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52 cubes of goodness
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246 Posts
Discussion Starter #1
As many of you already know, I picked up a GT 19.9 and have been getting it ready for winter duty. When I got it a few months ago, it had been sitting for 2 years. I dumped the tank (plastic), filled with fresh gas, new battery, and after about 3 revs it was off and running. Lately however I've been noticing that it has an idle fluctuation, like its surging off of the governor. Runs fine when throttled up, just seems to surge at lower speeds. Kind of a pain when you just want to loaf along. It makes you want to wind it up to get it over the 'hump'. It didn't intially have this problem. Before i tear into points and carb, i wanted to get some of your thoughts on this. Thanks. you all have been great so far. :trink39:
 

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Super Moderator
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32,747 Posts
Several things could be happening here:
1. Dirt in the carb idle circuit
2. Leak in a fuel line (if old and cracked replace them)
3. Fuel pump not delivering fuel correctly (this could be different than the 18 Onan so hope someone else gives you procedure)
4. leak between carb and intake manifold (check with unlit propane torch should change pitch of engine)

Good luck!
 

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Cranky Motorsports
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15,266 Posts
Thats actually normal for the carbs when they are dirty or not adjusted right. Take the top off the carb, clean everything thoroughly, take the fuel pump off, clean everything thoroughly, put a new fuel filter in it, and adjust the main screw to 1 1/4 turns off seat, and the idle screw start about 3/4 turn and see how she runs.
 

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Just went thru a similar situation with a B48G Onan 19.9 in my Cub 982. I pulled the shrouding, fired her up and sprayed carb cleaner at the base of the carb, along the intake manifold and at the intake manifold gaskets. I ended up having a blown manifold gasket. I replaced the intake, exhaust and both carb gaskets while I had it apart. It runs like a dream now. Good Luck!
 

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52 cubes of goodness
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246 Posts
Discussion Starter #5
I will fool with it this weekend. Is there a good outlet for Onan carb/fuel pump overhaul parts? Anyone have a PDF manual for this tractor, or at least something for the onan? :thanku:
 

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It's probably a dirty carb. It could very well be the intake manifold gasket though but that's a little more rare than a dirty carb.

The overhaul kit for it is around $50 and includes the parts to do the fuel pump if you have the vacuum operated pump.
 

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52 cubes of goodness
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246 Posts
Discussion Starter #7
Wheres the best place to get them? Any good site sponsors for this?
 

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I'm not sure for your particular engine. I get parts for my Onan from a MTF member who is an Ingersoll dealer.

Try Ebay.

I would first try cleaning it really good. The passages in these carbs are very small and it take just 1 very tiny piece of gunk to mess things up.

You can buy a 1 gallon can of carb cleaner at auto parts stores that you dip the carb parts in and let them set over night to soak. I use the metal part of a bread bag twisty tie to poke through the smallest jets carefully.
 

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Cranky Motorsports
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15,266 Posts
www.onanparts.com

there is also a member on here I think "onanparts" that sells them
 
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