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I know this is probably the wrong section but I thought that maybe some of you experts would have some knowledge or ideas. Heres my question,My 10 year old son has a 2002 AC 90 quad. He has been competeing for several years in the local youth Quad Grass drags. This year I am looking to give him an advantage. Can someone suggest a good set up for 400 feet? I am sure I need to re-gear as he has been passed at the line numerous times, anyone have any suggestions as to what to gear it at? I know I should test and we will but just looking for a good starting point as we race on a limited budget. By the way my son is 10 yrs old weighs 80lbs and his machine is stock except I removed the restrictive tip off the exhaust. Any help would be greatly appreciated.Thanks
 

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I've been thru those bikes so many times and still have 4 motors for minis. The cat 90 is what my kids have raced for like 6 yrs. I built those 90cc 2 stroke motors for quite a few years and still have a bunch of used stuff for em. Cylinders,pipes,carbs etc. For free and cheap mods you can do that bike has a few. Take off the spark arrester/ muffler end cap and drill out the little restricter pipe in it so it just has the 1 1/4" end/outlet. Then rejet up 2 sizes..I believe they have a 72.5 stock go to a 77.5. that will help everywhere for a buttload of power over stock. If you take off the clutch cover from the left side you'll see the front and back clutches the front one is called a variator and has a 14mm nut on it. Take off the nut and take out the wedding ring looking spacer between the two variator halfs. The spacer limits the travel of the clutches so it wont shift out to basically the top gear of the transmission. Then reassemble. If you want to take off the 17mm nut on the rear clutch and remove it. Then take off the (spring loaded) stamped nut on the backside of it and take apart the clutch and shoes and drill as many 1/4" holes as you can get in it without it coming apart and that will raise the stall speed slightly (not a lot) so it comes out of the hole harder. Total cost $5. Just those mods will get you about 15 mph more top speed and much harder acceleration probably 1/2 to 1 second in 400 feet. My girls bike is an 02 cat 5mm stroker 4mm bigbore drag ported, inframe drag pipe, drag/dune clutching. Stalls about 6,000 rpms. Heres an eton i did the motor for a while back for Airforce 1's boy. They can really haul. Eton 90 ALKY DRAG
 
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