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Lingering 318 Onan B43 issues

8446 Views 41 Replies 11 Participants Last post by  D-Dogg
Hey all. I've been spending some time under the hood of the Tree-18 today. Still having some problems with the tractor not running well (close to at all) at full throttle or a load. It boggs down and backfires as I move to WOT. Nothing near a smooth throttle response. It idles great. I have also got some coughing out of the bowl with a little flame. At about half throttle it hunts and surges.

So here's what I've done:
- Carb teardown and cleaning. Took the top off cleaned the jet in front. Emptied the gas reservoir and blew it out with approx 10psi. Blew in the bowl too. Put back together correctly.
-Adjusted the carb. Turned idle mix screw in all the way and backed out 1 and 1/8 turn. No effect on the full throttle problem.
-Checked for intake leaks by slowly covering more and more of the carb opening. As it got close to being fully covered it started to choke out and die so I don't think I'm leaking air.

I'm thinking this may be electrical. A similar post on WFM indicated the same problem being rectified by a points and condenser. You think that's me too?

Also , the voltage regulator is still dead and out of the circuit. Battery was charged up full last night. Picking up the new VR on Monday.

Thanks all.
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I'd check the wire on the condensor. See if there is any cracking of the insulation and check the connector real good. But a condensor not working will give those symptoms.
There is another jet on the left side of the carb under a little gasketed screw on cover. On the P218 you need to remove some sheet metal cover to get to it, not sure about the B43. Once you take the little cover off, about a 9/16 or so wrench, the jet screws out with a flat screw driver. It is possible that main jet is stopped up.
You need to take the carb completely apart and give it a thorough cleaning. Taking the top off and blowing some air down the holes isn't going to cut it.

You should soak it over night in a cleaner made for carbs.

I would almost guarantee your carb is still dirty. It doesn't take much to make it run like crap.
mine was doing the same thing , I had to reset the plug gap and do the points file thing and reset the points. Just watch that little white wire when you put the metal cap back on and not pinch it or it will short to ground and never run right till you replace it.
Weird how so many things could have gone wrong after the volt reg died/shorted. The carb might still be the culprit I ill dissamble and soak tomorrow.
How about the fuel filter. I had the tractor running okay after I replaced it last week. Maybe rthis new one is plugged and causing problems? Should have rthought of that before the dealership closed today.
You need to take the carb completely apart and give it a thorough cleaning. Taking the top off and blowing some air down the holes isn't going to cut it.
I totally agree. If you're going to do it,do it right.:) As Randy stated about removing the main jet,yeah that's fine,but you will not(unless someone has a trick) get it back in with the carb mounted on the manifold. My .02

Can the carb come off without pulling the intake manifold? Looking at the parts view it appears it cannot.
Hey yardwork,
A crows foot is about all you could use. They are bolts,not studs and nuts. I tried, it is very awkward. I just decided to remove the intake,much easier that way.

It's only 4 bolts. You can have it off in 15 minutes.
Yes, I see the four bolts you're referring too. I guess that doesn't look too bad. Just ending up going deeper than I anticipated.
I agree the carb needs a thorough cleaning, but don't overlook that condensor lead PA318Guy mentioned. You've had other wiring issues.

Did the valves ever get adjusted, btw?
I totally agree. If you're going to do it,do it right.:) As Randy stated about removing the main jet,yeah that's fine,but you will not(unless someone has a trick) get it back in with the carb mounted on the manifold. My .02

I did. Just takes a short screwdriver. But, you have to get the sheet metal cover over the exhaust manifold out of the way. I didn't have a carb gasket and was afraid I would ruin the one on it taking it off, so I just left the carb on there. If the low and high jets are clean and the metering valve and needle are clean, I don't know what else there is in there to clean.
I cleaned my neighbors carb for same trouble, no help. Someone on this site said points. Got points from local small engine repair (cheaper than JD) and it runs perfect now. It had only 600 hrs and points were burnt. They were not hard to change. As been said don't pinch wire or drop parts.
I thought changing points was easier than doing carb.
Thanks all for staying tuned and providing input. I'm inclined to believe my problems (tractor related anyway :drunkie:) due to remaining electrical gremlins. This is based on the fact that a short brought it to its current state a month or so ago (and as Raisin mentioned, its a lot easier to work on with a bazillion fewer heat shield screws to remove.) Also the carb should have been protected from debris by the fuel filter (x2). I put a new filter (x3) on it tonight, I have the new volt reg ready to go.

Now all I need is some time. While at the dealer I got some additional tips on what to look for on the points to see if they're shot.
Raisin is right on,points (not wide enough gap) m2cs worth
Time has not been on my side the last week. Today I found some and spent it working on the tractor. I took the points out and they weren't too pretty so I ran sandpaper between them for a bit and cleaned them up. I put the cover, air cleaner and all that back on and took it for a spin. It did not want to run at full throttle or under a load.... bleepedy bleepedy bleep.

So in I went to get the carb out and that is no easy task. First I went after the dozen or so screws holding the heat shields in place. The the exhaust has to come off which requires the hood and supports to come off. Then you can take the intake off. So I've got the carb off and disassembled. Tomorrow I'll stop and get some carb soaker and let it sit a few days while I'm out of town. In the mean time I'll order some points and condenser (if you think I need to based on the photo below.) There is some pitting.

Lastly, what should I do as long as I'm in here? I bought new gaskets for the valve covers, I might as well make sure they are adjusted properly.

Oh yeah, when I get done with all this, my stator is bad so I'll have to pull the motor. I'm going to get it running first though.

Yippee... push mowing is great! :banghead3


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While you have it torn down as much as you do....go ahead and adjust the intake and exhaust valves to spec and reseal the intake manifold where the two pieces clamp together. Both of these are common "maintenance" items for the older Onans.

Did you try running the engine a half choke when you were at full throttle? If half choke smooths out the rpms and the engine then you are pulling a vacuum somewhere. Many times this is through the intake manifold where the two halves seal together or a bad carb gasket between the top and bottom section or where it mates to the manifold. Just a couple ideas...others may chime in here with some other items. Good luck! :trink40:
I have a couple of quick questions. How long can you leave a carb soak? I dropped in the stuff tonight and I'm leaving town for two days. Should I pull it out before I go?

Also, do those points look bad to you guys? If I keep going with the sandpaper I can probably get rid of the pitting. Regardless of what I do, what should be feeling for when I put the feeler gauge in there? Since its spring loaded its hard to get a sense of whether or not its correctly gapped.

Point can only be sanded so much. Once you break all the way through the plated surface, they burn up pretty quickly.

You need to get the blade of the feeler guage straight between the points, any angling will throw your adjustment off. The blade should slide in between with a little friction, but not so much as to actually spread the points.

Depending on the solvent you are using, two days is probably fine. If you're not sure pull it out and put it back in when you get back.
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