Board index Flathead Power-Technical Questions, Answers, and Suggestions Pans A little help with carb. / timing issue please

A little help with carb. / timing issue please

Moderators: Curt!, Pa

Posts: 39
Location: Seattle, WA, USA
Gentlemen, hoping for your input.

Cotten rebuilt an M-74b for me and I've just installed it on my '53 with a later model O-ring intake manifold. I followed the manual to a T on the low speed needle adjustment, made sure my throttle butterfly fully closes, and lit her up, but I can't get it to idle down as it should regardless of where my low speed adjustment is set. As soon as I adjust it the motor begins to cut out and I need to put my hand over the carb. to bring it back to life. This says lean to me, as do the plugs. The bike is tough to kick too.

I'm wondering if my timing is set too far advanced hence the difficulty in kicking and the lean issue, or if this sounds like more of an intake leak? I won't be able to tinker until Wednesday evening and would appreciate your input in the mean time. FYI- We timed the bike with the flywheel mark in the rear 1/4 of the window.


Posts: 3010
Location: Central Illinois, USA

First, please pressuretest your entire manifold assembly as per That means using a large cork or rubber stopper to test the nipples separately.
Far more O-ring conversions have boogered early heads than even hardened seat replacements.

Second, please return your timing to spec: the middle or the hole, or to the front if pump gas pre-detonates.

Third, the throttledisc never closes completely in service. An initial setting would be a turn and a half open at the idle screw, so that it can be trimmed down after the motor is warmed.

Fourth, and most important, the carb will never run right until you send me the remainder on your tab!


Posts: 39
Location: Seattle, WA, USA
Doh! Digging through email and sending now via Priority mail with interest. My apologies for the delay and thanks for the reminder.

Will definitely test the intake w/ that method and re-time w/ mark in center. My manual (later Pan & early Shovel) has the mark in the rear of the hole though- did the earlier spec.'s differ slightly?

Update: Here's the USPS tracking number on the funds Cotten- 03073330000153577311

Posts: 39
Location: Seattle, WA, USA
It was the butterfly not closing enough and it was my mistake. I'd accidentally rotated the piece your throttle cable goes through that rides on the butterfly shaft. Fixed that and the bike idles really well now. I tested for intake leaks with the carb. off too and I don't have any. Thanks Cotten.

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