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Old 10-19-2020, 09:32 AM   #1
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Onan carby fix + 'no starts' look elewhere

After using 2 cans of carby cleaner on 2 carbies and multiple pull aparts etc, I still could not get them to run on my Onan 3.6kv. Maybe a proper clean is needed and not what or how the book suggests!.

Onan's option is 'buy a new one' as no repair kits around..expensive in the US but even more so in Aus.

I solved my problems by making a mix of about 20% 'orange oil' (also called citrus cleaner, gunk or label remover - must be based on citrus fruit) and water and dunking the carby in a small ultrasonic cleaner - I ran that for about 1/2 hour, removed the carby and filtered the liquid thru kitchen paper. Despite being visually 'clean' before this, I was amazed just how much black fine 'powder' (when dry) that came from the carby. I then did the same again using white vinegar this time - again filtered liquid and again found same very fine 'black powder' but far, far less. Reassembled, back on the engine, hit the start button and she runs like new.
The other carby was given me by a dealer for parts as it was 'stuffed'. same procedure, got same result, now runs fine.

Investing in a ultrasonic cleaner - maybe less than $100 on Amazon etc, - beats the price of a new carby hands down. Get one with enough size to hold a carby, watch for those who have timers that shut down, needing restarts every few minutes and for those without timers which could overheat if left unattended. DON'T use anything like paint thinners, fuels or other very inflammables etc in these cleaners as they will most like EXPLODE..(orange oil mixed with water ok.) - even so don't leave unattended!

As for other "no start" problems, if all the usual start items, fuel, spark, air are there, then pull off the valve cover and check the valve clearances - rotate and recheck.These seem to be quite critical on Onan's where other brands are more forgiving.

My inlet valve had a problem that when the clearance was set and the adjustment nut held while the lock nut was tightened, I discovered there was wear either in the rocker stud or adjustment nut threads or both, that meant tightening the lock nut actually moved the adjustment nut down the rocker stud quite a fraction - causing the valve clearance to be wrong. A fix was to loosen off the adjustment nut, lock up and then check for correct clearance afterwards - if not redo until correct. Replacement stud and adjust nut is on the cards now. Never seen that happen in 50 years of motor meddling!
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Old 10-19-2020, 09:54 AM   #2
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Great idea to use an ultrasonic cleaner. I had to check, and Amazon has them from 35 to 300 CDN dollars.

The big problem here is people who don't run the genset often enough. The gas has ethanol in it that evaporates faster than good old straight gasoline, leaving deposits that plug the jets.

I have cleaned lots of carbs for friends in the Spring because they "forgot" to run them.

Happy Glamping, and I hope you get to enjoy your Summer coming up.
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Old 10-19-2020, 10:27 AM   #3
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Usual procedure for me with the yard equipment is a carb cleaner enema in every accessible orifice followed by a thorough blowout with a compressor blow gun. The ethanol gas here turns to amber goo if left to sit and invariably I end up repeating this exercise often.

Mark B.
Albuquerque, NM
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Old 10-19-2020, 12:01 PM   #4
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Sounds good to me. Except also using compressed air to blow through all chambers.
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Old 10-19-2020, 06:48 PM   #5
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I have an old genset in the garage that usually will not start after sitting 6 months. I began adding SeaFoam to the transport gas cans. After a running a tank of fuel through the carb it now starts like when new.
A new replacement carb is only $39, but still.
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