Little confused....

[ckassen]

I have a 00RM250, with a Eric Gorr, 265 kit, low to mid range porting, boysen dual stage power reeds, stock pipe, clean twin air filter, good compression (160ish)...It runs good(slow, but the plug looks good, smokes a little, very little sploog) starts first kick every time...

My friend just got a rough 94 YZ250, it has the stock size piston, most likely some porting(not sure), stock carb, fmf full system, some dual stage reeds, maybe other mods, not sure, crappy dirty air filter, runs terrible on the bottom end(rich), TONS of sploog, less compression(130ish), and a pain to start......and we are running the EXACT same gas oil ect...

I can get the bike out of the hole by half a bike and then he just BLOWS by me, beats me by probably 6-7 bike lengths as soon as he tops out. This is on concrete so the traction is not a issue...And no it is not the rider, we can switch, put 2 different guys on the bikes ect, the yz is way faster...

I just dont get it, what is killing my bike? does the Low-mid range porting make the bike that much slower on the top end, or is my bike just not tuned properly? What have I done wrong, there has to be something...

 

[IndyMX]

Could it be the gear ratios? Perhaps you have a much bigger rear sprocket than he does?

 

[CarnageZ28]

And everything with a engine is a trade off. What you gain up high, your usually losing down low, and what you gain down low, you are losing up top.

Its possibly that you lost that much top end, but I would be looking more towards the jetting and gearing right now ...

 

[_JOE_]

Also, the displacement difference is extremely small. If you got it ported for low end I would almost expect a stock bore with mid top porting to be faster down the road. You should look into a pipe designed with a low end power curve to complement the porting. Don't rev it out, short shift it and keep it in the meat. Usually a low end power curve is best for lower speeds like woods riding and most often gearing is tightened to work best with the engine. Did you have the motor done or did you buy it like that? If it came like that make sure the jetting is spot on.

 

[ckassen]

I have checked the gearing, they are almost the exact same, within a few teeth. I had the motor done myself when it blew... I am trying to look at my jetting, I am thinking that I am going to go up one on the main and see what that does...What about a pipe, arey the overrated or do they really make a difference?

I just feel like I did something wrong(my bike was faster in a straight line while it was stock)...

 

[_JOE_]

How long ago did you get it done?

 

[robwbright]

From what I've read about Eric's 265s, there is something going on. . . I'd think you'd smoke him.

Just curious - Is the power valve working?

 

[whenfoxforks-ruled]

Something is amok, on both bikes, beautiful! Jetting, reeds, packing and air filter to start. Gearing needs may differ with the porting on your engine?

 

[ckassen]

On my bike, the air filter is clean, reeds are brand new, the packing probably need to be replaced(i would guess) and top end is only...5-8hrs old....

And if it gives any comparison, my friends bike(94 yz250) would beat a 07 yz250f(stock and brand new) by 2 lengths(on average), 2 good riders....

I am 90% certain that the power valve is working, but is there any way to check it to be 100% positive...Like actually see it move?

"gearing may need differ"? need to make the gearing shorter?

 

[whenfoxforks-ruled]

Does the bike pull hard off bottom? Then I would try a smaller rear sprocket. There should be a cover that you can take off to view the power valve move, you have to rev it pretty high. The rod or levers on the valve?

 

[gthoma23]

not a 100% sure on the RM, but take the cover off and rev it to the limiter. my manual says i have to rev up to 7k, which is almost the limit. it should be able to move freely by just using your hand, but the best is w/ the cover off and reving it.

and u say the plug looks good? if it is, i'd check the fuel filter and go up one on the main. my bike always had a dark plug, then i cleaned my PV, and now it shows the plug runnin lean. so make sure it's clean and working properly.

 

[ckassen]

I did check the PV, its perfect...I also went up to a 160 main...Up one clip on the needle(to lean out mid. with the bigger main) and adjusted the PV to 3/4 turn instead of 1..It runs like a top...twice as fast(by seat of the pants)...Raced a friend of mine (the one with the 07yz250f) and smoked him...no more problems...

I am thinking that I could probably go up to a 162 main and gain a little more, but that might be too fat...We'll see...

It is unbelieveable, the powerband is super smooth/predictable(it doesnt all of a sudden just "hit") and has tons of torque, and now it has a very strong top end.....runs almost like a 4-stroke....I feel that i will do alot better this weekend at the track(and the occasional drag)....Thanks for all the replies!...

 

[ignition retard]

Maybe try shifting sooner.

 

[whenfoxforks-ruled]

That power valve tension adjustment is for the powerband/exhaust valve hit. Less tension= later hit. Year to year its adjustment varies. I thought the 00 we had was at 1 3/4 turns.