P220 Onan Carb Question

[boovuc 1,090]

Guys,

 

My 1991 520-H is having surging/idle issues. I have a question from an old post that I can't find regarding where the Main Needle valve is located. (Duke posting).

 

I have the EPA plastic limiter screw on mine and I know that can be removed gaining access to the idle mix. My question is, isn't there a metal plug that can be pried off that exposes the main mixture needle? I was thinking that it was located just above the idle mixture needle.

 

The side of the card that faces the dash has a welsh plug that removes but I thought I read where you can get to an adjuster that is behind a metal "plug" that also needs removed. I'm going to blow out the idle mix with seafoam and air but I wanted to get the main if it is accessible. (High speed is fine but it is leaner than what I want it so it too is probably getting gunked up).

 

I already cleaned the tank and changed out the fuel lines, new fuel filter, etc.)

 

Thanks and sorry for the long post!

[SAM58 30]

BooVuc,

 

  I had the same problem with my 1996 520H, all I did to fix was to remove the top of the carb and clean out the bowl and jet with some spray carb cleaner.

Then sprayed and cleaned all openings and jets in the top of the carb, Followed up with seafoam in the gas and it fixed my problem of surging.

It ran a little rough for about 30 minutes but then started to run fine, so I just used it for about 3 hours after that. That was over a year ago and it still runs fine.  Some how fine dirt gets past the tank filter and inline filter on the fuel lines and just need to be removed.

   I read in one of the threads that you can cause some real problems trying to adjust the mixture on the Onan carb.

If it ran good before it got junk in the carb, I would think it will run fine again after you get the junk out without adjusting anything.

My 2 Cents

 

[Earle 3]

Boovuc....Earle here, I use Premium (hi-test gas) in my small engines this may help.... Earle

[JackC 617]

Cleaning the carb is probably the better way to go rather than changing adjustments.   Ethanol in fuel can absorb moisture even after the filter and in the float bowl and particles will form to screw up the carburetor.  After cleaning try to find and stick with pure gas.  Drain fuel before long term storage if possible rather than relying on stabilizers. Having a new or cleaned spare carb to swap out will keep down time to a minimum.

[MalMac 1,332]

I have done what SAM58 has done. I even found that I needed to wipe the floats down because they had a very slim film of crud on them. Once I got it cleaned out and put back together I started using 94 octane in it. That seemed to have helped. I thought it was adj. also but went through all this first and it did correct the problem. I don't know what it is about these carbs because I have a Zero turn machine with the same carb as the 520 and it needed the same thing. Just my opinion here but these carbs are the biggest POS carbs on the market. Think about all the problems you hear here on RS, this is just a small insignificant number of people that deal with them compared to the total amount of people that have them through out the country and also used internationally.

[Brian K WheelHorse 28]

I ended up replacing the EPA compliant carb on my 97 520H. I found a non-EPA carb for around $150 and it runs great. I have been using Seafoam treatment in my gas since I replaced it but I agree that that draining out the carb for long term storage is best, especially if you have regular gas with ethanol in it. The previously owner tampered with the original carb and made a mess of it. It had the accelerator pump on it and I figured that by the time I invested in the parts for the used carb - I could just buy a new one.

[boovuc 1,090]

Thanks for the reply's guys. I only use hi-test and every drop in my cans have Seafoam additive added to them.

I have new fuel line from the tank to the pump and then to the carb inlet. I cleaned the screen in the tank and gave it a rinse to assure I had no contaminants on the bottom. (This was all done in the fall last year).

 

Today I removed the idle needle and cleaned it out with a shot of spray Seafoam and a poke of fine wire. Seafoam sprayed the inlet again then blew canned air through it. Left the muffler tin off but put the air cleaner assembly back on, tightened it all down and fired it up. It now idles smooth but I know I have some wide open issues as every so often I can hear the motor work harder for no real reason and my vacuum gauge goes from 45% to 75% then back.

 

I saw an older forum post from Duke on here that stated there was a plug that covered another needle valve that was accessible without the carb being removed. (Or so that is what I thought I read). I searched under "engines" but couldn't find it. I was hoping someone remembered it and could give me a straight answer as to it is there or it isn't. I know the main is behind the welsh plug at the front of the carb.

 

I'll open the top up and do a clean out and see what my results are. I have no problems pulling Kohler carbs off and soaking them overnight but I see these Onan carbs as a Pandora's box of issues. I'll pull it and do a soak if a top-end clean out fails. It idles great now and it always runs good wide-open with the exception of that blip I feel and see about once every three mowings. I have another whole P220 on my bench that if push comes to shove, I can pull, clean it up and mount.

Thanks again, guys!

[boovuc 1,090]

PS.....I wasn't looking at adjusting the needle valve on the idle mix. I only wanted to remove it to do a clean-out of the orifice.