one pre made plug wire attached it to plug #7. Next set of clean plugs - #7 still black

Checked for smoke out of tail pipe.. none. Even had neighbor come to look at first morning start.. nothing..
Did seafoam through carb/manifold .. smoke.. but not for long..

Vacuum leaks?
Sprayed carb cleaner to see if engine rpm changed looking for vacuum leak... Noticed if I sprayed a bunch near the air filter the rpm would drop..
Changed the gasket b/t the carb and the manifold.
There was a PCV valve not hooked to anything.. I took it off and added a breather..
tranny and breaks are only vacuum
Break booster Pinched off.

noticed transmission shifts differently depending on the vacuum.
There might be small oil leak in driver side valve cover.. manifold looks dirty
Truck isnt burning oil. Just changed oil.
Everytime I change the spark plugs I can get perfect vacuum reading - rock steady.. But it doesnt last..

I finally have gotten the truck to idle at 800 and drop to about 600 under load. But when I floor it.. the carburetor seems to gasp for air or gas and sometimes I get a backfire..or stall.. Other than that no backfire.. Timing is either 6 or 8 BTDC - .. vacuum is 10 --Vacuum will stay steady for a good bit of time and bounce + - 5(misfire?) intermittently --and then remain steady.. no pattern

what I am guessing..??
Leaky valve? and sticking? The miss doesnt happen all of the time.
spark plug wires? I just swapped them around to check for this - hoping a different cyl would foul.
If I have vacuum high enough when throttle closed and opened rapidly vacuum reads ok.
But now with the truck at a good idle and with a needle that will stay steady most of the time - [Vacuum will stay steady for a good bit of time and bounce + - 5(misfire?) intermittently --and then remain steady.. no pattern ]when I open /close throttle - carb sometimes has stalled -- needle cant rebound.. Am I just Retarded?
Should I change out plugs again to see if all of these other things have fixed the problem that was fouling the 2 plugs.. and I am just having problems b/c of those 2 plugs..

I just dont know enough. Im trying..

Thanks for your help!!!!
patina


Distributor Tuning and Theory - Part 1
oh yea.. one more thing - I read some article on here and have my vacuum advance ported direct - manifold -but I never bought Echlin #VC-1810 --

I think I need a VC1838
since I have an Hei

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Last edited by 1960chevyapache; 04-03-2009 at 11:41 AM. Reason: had wrong vacuum adv info
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Old 03-26-2009, 06:40 PM
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Looong post, and a lot to figure out, but, try this simple test first. Be assured you are getting a solid 12 volts to the distributor if it`s a HEI, if it runs on any less you found the problem. If your using points that`s one problem on it`s own, as the best place for points is the trash. I would check it for vacuum leaks, check the carb`s base gasket, check the carb for tightness, check over all the lines with a fine tooth comb. Next check the firing order, it`s 1 8 4 3 6 5 7 2, with bank 1 3 5 7 on drivers side. pop the distributor cap and check the mechanical advance, make sure it moves freely and isn`t frozen. Is the vac advance connected? if so it should be connected to a manifold vacuum source or one that pulls vacuum full time. If everything checks out okay the last thing I would do is yank the valve covers and with the engine running, make sure all the rockers are moving equally to all the others, if there`s one or more barely moving the cam is worn out. You can find the cubic inches of your engine by checking the casting number on the drivers side bellhousing flange and look it up on mortec.com. Hope this helps. Good luck.
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Old 03-26-2009, 07:04 PM
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.

I had similar problems with my recent 305. Went throught about 6 sets of plugs, wasn't burning oil, tried 4 carbs, new distributor, new spark plug wires, new coil and was still doing it, in the end I researched on the net and found out I could be using spark plugs that were to hot. They didnt appear to be fouling but were infact burning the guts of them out. The shop I was getting my plugs from said it couldnt be to hot spark plugs as thats what ngk recomended so i changed from a 5 down to a 6, never missed a beat since, and plugs burned clean as i have ever seen them and not black like the hotter 5's. I just put it down to the 305's higher compression heads. My mechanic also told me for every 50 odd hp to put the next stage colder plug in. May lose a couple of hp on dyno but will let you drive it day after day. I don't know, just a thought. As I had all plugs firing but some were weak as then next time I started it up they were gone, big backfires, numerous power valves. haha. The simple backfire can be annoying as it could be a number of things
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Old 03-27-2009, 09:57 PM
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Trying to identify 305/350

I have spent all day trying to find the numbers on the engine and what they mean..

The number drivers side front / near generator area
30570NN ACI@

None of the suggested webistes have anything like this ..

so does this mean that the engine is a
305 made in 70 in nancy's nursery ?

On passengers side front of engine
IM0826 4VP

Im not even going to guess on that one!

And the number that is supposed to be listed behind distributor on bell housing- I climbed into the truck engine bay with a flashlight and a can of engine degrease.. Should I get under the truck?

--
I opened up drivers front valve cover - very easy to do -
#452624
1979-1985 350

Last edited by 1960chevyapache; 03-30-2009 at 10:59 AM. Reason: Found code under valve cover
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Old 03-27-2009, 10:32 PM
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back to double vision.

Found small pool of oil on driver side intake manifold. I have noticed it B4. =Vacuum leak??

The gasket from the radiator to manifold looks like someone made it out of a blue gas station paper towel. It looks moist.
=Vacuum leak?

As for the hei - I have a voltmeter in the truck.. It usually is at 14v - but It swings with the engine rpm.. when I am in gear with my foot on the pedal it will bounce down around 8. I have a generator - not an alternator - could this be a problem?

thanks for your help
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Old 03-27-2009, 11:05 PM
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yes, i believe you found it, wait to see what others say...
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Old 03-28-2009, 12:45 AM
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Quote:
There was a PCV valve not hooked to anything.. I took it off and added a breather..
I'm not entirely clear on the PCV valve that you removed and replaced w/a "breather".

If this hose is connected to a vacuum source, it HAS to be plugged, if it's not being used as a proper PCV.

This is a massive vacuum leak, if hooked to the carb or intake manifold.

Other than that, you may have a leaking intake gasket.

As for the oil pooling on the manifold- it is likely coming from the intake manifold bolt that goes through to the valley, oil will seep up past the bolt.

Remove the bolt, clean it and use sealer when you replace it.

Quote:
As for the hei - I have a voltmeter in the truck.. It usually is at 14v - but It swings with the engine rpm.. when I am in gear with my foot on the pedal it will bounce down around 8.
This isn't normal at all. As was said before, you need full battery voltage to the HEI.

Quote:
The gasket from the radiator to manifold looks like someone made it out of a blue gas station paper towel. It looks moist.
Which gasket is this again?
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Old 03-28-2009, 12:12 PM
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HEI voltage/generator/timing/backfiring

The "breather" is on the valve cover. A friend said that I didnt need the PCV, and since it had no hose connected to it when I got the truck, I removed it and put what is basically an air filter in its place. The PCV just rattled.

The Radiator Hose to Manifold.. http://www.jegs.com/images/photos/900/925/925-8000.jpg
at the front of the manifold there is a place for a fat hose from the radiator to fit. The gasket looks rigged. I dont know if this has anything to do with vacuum.

HEI voltage.. I am going to have to look and see where the HEI positive is connected. ??Its supposed to go to the starter solenoid? through a fuseable link?? the volt meter in the truck is connected directly to the generator.

I just found this online chevy manual for novices - The Charging Circuit -
http://chevy.oldcarmanualproject.com...M300/index.htm

Im going to read over this I dont really understand the wiring for the HEI and I dont have a schematic. But I would think that the generator would be B4 the battery - but I dont know if a car runs off of the generator only once the car is started..

thanks for your help.

Last edited by 1960chevyapache; 03-28-2009 at 12:16 PM. Reason: adding title for easier reference/search
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Old 03-28-2009, 12:24 PM
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You need to check the Battery or b+ plug at the HEI to be sure it has at least 12 volts first.
Next, check the firing order carefully. Pay close attention to # 5 and 7 as they are right next to each other on both ends.
Make sure all the wires are completely on on both ends. IF all that looks good, a compression test may be in order.

On a stock engine 17 inches of vacuum is a little low. I would expect to see 19-21. This can be due to late timing or a leak. The reading should be steady.

If it wasn't skipping prior to anyone touching it, most likely it is something you did.

Eliminate one thing at a time until you find the issue.
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Old 03-28-2009, 06:52 PM
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Testing Hei for 12v

For the other new people out there:

I took off the plug that was for C- GRD B+
I shoved the positive probe into the B+ and put the plug back on the HEI
I took the negative probe and had it touching metal on the truck.
Started engine

I was getting at least +12v more like +13V

I bought an inline ignition spark tester to test for spark at each cable
http://www.harborfreight.com/cpi/pho...4499/04424.gif

Some of the plugs/ wires are getting a hotter spark than others.
The truck came with acdelco R45TS so that is what I bought.
I left the gap at stock 0.35 b/c I dont know if I have 350 or 305
I think I might have to take off a valve cover to find out.

I guess its time to get new spark plug wires and a HEi coil.? I just changed the distributor cap and rotor.
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Old 03-28-2009, 07:21 PM
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vacuum leak and timing

I think that I do have a vacuum leak. I have set the timing to 10deg btdc
I have to have the idle at 1000 rpm to get a steady vacuum reading of 11psi.
Although once the engine gets hot then the needle spazzes b/t 9 and 14 psi

Instructions for vacuum gauge cp7803 :

A pointer which sweeps or wanders erratically through several inches indicates a malfunction affecting all cylinders unequally and inconsistently . To help isolate the troubled area, rum engine about 2000 rpm. If pointer steadies check for :

Ignition and or timing
carburetor mixture adjustment at idle.

I feel like I am going around in circles.

WHAT WOULD HEAT CHANGE?
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Old 03-28-2009, 07:45 PM
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Quote:
Originally Posted by 1960chevyapache
For the other new people out there:

I took off the plug that was for C- GRD B+
I shoved the positive probe into the B+ and put the plug back on the HEI
I took the negative probe and had it touching metal on the truck.
Started engine

I was getting at least +12v more like +13V

I bought an inline ignition spark tester to test for spark at each cable
http://www.harborfreight.com/cpi/pho...4499/04424.gif

Some of the plugs/ wires are getting a hotter spark than others.
The truck came with acdelco R45TS so that is what I bought.
I left the gap at stock 0.35 b/c I dont know if I have 350 or 305
I think I might have to take off a valve cover to find out.

I guess its time to get new spark plug wires and a HEi coil.? I just changed the distributor cap and rotor.
Your distributor shaft bushings could be worn, causing the air gap at the reluctor to widen, and or narrow. This in turn effects the ignition timing, and amount of spark energy to the spark plugs. To test for this check as follows.

Take the cap and rotor off. Grab the top of the distributor shaft and check for any sideways movement. Try this in 90 degree increments. If you have more movement in any increment the shaft, or bushings are worn. Replace the distributor.

I hope this helps.
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Old 03-28-2009, 08:39 PM
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OK first of all, you should have 12.4-13.6 battery voltage to the HEI with key on and around 14.6 volts to the HEI with the engine running. One thing not addressed by anyone here is the possibility that you may have jumped a tooth on the timing gear, due to a worn and/or stretched timing chain. You will need to disconnect the power to the HEI, follow the number one spark plug wire from the plug to the cap and use a marker, whiteout, or scribe a mark on the side of the distributor housing, just below the number one terminal on the cap. Bump the ignition over until you get the number one piston at top dead center on the compression stroke. Pull the number one spark plug, place your thumb over the spark plug hole, and have someone bump the engine over. As the piston comes to top dead center on the compression stroke, you will feel your thumb being forced off the hole. Watch for the rotor to point at the mark you made on the distributor and also look at the timing mark on the harmonic balancer to be right at the "0" mark or TDC mark on the timing mark. If you get your engine to top dead center on number one cylinder and the timing mark and/or rotor does not line up, you have jumped timing and will need to replace your tiing chain and gears.
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Old 03-29-2009, 02:31 PM
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Timing/distributor/TDC/balancer missing bolt- SPECKS?

I thought that I would take on both checking the distributor bushings and checking for timing chain.. I dont have a second person to bump the engine over - to find TDC, so I looked around the internet to find out what to do.

I took out all of my spark plugs and I was going to "turn the engine by hand" -
It said put a cork in the #1 hole and wait until it pops out.

I looked for the crank pulley bolt / bolt in the middle of the harmonic balancer, and there isnt one.
[ thinking back- I noticed that the balancer was wobbly- ]

I put an ink pen into the hole where the bolt should be and it bottomed out at 2 1/2 inches .. hoping that someone didn't break a bolt off ---

I found what I need.

http://store.summitracing.com/compar...s=P%5FRank%7C0

Thanks!
Its so beautiful here that I just hate to call it a day.
patina

Last edited by 1960chevyapache; 04-03-2009 at 11:42 AM.
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Old 03-29-2009, 07:35 PM
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Lots of good info here but no one has suggested a plug gap of .045 for GM HEI systems. That may effect idle and smoother running.
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