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It's almost like you have to meter air and fuel...

Starfury

Well-Known Member
The fastback has been running strange for a while, idling rough and inconsistent, misfiring under load below 3k, and flooding out when trying to restart after shutting it down.

I tweaked the advance curve a bit a couple weeks ago when I realized it was giving me 25deg total by 1500rpm.

Once that was fixed, I stuck a vacuum gauge on it to retune the idle mix, and the bouncing needle pointed me at a vacuum leak. I couldn't for the life of me find it, though.

Today I tore the carb (Summit M08600VS) apart and found that the previous owner of the carb had pinched the vacuum secondary diaphragm, causing it to tear. Vacuum leak!
Further teardown exposed a power valve that was both torn and double gasketed. That answers the cloud of black smoke at WOT and the poor restarts.

Cleaned the whole thing out, replaced the junk bits with some stuff from a 4150 rebuild kit at the LPS, reinstalled, and VOILA!
Adjusted the floats and idle screws, vacuum holds a fairly steady 11-12" at stable 700rpm idle, no more black cloud under WOT, and I can cruise and accelerate at 2k rpm again.

Looking good for MITM in April!
 
Nice job. I have a love hate thing with carbs. Mainly because I never fully got to the point of understanding them enough to get them set up right. I'm struggling right now when thinking about the F1 build knowing I intend to use multiple vintage style 97s on top of a blower. It's the stuff of nightmares for me!
 
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