ok i now use a ramair air filter on my bike with a stage six exhaust. iv had the exhaust for a while now and only just fitted my high flow air filter. obliviously i had to up jet my carburetor. i was not 100% sure what size but from the information i looked up, 85 was the best. i bought a jet pack containing 75 - 98. i fitted size 85 then took my bike for a spin. my acceleration slowed right down. 2-3 seconds it would be sloppy then the revs will pick up fine and gain speed fast to 30. Now this is the problem?... the bike will only hit 40. so i up jetted it again to 90, Same problem again. So i tried 95. The engine would still sit on 40 "flat point" for a while but as soon as i hit a hill the bike will shoot to 60 mph+. Now i know 40mph is the flat point for my set up. keep up jetting my bike just got beyond a joke!. one of my mates have the same kind of set up but with a different air filter but 85 main jet works fine with his bike. Im confused on what i should do. my setup:

Stage six exhaust.
Ramair Air Filter
Malossi kevlar belt
Malossi cdi
Polini 7.7 gram rollers
85 main jet < wrong set up

Any ideas what my problem could be.

Bradley, January 2011

not piston sorry i meant sparkplug... :D

Nathan, August 2012

This could be right to ^

also the Problem could be Your going the wrong way on the jet......you current problem is that you are running to rich.....you can tell weather your running rich by taking out your spark plug and if it is soaking in oil your to rich........to test this you will have to go down the road flat out and then just kill the engine and stop and check your spark plug.....if its soaking your too rich so you need to go down the jet size...you want your piston looking like it a little damp if your using it on the road as its best to keep it a bit richer to prevent your bike blowing up...........On the other hand you can tell if your to lean(weak) by riding your bike and it has no top speed it just goes flat and refuses to pull.......if this is the case then your jet is to small so you need to go up in size.........its a game getting it right but when you do you know its right ......... have fun and tell me how you get on with it .....

Nath

nath (2 Time Metrakit Champion) Currently races in BSB 125cc, August 2012

mine has a 92 main jet but after about 3 mins of riding it starts spluttering and backfiring, flames come out of the exhaust and the speed drops from 50 to about 30mph, i think my jet is too big but not sure.

Jamie, November 2011

If you up jet then all it will do is make the bike slower. you need to go down the jet sizes. Only 1 at a time! the smaller the jet you have in your bike the less fuel your engine will be needing to burn. you just cant go too small on the main jet or the engine will seize. Its a fine line which you will just need to play with. try going down 1 at a time and see if this helps.

John, April 2011

Hi it could be your rollers causing the problem... you will be surprised on how fast your variator will ware when it de-restricted. i don't recommend this but try using a little bit of oil on your rollers and see if that helps for a short while. you can also try your Engine Compression and see if it is low .ie -100psi. should be 120 - 150+. if none of these are your problem then it could be your exhaust pipe...

Engine Master, January 2011

no thats not the problem mate. as i said the bike was fine until the last few days. the exhaust and the rollers have been in my bike for a while, thay cause no problems

Bradley, January 2011

the problem is the expansion chanber exhaust you have on it,they are good but need alot of back pressure to get the engine running right,i would try some lighter rollers like 5 grams or try taking 3 rollers out and leave 3 in in a triangular posistion.as the rollers do not let the engine rev fully it doesnt allow enough exhaust gases to go through and create the back pressure

adam bike doctor (of milton keynes motorcycle centre), January 2011