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Discussion Starter #1
Help is needed I am at a wall of my knowledge.

B43 onan in my 318 was running perfect.

Recently while mowing the lawn it just started spitting and sputtering and I limped it back to the shop then cleared up.

Went back out to cut and started again.

In The shop I have verified fuel, Compression, and what looks like ok spark in my spark tester.

tested coil and although not perfectly in specs, was running fine earlier with same readings. Swapped also with spare coil just for
testing purposes. Same result.

Tried to eliminate voltage issue at coil by applying 12v directly to Pos term with same result.

New plugs gapped at .025 and re-checked gap on recently new points gapped at .016

What am I missing here?

Thanks in advance!!
 

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Hmm, if sputtering and then clearing up, I'd look at your fuel system. Possibly debris in tank blocking pick up filter, debris in fuel line, debris in carb, float needle shot, or bad/dying fuel pump. Sorry I'm not much help, but I would definitely look at fuel rather than spark. Bob
 

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Have you ever replaced the fuel lines, tank grommets, and fuel pickups?
If not, those can all cause issues.
Its not a real expensive fix, but can be time consuming, especially the cleaning out the tank part.
One of the two pickups is a strainer on the end of a hose. That hose deteriorates, and being a B43 Onan, yours is an 86 or older, and that one is likely toast.
The other is a metal line, also with a strainer, and those tend to corrode over time, especially if the tank was left low.
Ethanol isnt friendly to any of it either, which is why I do my best to NEVER run ethanol fuel in any of my equipment any more. Luckily there is a station not too far away that sells non-ethanol gas.
 

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Discussion Starter #4
Thanks for the suggestions re-fuel!

Little more background 1 1/2 months ago I completely cleaned machine including removing pan and under screen.
Removed tank and replaced all fuel lines with new filter to carb.

Took off engine tins and cleaned as well as points, condenser, and plugs.

Tank was cleaned well inside at that time.

Fuel does have methanol but its fresh 94 octane as I go through a lot of fuel seasonally.

I just put an old spare condenser on it, pulled the main jet out cleaned and replaced.

With 12v direct to the coil it fired up came up to speed and then declined back to spitting and sputtering with in seconds.

I can see fuel spitting into the carb and when it starts to slow like a stall fuel splashes out of the carb.

Maybe I should rebuild carb and go from there?
 
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