20 hp riding mower " hunting "

Looking for suggestions -
1991 Wheelhorse 520H hydro - the normally smooth running
20 hp Onan has started to hunt during operation
< engine speed going up & down in steady waves >
I installed a new fuel filter this morning - no change.
Any useful advice is appreciated.
John T.
Reply to
hubops
Sounds like it is running lean - likely a jet plugging up? What gasoline are you using? Try opening the mixture screw 1/4 turn - I think a 1991 still has adjustable jets? If not (or even if -- - ) buy some SeaFoam fuel conditioner and give it a good dose in the tank.
Running ethanol fuel (even E10) can also lean it out enough to make it surge - I always use premium Shell or premion Canadian Tire or Costco fuel (no ethanol) in my small engines.(here in Waterloo Ontario - so it will be the same for you out in your neck of the woods)
Reply to
Clare Snyder
On Sat, 19 Sep 2020 23:07:26 -0400, Clare Snyder snipped-for-privacy@snyder.on.ca> wrote:
Thanks Clare - I'll give the Seafoam a try & premium gas. I've just been using regular gas and adding some stabilizer up-to-now. It's overdue for the annual oil change also - so I'll replace the air filter as well ... perhaps I'm just paying-the-price of neglecting that bit of maintenance ... John T.
Reply to
hubops
Like another post said, a jet is probably plugged up.
Mine was having problems, until I took a tip cleaner for a cutting torch, the kind that have tiny drill bits, and drilled out the jets. The bit I used to finally get it unclogged at first seemed a little big, but now it runs like a new one, and it's 22 years old.
Most welding shops have one, and ebay has them.
It runs so smooth......
Reply to
mysterious traveler
Agree, first suspect in anything like this is a fouled carb. I would identify it and get a rebuild kit, they are available on Ebay for common carbs for under $10 bucks. The kit includes new seals, needle valve, welch plugs, etc. Take it apart, take pictures if needed as you do it. Clean it out with carb cleaner or brake cleaner, blow it out. Be careful blowing it out, make sure there are no parts left that you will blow out and lose. There are Youtube videos too. Whole aftermarket carbs are available on Ebya too, typically for $25 or so for many common carbs. He can probably take it apart, clean it out, reassemble without the rebuild kit, but it's better to have it.
One note, the rebuild kits typically don't include the gasket between carb and intake. So check and if you need one of those order it separately.
Reply to
trader_4
On Tue, 22 Sep 2020 05:40:40 -0700 (PDT), trader_4
Thanks for the input. I hope to look into it today. I'll try a few preliminary & simple things before a carb re-build.
First thing will be figuring-out the fuel pump - it has a fuel hose going in a fuel hose going out - and that's it ! .. must be a vacuum port behind/under where it's mounted < ? > Also a good cleaning around the carb linkages. I bought a can of SeaFoam yesterday to try in the gas tank. John T.
Reply to
hubops
In article snipped-for-privacy@4ax.com, snipped-for-privacy@ccanoemail.ca says...
In simple terms there is a diaphram on the back of the pump. There is a hole in the crankcase (not the actual cylinder where the piston is) behind the fuel pump and as the piston goes up and down the air pressure works the fuel pump diaphram.
Reply to
Ralph Mowery
I never ever run anything but non-ethanol gasoline in my yard equipment - that is chainsaws , tractor , tiller , line trimmer and log splitter . Same with my generator , nothing but pure non-eth gas . Since Stihl calls for minimum 89 octane gas for their line trimmers and chainsaws , I've been mixing 92 and 87 50/50 for those tools that use oil mix fuel . The tractor , generator , tiller , and log splitter get straight 87 . I am luckier than many , we have several stations that sell non-eth gas in both flavors here . Around here alcohol is for drinkin' , not burnin' .
Reply to
Snag
On Tue, 22 Sep 2020 07:35:25 -0600, rbowman snipped-for-privacy@montana.com wrote:
No - there's a photo in this thread if you scroll down :
formatting link
.. which also has me thinking about the surging being caused by a fuel pump problem.
John T.
Reply to
hubops
On Wed, 23 Sep 2020 15:59:00 -0400, Tekkie® snipped-for-privacy@comcast.net wrote:
Yep - I just re-discovered it . Downloaded the Manual for my Onan P220 engine ! There was also a good Yahoo-Group for WheelHorse but I haven't looked there in years. John T.
Reply to
hubops
Finally got a-round-tuit today. Dumped some Seafoam in the tank and gave it a good shake-up. Started the motor & gave it a few minutes of running - revving it up several times. This was just to get the Seafoam into the carb. Let it sit for a few hours while I trimmed with the little push mower. Started it up again - not much difference - so I revved it out some more and shut it down. Removed fuel hose from tank outlet and forced some air <back-flushed> back through the valve into the tank using a big plastic syringe. Flushed the fuel hose from fuel pump to tank outlet ; partly removed the fuel pump & cleaned crud from around the outside / backside ; tapped & wiggled the fuel pump to clear any debris ; removed air filter housing - I should have taken a photo of the years of crud build-up around the carb ! Clean shop-cloth into the carb top to keep it clean. Used the shop vac & old toothbrush to clean it up ; a drop of oil on the carb throttle linkage - considered pulling the top off the carb - decided to see what these preliminary efforts would do - - put it back together & it wouldn't fire ! AAgggh ! Took a sanity break & looked for the simple things - noticed the coil plug-wire that I removed wasn't fully seated - duh. It fired up and ran like a champ - mowed the lawn on even revs - ... at fairly low RPM which was not possible before. I'm still pretty happy with my 1990 lawn tractor. It will still need some re-build work - for the next 30 years - : carb-job : all new rubber lines fuel ; vacuum ; hydraulic ; Rock solid engine & tranny - if I am any judge. ... I think I'll keep her .. John T.
Reply to
hubops

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