View single post by Mark Rosenbaum
 Posted: 09-22-2005 07:31 am
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Mark Rosenbaum



Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
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 I'll assume you have normal fuel delivery and serviceable carburetors.  A 907 in good shape should start with just a few seconds of cranking using an open throttle and 1-2 fingerwidths of choke.  If not, perhaps the engine's compression rings are not sealing properly, the 'choke' valve isn't working properly (they are very easy to mis-assemble during a carb rebuild), the fuel floats are set too low, the timing is a bit retarded, the starter motor is turning too slowly, or some combination of these.

For the rings, test the compression on each cylinder after the engine has been run to the point of being fully warmed up.  If you have generally low compression, you've likely found the cause of your problem.  Otherwise, let the car sit for however long it generally takes for the problem to develop, then make another compression check, using the same gauge, with a cold engine.  Compare the data for the two compression tests.  If the readings are significantly lower with a cold engine, suspect the rings.

Even with poorly-sealing rings, a rebuild might not be necessary.  In a lot of cases, there's a tremendous improvement if you sort of break in the engine again, as if it were new -- only this time you're getting rid of cylinder and ring roughness caused by rust rather than by fresh machining.  Ideally you'd do this just before a regularly scheduled oil change.

The remaining possibilities are all fairly easy to check out.