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Old 08-09-2010, 12:06 PM
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Too much time after rebuild?

I have a 350 SBC that was rebuilt about 8 years ago. It sat, covered with a few moving blankets in the corner of the shop till installation. After market Comp cam, 9:1 compression, All Star distributor, Edelbrock intake, 650 Edelbrock 4 bbl. I am finally getting the car sorted out (my 36 Ford) but it has issues. At low acceleration, it pops, bogs down, sounds like a flat cam. Get the rpms up to around 3500 and it levels out, runs pretty good. I'm getting various opinions on this: Lifters sticking, a flat cam, rust in the cylinders, Loss of compression from the rings not seating. I have had the valves run twice, carb rebuilt, and added a quart of some Rislone stuff to free the lifters. Granted, I have only run the car about 20 miles, should I run it out and maybe wring it's neck a little? It idles fairly well, and seems to cruise along pretty well at about 60 mph. I don't want to tear this thing up, it's too dang hard to get the engine out now. Also, all plugs are firing.

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Old 08-09-2010, 12:43 PM
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I don`t think the cam is flat, if it were it would pop all the time. You have checked the firing order and made sure none are crossed? Is the float level correct? Is the carb getting enough fuel?
You did do a break in procedure? what`s the timing set at?
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Old 08-09-2010, 01:55 PM
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Quote:
Originally Posted by DoubleVision
I don`t think the cam is flat, if it were it would pop all the time. You have checked the firing order and made sure none are crossed? Is the float level correct? Is the carb getting enough fuel?
You did do a break in procedure? what`s the timing set at?
Is the carb getting enough fuel? It sounds to me like the primary side is jetted a little on the lean side .
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Old 08-09-2010, 05:48 PM
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Quote:
Originally Posted by dinger
I have a 350 SBC that was rebuilt about 8 years ago. It sat, covered with a few moving blankets in the corner of the shop till installation. After market Comp cam, 9:1 compression, All Star distributor, Edelbrock intake, 650 Edelbrock 4 bbl. I am finally getting the car sorted out (my 36 Ford) but it has issues. At low acceleration, it pops, bogs down, sounds like a flat cam. Get the rpms up to around 3500 and it levels out, runs pretty good. I'm getting various opinions on this: Lifters sticking, a flat cam, rust in the cylinders, Loss of compression from the rings not seating. I have had the valves run twice, carb rebuilt, and added a quart of some Rislone stuff to free the lifters. Granted, I have only run the car about 20 miles, should I run it out and maybe wring it's neck a little? It idles fairly well, and seems to cruise along pretty well at about 60 mph. I don't want to tear this thing up, it's too dang hard to get the engine out now. Also, all plugs are firing.
How much cam duration and lift? This sounds like a big cam in a slow turning motor, hence the question. Add compression ratio to the question.

Bogie
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Old 08-09-2010, 07:10 PM
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Quote:
Originally Posted by dinger
At low acceleration, it pops, bogs down, sounds like a flat cam. Get the rpms up to around 3500 and it levels out, runs pretty good.
Now that it's up and running, check the vacuum to see where you are at in that regard. You can also do a compression check or leakdown test to see how the rings and valves are sealing.

If the timing hasn't been sorted out yet, I'd suggest a baseline of 14 initial timing, about 36 total (not including vacuum) all in by about 2600 to 3000 RPM. Use a vacuum advance supplied w/manifold vacuum to add to the initial timing- no more than 10 is usually needed. This set-up will be sufficient to remove the timing curve from being the problem, IMO.

A couple things to make setting the the timing curve up, is a vacuum advance limiter plate, Crane #99619-1: 99619-1 INSTRUCTIONS.

If needed, you can instead use an ACCEL #31035. It is an adjustable vacuum advance can for GM HEI that allows infinite adjustment to BOTH the amount and rate of advance. Comes w/instructions and tool.

Be sure the wires aren't run parallel to one another for long stretches (can induce cross firing) and that the cap and rotor are good. If using an HEI distributor, be sure the dist. is getting full battery voltage, w/no resistor wire or ballast resistor in the power wire.

The carb may need tuning of the accelerator pump shot and step up springs/jets/metering rods to suit the engine and vacuum made w/the cam. Edelbrock has calibration kits w/the necessary parts to tune the carb.
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Old 08-10-2010, 01:00 AM
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Thanks for the advice, this gives me a few new ideas. The cam is a comp 280, quite a bit of lift, 480. I've checked the wires, I will check again. I will have to check the vacuum. The distributor is an All Star, a HEI type, takes the smaller dist cap, I have a tight squeeze. I will look more into stats for it. The miss is heavier with a load, it doesn't miss much at all when idling and zapping it out a little. Advance issues? Cobalt, some good advice, I will probably have a friend get involved with some of your suggestions, I really don't have the expertise to mess with this. The guy that rebuilt the carb should be willing to dial it in, I don't want to fry any engine parts with lean mixes. Thanks again, hopefully I can get this sorted out. This car has come a long way, now I need to get dialed in. Dan
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Old 08-10-2010, 01:25 AM
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Quote:
Originally Posted by dinger
The miss is heavier with a load, it doesn't miss much at all when idling and zapping it out a little. Advance issues?
With what you've described, I would lean towards it needing more initial timing. This is somewhat of a guess- there could be vacuum being lost through leaks in the intake gaskets, base gasket, etc.- something that you may be able to pin down w/a vacuum gage. That is a healthy cam, so the idle vacuum won't be all that high, nor all that steady at idle but you should be able to tell a vacuum leak from no leak.

With the engine at an idle, the step up springs should allow the metering rods to remain all the way down. If the rods are able to lift up too soon (step up springs too stiff), this will cause a too rich air/fuel mixture- the step up springs work something like a power valve in a Holley, or a power piston in a Q-jet.

Even the plugs could be contributing to some roughness if they're not getting fully up to temperature and are seeing a good bit of time w/the engine at an idle- so be sure the plugs are nice and clean.

I'm sure you already have one, but in case you don't here's the Owners Manual. You have the AVS Edelbrock 650, right?
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Old 08-10-2010, 07:17 AM
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Did you break in the cam properly? And what kind of oil went in it? Did you add any ZDDP, GM EOS, or Break-In additive?
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Old 08-10-2010, 09:17 AM
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For the 280H cam The distributor needs to be recurved. 24deg at idle 34-36deg at full advance.
shorten the mech advance to around 10-12deg

Then vacuum advance should be limited to around 10-12deg.
Check for accurate timing tab location using a pistons top.
All aftermarket timing tabs are off some.
Use a 4" rated carb power step spring.
Check the voltage to the distributor. 12v +

look for manifold vacuum leaks.
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Old 08-10-2010, 01:34 PM
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Quote:
Originally Posted by cobalt327
With what you've described, I would lean towards it needing more initial timing. This is somewhat of a guess- there could be vacuum being lost through leaks in the intake gaskets, base gasket, etc.- something that you may be able to pin down w/a vacuum gage. t?

I agree. Start up your motor and get an oil can and squirt a bit on the edges of the intake gaskets. If the oil gets sucked in then there is your problem. Another way to check is to start it and let it idle and spray starting fluid around the edges of the intake, if the motor revs up then that means it sucked the ether in and you have a vaccuum leak. The problem could also be at the base of the carburetor.

If there is nothing there then I would start looking real close @ timing and the distributor. You might also double check rocker adjustments.

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Old 08-10-2010, 02:17 PM
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It sounds like your having a similar problem I had with 305 with an old rochester 2bbl; when i gave it gas it would bog down then rev up very slowly while making a popping, crackling kind of noise out of the exhaust. I got a new carb, and problem solved. Maybe try cleaning it first though before you waste you money.
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Old 08-10-2010, 02:50 PM
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I would try switching out to a known good working carb/fuel filter to see if that helps.Next i would be getting an advance curve kit and follow F-Bird 88's advice.
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Old 08-11-2010, 07:40 PM
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first off, thanking all of you for the help, I am not an engine guy.

Did you break in the cam properly? And what kind of oil went in it? Did you add any ZDDP, GM EOS, or Break-In additive?

Yes, ZDDP, if I remember right. I got the bottle when I had the engine built 8 years ago, the guy that broke the engine in is a good wrench. Valvoline oil. I also added a bottle of Rislone recently to see if that would help any stuck lifters or seat the rings.

I had the carb built by one of the better shops in town, it too had sat for about 8 years. I am going to bring it (the car) into his shop Friday for some tuning, also to see if there is anything else that is not right. No vacuum leaks, valves have been adjusted twice, I have fresh gas, 89 octane, I am leaning toward the timing end of things here, I should find out Friday. The shop I am taking it to has drag racing experience, do much of the race engine building in the are, pretty sharp guys I have known of for many years. I will keep you posted. Thanks again, Dan
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Old 08-19-2010, 07:58 PM
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I just got my car back today. There was a fried plug wire, some carb adjustments, valves were re-adjusted (all were ok), one small vacuum leak and still had a terrible miss after it warmed up. To make a long story short, the brand new Allstar HEI distributor was bad. Replaced it, it runs like a top. Thanks to all for the help, you could say the timing was the culprit. Dan
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Old 08-20-2010, 10:36 AM
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Quote:
Originally Posted by dinger
I just got my car back today. There was a fried plug wire, some carb adjustments, valves were re-adjusted (all were ok), one small vacuum leak and still had a terrible miss after it warmed up. To make a long story short, the brand new Allstar HEI distributor was bad. Replaced it, it runs like a top. Thanks to all for the help, you could say the timing was the culprit. Dan
GREAT ! Now you can get back to enjoying your ride ! :-)
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