banoe
New Member
Posts: 13
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Post by banoe on Jan 10, 2022 22:58:24 GMT
My 72 250 single just started backfiring on the way back from ice fishing. I slowly limped home if it gave it any gas it would backfire. It idles just fine is it possible that it got out of time somehow? I caught a nice walleye by the way so it's not all bad.
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Post by dando127 on Jan 11, 2022 3:27:13 GMT
Any chance that the carb is out of adjustment a little? Try and open up the low jet a little more (1/4 to 1/2 turn) and see how it runs.
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Post by Doo640ER on Jan 11, 2022 14:37:40 GMT
If the carb adjustment doesn't fix it, I'm suspicious that you might be dropping the condenser? Is it backfiring, or is it more of a popping sound and losing power at the same time. If the engine was really good and warmed up or even running hot (pulling a trailer behind you possibly??) then the condenser might be failing and your loosing spark intermittently. Also couldn't hurt to try a different plug.
Next time you run the sled, see if it happens right when the sled starts up, when the engine hasn't gotten too hot yet. If the problem happens after the engine is up to full operating temp, then, again, I would suspect condenser.
Now that I think about it, it also could be the ignition coil also since those can get heat soaked and drop spark also. Does that engine have the external secondary coil you could swap out easily?
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banoe
New Member
Posts: 13
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Post by banoe on Jan 12, 2022 13:47:01 GMT
Well I was towing a jet sled it was about 10f so hard to tell if it was getting hot but I suspect it was. I didn't get to work on it yesterday morning it was -15f
I did pull the plug and it looked ok could be a little richer. It was a new plug when I started the day. The coil is internal so no easy fix there. I allways wanted to change my singles to external coils to make life easier but I never have gotten the moment to do it. I will be back at camp this weekend with the grandkids so I will look at it then. Thanks for the replies
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Post by greenandgold on Jan 12, 2022 19:36:15 GMT
In addition to the excellent suggestions above, some other things to consider:
- Vacuum leak. Loose/cracked intake or exhaust parts and pieces. Gaskets, studs, cracked exhaust can (singles were tough on those solid mounts---all of mine split eventually.) Crank seals oozing oil?
- Voltage leakage. Start at night with the hood removed/tilted. Look for arcing and halos. Cracked plug boot, split cables. Double check plug cap to plug wire interface.
- Plugs sometimes get wonky for no apparent reason. If your plug has a terminal stud, make sure its tight.
If you have a timing light and battery you could verify the mag timing pretty quickly.
Good luck.
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banoe
New Member
Posts: 13
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Post by banoe on Jan 19, 2022 15:09:12 GMT
So I got a chance to for about 10mins yesterday. To start this sled up and ride it in about 10-12" of fresh snow. I started ok and idled. When I throttled it up it bugged and popped two times then it caught and ran well while I played around in the powder on the feild. When I got back to the shed it idled for a minute or two and then it slowly kept going slower and slower at idle I could catch it before it died and fether the throttle back up to idle. I am wondering if this may be a fuel issue I plan on opening up the low speed jet a little more and seeing if it makes a difference
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Post by olyman on Jan 27, 2022 12:12:45 GMT
maybe a loose gas filter, or leak in a gas line?
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