Carb main jet MIA
 

Hey fellas, been along time since I've visited the site ..

Last Friday my two sons and I competed in the local fair pulling competition .
One of our tractors didn't seem to run very well in exhibition class and was going to post our problem here for any insight .

The previous owner of this Tractor said he modified the carburetor to run with race fuel, alcohol. I have no prior experience using race fuel or alcohol so this is a big learning curve for me.

When we first got this tractor I obtained some race fuel from the local dragstrip and the engine seems to run well ....our limiting factor in the competition was we needed to add more weight to the rear of the tractor ..

The last two times we use this tractor I was not able to get to the dragstrip and get more alcohol/reschedule so I just use high test gasoline .
Both times the engine never ran smoothly or opened up intohigh rpm into its power curve.

When we got home I remove the carburetor to disassemble and clean out any potential dirt , I found there was no main jet in it it has been removed by previous owner !
Lol

I have been asking some drag strip friends about alcohol and what is needed to make it work correctly , what I have been told, whether it's true or not?, Is that twice as much race fuel/alcohol is needed then gasoline to get the full power potential ....

So.... maybe this is why the previous owner removed removed the main jet to allow more fuel to enter cylinder, and why the motor never seems to smooth out with gasoline, too much being introduced into cylinder to allow it to run efficeintly???

We have two weeks until our next big pull and I would really like to get this motor straightened out because I believe my son on this tractor will do very well once we get it right ..
Thoughts?

The motor is a Kohler oppossed cylinder twin I believe 20 hp .

Put a main jet back in it and tune it to run. Might have to change the orifice size. You say nothing about how the rest of the motor is built, so I can't really be any more specific than that.

Jonathan, I really don't know much else about the motor other then it sounds like it has a different cam in it?
Brian...

Even if it does, it will run on gasoline.

If you're going to be a puller, and attempt to work on your own motor, you need to know what you have.

I have a decent history of engines and mechanical adventures...
I just have never messed with fuels other than gasoline and diesel.
I was asking opinions if I should go back to alcohol without the main jet?
Or replace the jet and stick with gasoline...
Thanks in advance for any suggestions. Brian

Replace the jet and stick with gasoline. Unless the guy did a lot of engine work, it takes more than dumping more fuel in to make them run well on alcohol.

Post some pictures of the Carburetor. It may have been reworked for bottom adjust. If it ran well on Alcohol it won't run with the same carb on gas. It takes 30% more jet size to run alcohol.

Went to local small engine shop looked in book at exploded view and there is no main jet for the orifice to go into. Although the threaded hole that is surrounded by the float makes you think otherwise.
Turns out the high idle mixture screw was out five turns!

Set it at 2 1/4 turns reinstalled carburetor and runs much better!
adjusted engine from there ...
Brian