Jonak

Member
John Deere with Onan 18 HP Engine. Any suggestions to keep it from surging. The Onan seems to have that tendency to surge. Seems worse when warmed up. Thank You for any and all suggestions. Joe
 
The most common cause for this mod eng to surge is intake manifold leaking/sucking air at split in same,idle passages in carb plugged/restricted due to dirt or high/low speed needles mis-adjusted.

Check that manifold tight on block & gaskets good,if mounting ok,clean off intake manifold & carefully inspect for loose/broken rivets that hold manifold together & also check for hairline cracks in castings,if no loose/broken rivets or hairline cracks found in manifold,get a spray can of carb cleaner with plastic ext tube.

With eng running at slightly above idle & with ext tube installed in spray can nozzle slowly spray all the way around manifold where halfs joint,if eng speed changes while doing this either one/more rivets loose or gasket bad at joint.If you can pinpoint air leak & it's a small area try sealing same with red rtv sealer,if manifold leaking in several spots,either replace manifold OR drill out rivets & seperate manifold halfs,clean out joint & pack with red rtv sealer,reassemble manifold useing screws,lockwashers & nuts.IF no bad rivets/ air leaks found in manifold consider removing/disassembling carb & cleaning out/blowing out all passages in carb body & possibly rebuilding carb at same time.

Other possible causes of surgeing,problem in fuel delivery system(weak pump,plugged/restricted filter,bad fuel lines between tank/carb,dirt in tank plugging outlet,plugged vent hole in tank cap or cap bad)problem in ign system(coil may be going bad & dropping 1 cyl)internal eng wear or mech problem(worn cyl/rings,sticking valves/worn valve guides,leaking head gasket(s),hairline cracks in block/heads.
 
Thank You Joe. That is a Very Good descriptive answer to the problem. I appreciate it, Thanks again. Joe
 
I have no idea how the governor is set up on your Onan-- I had a surging problem with an old engine and noticed the spring between the governor and carburator arm had different notches to adjust the spring tension. Moving where the spring was hooked up (changing the tension) helped mine.
 
check the welch plug at the base of the carburetor and if it is present seal it up with some of your womans finger nail polish,it will work buddy i promise.lol
 
Thanks to all for the Great suggestions, Now to get to it!! Thanks again, It is appreciated:>))
 
I have a JD318 and all of the items mentioned I checked before I opened up the carb. and found dirt and water in the bottom of the carburater[not sure of the spelling] I cleaned it out and reassembled the carb. and it ran fine, no adjustments or even parts purchased. so I did purchase a new in line fuel filter and have been useing this tractor for two years no problems.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top