Onan P220g - Nikki Carburetor - have you ever....

[Brian K WheelHorse 28]

Got my 1997 520H with the Onan P220g just a few weeks ago and I've been going over it to make it run as good as possible. Finally pulled the carb back off and to my dismay - it is one of the "Spec G" California Emissions Regulations type carburetors. It has tamper proof buttons over the jets (except the main fixed jet) and I don't like carbs that I can't adjust. The engine runs well but still is splashing gas out of the carb under acceleration. The smell is quite noticeable at idle and I can see the gas "splash in" when I perch the throttle with the air cleaner off.

My questions are: 1. has anyone ever tried to get into the jets on one of these things? I wanted to make sure that the jets weren't all blocked up. The Wheel Horse Onan manual says "replace it". That's fine but they range from expensive to really expensive, and down the road I don't want to keep buying carbs.

2. Has anyone ever swapped one of these out and replaced it with a non-emissions type Nikki carb? I would really like to swap it out with a non-emissions carb with adjustable jets, if possible.

Any suggestions would be appreciated - thanks guys.

[JackC 617]

You could buy a used carburetor from an older Onan P220g. My 1989 520HC has the non emission carburetor with no acceleration valve.

I don't know of any reason why an older carburetor would not work. If you get one, clean it, and put an overhaul kit in it, it should be as good as new.

Sell or keep the emission carburetor as a back up. This is a case where older is better.

[Brian K WheelHorse 28]

Thanks for the reply Jack - and I think you're right. I was looking at pics online of the non-emissions intake manifold and it looks exactly the same as mine. I just can't see buying a new emissions carburetor and having problems down the road. I kinda had a melt-down when I read this from the Wheel Horse Onan Manual for my tractor: To satisfy California emissions regulations, Spec G engines have internal engine modifications and precision-manufactured carburetors with tamper-resistant fuel mixture jets. It should therefore be noted that, other than installing the optional high-altitude jet (Figure 4a), fuel mixture adjustments should not be attempted. Nor should. the carburetor be overhauled. Instead, a malfunctioning carburetor should be replaced.

Can you recommend a source for the overhaul kit? Do you know the number of the carb on your tractor?

Thanks again - Brian

[JackC 617]

You will need to double check me on this information but I believe spec A-F engines had non-emission carburetors through 1994. I believe the spec G engines had the emission carburetors starting in model year 1995. I would need to check my notes but I believe the part number on my carburetor was 146-0496. The part numbers for the non-emissions carburetors changed over the years but the carburetor was the same. Onanparts.com sells new non-emission carburetors for $156.00. The repair kit that I bought for my carburetor was 0146-0500 and I paid $80.00 + $7.50 shipping from a seller on eBay. I did not need or use all the parts in the kit. I cleaned the crud out of the bowl and soaked the carburetor but I did not need to touch the jets. I did use the gaskets from the kit. The engine started and ran like new after the cleaning.

Used carburetors seem to go for around $50 t0 $80. A used carburetor may or may not need the repair kit. By the time you buy a used carburetor and repair kit you might as well just buy a new non-emissions carburetor. Some get away with just cleaning the crud out of the bowl and do not use the repair kit each time they clean the carburetor. If you are careful you can reuse the gaskets. With the ethanol fuel available today the chances of needing a carburetor cleaning are about 100% and I would not want to replace the carburetor each time. You may still be able to clean your emissions carburetor without touching the jets like I did with my carburetor. That may or may not eliminate the problem you are seeing. It sounds like there may be an issue with the accelerator pump in your carburetor which may or may not be resolved by cleaning. Maybe owners of 95 and newer 520H tractors can share their experience with carburetor issues and cleaning.

Not sure what the Onan service manual is referring to when they say the spec G engines have internal engine modifications. The only thing I see different in the parts manual is the carburetor for spec G.

Seems like the non-emission carburetor would be better to have in the long run since you can clean it and you can replace and adjust the jets if needed.

The additional pollution you generator with a non-emissions carburetor will probable be nil if you keep your engine tuned and running properly. I assume the intake manifold is the same for both according to the parts manual. I don't know for sure but I doubt you will damage the engine by replacing the emission carburetor with a non-emission carburetor.

[Brian K WheelHorse 28]

Thanks again Jack. I don't see anything else on the engine that might suggest any other mods for emissions beside the carb either. One of my other concerns is that there may be no needle jets behind the tamper proof buttons - possibly only orifices. They seem to have put the clamps on anyone trying to mess with these at all - there seems to be no available exploded view drawing of this carb anywhere. I wasn't going to get to invasive with it until I had another carb on the tractor and it was running right. I'm going to find the numbers of a 97 model 520H that is non-emissions and cross reference the carburetor for it and just buy a new one. The kits are kinda pricey so I might as well pop for one. This is a great low-hours (under 400) tractor and I'm still excited about making it run right. Once I get the new carb I will post all my results for other folks who might be fighting with the emissions carbs.

Brian

[Brian K WheelHorse 28]

OK - the verdict is in. The new non-emissions carb is an exact fit and runs perfect!!! The engine idles and runs outstanding. I warmed it up and started mowing and I have made no adjustments. I hope this might help anyone else that is having a carb issue with the accelerator pump emissions carbs.

[JackC 617]

Good to hear.

[Brian K WheelHorse 28]

Good to hear.

Thanks again Jack.