M274A4 hesitation or backfire

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armyaviator
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M274A4 hesitation or backfire

Post by armyaviator » Wed May 31, 2023 1:49 pm

I have an m274A4 mule . Driving it I get either a hesitation or backfire. At least that is what it feels like. I have a new carburetor, condenser, fuel pump, and fuel filters. My timing is one tooth in advance to the left. It is a Hercules engine. Since it runs and is a reasonably strong engine it must be a electric or gas issue. I am not sure though.


Chuck W.
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Re: M274A4 hesitation or backfire

Post by Chuck W. » Thu Jun 01, 2023 8:27 pm

It is very difficult to remote trouble-shoot, but one thought comes to mind; was it running well before with the one-tooth-offset timing? Most engines run much better, but a few don't. I've had a few that absolutely didn't like it at all and I had to re-time back to "mark-to-mark".
One more thing, does the engine tend to "hunt" when it is idling? If so, you may have the linkage between the governor and carb too short.
Just shooting from the hip here....

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Re: M274A4 hesitation or backfire

Post by armyaviator » Wed Jun 14, 2023 9:23 am

I had more backfires or hesitations tooth on tooth. Is there a standard length on the control arm that I can check?

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Re: M274A4 hesitation or backfire

Post by Chuck W. » Thu Jun 15, 2023 11:10 am

I had more backfires or hesitations tooth on tooth.
Well, according to TM 5-2805-213-14, for AO-42-KM engines with a serial number less than KM003475, you set the timing with the mag gear TWO teeth CCW from the drive gear. You might try that.
Is there a standard length on the control arm that I can check?
Not really, just watch the rod when idling, it should be moving very little. If the engine seems to be "hunting", adjust the rod to make it longer. You don't want the governor and carb "fighting" with each other.

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Re: M274A4 hesitation or backfire

Post by armyaviator » Fri Jun 16, 2023 10:53 am

I did adjust the rod. i started with 3/8 thread on each end then adjusted based on idle speed(backed off some). My symptom happen when the engine is under a load not at idle and when the engine is hot. It seems when it is hot something expands and contact is intermittent like a spark plug wire or plug connection. I will look at my engine number and possibly move another tooth. Thank you for your help.

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Re: M274A4 hesitation or backfire

Post by Chuck W. » Sat Jun 17, 2023 1:31 pm

One quick and dirty thing you could try is to disconnect the magneto ground wire at the mag and then drive it and see if anything gets better, this could help identify an intermittent grounding problem with the wire and/or switch.

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Re: M274A4 hesitation or backfire

Post by armyaviator » Tue Jul 04, 2023 7:13 am

I finally am able to get back to looking at the mule. I was going to disconnect the magneto wire but wanted to put gas in it first. Since the tank was almost dry I looked in and saw a large paint chip(about 2 square inches). I got a scope and saw the whole inside peeling large chips. Enough of these floating around may momentarily reduce the required fuel and cause the engine to hesitate. So now I have to come up with a method to clean the inside before I go any further with my other issues. Thanks again.

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Re: M274A4 hesitation or backfire

Post by Chuck W. » Tue Jul 04, 2023 1:09 pm

You need to drop the tank, 4 bolts and two lines, not hard. There is a filter inside the gas tank on the pickup tube that will need to be changed. John Emery has a new type sock filter that works well. If you have an "old school" radiator repair shop near you, they might be able to hot tank it for you. If you decide to seal the tank, I have had good luck using Red Kote http://damonq.com/red-kote.html.
I have used it on 8-10 tanks with no problems. I used POR-15 on one tank and the liner turned loose in about a year and made areal mess. The tank must be clean and dry for any sealer to work correctly.


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