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surging

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#1 Bigfoot OFFLINE  

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Posted October 10, 2012 - 11:45 AM

I've got a John Deere 318 with a HP Linamere engine, at idle it surges up and down some, there are no adjustments on the carb. Higher speeds it seems to run smooth, but it bugs me not having it smooth at idle.
I've seen one other post about engine surging, I've been told by one guy to put some seafoam in the fuel tank, which I've done but I've not run it much since, so I'm thinking it takes some time before it might work. I've installed new plugs, na da. I'm thinking I might have to pull the carb in rebuild it, but I'm not ready to do that right now, got to much to do. Anyone had this problem and solved it?

#2 Trav1s ONLINE  

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Posted October 10, 2012 - 12:04 PM

Have you checked for a vacuum leak of some type? Maybe a bad gasket somewhere between the carb and combustion chamber. A few quick/short sprays of carb cleaner around the top of the engine would find one pretty easily. If it speeds up you found the leak.

#3 jms180 OFFLINE  

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Posted October 10, 2012 - 12:38 PM

I agree with the Rev could be sucking air somewhere maybe around throttle shaft or gasket

#4 HDWildBill OFFLINE  

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Posted October 10, 2012 - 01:24 PM

As Travis suggested check around the manifold for air leaks by using some carb cleaner. But it has been my experience that when the engine runs OK at speed but when you pull it back to idle it is a dirty or clogged idle circuit in the carb so you will probably need to pull it and clean it. You may also be surprise what you will find in the bowl.

#5 LilysDad ONLINE  

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Posted October 10, 2012 - 06:38 PM

If there are no adjustments, how do you deal with changes in the weather? That might mess with it.

#6 Bigfoot OFFLINE  

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Posted October 11, 2012 - 08:07 AM

I haven't checked for a vacuum leak but thats a good test, I'll try that asap. What I've done to check to see if the 318 engine is running rich or lean is; with the engine running at idle I slowly closed the choke to see if it smooths out or started to sputter and slow down.
What happened was it sputtered and started to choke out. That told me its running rich and not lean. So if there was a vacuum leak wheater it be at the manifold or throttle plate shaft, wouldn't closing the choke slowly at some point cause the engine to increase in speed? I will have to pull the carb off sometime and go thorough it cleaning it throughly I guess, kind of bugs me when though! Augh!! :(
What with the wife pushing me to redo all the ceilings in all three rooms, and Christmas coming, I've got several projects for gifts to do out of oak wood, (I'm a woodworker) I'm pushing it to do what I'd rather be doing! Augh!! :wallbanging:
Well now I feel better to get this off my chest.
Thanks guys!

#7 Trav1s ONLINE  

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Posted October 11, 2012 - 08:12 AM

Great thoughts on the choke. A vacuum leak would suck additional air so it would run lean. I would expect closing the choke to smooth it out and possible increase the RPMS. The Onan surge is a problem but I have never personally messed with it. I will do some research for you later today and post up some suggestions.

#8 Bigfoot OFFLINE  

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Posted October 12, 2012 - 09:57 AM

Have you checked for a vacuum leak of some type? Maybe a bad gasket somewhere between the carb and combustion chamber. A few quick/short sprays of carb cleaner around the top of the engine would find one pretty easily. If it speeds up you found the leak.


I had the time this morning to see if indeed there was a vacuum leak at the carburetor or intake manifold, so I did what you sugested, I sprayed Gumout carb cleaner at the base of the carburetor and it smoothed out and ran for 2-3 seconds well. :thumbs: so I guess there is a leak at the base, or intake. looks like the intake manifold is a two piece afair, upper and lower, with of course a gasket in between. So now I've got to get a set of gaskets for it, replace therm and hope for the best out come.
Thanks for the great advice!
  • Trav1s said thank you

#9 Trav1s ONLINE  

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Posted October 12, 2012 - 11:17 AM

I had the time this morning to see if indeed there was a vacuum leak at the carburetor or intake manifold, so I did what you sugested, I sprayed Gumout carb cleaner at the base of the carburetor and it smoothed out and ran for 2-3 seconds well. :thumbs: so I guess there is a leak at the base, or intake. looks like the intake manifold is a two piece afair, upper and lower, with of course a gasket in between. So now I've got to get a set of gaskets for it, replace therm and hope for the best out come.
Thanks for the great advice!


Sweet! I wondered if it was one of those gaskets. It should not be too bad to do... take your time and take pics to help with reassembly if needed. :smilewink:

Edited by Trav1s, October 12, 2012 - 04:05 PM.


#10 Bigfoot OFFLINE  

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Posted October 12, 2012 - 02:36 PM

I pulled the intake manifold off along with the carburetor, I didn't realize it was so much involved just getting the intake manifold out. I found that the two halves of the intake manifold were put together with some kind of silicone, no gasket. I would like to take them apart and re-gasket them but they won't come apart Without damaging either half.

#11 Trav1s ONLINE  

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Posted October 13, 2012 - 09:41 PM

How goes it?

Also, where in Ohio? My family is in the Findlay area and my wife's fam is in the Sunbury/Columbus area.

Edited by Trav1s, October 13, 2012 - 09:43 PM.


#12 Bigfoot OFFLINE  

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Posted October 14, 2012 - 08:24 AM

I've ordered intake and exhaust and carburetor gaskets for it, waiting to receive them As of yet.
I've checked the intake manifold for air leaks and couldn't find any off the engine of course. So I'm going to assume the intake manifold itself is okay. When I receive the gaskets I'll put it all back together and try it out and hope for the best.
Hopefully I'll not made it worse.
I'm located in Vermilion Ohio. Right on the shores of Lake Erie. Thanks
  • Trav1s said thank you

#13 Trav1s ONLINE  

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Posted October 14, 2012 - 11:40 AM

Been to and through Vermillion more than a few times in my life. Thanks!





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