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Onan Microlite 2800 No Start, Backfires Out Exhaust


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  #1  
Old 04-13-2018, 01:15:01 AM
Ogreman89 Ogreman89 is offline
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Default Onan Microlite 2800 No Start, Backfires Out Exhaust

Model: 2.8KVFA26100K Spec K
Serial: B080160362

Got her back together and got everything perfect, or so I thought. When I try to start it just cranks, then after a few seconds of cranking I get a backfire and a small plume of smoke out of the exhaust. I messed with the carb/choke and governor but the same condition remains. I'm thinking I didn't adjust the valves correctly.

Can someone please advise of the best way to adjust the valves? I set it at TDC of the compression stroke. Also, when I adjusted them thr manual said to recheck clearance to make sure it's the same with the locknut tight, which it was not, so I reset until the clearance was correct with the locknut tight. I checked the valves after several tries and they seem to have tightened up a little. I figured I'd check here to verify I'm adjusting the valves right.

Any other ideas? Got spark.

Thanks!
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Old 04-13-2018, 08:00:26 AM
KPack KPack is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

I had a 4ky backfiring the other day , turns out it was the magneto coil . From what Iíve read part of it goes out and throws the timing of.
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Old 04-13-2018, 09:08:41 AM
Ogreman89 Ogreman89 is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

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Originally Posted by KPack View Post
I had a 4ky backfiring the other day , turns out it was the magneto coil . From what Iíve read part of it goes out and throws the timing of.
Hm. I'll have to look into it! Was it running though? Cuz mine won't start and it backfires once out of the exhaust after about 3-5 seconds of cranking. Hoping I don't need to tear back down lol
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Old 04-13-2018, 01:45:20 PM
len k len k is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

Looking at schematic spark coil doesn't have any points and has a ground to kill wire just like lawn mowers do.

That means it has an internal electronic switch to fire the spark. I've seen many of those type coils fail on lawn mowers and other small engines. Electronics don't take heat well, guess coil gets hot.
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Old 04-13-2018, 04:29:30 PM
KPack KPack is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

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Originally Posted by Ogreman89 View Post
Hm. I'll have to look into it! Was it running though? Cuz mine won't start and it backfires once out of the exhaust after about 3-5 seconds of cranking. Hoping I don't need to tear back down lol
No it wouldnít run till I put a new coil on it. But it may be different than your gen
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Old 04-13-2018, 10:28:27 PM
Ogreman89 Ogreman89 is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

Are you guys talking about the ignition coil or the magneto coil on the end bell?
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Old 04-13-2018, 11:02:19 PM
len k len k is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

I was taking about the wrong gen model the KY, you have a KV

I just looked at service manual again, looks like the KV gen has a different spark coil. It has 2 parts.
But I hear they also fail.
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Old 04-13-2018, 11:09:49 PM
Thaumaturge Thaumaturge is offline
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Default Re: Onan Microlite 2800 no start, backfires out exhaust

The way I set valves, is to turn engine until the other valve just starts to open. By definition when one valve is open the other should be closed. TDC is just a handy point of refference when both valves ought to be closed. But in point of fact it really doesn't matter where engine is in rotation to set clearance as long as cam isn't trying to lift the valve. I don't know what sort of adjusters Onan uses, but I would assume similar to clones. In old days center screw set gap while outside nut retained setting. Nowadays that's generally reversed with center hex set screw locking and outside setting clearance. So box wrench around screwdriver shaft no longer works.

As to your symptoms.... tight or stuck exhaust valve, or erratic spark. For erratic spark check ground on coil. If it is loose or gets high resistance it will make spark erratic. Also check gap between coil and flywheel magnet and check for any rust or metal particles stuck to magnets.

Also check manual to see if valves should be set cold, or not specified. Will make a difference.
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Last edited by Thaumaturge; 04-14-2018 at 07:53:07 AM.
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Old 04-16-2018, 03:33:19 PM
Ogreman89 Ogreman89 is offline
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Default Re: Onan Microlite 2800 No Start, Backfires Out Exhaust

Coil ground is clean and tight, I'm going to try to reset valves like you and see how it goes, I'd really rather not pull everything apart to get to the magneto on the end bell lol.
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