[79TA7.6]

I have had my latest 250 for close to a year now. I have been riding these things for close to 20 years, mostly used for either checking pastures or chasing the cows in. They seem to have decent power, but nothing like the latest 250. This thing has a lot of power. I have heard of big bore kits but I have only personally heard of them on sport type bikes. My buddy has a couple of them that he plays around with in the sand dunes. Do they make big bore kits for the utility quads as well? If so how would I go about telling if it has been swapped out? Do they all have the size stamped into the castings like factory?

Any other reason this quad would have so much more power over the 4 others that we have? All are running the same size tires.

 

[shadetree]

chances are, piston/cylinder/bore is in better shape than the others ?. leave it stock, nothing gained from trying to '' hot rod '' it, you won't notice much difference if any at all ?. i don't know of any large bore kits for these utility models.

 

[retro]

If you suspect that your motor might be larger than 246cc you can check the bore diameter. Stock bore is 74mm. The TRX250A and TRX300 motors share the same exact cylinder (displacement marked accordingly and have different chain tensioners bolt up to them) , so any TRX300 BBK cylinder will fit on a TRX250 as well. Big bore kits add low end grunt, but add nothing to the topend RPM range (until you port and rework the head for more flow), in case you're wondering.

 

[79TA7.6]

Thanks guys. I have no intention in doing anything to this thing, they have always had enough power for what we need them for. We are ranchers so we are not playing with them, just for work.

It very well could be that this just has not been ran near as much as our others. This does not leak nor burn a drop of oil, the clutch does not slip either.

We did just inherit a 2001 TRX350TM. My brother in law had it so it is a little more abused. Will start a new thread on that one though.

 

[wheeler]

Big bore kits add low end grunt, but add nothing to the topend RPM range (until you port and rework the head for more flow), in case you're wondering.

Retro, you are kinda wrong on this one. A big bore kit, plus a cam will add a lot of top end power. Now mind you if you just toss a bbk in a quad, and leave exhaust, cam, air filter stock, well yes then you will gain low end but nothing else..

Case in point, my quad...

 

[retro]

But... that extra observed topend power in your example is the sole result of the camshaft change, none came from the larger displacement. Increase the effective valve curtain area and then you can attribute topend gains to increased displacement. Follow me...?

 

[wheeler]

I absolutely agree... I guess my statement basically follows right along with what you said. I stand corrected...

 

[retro]

Actually we were both correct. Because a camshaft change may potentially optimize existing flow capabilities throughout the entire RPM range, if in doing so you were not robbing from Peter (the bottom end) to pay Paul off on the topend. The stock factory cams are not optimum in either ranges, so the cam is a critical factor in all possible displacement configurations.

 

[fishfiles]

79 , if you think it is weaker , do a compression test , if it is low you can do an upper thru G+H for a little over $200 for everything you need , I would add in a timing chain while it is a part ---- those trx250A's are very fast and power machines as is , I have had a few of them