[billy_cravens]

I'm having an issue with my 420 with P220G surging at higher rpm. I have read many posts on this issue including one started by me back in the summer. Last summer it would surge at any rpm so I cleaned the low idle jet in the carb and that seemed to help for a while. I then flushed the tank and replaced the pickup tube and the fuel line all the way to the carb bypassing the shut-off valve. It did ok for a while after that but has started again. This week I cleaned the carb and blew through it and now it doesn't surge at idle. I can go WOT and it surges bad but if I hold the governer linkage it runs flawless. I adjusted the spring into different holes to decrease the sensitivity but didn't help. Yesterday, I disassembled the carb, used a drill bit from a pocket drill in all accessible holes, blew air through holes and sprayed out with carb cleaner. I also disassembled the intake manifold and resealed while I was there. I also have 2 new inline fuel filters back to back between the fuel pump and carb. New intake, carb and exhaust gaskets when I went back together tonight. Still surges above idle and gets worse as rpm is increased. If I hold the governer, it is flawless. It also seems to run ok if I put a load on it. It has always smelled like it is running rich so I pulled the plugs yesterday and they are a dark gray but not black. I have had the tractor since Feb 2010 and have put a whopping 14 hours on it and I put a new carb on it not long after I got it. I am contemplating trying an electric fuel pump and/or an alternate fuel source to eliminate my fuel system before the carb. Does anyone have any ideas that I haven't covered?

 

[boomers_influence]

billy
it is very possible that the plastic camshaft fly ball spacer is loose or broken.
do a search on this. it is VERY common.
onan used the steel spacer until mid to late 1985.
i do stock the steel spacer. ( used )
[email protected] or call 651 437 2826.
thank you. boomer ( the used onan engine parts guy )

 

[billy_cravens]

I tore the engine down this morning to check this out. Everything looks good to me. What is your opinion? The rpm never goes too high. It just surges and gets worse as the rpm is increased.

(Message edited by treed on February 19, 2014)

 

[chuckv]

Billy,

The long tab on the ball spacer that fits into the notch in the internal wall of the gear means that you are NOT having an over-rev issue from the governor itself. That newer style arrangement cannot slip relative to the housing.

Most surging issues are fuel/air related...and if it is only at low speeds can be attributed to air leaks in the manifold or gaskets below the throttle plate. If happening at most speeds (but lighter loads) look for a plugged low speed jet in the carburetor. Clean the carburetor really well and look at the small hole in the bottom of the siphon tube as discussed in several threads here on this topic -- Kurt and others have been quite descriptive on what to look for and how to address it.

Chuck

 

[billy_cravens]

Yes sir,
I have looked at every post on the forum about this issue and have done everything that has been talked about. I even tried a different carb this morning before tearing down and had the same results. I have felt all along it was a fuel / air issue but can't pinpoint it. The only thing I haven't tried is a different fuel pump or fuel source. I'm thinking about trying my electric fuel pump and pull out of a fuel jug to see what happens. I'm not really satisfied with the small amount of fuel in my fuel filter. This teardown wasn't wasted because I had a couple of gasket leaks that needed attention anyway. Thanks for the advice Chuck.

 

[chuckv]

Billy,

One more thought -- how worn are the bushings on the throttle plate shaft? That can be a source of air leaks as well...usually won't show surging at higher engine speeds though.

Chuck

 

[KB]

I'm wondering if two fuel filters are starving it. Are they paper or mesh? Mesh woundnt worry me paper would.

 

[gzec]

If you have the same fuel pump as my b48g, take it apart and clean it. Check the hose that draws the vacumm from the rear of it. It might have failed. Its a b%^*h to put back on. So be prepared.

 

[gzec]

Although you can check the fuel pump easily by seeing how far the gas shoots out while cranking. Should be 3-5 ft.

 

[billy_cravens]

Chuck, I replaced the carb not long after I got it, so it has less than 14 hrs on it.
KB, they are paper and I have wondered this but I used this style filter before this issue started with no problems.
Glenn, I have the engine torn down now, so it will be getting a new hose.
I won't have new gaskets until Wed afternoon so it'll be at least Thurs evening before I get it back together.

 

[trapperjohn]

One way to eliminate the fuel system as the problem is to hang a small lawnmower tank above the engine and attach to the carb. making it a gravity system.

 

[chuckv]

Billy,

It may not be likely that there is a fuel delivery issue if the surging goes away at full RPM and a heavy load, as that is the time you need maximum rate of delivery.... However, the paper filters are something you need to question if you have ethanol in your gas -- it attracts moisture and any emulsion would tend to coat and clog a paper element.

Chuck

 

[billy_cravens]

Thanks Chuck. I didn't think about that. That could very well explain why the filter doesn't have very much fuel in it. I should have thought about this as much as I preach to the farmers about changing fuel filters on their equipment.

 

[cdisbennett]

Not sure if you have the 2 piece manifold but I read somewhere here that if you spray a little ether near the manifold and the motor surges it is getting air through the manifold.

There are also several fixes for this in the forum.

Charlie

 

[jameszmcnelley]

HI BILLY, I been watching this post from the start, and I also suspect the intake manifold. good luck, J.Z.M.

 

[knottyrope]

I had this issue with my 420 and it was from crud in the fuel system. clean the carb and it would run fine for a bit then surge again. I took tank off and cleaned it. replace all lines, remove fuel pump and clean it. clean the 90 at carb and then cleaned out carb one last time. then it was fine for a summer. then the carb corroded again with sand like substance. so then added in some 2 stroke oil to gas and have not had the issue since last cleaning. why 2 stroke oil? my dirt bikes and chain saw never had this issue in over 20 years.

 

[billy_cravens]

Charles D, and James M., I had noted in my opening post that I took the manifold apart and resealed it.
KnottyRope, I had read a comment you had made before about the 2 stroke oil and I think I am going to try that. My gaskets should be in this afternoon so I hope to get the engine back in the frame by tomorrow night. The only part of the fuel system that hasn't been cleaned is the fuel pump.

 

[knottyrope]

my fuel pump was plugged up bad with crud when I took it apart and the 90 inlet at the carb had a munch of crud too.

 

[cdisbennett]

Bill
I would still try a little ether, just to check the work. Only takes a second

Charlie

 

[billy_cravens]

Got the engine back together this evening. Took the fuel pump apart and it was clean inside. Ran engine for a couple of minutes and it still surged. Going to put my practically new carb back on and connect my electric pump from another fuel source and see what happens.
Charlie, I had already sprayed ether around the intake before and after I resealed it.