Onan P220 stalled

[evanloock 221]

The Onan P220 on my 1988 520-HC stalled while mowing today.  Runs strong and no issues with no load, but when the mower is engaged I noticed that the vacuum gage is registering around 5 instead of the normal 10 or so.  When mowing over a small pile of leaves the vacuum gauge went down below 5 and eventually stalled.  I checked the air cleaner.  The pre-cleaner was a little dirty so I removed it.  Mowed some more and vacuum gauge is still below 10 and closer to the 5 mark.  I am planning on removing the heads after the summer and de-carboning the cylinder and adjusting the valves.  Still starts easily.  Does seem to hunt a little around 2500 RPM no load. I know the deck is not the problem.Small for this tractor as it is a 37 inch side discharge.  Bought it NOS 2 seasons ago.  Any suggestions?  Carb cleaning maybe?  I have rebuilt Kohlers, Clintons and Tecumsehs, but I don't want to be tearing into this thing it is a simple fix.  Thanks in advance for any info.!

[gwest_ca-(File Mod) 11,041]

Try running it with the muffler removed. It may be restricted.

[cleat 5,969]

I wonder if you are actually running on one cylinder.

Try pulling each plug wire one at a time and see what happens.

 

[lynnmor 7,306]

Your paper air filter may be plugged, you need to check it with a light on the inside, you can't tell by just looking.  I would replace it.  The pre-filter takes all the large particles and fine dust is hard to see.

 

Since the engine is hunting, there may be dirt in the carburetor.  Do not continue to run it if there is dirt and the mixture is lean, that will cause overheating and loose valve seats.  But then you could blame Onan instead of lack of maintenance.

 

Valve clearance reduces as the engine heats up and valves may then leak, get them adjusted.

 

Your implements should turn freely by hand with the PTO disengaged.

 

A low reading on a vacuum gauge simply means that the throttle is open farther than a higher reading.

[clueless 2,991]

Can't help you with the Onan not an Onan guy. Just curious as where you got the NOS 37" deck from down here?

[evanloock 221]

No signs of a plugged exhaust as it throttles up from idle no problem.  Air filter is clean.  Was just replaced at the end of last mowing season and I use a foam pre-cleaner to trap most of the dust.  Pulled the plug on each cylinder and confirmed both are running with no odd noises.  I think I may have found the issue.  The tractor sat for a few months without being started as the battery was in need of replacement.  I normally start the tractor every other week to keep everything up.  When I went to start it this time the fuel pump had lost its prime.  Fuel hoses were also rock hard so I replaced them as well as the filter.  When I first started the tractor up the fuel was pumping, but there was just a small amount going into the fuel filter (genuine Onan filter as it had before).  Normally the fuel filter is at least half full.  I think the engine was starving for fuel.  I ran it for awhile and the pump's output increased.  I am sure the diaphragm in the original pump is getting old and being dry for several months didn't help that.  Now it's completely filling the fuel filter and I haven't had any more hesitation/stalling issues.  I don't see where there are any rebuild kits for these pumps.  Anyone have any info on that?  I know they have new replacement pumps, but I am sure they are Chinese made junk.  Would rather keep the original one going.  As for the NOS deck, I bought it off eBay years ago.  Thanks for all the suggestions!

[lynnmor 7,306]

The amount of air inside the fuel filter means nothing, there is always some air that doesn't flush thru.  The fact that performance improved may have come from debris being cleaned out from running after little activity.  You are correct about the aftermarket fuel pumps being suspect, but most work OK.  Also, the pulse line on the backside of the fuel pump should be replaced since the fuel line was spent.

[evanloock 221]

1 hour ago, lynnmor said:

The amount of air inside the fuel filter means nothing, there is always some air that doesn't flush thru.  The fact that performance improved may have come from debris being cleaned out from running after little activity.  You are correct about the aftermarket fuel pumps being suspect, but most work OK.  Also, the pulse line on the backside of the fuel pump should be replaced since the fuel line was spent.

Good idea.  I'm sure that line is in the same shape.  I had never seen the amount of fuel this low in the filter.  You could hardly see it and there were bubbles from the intake side of the filter.  I've had the tractor for a few years now.  I keep up the maintenance religiously like with all my other equipment.  Not sure how well it was maintained before I got it.   I always run ethanol gas.  I did the replace the gas tank bushing and shut off valve with the filter last season.  It did look a little crusty.

[lynnmor 7,306]

10 hours ago, evanloock said:

 there were bubbles from the intake side of the filter.    I always run ethanol gas. 

 

Tilt the fuel filter up so that the input side is lower and immersed in gas, then watch for bubbles as it runs.  If you see bubbles then perhaps the fuel line or valve is sucking air.  Most newer fuel line is ethanol resistant, but check yours to be sure.