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Author Topic: Idle jet on 20HP Onan  (Read 505 times)

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Offline azmtnman

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Idle jet on 20HP Onan
« on: September 13, 2018, 10:21:01 AM »
  Lately, I can't get more than about 6-8 hours of running time out of a carburetor cleaning. I switched to ethanol-free gas (87 octane) and keep my air filter clean. 
   When the idle jet gets clogged, it "hunts" and won't run right. I have had to take the carb off to clean it as taking the idle air adjustment screw out and spraying it and down in the carb hasn't seemed to work.
   Any suggestions? What am I missing? This is a new gremlin that just seems to keep coming back.
Matt
1983 LT 30, 1954 Ford NAA, 2006 Polaris 500 EFI, '03 Dodge D2500 Cummins powered 4X4 long-bed crew cab, Cummins powered '88 Chevy R30, Stihl MS250, MS311 and MS661--I cut trees for my boss who was a Jewish carpenter!

Offline Andries

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Re: Idle jet on 20HP Onan
« Reply #1 on: September 13, 2018, 10:35:12 AM »
You might have crud further 'upstream' on your mill.
Have you checked the tank and lines ?
Fuel filter ok?
That gunk has to be coming from somewhere . . . 

Also, up here in Manitoba, our gas is 87 , 89 and 91 octane.
The 91 is the only one without the ethanol.
The older engines weren't made to be ethanol friendly.
My Onan had similar problems until I swore off any fuel with alcohol in it. 
Sent it to "AA".   :D  :D
LT30G24
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Offline azmtnman

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Re: Idle jet on 20HP Onan
« Reply #2 on: September 13, 2018, 11:43:03 AM »
Fuel filter is new. It's a see-though and looks good. I've ran about 3 gallons of ethanol-free through it so far. The only ethanol-free I can get here locally is 87 octane. I would pay for higher if it was available. 
   I didn't think about cleaning the tank but it should be good (and looks clean) after that much pure gas going through it. 
   Does your air cleaner seem to keep the sawdust out well?
1983 LT 30, 1954 Ford NAA, 2006 Polaris 500 EFI, '03 Dodge D2500 Cummins powered 4X4 long-bed crew cab, Cummins powered '88 Chevy R30, Stihl MS250, MS311 and MS661--I cut trees for my boss who was a Jewish carpenter!

Online charles mann

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Re: Idle jet on 20HP Onan
« Reply #3 on: September 13, 2018, 11:59:13 AM »
Iv got an onan on my miller 225 bobcat and at an idel 1 day, it just died on me. I could start it with a spray bottle of gas and spraying a mist into the throat of the carb. I put an inline squeeze buld to see what if happening, thinking maybe my pickup tube was broken. Not the case, i could squeeze fuel through and up to the carb. Once cooled down, it would start back up. Talked to the local welding supply store and he said it sounded like the mechanical fuel pump. I by-passed the mech pump, squeezed fuel to carb and it worked as advertised. The mech of the welding store said it run that way till the carb wore out, but recommended a new pump. I put an inline pump and wired it to the run switch. 
May try looking into the mech pump. 
Temple, Tx
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Offline ladylake

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Re: Idle jet on 20HP Onan
« Reply #4 on: September 13, 2018, 12:46:44 PM »
  On a little Briggs the fuel line between the filter and carb was disintegrating sending chunks of rubber into the carb,, gave me fits until I found it.  Steve
Timberking B20 12000 hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Dino setter Volvo MCT125c skid loader

Offline jb616

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Re: Idle jet on 20HP Onan
« Reply #5 on: September 13, 2018, 04:42:28 PM »
I would agree with the electric fuel pump and ditch the mechanical. Chet recommended this to me when I picked up the 224 from Jeff. I just ordered a Mr. Gasket 42s for mine from Advance Auto.

Offline azmtnman

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Re: Idle jet on 20HP Onan
« Reply #6 on: September 14, 2018, 12:12:59 AM »
I've had this problem too many times before. It will run high speed fine and cuts fine (except it hunts under no load) so it's not the fuel pump. I'm pretty sure the idle jet is clogged again. 
  I've tried the hand job, lots of carb cleaner and took the idle air adjustment screw out and sprayed it. I'll probably have to take the carb off again. I'm just wondering how to prevent it.
1983 LT 30, 1954 Ford NAA, 2006 Polaris 500 EFI, '03 Dodge D2500 Cummins powered 4X4 long-bed crew cab, Cummins powered '88 Chevy R30, Stihl MS250, MS311 and MS661--I cut trees for my boss who was a Jewish carpenter!

Online charles mann

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Re: Idle jet on 20HP Onan
« Reply #7 on: September 14, 2018, 12:55:41 AM »
What blend of fuel are you running? 
Was it a fresh tank of fuel when this happened before? 

Just wondering if a the tank/s prior to acting up contained enough water to gunk up your carb after shutting it down after last use. 

Temple, Tx
Fire Fighting and Heavy Lift Helicopter Mech
Helicopter and Fixed Wing Pilot

Offline sealark37

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Re: Idle jet on 20HP Onan
« Reply #8 on: September 14, 2018, 08:57:26 AM »
To eliminate the ethanol contamination problem, just add the recommended dose of "Seafoam" additive to your ethanol-free fuel for each tank full.     Regards, Clark 

Offline azmtnman

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Re: Idle jet on 20HP Onan
« Reply #9 on: September 14, 2018, 03:55:43 PM »
What blend of fuel are you running?
Was it a fresh tank of fuel when this happened before?

Just wondering if a the tank/s prior to acting up contained enough water to gunk up your carb after shutting it down after last use.
Could be. 
I cleaned the carb and changed the fuel filter then switched to ethanol-free and ran about 8-10 hours after the switch. 
I've always wondered if I'm getting sawdust sucked through the air filter but I don't think that would clog the idle jet. 
1983 LT 30, 1954 Ford NAA, 2006 Polaris 500 EFI, '03 Dodge D2500 Cummins powered 4X4 long-bed crew cab, Cummins powered '88 Chevy R30, Stihl MS250, MS311 and MS661--I cut trees for my boss who was a Jewish carpenter!

Offline slider

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Re: Idle jet on 20HP Onan
« Reply #10 on: September 14, 2018, 05:44:35 PM »
I think Steve is correct on replacing the fuel lines . it is just one more simple thing you can do to resolve your problem.

You said your tank looked clean so that may not be the problem. i have a honda on my wood splitter that gave me similar problems. crud in the tank . we have a product here called etch prep that will stop rust. it is made by clean strip. This stuff works. I have used it on rusty metal and 2 years later without painting it is still rust free.
al glenn


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