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Throttle Question - Probably Simple!


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#1 Ardy OFFLINE  

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Posted April 10, 2012 - 06:32 PM

I have my roper - just got it running again with a few things. I just redid the ignition on it and it fires right up. My question:

The tractor does NOT like it when I throttle it up. it sputters and spits and barely runs. It idles fine, but does not like throttle at all. any suggestions? or should I just keep playing with the mixture and jet screws? I think I'm going to tear the carb apart tomorrow and see what I can accomplish.

My other question is should the throttle go back and forth? Like on the actual carburetor. The actual throttle switch or whatever you would call it bounces back and forth between open and closed while it's running and it seems that would be why the engine is surging and acting weird.

How can I fix this? Am I missing a spring or something that stops the throttle from bouncing like that?

Edited by Ardy, April 10, 2012 - 06:49 PM.


#2 JDBrian OFFLINE  

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Posted April 10, 2012 - 06:51 PM

It sounds like your tractor could be running lean. You can try turning the high speed jet out 1/8 turn at a time to see if it helps. Do you have a service manual to tell you where to start with the adjustments? That will give you some baseline settings to work with. You are hearing and seeing the governor operating to try to keep the speed constant. Have you checked the air filter and the governor linkage to make sure it's all in good shape. You could have a carb problem as well that is causing the surging. Bad gas is a potential problem as well as plugged gas lines or fuel filter. Lots of possible suspects!

#3 Ardy OFFLINE  

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Posted April 10, 2012 - 06:54 PM

It sounds like your tractor could be running lean. You can try turning the high speed jet out 1/8 turn at a time to see if it helps. Do you have a service manual to tell you where to start with the adjustments? That will give you some baseline settings to work with. You are hearing and seeing the governor operating to try to keep the speed constant. Have you checked the air filter and the governor linkage to make sure it's all in good shape. You could have a carb problem as well that is causing the surging. Bad gas is a potential problem as well as plugged gas lines or fuel filter. Lots of possible suspects!


Hey thanks for the prompt reply, I would agree that it was running lean before but definitely need some adjustments.

Things to rule out:

Fuel line was replaced.
Gas is fresh.
Air filter has not been on carburetor while I've been testing.

I'm not sure if I have a fuel filter - at least not one that I'm used to - there's nothing between carb and gas tank other than fuel line (which I just replaced two days ago). Maybe there's one on the bottom of the tank? I'm not sure.

#4 JDBrian OFFLINE  

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Posted April 10, 2012 - 07:00 PM

If you have other problems in the engine such as a bad head gasket or poor spark for instance it will also give you the surging you are seeing. It is worth taking a look at the governor linkage to make sure all the parts are there and that nothing is bent or binding. Personally, I hate cleaning carbs and check everything else first before going there. You may find that a dirty carb is the problem. If the tractor had been sitting for a long time before you got it there's a good chance the carb is gummed up. Good luck with it.

#5 Ardy OFFLINE  

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Posted April 10, 2012 - 07:35 PM

It sat for a while before I got it, so hopefully it's just something in the carburetor. Will report back!

#6 HowardsMF155 OFFLINE  

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Posted April 10, 2012 - 07:45 PM

It is barely possible that lack of the air filter is causing the mixture to be lean. Have you tried slowly adding choke to see if the problem gets better, worse, or stays the same? That may help point you in the right direction. I had a new motor with an inline fuel filter and used an old tank. The new motor ran great for about 1 hour, then I finished the installation in my tractor, which meant replacing the new exhaust (wrong routing) and a new filter (matched existing hole in grill). Right after that, the tractor ran lean at idle. I finally broke down, disassembled the carb after blaming everything else, cleaned it and it started running great again.

I ALSO had a Kohler engine with a bad magneto coil which kept looking like a carb problem. I replaced the carb and the problems continued. Finally isolated the problem by rigging up an alternate coil.

#7 Ardy OFFLINE  

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Posted April 10, 2012 - 07:48 PM

When I got the tractor she had no spark - I've since replaced the coil and spark plug and has pretty decent spark - maybe I'll have to look at that - but I have my doubts that it's the spark.

I'll play with the choke a bit tomorrow, and probably see if I can get it to run richer and see if anything improves.

#8 mjodrey OFFLINE  

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Posted April 11, 2012 - 05:16 AM

Hope you get 'er figured out soon.

#9 justwalt OFFLINE  

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Posted April 11, 2012 - 05:46 AM

a bad condenser, (if it has one), will let the engine idle fine but sputter at higher RPMs.

#10 HDWildBill OFFLINE  

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Posted April 11, 2012 - 09:21 AM

It has been sitting and no fuel filter, to me the carb is suspect but like Howard suggested try adding choke and see what happens.

#11 Ardy OFFLINE  

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Posted April 14, 2012 - 08:22 PM

Well tore the carb apart today. Was pretty dirty in the bowl but with that being said everything wasn't horrible. Hopefully it'll make a difference, I'm also going to readjust the coil and re-gap the spark plug and hopefully will have some good results. I've never tuned a carburetor before so it's going to be fun trying to teach myself - HA!

Will report back tomorrow when I get a bit to work on it. Off to the vintage snowmobile show tomorrow!

#12 caseguy OFFLINE  

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Posted April 15, 2012 - 07:15 PM

Well tore the carb apart today. Was pretty dirty in the bowl but with that being said everything wasn't horrible. Hopefully it'll make a difference...


You'd be surprised what a VERY thin layer of shellac will cause in a carburetor!

...I've never tuned a carburetor before so it's going to be fun trying to teach myself - HA!


If you have the manual for your tractor, it should outline the basic starting point and subsequent adjustment procedures.

Will report back tomorrow when I get a bit to work on it. Off to the vintage snowmobile show tomorrow!


We'll look forward to hearing the results!




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