hgc.micha Posted March 21, 2019 Share Posted March 21, 2019 Hello, I have a problem with my 1951 Chieftain with 268 straight 8. I have replaced all parts on the engine, checked and nevertheless the engine runs too lean, I suspect that it sucks in false air. Only the gasket for the Heat Riser was not replaced, can it be that this is the problem? Can the engine suck in false air at this point? Greetings Michael Link to comment Share on other sites More sharing options...
PONTIAC1953 Posted March 21, 2019 Share Posted March 21, 2019 (edited) 3 hours ago, hgc.micha said: Hello, I have a problem with my 1951 Chieftain with 268 straight 8. I have replaced all parts on the engine, checked and nevertheless the engine runs too lean, I suspect that it sucks in false air. Only the gasket for the Heat Riser was not replaced, can it be that this is the problem? Can the engine suck in false air at this point? Greetings Michael most likely the leak is where the intake manifold is bolted to the block, did you copper coat the gasket or installed dry ?, false air cannot come from the heat riser but a exhaust leak can there. you may have to remove the manifold assembly and have the mounting flanges checked for flatness and straightness, may have to have the manifold flanges surfaced by a machine shop. a cheap fix might be to use two gasket sets instead of just one set. p.s. did you install a thin carburetor base gasket in between the manifold and the heat shield and a thick insulator gasket in between the heat shield and the carburetor ? Edited March 21, 2019 by pontiac1953 (see edit history) Link to comment Share on other sites More sharing options...
pont35cpe Posted March 22, 2019 Share Posted March 22, 2019 I`ve always used wd-40 to find a vacuum leak. With engine idling(with a vac leak engine runs ruff)spray wd-40 where intake bolts to head and around base of carb., spray each place one at a time, if the engine smoothes out for a few seconds that`s where the leaks is.. 1 Link to comment Share on other sites More sharing options...
Summershandy Posted March 27, 2019 Share Posted March 27, 2019 I read somewhere that you could develop a vacuum leak from any of the tubing associated with the wipers. I cleaned up the metal tubing and replaced all the rubber tubing for the engine anyways and used those little black clamps you squeeze to open. You can't really see them and they should help that much more. Link to comment Share on other sites More sharing options...
john hess Posted March 27, 2019 Share Posted March 27, 2019 Also look at vac advance on dist.. make sure diagram holds vac... Old rubber cracks.., also I agree with Mark.... Wiper tubes go bad.... Unhook and plug line at vac/fuel pump to check this.... John Link to comment Share on other sites More sharing options...
john hess Posted March 27, 2019 Share Posted March 27, 2019 You say only gasket to heat riser not replaced. Did you have it apart ?... If so, make sure to leave the 4 bolts loose until the intake/exhaust stud nuts are torqued. Ask me how I know... John Link to comment Share on other sites More sharing options...
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