Help with 90 Gearing/Clutch

[tarzan271]

Ok, we have a Thumpstar 90 Pro with the following configuration:
High comp head (9 to 1)
Race pipe
Liquid Cooled
24mm carb
Uni filter
18x9.5-8 Duro rears
5.5gr weights x 6
1500 rpm main & shoe springs
FRC Lightened clutch
19T front
28T rear

I have tried every concivable configuration on the clutch to try to get it to hook up off the line, but it has NO low end. It feels like the clutch is slipping. Our stock 90 predator will kill it off the line so I got to wondering about the sprocket size since it flies on the top end once it is going. When I counted the teeth on the sprockets that is when I realized they seem awfully tall. Since we mostly ride trailes/dunes, this bike tends to overheat which should never happen with liquid cooling and engine ice. Now I am thinking that the rear sprocket should be about a 32T for the low end we need. Can anyone please help me out with some advice? I am pulling my hair out over this thing.

[bigdaddy]

We had the same problem a while back with 19 and 31 sprockets. I took out the frc clutch and put the stock rear clutch, small springs and big spring. Took out the lag and will stand straight up in the air.

[camsdad]

too much roller weight...try 4.5g x6....overheat =probably an air pocket or the psi on the cap is too low and allowing it to puke the coolant out.

[tarzan271]

Bigdaddy, these are all the stock springs and clutch. I even tried swapping the whole clutch setup from the stock predator 90 with the same lag problem.

camsdad, don't lighter rollers make it engage the clutch even later? What do you mean by the the psi on the cap? It will boil the coolant in the bottle when it overheats.

Does anyone think that a 32T rear sprocket will help off the line? It is suppose to have 11+ HP so it should stand up if setup correctly. Thanks again guys.

[bracey]

what size pilot jet do you have i have a 28mm carb and we run a 50 to 55 pilot jet try that and see if it helps on yopur 24mm carb

[tarzan271]

Good idea. I'll try changing the pilot jet.

[LT80]

I think you should try the bigger rear sprocket (or smaller front).
Then see what clutch tuning you need. :)

[miniquaddad]

I agree with LT80. Drop to an 18 in front or bigger in the back/or both. Once your in the ball park then tweek the clutch to tune it in. 19/28 is way too much speed not enough getting there.

[tarzan271]

That was my original thought. I will try that first.