sbc engine guru's ??

I have a 350 Chevy in my current build(yes I know I should went with something more unusual).Fresh build engine and have got it running but something is not right.Motor seems to be laboring and will not hardly idle.Rear 2 cylinders also seem to be running alot hotter than any of the others.Distributor has been checked and plug wires are correct on engine.Timing shows approx 12 advanced and should be 8 - 10 but will run even worse and wants to die.Sorta seems like it is flooding but this is not the case.Any body got any idea's on what I have done wrong?
Thanks,
Mike

 

what intake, carb, cylinders are hot? 7&8 or 6& 8 or 5&7? recheck valve lash, vacuum reading and check back in,could be a simple leak. try timing it with a vacuum gauge after you re lash the valves.

 

7 and 8 are hot.Am going to check vacuum,just thought it odd that just these 2 cylinders are hot.Thanks,
Mike

 

If those rear cylinders are hot, you may be running lean on those cylinders. Have you pulled the plugs to read them? Put a vacuum gauge on?
Rear intake gasket leak? letting air in / leaning out those cylinders maybe. Do you have enough coolant flow?

 

Index your timing off a verifiable TDC. Too many combinations of timing marks on tabs, balancers, etc to trust anything but a true TDC and a timing scale on the balancer indexed to this TDC.
This is the place to start and when you get a handle on that you can deal with the 50 other things that can (and do ) go wrong. Being slightly sarcastic here, but not much, get the basics right and your a winner.

Frank

 

All of the above! Have a beer and if symptoms persist call in the morning>>>>.

 

I'm with fab32. What I thought was the timing mark in the Harmonic Balancer turned out to be a valve phasing mark put on by the builder. When I thought I was setting it to 6 BTDC, it was actually 4 ATDC.

Futzing around with it one day, I could juuuust see the right mark in the timing light. Rotated the distributor so I could see it and the motor got a little better, stopped the motor and moved all the plug wires one way (to clear the Lingerfelter Intake), and had enough slack to get the mark to 6 BTDC.

The best way to describe it is that the motor seemed to relax. The idle smoothed out, all the heat went away, I stopped melting vacuum lines ( )

Verifiably check your base timing.

 

wouldn't incorrect cam timing affect all the cylinders, not just two rear ones?

 

I may have it figured out.No vacuum.Intake was leaking at frt rt side at the very least.Intake was purchased on ebay....one of these days I will learn my lesson from ebay..Gonna have a beer.Cuss a little and redo intake.Will post on this when I get it running.Thanks guys.
Mike

 

good to hear you found the problem. enjoy the pop.

 

One more thing to check is to make sure that any vacuum lines that may be attached to the vacuum port on the back runners of the manifold do not have have a leak on the other end of the line.

I'm inclined to think that it either has a vacuum leak or the timing is off in the ignition.
As one of the guys above mentioned there are a lot of different locations for timing marks on these engines depending on the year and application.
I'd make sure that the timing mark is lined up with the 0 on the tab at tdc first. Once you are sure the timing is right then check to see if those two back cylinders are lean and why.

Whew, You have to be quick around here. Good going on finding the problem.

 

Nah, don't blame ebay or the intake. I wanna think I fixed three or four fukups before the motor got running right. Intake leak, vacuum leak, two plug wires swapped, distributor timing. Franky, it's amazing how screwed up a SBC can be and still run.

 

Everything is good in the world again..Tore down and ***embled last night.Engine runs great this morning.Still baffles me how a leak at the frt of intake could cause #7 and 8 cylinders to run hot.Great to have a place to ask questions and get real answers.Thanks
Mike