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03-28-2019, 05:09 PM | #1 |
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Join Date: May 2010
Location: So Minn
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Fresh Flathead bucking
My rebuilt stock flathead has only about 500 miles on it but out on the highway at about 50-60 it will occasionally 'miss' and 'buck' just once, not a continuous series of bucks. If I pull out the choke just a little bit it doesn't do it. Any ideas on what the cause can be? Dirt, timing, bad plug, lean carb, leaking gasket..?
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03-28-2019, 05:18 PM | #2 |
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Join Date: May 2010
Location: Star, MS
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Re: Fresh Flathead bucking
A lean mixture (like at cruise) is harder to fire. If your carburetor is clean and ignition up to spec, I would try larger main jets.
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03-28-2019, 05:22 PM | #3 |
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Re: Fresh Flathead bucking
First thing I would is pull the top of the carb and the main jets. Check the bowl for specks of dirt and blow out the main jets
Easy first step in trouble shooting. John |
03-28-2019, 05:24 PM | #4 |
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Re: Fresh Flathead bucking
What model (year range) is the engine and the distributor?
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03-28-2019, 06:18 PM | #5 |
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Re: Fresh Flathead bucking
Sure sounds like one of the main jets is partially plugged or you have a condenser starting to give you trouble.
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03-28-2019, 08:24 PM | #6 |
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Re: Fresh Flathead bucking
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03-28-2019, 09:26 PM | #7 |
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Re: Fresh Flathead bucking
Try this it's cheap. Had the same thing. Idled great, but underload bucked.
Pour mmo down the carb at high idle till it almost stalls. Let it sit a couple hours. Do it again and then drive it hard. Will free up valves sticking. Yes they stick on a new rebuild. mmo is cheap. Choke added at speed, maybe fuel flow/lean also. But it could be a lot of things... sorry . Last edited by Tinker; 03-28-2019 at 09:43 PM. |
03-29-2019, 09:14 PM | #8 |
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Location: So Minn
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Re: Fresh Flathead bucking
I never thought about the valves sticking. That would make it act like it is acting. Just happen to have MMO on the bench so I will try it. If that doesn't work then it is time to check the float bowl and main jets for debris.
Thanks, all |
03-29-2019, 09:43 PM | #9 |
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Re: Fresh Flathead bucking
Could be high speed air bleeds but normally it would be constant and when pulling choke goes better. I had a similar problem and uncle Max said check that, sure enough, blocked high speed air bleeds......worth a look.
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