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View Full Version : 250 SX engine mods?....Big Bore?



Dynamo^Joe
09-30-2005, 01:35 PM
Hi:
**1st post**

I am original owner of a 250SX.
Bought it when I was 16, making $5 bucks an hour, worked my butt off to pay it in 2 yrs.
It's been damn good to me, I beat it like a redheaded stepchild and it looks like its fallen off the truck about 20 times...
...but keeps on ticking.

Over the last two seasons, Im treating it much better now. Replaced all the cables with oem, new brk pads, handlebar, every single bearing new on rear swing/axle, front axle....ouch, exxxpensive, but oh well.
Just got a 1st over piston with complete gasket set.

I figure I have about 20000 miles on it, im on my 4th set of tires however instead of the "oats" im running a set of wooly boogers on the back.

I have the piston sitting here but Im tentative to install it.
Back in the late 80's...circa 87~88 there used to be an advert in a dirtbike zine which showed a 327 big bore kit. The kit c/w oil cooler and some accessories. Had the option of original carb or buying a carb from the BB supplier.
There were levels of stock performance to race mode with different rev limiter, an ignition from a 350 x or something like that.

Im sure this 85/250 engine is the same as newer year trx 250's and 300's or at least they look damn close to the same.

Would anyone know of companies who offer big bore's to these newer quads with engines like my old 250?
What size of big bore have you heard of?

If I can find something that won't sacrifice the use of 87 octane and seem reliable [i do a lot of running in 2nd gear now - muddin it], I want more grunt to turn the Wooly booger tires.

I thought of trying a gear from a honda 250 big red as I know the tranny gears are lower, however I don't really look forward to having a big step between ratios say 1st and 2nd being really low, then have the big drop in rpms changing up to 3rd.

Regards
Joey

my90rulz
09-30-2005, 07:24 PM
Im not sure if the 87 250 trxX is the same but check it out... http://www.powroll.com/P_HONDA_TRX250X-300EX.htm

250SXwheeliepop
10-05-2005, 06:48 PM
if you want a simple mod that will get you more umph, get a 350x carb and take the jet to a size smaller than 135 for a pure stock machine.

firefirefire90
10-05-2005, 10:39 PM
check out any mods for the current 250ex ATV. That is shaft drive 250cc and should be the same motor. Anything for that should be for yours. I think i am correct on this...i think...

84200s/m
10-28-2005, 11:51 PM
isn't the 250ex a pushrod motor thats mounted sides ways to reduce on drivetrain restriction

Glenn
10-31-2005, 12:06 PM
Yep, totally different engine.

FUELATV
11-10-2005, 03:14 PM
My buddy has one of those engines done up in a golf cart. I will try to find out what is done. I think it has a big bore kit.

FUELATV (http://fuelatv.com)