fastest atc us 90

[SCRAMCHARGER318]

just curious my father has one of the old atc 90's (1972) which he has pumped way up, 14:1 compression, megacycle race cam and valve springs, left side carb of a 175 twin street bike, head is ported and custom conduet exhuast, and a poweroll stroker kit, this thing hauls! the motor now is a 128cc and he is planning on going bigger. good thing my 250sx has 5th gear otherwise i'd never catch him! i was wondering if anybody else out there has a wicked pumped up 90 like his using the stock engine. he is wanting to know if anybody has put a cdi ignition on a 90 becuase he fowls plugs about 1 a hour.


1986 honda 250sx (reckless abandon)
1974 dodge dart (swamp rat)
1992 dodge ramcharger 4x4 318 magnum MPI
1995 dodge 1 ton cargo van 360 magnum (trike hauler)

[300rman]

sounds like alot of money to put into a 90,when a 200x in stock form will probably beat it down :/

[SCRAMCHARGER318]

well up hear in grand rapids my granfather bought the second atc 90 that came into gars honda, he used it on the railroad on service calls because it would fit in between the tracks, not long after that he bought one for my dad, aunt, uncle, and grandma. they built all of them up in the 70's but my father kept his and built the engine that's in it over 10 years ago. everyone has got to be into something he likes his 90, and yes it will suck up a stock 200x bottom end, the x will drive around him top end. he just wants cdi ignition to make his plugs last.

[atctim]

CDI Ignition has not much to do with him fouling plugs. More likely a rich carb condition is fouling his plugs. Have him tune his carb correctly and that plug fouling problem should go away.

[brapp]

the problem with the us 90 is ther eis no timing advance so it can not burn the added fuel at full throttle afficently check otu the cdi set up off a atc110 it may work i belive the botom ends are fairly close or a even closer fit woudl be the trx90 from 93- curent.

[Vealmonkey]

I have a bored and stroked atc90 that is 183cc's or so. Sounds like the carb needs dialed in a little bit more. Trouble is, you can only dial them in for wide open throttle or dial in towards the lower end. A hopped up 90 makes a bad trail machine. Post some pics on what he has done so far with the trike. There are a couple tricks he might be missing.

[SCRAMCHARGER318]

carburetor does not run rich, starts first pull, and no black smoke, just like the old cars w/points ignition if you let them idle a little too long they'll load up, that's why he wants to go with a cdi set up, he will be driving it at low speeds and suddenly it will start to pop and bang, put a new plug in it and she runs like a champ again, when you race it continously you will not fowl the plug. hes got a 125m engine but all the electroics are long gone, what hes really looking to know is if you can convert a 110/125 electronic system over 2 a 90 without changing the engine over. or if somebody offered a aftermarket set up. i know these old
90's are ancent but he wont buy anything else. he bought a 350x and sold it the next day to his buddy, he never even rode it.