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thedude

Onan issues-shocker...

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thedude

So i started to cut the grass on my 520 and noticed the onan was running rough. eventually it got worse, to the point where it was missing, popping up through the carb (fire!) and generally sounding like a helicopter. The weird this is, it fires right back up running smoothly again for about a minute and does it all over again. Just a little background, I just had the valves adjusted in the spring....Give me wisdom and guidance before I drive it into pond!! Thanks.

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ericj

do a compression check it sounds like the valve seat might have come out. does it loose power under a load when it starts to miss ? is it spitting gas out of the carb and run better with the air cleaner off ? if this is the case then it is the valve seat let us know what you find and i"ll give more advise where to go from there.

eric

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thedude

Yes Eric, all that, and dammit. Sounds like you have been down this road before? The carb is totally spitting fuel out and it does run better sans air cleaner.I am impressed, thank you for your quick and accurate repsonse! Any idea on what I can expect to spend and or replace on this venture? thanks again.

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Hydro

It's all too common with the Onan. Check your bore, my cross hatching was bad too. 450 hours on the engine when it went. Costs up here were $2000 plus. Some want to re-set the valve seat, I would not risk the expense of having it go again. Just my opinion.

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sorekiwi

I'd look into it a little more before assuming it is a bad valve seat, not every Onan loses one!

It could be something as simple as dirt in the carb, a blocked up fuel filter or an electrical issue. The compression check will tell you for sure.

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Rooster

Resetting the valve seat if done properly is a good fix. Any flat head I take apart I Fix the seats where they all but cannot come out. Most of the engines I work on however are high performance with a lot of modification. The Onans are strong engines I have one waiting for me to have a chance to get at it!!

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thedude

Well< i think i got fixed. I checked the 9 pin engine harness connector and found some dirt in it , its also possible that it was loose, so i blew it out and re-connected it. Then i did a compression check and found that both cylinders had the same pressure, so i checked the plugs and found that the rear plug was almost completely closed, so i re-gapped it and everything seems to be normal, thanks for all the great info and ideas guys, thats why i love this forum so much, very helpful.

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ericj

sorry i had trouble with google chrome loading hence getting back on rs. sounds like you got it sraightened out thats good. you got lucky with those symyoms and not looseing a vavle seat, but thats why a compression check is important so you don't jump to conclusions, i will be more carefull when i come upon something like this from now on. yes i've been down that road before. the first 520 i bought had a bad vale seat but thats why i could afford to buy it. it cost me about $150.00 to fix doing all but the machine shop work my self. i now have six 520 and one is a 520-8

eric

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