Hard start & poor off-idle acceleration

[JerryWang]

Hello! I have a 1967 Chevy K-10 pickup with a 1963 327 V-8. It has an Edelbrock "performer" intake manifold and an Edelbrock 650 cfm 1405 carburetor. I replaced the intake manifold gaskets a month ago, it ran great for a few drives, then started to misfire and was VERY hard to start/drive. I recently replaced the entire ignition system to try and diagnose the problem (new battery, coil, points, plug wires, spark plugs, distributor cap and rotor, vacuum advance unit) and all new vacuum lines. The gasket under the carb was also replaced. All seems to be working fine (no visible leaks in gaskets or vacuum lines) but it still is extremely hard to start. Once started and warmed up, when I go to apply the gas right off of idle it wants to muffle out and die, as if my advance was not working properly. Once in the higher rpms the motor runs almost fine, with a slight lack of power. Backfires occasionally out tailpipe and out carb if accelerated too quickly.. Could I be overlooking something? Maybe a fuel pump?

-Jerry

[brad_man_72]

is your accelerator pump working?

[JerryWang]

Yep!

[wiggins]

Well you've done all the basics. I had a similar issue with a 327 one time and it ended up being that aluminum intake. My motor was also pumping oil in the #8 cyl. A guy told me to check that #8 and said to put my old intake back on and viola it was fixed. It has to do with the aftermarket intake not seating off properly on that back corner. Could probably take the intake to a machine shop and have it fixed also.

[jhwkns]

Jump time? Flat cam? worn distributor bushing?

[JerryWang]

As far as the oil in cyl. 8 goes there aren't any signs of smoke coming from either exhaust pipe. I'll try re-tightening my intake manifold bolts and seeing if that helps. If I have to replace the intake gaskets (again) is there a certain kind or thickness that I should use? Or should I use a certain goop when I put them on this time?

-Jerry

[wiggins]

None of that worked for me, but once I replaced that intake it was gone. I always put extra rtv in the corners anyway but that did not help in that case. My motor was not smoking but when I pulled the plug out it had fresh oil on it.

[CCCC]

I have never experienced this problem, but almost would bet it is some kind of leak at the intake manifold, especially since it is a new factor and you have checked almost all of the other essentials. An air leak after carb may be infrequent enough that most of us do not encounter the issue very often, and if that is it the problem should tend to diminish at higher rpms (increased air volume) because the flow through carb is greater enough to overcome some of the leak effects. I would start there. next.

I forget specifics of the trick, but have seen guys check for vac leaks (which this would be) with a small flame or light smoke - see where the flame or smoke is drawn to leak. If you find such a leak, try to stop it temporarily with some safe filler firm enough not to be drawn into the manifold cavern, and see if it solves the problem.

It manifold is leaking, better check plane of both manifold/head mating surfaces. Cheaper fix might be a fatter gasket. Once somebody told me about using JB Weld to plug such a leak, but don't think I would do that except as a very temporary fix.

[CCCC]

Originally Posted by wiggins

A guy told me to check that #8 and said to put my old intake back on and viola it was fixed. It has to do with the aftermarket intake not seating off properly on that back corner.

Maybe pull the plug for #8 and #6 to compare. If you are sucking oil or coolant into #8 it should show something different on the plug.

[piecesparts]

With all that you have verified, I did not read that you verified the timing setting? Are the spark plug wires in the right places? THe description that I read, indicates to me that you have an ignition issue--either timing has slipped or the timing chain to the cam is not right. Just my .02 worth.

[NoNeck]

Before I pulled the intake off, I would start the engine and spray carb cleaner or WD-40 around the intake. If the engine rpm speeds up at any point, that would indicate a vacuum leak.
Also, some generic, cheapo intake gaskets don't completely seal under 4 critical "ears" on the intake.
I always use a hefty seam of RTV for the front and end seals and throw the cork (or rubber ones) away.
It also sounds to me that your timing is too high... maybe you re-installed the distributor a tooth or two off, which would give you a false reading on the timing light. Sometimes it's better to tune it by ear, using a vacuum gauge to get the max vacuum, disregarding what the timing light indicates.
Just me...

NoNeck

[ItsRandy]

Sounds like it is running lean to me. Check the plugs. If they are white...lean. Check the PCV valve, is it stuck open or installed in the wrong port on the base plate...lean. All of the sneezing out the carb and exaust makes me think it is (have I said this?) lean. Do the squirt carb cleaner or WD40 or ATF along the base of the carb and where the manifold mates to the head, a change in idle says vacuum leak, however, have the heads been milled? The leak could be on the bottom in the lifter valley.

[edhtrd71]

Make sure you have proper voltage to the coil which should be battery voltage during cranking and a little less when running due to resistor wire. You have done a good job of eliminating lots of parts. It does sound like a lean condition because rich would pretty quickly foul plugs with weak points spark output, also the engine would tend to have almost normal power at high rpms and high throttle position. Check the fuel pump with a gauge 3 to 5 psi. Without a gauge run the pump hose to a cup and crank the engine, should fill it quickly. You will know if its bad or not. If it can fill a cup it is pumping enough fuel to start the engine, it doesnt take much pressure to fill the empty carb bowl and doesnt take much fuel to start the engine. The edelbrock has screens inside before the float needle and seat that can clog and are easy to check. If all this is good and assuming timing and all other parts installed correct It sounds like big vacuum leak. You might also check all plugs, they should all look similarly good or bad.