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Onan engine surging


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#1 Alc OFFLINE  

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Posted May 28, 2020 - 05:46 AM

Trying to figure which direction my troubleshooting should go on my John Deere 318 with a newer ( 15 years ago )  20 HP engine . For the last few years after sitting it would take a while to get fuel up to the carb but kept putting off adding a electric fuel pump like just about everyone else did but anyway . This spring it needed starting fluid and was surging , rpms not constant .The fuel lines looked bad and I've replaced them and filter ,  though the years so figured that was the issue but still not much better after replacing  .It worked good enough to get the grass cut a few time enough that it needed to be filled up . Installed an electric fuel pump last night and no better ,it's strange because it seems like a fuel issue but at times ran fine even going through pretty high damp grass . I'm thinking the carb has some dirt and when it transition for  low speed to high speed ( jetting ?)  You can watch the fuel spray above the throttle plate while it's surging and the governor just goes crazy .  If anyone has suggestion I was going to pull the intake and carb off and rebuild the carb . This engine has under  700 hours I'm guessing and never touched anything as far as valve adjustments , heck I don't even know if it has points lol it's been great for years


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#2 KennyP ONLINE  

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Posted May 28, 2020 - 06:19 AM

Sounds like the carb needs a good cleaning. That may be a P220 engine, has no points.


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#3 Achto OFFLINE  

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Posted May 28, 2020 - 06:21 AM

Definitely needs a carb cleaning. I have seen this issue many times on an Onan twin, my Wheel Horse 520H included. A good carb cleaning will solve the issue most of the time.


Edited by Achto, May 28, 2020 - 06:22 AM.

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#4 Trav1s OFFLINE  

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Posted May 28, 2020 - 06:24 AM

If the ignition stuff is sorted out (good wires and new plugs gapped to the proper specs) then the carb is the next area of focus.  

 

Have you tried running Seafoam through it?  Did you clean out the tank and replace the pickups when you replaced the fuel lines?  


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#5 Alc OFFLINE  

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Posted May 28, 2020 - 07:57 AM

Trav1s I only replaced the lines up to the tank , though I'm running a clear fuel filter and it seems full or partially when the surging , I download the manual or what's close to it .   Thinking about trying to hold the governor linkage in a fixed position just to see what happens at idle and high idle If I have to take  the tinwork off  may as well check the points if it has  them ,timing  valves and  go through the carb .

 

EDIT:  I remembered that before I hooked up the pump I tried using an external transfer pump I have and it didn't help at least running it in the garage


Edited by Alc, May 28, 2020 - 07:59 AM.

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#6 secondtry OFFLINE  

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Posted May 28, 2020 - 09:11 AM

   I have when dealing with the same, and very similar symptoms simply ran the engine up against the governor with the air cleaner off and then hand choked it to the point of very nearly killing it. The point being to suck massive amounts of fuel through the jets in the carb to try to flush them out. Sometimes it works sometimes not.

Don


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#7 propane1 OFFLINE  

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Posted May 28, 2020 - 12:06 PM

Vacuum leak some where. Just a guess. 

 

Noel 


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#8 Leonard VanCamp OFFLINE  

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Posted May 28, 2020 - 06:21 PM

Like Noel said, surging with a Onan is usually a indicator of a vacuum leak. Check the intact manifold for fit to the block and fit to the carb. You may need new gaskets. 


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#9 Alc OFFLINE  

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Posted May 29, 2020 - 05:31 AM

I tried what secondtry  suggested but no luck so removed everything , the carb looks dirty , I have a carb kit coming though the power valve isn't included , the valves were only slightly on the tight side a thous or 2 , adjusted them . No points , the kit should be here by Monday so I'll have to get this done asap , now that the weather is warm and it's been raining I think the grass is growing as I'm typing this lol


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#10 Alc OFFLINE  

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Posted June 05, 2020 - 07:23 PM

Finished the carb last night and put all the covers and exhaust hood ect tonight . Runs better but at times seems like the governor is lagging/sticking but WOT cutting was fine . I did have a hard time setting the float but at least I should be able to recheck it by only taking the top of the carb off , I think anyway 


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