manifold confusion

[redmonster]

Hey amigos need help I'm dumb founded
I have a 250 l6 in my 72 GMC I took the advice of
our compadres from here I put a 292 exhuast manifold
in place of the original one now my truck sounds like its missing
y y y your help is needed
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[redmonster]

Anyone
Why does my truck sound like its missing with this manifold
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[geezer#99]

Vacuum leak. Did you use a new gasket when you put it back togethor. Are the washers on the bolts in to the head all making contact on the intake and exhaust flanges.

[redmonster]

brand new gasket
where could the vacuum leak be
there is also a slight smoke that comes from somewhere if i idle it
hard enough

[geezer#99]

Vacuum leak and smoke could be because your intake and exhaust aren't sealed tightly to the head. Look at the washers on the bolts that hold the manifolds on the head. Make sure they make good flat contact. And you have them all in the right place.

[68gmsee]

Can you reinstall the original or was it broken?
Did you install the exhaust/intake complete or just the exhaust?

How is the heat riser? It should move freely. If it doesn't it could be frozen in the closed position.

Plug up all the vacuum ports, hook up a vacuum gauge to manifold vacuum and with can of fuel starter spray around the gaskets to see if vacuum jumps.

Once you're absolutely sure there aren't any leaks, do an ignition tuneup. Distributor cap and rotor, condeser, plugs, points, etc. The miss may just be coincidental.

Also, if you don't find leaks and after you do the tune up it smokes, you may just have worn valve guides or rings.

[Wrenchbender Ret]

You probably have vacuum leaking at one of the ports. 292 engines run hot & often the manifolds are warped. Retorque the mounting bolts. The gasket compresses from the heat & shrinks up. Pull one spark plug wire at a time with the engine running useing insulated pliers. Compare the effect with each cyl. If 2 have little effect & are on the same runner that is where the leak is. If one cyl seems weak check the plug & wire going to that cyl. Sometimes a lot of idling can carbon up the plugs.

[PanelDeland]

When you installed it,did you follow factory procedure?The intake and exhuast manifolds need to be gasketed together,bolts installed loosely,then gradually tighten the bolts for the mani fold to head and the manis to one anther.If the intake and exhuast are tightened together before they are tightened to the head they may not be even and seal.