1992 marathon backfires

Rex3 · 07-22-2018, 09:33 AM

Hoping someone can help me out, I have a 92 marathon that backfires when you let off the gas. I have put new plugs, new carb, new fuel pump, adjusted valves, new fuel lines, new fuel filter. It is also sluggish when you take off. My top speed is 11 mph. Any help would be appreciated.

Shepard · 07-22-2018, 10:26 AM

Does it have a air/fuel adjustment screw? You need to enrich the idea mixture.

Rex3 · 07-22-2018, 10:30 AM

Yes. I have it set to 1 1/4 turns out per the manual.

Shepard · 07-22-2018, 11:19 AM

The manual's adjustment is just a starting point to get you running. Open it up another 1/4 turn and see if the problem starts to go away.

StoveBolt · 07-23-2018, 04:57 AM

See that the throttle plate is closing all the way when you let up, if it has an idle adjustment screw back it out all the way or remove it.

Rex3 · 07-29-2018, 08:14 PM

I'll give that a try. I was looking at it today and noticed a lot of play in the linkage, shouldn't this be somewhat tight and responsive? Also I broke one of the aluminum linkage rods and the ball socket piece, is there an upgrade for the linkage? I was going to get some all thread and make my own, just curious if anyone has done this or something different.

Cartmaster · 07-30-2018, 01:03 AM

Stovebolts advice is spot on. But additionally, a simple test once you have repaired the link (allthread is fine) you need to watch the carb cam / butterfly while slowly pushing the pedal. listen carefully for the microswitch to click under the floor and note if the click comes first or the butterfly starts to move first. If the butterfly moves before you hear the click, you need to adjust the cable/linkages to make sure the switch activates before the butterfly opens.
But as Stovebolt says, you need to make absolutely sure the butterfly is fully closed with the pedal up.

07-22-2018, 09:33 AM	#1
Rex3 Not Yet Wild Join Date: Dec 2017 Location: Ohio Posts: 25	1992 marathon backfires Hoping someone can help me out, I have a 92 marathon that backfires when you let off the gas. I have put new plugs, new carb, new fuel pump, adjusted valves, new fuel lines, new fuel filter. It is also sluggish when you take off. My top speed is 11 mph. Any help would be appreciated.

07-22-2018, 10:26 AM	#2
Shepard Crazy Ole Man Join Date: Jan 2016 Location: Owego NY Posts: 2,758	Re: 1992 marathon backfires Does it have a air/fuel adjustment screw? You need to enrich the idea mixture.

07-22-2018, 10:30 AM	#3
Rex3 Not Yet Wild Join Date: Dec 2017 Location: Ohio Posts: 25	Re: 1992 marathon backfires Yes. I have it set to 1 1/4 turns out per the manual.

07-22-2018, 11:19 AM	#4
Shepard Crazy Ole Man Join Date: Jan 2016 Location: Owego NY Posts: 2,758	Re: 1992 marathon backfires The manual's adjustment is just a starting point to get you running. Open it up another 1/4 turn and see if the problem starts to go away.

07-23-2018, 04:57 AM	#5
StoveBolt Gone Wild Join Date: Feb 2008 Location: Brooklyn, Michigan "Home of M.I.S." Posts: 3,667	Re: 1992 marathon backfires See that the throttle plate is closing all the way when you let up, if it has an idle adjustment screw back it out all the way or remove it.

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07-29-2018, 08:14 PM	#6
Rex3 Not Yet Wild Join Date: Dec 2017 Location: Ohio Posts: 25	Re: 1992 marathon backfires I'll give that a try. I was looking at it today and noticed a lot of play in the linkage, shouldn't this be somewhat tight and responsive? Also I broke one of the aluminum linkage rods and the ball socket piece, is there an upgrade for the linkage? I was going to get some all thread and make my own, just curious if anyone has done this or something different.

07-30-2018, 01:03 AM	#7
Cartmaster British born Nincompoop Join Date: Feb 2007 Location: United Kingdom Posts: 2,461	Re: 1992 marathon backfires Stovebolts advice is spot on. But additionally, a simple test once you have repaired the link (allthread is fine) you need to watch the carb cam / butterfly while slowly pushing the pedal. listen carefully for the microswitch to click under the floor and note if the click comes first or the butterfly starts to move first. If the butterfly moves before you hear the click, you need to adjust the cable/linkages to make sure the switch activates before the butterfly opens. But as Stovebolt says, you need to make absolutely sure the butterfly is fully closed with the pedal up.

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