Another Onan question

jon f mn · Mar 23, 2021

Well the saga continues. After finally getting the leaks fixed
and the governor working the onan ran great for a while, then
started acting up again. Now after 0 hours or so of run time
it's back to as bad as it was before. Hard to start, floods out,
pops back through the carb and no power. Can here the
valves leaking back through the carb. Do I have a bad cam?
Or could the new valves set in so far that they are just out of
adjustment? I'm about to light it on fire.

gbs · Mar 23, 2021

does it have an electronic ign or points

jon f mn · Mar 23, 2021

Electronic

Janicholson · Mar 23, 2021

Winter gasoline is a more areomatic blend and can vaporize easily. I would try insulating the fuel lines and carb to keep them 20 degrees cooler. Putting fiberglass with foil backing is an option. Jim

sotxbill · Mar 23, 2021

I have a 6500kw onan that the intake valves are bad about sticking on.... and it does that off and on.... If I run it often enough, it doesnt do it.

gbs · Mar 23, 2021

if your ign is controlled from a magnet on the flywheel check to see that it didn't shear the flywheel key as that will throw the timing off, next check the compression, even if it is good check the valve clearance as some engines run a tight tolerance to accommodate a compression release for starting, had rocker arm crack on a Briggs and it was doing as you describe it was allowing to much valve lash. if all checks good or is known good then start testing the electronic ign system, if your has an ign module i have seen those on other engines intermittently fail and just about run a person fool trying to locate the problem and the cost of some of those modules is ridiculous, i have seen 2 honda 4 wheeler modules with the wiring changed to bypass some internal part of the module due to the part cost and availability that ran as good as a new one, a bad low oil sensor, ign switch ect. can also be part of the problem. but if has an ign module i would suspect that from what you describe.

kencombs · Mar 23, 2021

I don't remember what all you have done to that Onan. But, the P series are known to have intake valve seats loosen. And, you popping out of the carb symptom is one of the indications of that happening.

And, it never hurts to do a diagnostic procedure on the electronic ignitions on those. Easy enough to do, just attach a meter to the coil, turn on the ignition and turn the engine by hand. The meter should read battery voltage, and drop to 1v or less on every revolution. That tells you the pickup is working and the trigger ring is also. The magnet in the trigger ring can lose its 'charge' and fail to trigger the pickup or rhw pickup can fail.

Geo-TH,In · Mar 24, 2021

Small air cooled engines can be a pain in the ankle. Compression and leak down test were good. I had to grind the valves to fix the problem on a 20 hp Kohler with hydraulic lifters.

Other small engines have valve adjustment issues.

Go to Amazon or Ebay and see what a new carb costs.

$15 for a new carb for me 3500w champion. Best part it came with an adjustment screw for
fuel mix, not a dang California compliant carb with no adjustments.
George

jon f mn · Mar 24, 2021

We just did the valves and the seats were good. Also honed the cylinders and put in new rings at that time. I'm sure it's a valve issue because I can hear it. I'm just wondering if the valves can get out of adjustment that fast after a grind or is the cam the likely issue. I can adjust the valves again, but don't want to run a disintegrating cam.

Billy Shafer · Mar 24, 2021

Give me your model and serial number.I can look up the known problems. Give you some things to look at.

Onan tech since 1980.

Billy Shafer · Mar 24, 2021

Forgot to add 1-903-536-2816.

Den N Ms · Mar 24, 2021

jon f mn ,I would recheck the valve clearance,it sounds like they are to tight.

jon f mn · Mar 24, 2021

There is no tag on the engine that I can find. But it is a p216g by the info written in the service manual I got.

Billy Shafer · Mar 24, 2021

I would start by checking the out flow of the pump. Into a can or a clear line on the pump. Watch it while running. Those vacuum pumps tend to fail after a few years. Lets air into the system.

Check the valve settings cold page 2-1.

This is the hard one. Rotate the engine until the valve is off the seat.See if the seat shows any signs of being loose.

Check the intake manifold for leaks. This was a known problem on some units. Not sealed properly at the factory. Some units took years to show up.

What brand of spark plugs.

I will check my notes. For any odd problems I ran into over the years.

Gary in Indy · Mar 24, 2021

If you still need help, I would start by starting the engine and pulling one of the plug wires, reinstalling it and then pull the other one. Find out which side is causing the trouble.

I had problem similar to what you described and the problem was the bottom of the coil was melted, running on one cylinder.

Post back with results and we will go from there.

Another Onan question

jon f mn

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gbs

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jon f mn

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Janicholson

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sotxbill

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gbs

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kencombs

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Geo-TH,In

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jon f mn

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Billy Shafer

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Billy Shafer

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Den N Ms

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jon f mn

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Billy Shafer

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Gary in Indy

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