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Onan carb adjustments

1927 Views 7 Replies 5 Participants Last post by  rslaback
My 446 runs rich. It has ever since I bought it. I know this because it belches out a bunch of gas when it starts, it stinks while it runs (to the point my wife makes me shower after working on it or running it) and it likes to backfire every so often.

Tonight I figured I would adjust that. I planned to use the standard method of turning the mixture screw in and then out until the engine changed sound and then setting the needle in the middle of those extremes.

I got out my trusty manual to determine which needle was which. Case of course doesn't call them the mixture screw and idle air screw like everyone else. They are instead the idle screw and the power screw. To me that means the mixture screw would be the power screw. It is located on the right side of the tractor. I turned and turned and turned until that screw bottomed out and the engine didn't change or bog out ever. It acted almost like that was the idle air screw rather than the mixture screw.

Is that not the mix screw? Is my needle bad enough that it isn't actually een regulating the flow of gas? Do I need to set this thing on the curb with a sign that says free?
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See my previous post in your other thread, yes it all should be scrapped immediately, what is your address again?!?! :thThumbsU

Onans are foreign to me, so this one is for the old heads.

Just wanted to add my humor a little, but seriously you won't think about junking her when she is running right.
What RPM were you running the engine at when you were adjusting?

I not familar with an onan, but often if a power needle has no effect on adjustment then the carb is due for a cleaning.

I would PM Boomer, he often has posts on these threads. He knows the onan's and has helped allot of other members.

Sounds to me like the float is not set correctly, the needle/seat is defective or there is dirt in the seat. Excess gas on start means to me that is entered the engine upon shutdown as there is no likely way that it could get loaded up just by cranking a short time to start.

I would look for a plastic float hanging on the walls of the float chamber or badly out of adjustment. If it does have a plastic float, change it to a new brass replacement before going any further.
along with all the other tips from the group, you may want to be sure the o.p. installed the screws in the proper location.

i rec. one this year that had the screws mixed up.
when looking at the rear of the carb. the high speed (on the right) will have a o/ring on it.
the low will have a spring, and the needle head will have serrations on it.
good luck. boomer
Well I got the carb figured out. I pulled the mix needle all the way out. The rubber o ring that is on the needle was tearing apart. This was causing enough extra resistance that I thought the needle was all the way in. It was not. The drive end of the needle actually fits all the way into the housing when it is bottomed out. Before changing O rings mine was only flush.

I adjusted the carb as normal but didn't hear a point at which the engine sounded like it was flooding out. So I took it in until it was sputtering lean and then backed it out 3/4 turn.

If it seems to be running rich in the future I will adjust it in a smidge.
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