A little surging insight? Onan

[toyman]

I decided to set the carb on the Onan in my 982. When I was done, it seemed to be running fine. The next day I started her up and she ran flawless until after she warmed up and then started surging at all throttle positions. I removed the cleaner housing to get a good view, sprayed some carb cleaner while running and also at the base of the carb, the seam of the intake, and at the vacuum line on the carb and the fuel pump. Everything seems to be sealed tight. I re-set the carb again, and got it running very smooth at high and low rpms. I put it all back together, took it for a ride and it started surging again. Tore it back down, removed the plugs. The one on the left (from the seat) looked the way it should, the other was black and sooty. (showing rich) I replaced the plugs, started her back up, and slowly started the adjustment on the main circuit. It seemed to run fine at high rpm, but when I put it in the middle, it surged. When I dropped it to low, it putted right along. So, back to high throttle and I slowly turned out the adjustment screw about an 1/8 at a time until it really smoothed out. It was surging less at 1/2 throttle, but I could still see the governor working back an forth a bit. I put it all back together and it runs strong. I'll fire her up again today to see if it's corrected after a good warmup. The fuel filter is clean and flowing. I have some maintenance coming up. At that time I'll pull the engine covers and torque down the heads and the manifold bolts to be sure. Other than that, any other suggestions?

[dango]

Toyman
My 982 surges when I first start it up especially when it is cold outside, settles down when it gets warm. I have heard that the two piece intake could be a potential problem, also where the intake bolts on to the engine there are gaskets that could leak and cause the surging. Good luck.

[Methos]

[toyman]

C'mon guys, someone's got to have some insight! Here's where I'm at now. I pulled the tins, and found that I have a manifold leak at the right manifold connection. (Engine revved when I sprayed carb cleaner) I ordered manifold (exhaust and intake) and carb gaskets along with head gaskets and a carb kit. They probably won't be here til the end of the month, but here's what's happening.

She starts up fine and clear (no smoke). A quick change from low idle to fast is seemless before she gets warmed up. My daughter was riding around on the 1862, so I figured I'd join in last nite. She fired right up, idled at around 1200, fast idle at 3400, no misses or pops. Rode around the yard for about 15 minutes, and all of a sudden the surging starts. Similar to right before you run out of gas. So I limped her into the garage and shut her down. I had 2/3 of a tank of gas. I have a few thoughts:

1) When the engine heats up, the manifold leak expands and creates the surging?

2) Maybe I'm having an issue with the coil once the engine heats up?

3) Maybe fuel pump, but I don't know what the correlation would be with the heat?

It's very frustrating since it runs perfect for the first 15 minutes, and then falls on it's face. I'm not looking for THE answer, just some ideas of where and what to look or check for.

Thanks!

[gcbailey]

maybe if you let me "borrow" the 982 for a few years I'll be able to learn enough to have some good input.

The only thing I can think of is when I got my 127, it did similar, ran great till it was warmed up, then the engine did a quick rev and died like you shut it off. My dad said it was an electrical issue so I replaced the coil and condenser and it's ran great ever since. And by great I mean sitting in the garage on jack stands running for 15+ minutes at a time several times.

[Mountain Heritage]

Sort of sounds like what mine did before I did a complete cleaning of it. I'd have to read my post again as to exactly what all happened and what I did. I know I ended up changing the plug wires, plugs, fuel line & filter, rinsed out the gas tank, put new carb kit in it, new gaskets for the manifold on the exhaust and intake side as well as the one beneith the carb. I think I cleaned out about 20 years of baked on crap on the inside of the carb and it still wasnt' anywhere near perfect but it would have to do. Mine searches a little now and again, but I am thinking I need to do a little more fine tuning with the govenor. But then again, I think the linkage might be getting a little worn too, so that doesn't help any. Honestly - I think the biggest problem is it didn't get used enough in the past! I work it as much as I can now....the ATV does more sitting now that I have the 982 to do the yard work with.

[dango]

Toyman
When I had this problem I ran across a company that sells Onan parts on E-bay "GP Hope" I talked to Gary who was very knowledgeable with Onan's and friendly to talk with, his number is 989-689-5092


http://cgi.ebay.com/ws/eBayISAPI.dll...%3DI%26otn%3D2

[1250cubcadet]

I'd say it is your fuel pump. My best guess is go to autozone or something like that and buy a low pressure fuel pump. I did have a intake gasket leek on me case but it would surge and stall the second it was started so I would say you have a fuel problem.

[Matt G.]

I still think it's a manifold vacuum leak...my 1872 has a similar problem, and since the carb is rebuilt and adjusted properly, there isn't much else that can explain it. I just gotta find the time to look for it. Do you have a vacuum gauge? I just picked up this really cool small-engine book yesterday that explains all of the problems that can be detected with a crankcase vacuum check...

1250cubcadet-

I disagree. In my experience, fuel pumps have two common failure modes:

One, the diaphragm tears and the crankcase fills with gas (for Kohler mechanical pumps and all the vacuum pumps) or two, one of the check valves gets dirty or quits and it doesn't work, and the engine will only run at idle.

[Mountain Heritage]

So your thinking there is a hair line crack in the aluminum intake manifold Matt? If you don't have a vaccum gauge, how do you look for that crack/leak/pin hole?