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KT100 Carb tuning problems.

 
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nikita Chasov



Joined: 24 Apr 2013
Posts: 34

PostPosted: Mon Jun 17, 2013 9:18 am    Post subject: KT100 Carb tuning problems. Reply with quote

Hello.
I ran my KT100 once now and found a few problems.

1)It doesn't want to rev past about 11K

2)bogs down at full throttle above 6K
At 70-80% throttle it is good.

3)Wouldn't run with high jet needle closed. No matter how I adjust the low needle. It won't even idle. If I open high needle about 1/4, it will.
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al nunley



Joined: 13 Nov 2006
Posts: 3076

PostPosted: Mon Jun 17, 2013 10:44 am    Post subject: Reply with quote

The WB3 isnít all that great a carb. But if maintained, it can do the job.
Have you replaced the pumper recently?
Have you set the fulcrum arm heigth?
Not real important, but have you check the pop-off.
Have you taken the carb apart?
Thereís all kinds of things that can create the problems you say youíre having.
Do you have any idea what the air density is?
_________________
If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
45 years, in and around karting
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nikita Chasov



Joined: 24 Apr 2013
Posts: 34

PostPosted: Mon Jun 17, 2013 4:36 pm    Post subject: KT100 Carb tuning problems. Reply with quote

By the way it is WB20.
Today, I took it apart cleaned everything, set the falcrum height to .050 and pop off to 16psi.
I have not driven it yet, just started it in the back yard and so far no difference.
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Walt Gifford



Joined: 19 Jul 2002
Posts: 4390
Location: United States, South Jerrrsey,

PostPosted: Mon Jun 17, 2013 7:39 pm    Post subject: Reply with quote

Maybe you spark plug is fouled?
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nikita Chasov



Joined: 24 Apr 2013
Posts: 34

PostPosted: Mon Jun 17, 2013 10:10 pm    Post subject: KT100 Carb tuning problems. Reply with quote

Just came back from the track. It finally runs better.

It doesn't bog down at full throttle any more.

Now, it revs to 14k no problem.

the engine flattens out a little after 13k but I think it is normal with my exhaust setup.

It still wouldn't run with high neddle closed.

The weird think is, it runs best at 1 turn for low needle and 2.5 for high!

When I tried to turn low needle past 1 turn, it starts to loose low and mid range.

Actually, I'm quite satisfied with the way it runs now and the only thing that puzzles me are the unusual needle settings.
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Walt Gifford



Joined: 19 Jul 2002
Posts: 4390
Location: United States, South Jerrrsey,

PostPosted: Tue Jun 18, 2013 9:20 am    Post subject: Reply with quote

Are you sure the diaphragms are not reversed? If it's flooding on the low end check the circuit plate diaphragm, flap should be against the plate. Also, the metering gasket should be against the carb body with the metering diaphragm against the plate.

Are you sure the carb is made for gas and not modified for alky?

Have you tried 2 turns low 1/4 turn high? What kind of track and exhaust system? Why are you running a Wb20 and not a Wb3a?

Gif Cool
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Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
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nikita Chasov



Joined: 24 Apr 2013
Posts: 34

PostPosted: Tue Jun 18, 2013 2:25 pm    Post subject: KT100 Carb tuning problems. Reply with quote

It is my first KT100.
I bought it used with this carb already installed and have now idea if it was modified.
I checked all the things that you recommended and it was all the way it suppose to be.
I also had a WB3A that was torn apart that I got with the engine. So, I cleaned and put it back together. Just now, I finished putting it on and fired it up. Now, it definitely starts up easier and runs with high needle closed.
I will have a chance to drive it later today. Will post about the results.
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Jim White



Joined: 21 Jul 2001
Posts: 1006

PostPosted: Tue Jun 18, 2013 3:18 pm    Post subject: Reply with quote

Not trying to be a smart azz Very Happy but are you sure you know which needle is which? The low is the one closest to the engine. Just thought I'd toss that out there.
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nikita Chasov



Joined: 24 Apr 2013
Posts: 34

PostPosted: Tue Jun 18, 2013 4:49 pm    Post subject: Reply with quote

On my carb they marked H and L so I couldn't miss that one.
Thanks anyway.
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Rob Kozakowski



Joined: 05 Apr 2010
Posts: 321
Location: Canada, Alberta, Edmonton

PostPosted: Tue Jun 18, 2013 6:52 pm    Post subject: Reply with quote

Jim White wrote:
Not trying to be a smart azz Very Happy but are you sure you know which needle is which? The low is the one closest to the engine. Just thought I'd toss that out there.


That's a surprisingly common mistake for many newbies! I think it comes mostly from a misperception that "Low" represents the small needle that sits lower to the carb and "High" represents the bigger (often flex-T) needle that stands up taller (high).
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