Warning! Newbie question
I put in a new motor about a month ago (400 w/ a mild build) and have developed an issue. I can get the truck to idle happily in park/nuetral but not in gear with the brakes on. I am also hearing an exhuast leak which I believe is coming from under the manifold.
1-can exhaust leak come under the intake manifold or am I nuts?
2-would that explain the idle issues?

I don't have a vacuum gauge, but a few shots of carb cleaner tells me that there is a leak.

 

It could be. I mean, at idle you may have compensated for the leak through carb adjustments. The load placed on the engine by shifting it into gear means it needs more air and fuel to keep it idling smoothly.

It could include a bad vacuum advance. Plug both ends and see what happens when shifting into gear.

$0.02

 

a manifold leak can sound similar to an exhaust leak from crankcase pressure.. if you have for sure found a leak with carb cleaner then pull the intake, clean, inspect and reseal....

 

1) Yes, there can be an exhaust leak under the intake manifold.
Are you using the stock intake or an aftermarket?
The stock manifolds have an exhaust crossover passage in the intake manifold.
When the engine is cold the exhaust heat riser valve is closed, this diverts exhaust from the left bank of cylinders under the intake manifold and out the right side exhaust.
The purpose is to speed up the carb warm up.
2) If there is an exhaust leak it would be a safe bet that the intake gaskets are leaking and could explain the idle issues.

 

Thanks for the responses. I'll pick up a new gasket set today and try to put it in over the weekend. I'll throw the ends away this time and go with a bead of rtv instead.

I'll also try disconnecting the vacuum advance this morning just for giggles. It's a new reman dizzy, but you never know...

 

yup, it was leaking. There was oil all over the top of the gaskets . Hopefully I'll have better results this time around...