TB 88cc Carb Troubles (the bog)



8 replies to this topic
  • Wogger

Posted April 25, 2011 - 12:23 PM

#1

Hey guys,

I recently installed the TB 88cc kit with race head and BBR big bore exhaust, I just cant win with this POS 20mm no name carb. I get the best top end with an 89 main jet, but I just cant dial in the mid range. The bike just bogs if I go WOT at lower RPM. I've tried every needle clip position with no success, if i drop the needle all the way to the top clip position it helps the mid range but really messes up the low revs right off idle and low rpm. It starts miss firing like crazy and will almost kill the motor around 1/4 throttle, but mid rannge 3/4 to full throttle is better. If I raise the needle all the way to the bottom clip position my off idle and low rpm 1/4 throttle problem is fixed but then the mid range gets a terrible bog any where from 1/2 throttle to full throttle. But as soon as it gets in the upper rpm range it runs great and pulls really strong.

With the 89 main jet my top end full throttle is great no matter where I have my needle position so I know the main is good to go. I just cant win with the low and mid range. I can fix the mid range but screw up the low end, or fix the low end and screw up the mid range.

Any suggestions? Can I even get other needles with different tapers or diameter for this carb? or is this carb just a POS?

Also I am thinking of ordering the TB 108cc stroker crank that comes with the Mikuni 26mm carb, will this setup give me the low to mid range snap i am looking for?

Thanks

  • dirtbkr188

Posted April 26, 2011 - 11:14 AM

#2

IMO, the 20mm ShengWay carb is easy to tune right out of the box. It comes with the #89 main and a #35 pilot jet, both of which you can buy the extra jets from TrailBikes or any TB sales rep. As a baseline setting, I use the #90 or #92 main jet, the #38 pilot jet, set the jet needle at the 3rd (middle) notch, and the air screw at 1-1/2 to 1-3/4 turns OUT from seated. Make the necessary air screw adjustments IN to richen it a 1/4-turn at a time and see what the bike does. With some of the carbs, I've run it to within a 1/2-turn of being all the way IN to get rid of 98% of the off-idle hesitation. You might have to lower the clip to raise the needle a notch, depending upon your altitude, I'm at sea level.

  • xtreme6669

Posted May 24, 2011 - 08:48 PM

#3

I have the exact same issue with mine! Still playing with settings but it has a nasty bog that I cant seem to cure. I'm going to give your settings a try 188, I'm at +/- 1000 feet altitude.

  • tennz

Posted June 02, 2011 - 07:28 PM

#4

Hey guys,

I recently installed the TB 88cc kit with race head and BBR big bore exhaust, I just cant win with this POS 20mm no name carb. I get the best top end with an 89 main jet, but I just cant dial in the mid range. The bike just bogs if I go WOT at lower RPM. I've tried every needle clip position with no success, if i drop the needle all the way to the top clip position it helps the mid range but really messes up the low revs right off idle and low rpm. It starts miss firing like crazy and will almost kill the motor around 1/4 throttle, but mid rannge 3/4 to full throttle is better. If I raise the needle all the way to the bottom clip position my off idle and low rpm 1/4 throttle problem is fixed but then the mid range gets a terrible bog any where from 1/2 throttle to full throttle. But as soon as it gets in the upper rpm range it runs great and pulls really strong.

With the 89 main jet my top end full throttle is great no matter where I have my needle position so I know the main is good to go. I just cant win with the low and mid range. I can fix the mid range but screw up the low end, or fix the low end and screw up the mid range.

Any suggestions? Can I even get other needles with different tapers or diameter for this carb? or is this carb just a POS?

Also I am thinking of ordering the TB 108cc stroker crank that comes with the Mikuni 26mm carb, will this setup give me the low to mid range snap i am looking for?

Thanks


I'm going through the exact same thing man and I'm stumped. I really enjoy getting motors tuned properly but this carb makes it no fun at all! I'm about ready to get a Keihin and trash this one.

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  • IAoffroader

Posted June 22, 2011 - 06:05 PM

#5

I tried for a year to get the 18mm Keihin to work on my 80cc engine and I finally gave up and went with the stock Honda CRF70 carb. Works great on my Z50! To get this carb to work on the Z frame use the ATC 70 intake manifold - fits perfectly. On my 100cc Powroll stroker engine (CRF70) I used Powroll's 19mm kit and it worked fantastic right out of the box. This carburetor will not work with the Z50 frame however (I tried).

  • peddeler

Posted June 24, 2011 - 10:38 PM

#6

IMO, the 20mm ShengWay carb is easy to tune right out of the box. It comes with the #89 main and a #35 pilot jet, both of which you can buy the extra jets from TrailBikes or any TB sales rep. As a baseline setting, I use the #90 or #92 main jet, the #38 pilot jet, set the jet needle at the 3rd (middle) notch, and the air screw at 1-1/2 to 1-3/4 turns OUT from seated. Make the necessary air screw adjustments IN to richen it a 1/4-turn at a time and see what the bike does. With some of the carbs, I've run it to within a 1/2-turn of being all the way IN to get rid of 98% of the off-idle hesitation. You might have to lower the clip to raise the needle a notch, depending upon your altitude, I'm at sea level.


I just installed my 2nd TB 88cc bore kit with the race head and the shengway carb with the stock exhaust on my second 1992 CT70. Using what I learned from the first one, I set up the carb with the 90 main jet, 38 pilot, air screw 1 1/2 turns out, needle clip middle position. The bike pulls hard in every gear from idle to WOT, no bogs. I tinkered with the first one for about a week before I finally found the right combination. With a little patients, and having the right jets, the shengway carb will perform quite well, in my experiences anyway.

  • fiddiesracer

Posted January 23, 2012 - 08:27 AM

#7

IMO, the 20mm ShengWay carb is easy to tune right out of the box. It comes with the #89 main and a #35 pilot jet, both of which you can buy the extra jets from TrailBikes or any TB sales rep. As a baseline setting, I use the #90 or #92 main jet, the #38 pilot jet, set the jet needle at the 3rd (middle) notch, and the air screw at 1-1/2 to 1-3/4 turns OUT from seated. Make the necessary air screw adjustments IN to richen it a 1/4-turn at a time and see what the bike does. With some of the carbs, I've run it to within a 1/2-turn of being all the way IN to get rid of 98% of the off-idle hesitation. You might have to lower the clip to raise the needle a notch, depending upon your altitude, I'm at sea level.


Just did the install of the TB 88 kit with race head, cam, HD clutch, supplied oiled air filter, etc. Running a leo vince pipe. I'm at about 2000' elevation. Do you think your recommendation of a 90-92 main, 38 pilot, needle in third position, and air screw out 1-1/2 to 1-3/4 would work for me as a starting point or should I change something because of the altitude? I would appreciate your input it's very helpful. Thanks.

  • dirtbkr188

Posted January 23, 2012 - 12:43 PM

#8

I would try the #92 or #95 main jet, due to the higher elevation. and you might have to lower the clip one notch (to the 4th groove) to raise the jet needle, also due to the elevation difference. There is no #40 pilot jet available from TrailBikes yet, so turning the air screw IN to richen it from off-idle to 1/4-throttle may be necessary, as well. Be patient and good luck, jetting the 20mm ShengWay carb takes time to get dialed in right. Using a baseline to work from takes a lot of the frustration out of jetting, in my opinion. It gives you the ability to return to the baseline and start over if you need to do so.

  • fiddiesracer

Posted January 25, 2012 - 06:20 AM

#9

I would try the #92 or #95 main jet, due to the higher elevation. and you might have to lower the clip one notch (to the 4th groove) to raise the jet needle, also due to the elevation difference. There is no #40 pilot jet available from TrailBikes yet, so turning the air screw IN to richen it from off-idle to 1/4-throttle may be necessary, as well. Be patient and good luck, jetting the 20mm ShengWay carb takes time to get dialed in right. Using a baseline to work from takes a lot of the frustration out of jetting, in my opinion. It gives you the ability to return to the baseline and start over if you need to do so.


Thanks for the reply. Based on your response I will start at 92 main, 38 pilot, and 1 drop in needle position to enrich the mix, then fiddle with the air screw as needed. Hopefully I'll get lucky and this setup will work or at least get me very close.

I have a question I'm not understanding about the carb setup and elevation. The material I read says that as you go up in altitude you actually get a richer mixture because there is less oxygen (thinner air). If thats true why do we need to install much larger jets and enrich the mixture in the carb? Wouldn't the increase in altitude actually cause the carb to be TOO rich? LOL. I guess I'm just not understanding how this works or why. Thanks again for helping me out.





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