IH 345 idle on 4 cylinders-need more help

[semn john]

So - on to the 345. Has (I think) a 2300 Holley carb. Has a governor on the carb. Good runner, always strong on power. Problem is some times it will decide to idle on four cylinders and will produce a backfire and very poor power coming out of idle. The start of the run up in a gear is very unpredictable, some times after a backfire it will even die.

When this engine is running right it is so smooth-- I swear it must be balanced and blueprinted!

Any Ideas on this one ? ?

Thanks in advance.

[Allan E.]

Depends completely on which cylinders as to what is the problem.

1 x
x 4
x 6
7 x

The intake manifold feeds the cylinders marked X from one side of the carb, and the numbered cylinders from the other.

If it's that pattern, either side, you have a jet not feeding fuel.

If it's a different pattern, you have a distributor problem, most likely.

I would bypass the vacuum advance and see what effect it has. An intermittent vacuum leak on that circuit would cause similar problems.

[semn Dad]

Ya, I'm guessing it's the carb too. I've gone thru this twice before, but it always winds up coming back later after a carb kit is put in. Other times it seemed if you could get it to backfire real bad, or cross the plug wires it would clear up the 4 cylinder idle. I hate to intentionally backfire a motor cause it's got to be hard on carb gaskets. I hadn't thought about pulling plug wires to identify the cylinders. Thanks I really appreciate the help. (previous post 304 backfire) : It was the vacuum advance on the 304! not a one available anywhere ! ! found a rebuilt Dist. with one one at Advanced Auto parts