Marvel Carburetor Troubleshooting

[atypicalguy]

Yes it is the David Lowe STC.

[6643]

So the carb is appropriate for the engine. Not relevant, though, since it worked fine up until the point where it went south. Do you have the two piece venturi?

[4004]

I think you should reconsider your diagnostic logic. If an engine has performed satisfactory for the 40 hours you have had it, then why go worrying about part numbers, etc. Look for what has changed suddenly!! As John C says, have some one open up and check, but don't touch,unless repair needed, positioning of the discharge tube in the venturi is critical - key item is condition of float and correct height also pump condition. As MS suggested check primer pronto.

"All gut parts are O-200" - IIRC the stroker STC did not change the cam - a critical item "legally" which possibly permitted the STC approval.

I repeat, look for what has changed after 40 hours - hardware not numbers. 2c FWIW

Edit PS Just saw John C latest comment re inspection and had another thought. How much history do you know since OH. Some inexperienced person who has heard the terms, Mo gas & auto gas, thought it meant the common auto fuel and had used some instead of the STC required alcohol free gas with testing to assure no alcohol. The modern foam floats may or may not tolerate alcohol, another case for the inspection.

[a64pilot]

Years ago when I bought my 140 it ran slobbering rich at low power, never fouled a plug though.
Upon disassembling the carb, I found the float had a lot of fuel in it, and of course that was the problem, pretty easy to drain and re-solder the float.
An incorrect float level can cause rich running