1/4 mile gearing for asphalt track

R

racer_2828

Member
I am planning on doing some testing at an old running track before heading back to the races. I am running 21/57 jack shaft ratio and will want to turn the motor around 15,500 rpm. what would be a goodratio to shoot for while running this track?
 
If the turns are big and you can really whail on it, about a 26 driver and 60 axle..so a 6.26 overall ratio. +/-
 
Do you have a body on your kart? What engine are you running? Is it a stock engine? What's the turn radius? How long are the straightaways? How much staggered are you running?
Depending on the engine, I could see 15,500 on a Sprint track, but that would be with a much lower gear ratio.
Why the jack shaft? You could easily get 6.26 without it.
a lot depends on how much RPM you'll drop in the turns. Give it a try, but be prepared to take some teeth off the secondary and the axle. And of course it all depends a lot on what engine you're running.
Comments compliments criticisms and suggestions always welcome
 
I am running a Parilla JICA piston port 100cc motor. It has moderate porting, 360A on alky and a RLV L-2 pipe. Some have said to turn them up to 17k but I dont see that being necessary. As far as RPM drop I am letting it roll through the corner to where I can accelerate hard down the straight and get a good pull of the full RPM range. I am having a lot of trouble getting the carb worked out on my motors. I am tired of paying entry fees at tracks and only getting 3 chances to throw a set up at the carb so I am going to spend the weekend here. The track I am going to be running on is at a recreation department. I am running the jackshaft due to the dependability of the smaller clutches that are built for these motors. Currently I am running a Tomar 3 disk and have had really god results from it.
 
How long of flex have you been running? What kind of problems you having with the carb?
 
I am at 7.5 on the flex. If I am correct the L-2 requires shorter flex length than most pipes.

I am lost on the carb. It shows fat conditions due to tons of heavy thick smoke and blowing raw fuel out of the pipe but it wants to cut out on the top end. When it cuts out its almost like the motor cuts completely off. It starts cutting out at about 13k and will go dead if I do not pick up the throttle. I have tried running pop off as low as 7 on up to 13. I have tried running the high side needle completely shut off and 3 turns out. I have tried my arm height at .075 and .065 with just about any combination you could think of. If anyone has a baseline setup that I may be able to work off of please let me know. I have ordered a couple of different plugs that are a little hotter than I am running now and will see if that changes anything.
 
YOu're close on the pipe, may go 1/4 shorter but that's not the problem. When you say it cuts out like the motor cuts completely off, does it stop just like someone turned a key? Is it more like a blubbering, missing then slowing down then stops?
 
any idea what the timing is set at? my nephew got a JICA from neo about 3 or 4 years ago and timing was set at 0.085 ( piston in the hole from TDC ) on gas and this motor is still running strong :)
 
yeah that's probably your problem. The factory vent hole will never work on Alky. It will run fine on the stand but a lap or two on the track and it'll shut off like somebody turn the key off. Been there done that.

Good luck!!!
 
That has to be it. I will have to make me an extra vent and see how she runs. What do most people do for a vent? Anyone have a picture maybe?
 
It's pretty easy. We drilled a hole in the top of the tank, fixed a connector for the 1/4" hose (any length) and put a cheap fuel filter on the end to keep the dirt out. Tie wrap it to the steering support if need be.

DK
 
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