KT100 question / help

mtbikerbob

mtbikerbob

Member
My son is running a KT100 with a 4 hole can. At the last race he started having an issue with gas mist coming out of the air box (or at least that's what I think). Enough so that the kart side pod, front of the motor and his suit were covered. We run an oiled filter in the air box, there does not appear to be excess gas inside. I did make one change before his race by removing the fuel filter. We have had 2 race days and 1 practice day since the carb was rebuilt, pop off at 10psi. Any ideas as to why this happening?
 
It could be a few things - if the low speed is opened two or more turns, the carb will ‘fog’. When we ran the air box, I took the filter out of the box and ran the Outerwear external filter. Worked great and no issues with dirt in the motor. This was on asphalt btw...
 
mtbikerbob said:
My son is running a KT100 with a 4 hole can. At the last race he started having an issue with gas mist coming out of the air box (or at least that's what I think). Enough so that the kart side pod, front of the motor and his suit were covered. We run an oiled filter in the air box, there does not appear to be excess gas inside. I did make one change before his race by removing the fuel filter. We have had 2 race days and 1 practice day since the carb was rebuilt, pop off at 10psi. Any ideas as to why this happening?
Click to expand...
It would help the problem if you could expand a little more on your answers, like what change in gears, what change in RPM, what change in lap times? Is this on dirt? I understand dirt can get faster through the night/afternoon! Faster/slower?, where do you get that information?
 
Have you had the carb apart yet? If not might recommend a complete disassemble and thorough cleaning, sounds like the carb is flooding.... maybe the inlet needle isnt closing all the way... maybe a welch plug popped out of its place....fulcrum arm spring broken/missing/popped out of place.....
 
Thank you all for the input. The motor is on a crg / sprint road course kart. The only changes from previous outings was removing the fuel filter. Same basic settings on the carb, 2 on the low and 1/4 ish on the high. He actually ran very well, was consistent with lap times and was competitive finishing 4th in a field of 14 pipe and cans combined. I've been on and off on filters. I will say I noticed the flow was much improved without the filter, so it is possible the carb might need a once over.

I would think if part of the piston was broken that would cause more obvious issues, but I will inspect that as best as I can.
 
mtbikerbob,

I've seen situations before where when the kart is sitting, the tank vent may not allow any pressure buildup to escape (i.e. the tank vents OK when fuel is being consumed, but not the other way). If the kart gets hot sitting in the sun, and the inlet needle in the carb is not sealing well (completely), fuel can be pushed past the needle, run out the front of the carb and collect in the air box. This is more likely to happen if the engine is tipped "forward" a bit. If the engine is mounted flat, the fuel can run into the engine (crankcase) and make the engine difficult to start the next time.

PM
 
alvin l nunley said:
It would help the problem if you could expand a little more on your answers, like what change in gears, what change in RPM, what change in lap times? Is this on dirt? I understand dirt can get faster through the night/afternoon! Faster/slower?, where do you get that information?
Click to expand...
this got posted in the wrong thread.
 
Pete_Muller said:
mtbikerbob,

I've seen situations before where when the kart is sitting, the tank vent may not allow any pressure buildup to escape (i.e. the tank vents OK when fuel is being consumed, but not the other way). If the kart gets hot sitting in the sun, and the inlet needle in the carb is not sealing well (completely), fuel can be pushed past the needle, run out the front of the carb and collect in the air box. This is more likely to happen if the engine is tipped "forward" a bit. If the engine is mounted flat, the fuel can run into the engine (crankcase) and make the engine difficult to start the next time.

PM
Click to expand...
 
The air vent could be a possibility too. Not sure how though, we are consistent with fuel levels. We don't run a catch can, just an open piece of tubing. We did not have any issues starting for each race.
 
mtbiker,

Sounds like you've got venting covered. Just thought I'd toss that out there since it's something I have encountered before.

I'm in agreement on the carb coming apart every race weekend. One thing to check when doing that is the condition of the fulcrum arm. They tend to wear fairly quickly where the fork interfaces with the needle and the diaphragm. The top of the needle where the fork touches it can wear as well, though not as quickly as the arm.

fwiw...

PM
 
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