i just bought a lt500r bored 100 over ported greatly not to sure of the compression but it needs 108 or more octane or it will ping i think it has a 39 mm keihin carb. and an fmf gold exaust and the moter has about 10 hours on it since the entire rebuild so it sould be all right well my question is about how high are these supposed to rev it is a low end monster but the top end is just not there like a 2 stroke should be it runs like a desiel it will pull the tiers in 3rd grear without a prob but then runs out of power quick are these supposed to run out of power quick like this or sould they keep pulling. and about what rpm should the rev to

 

Have you raced anyone? If your used to 250`s or banshee`s the 500 sounds slow on top, but you are actually hauling a$$. If your not smoking people when racing I`d say you probly have something wrong. Like I said the 500 seems slow(by sound, Low revs) but is actually very fast. I cant remember but I think they only spin around 8000rpm`s.

 

Critical piston speed is around 7,000rpm... They don't "rev" like the smaller displacement 2-strokes (e.g. 250R, banshee, 125's)
This is a big bore that is meant to have a killer bottom and midrange. The Suzy's are typically lazy on the top unless they've been modified to breathe.
(Mine pulls like a freight train up to 6,800)

Depending on what mods (If any) to the cylinder head... you might have to run high octane fuels. (Squish velocity and angle determine this)
What's your static compression? if it's higher than ~170#, you'll probably need the good stuff. If it's 'pinging' or detonating, it could also be a lean condition. Ever done a leak-down test? Not a bad idea, especially since someones recently been inside the motor tinkering..

Hope this helps

 

it has been ported alot but i havent raced anyone yet execpt a cr 250 and it will almost keep up to that but it seems to fall off about 6500 i would guess so it look like thats just the way they run no i havent done a leak down on it. but it is realy hard to kick but it starts easy usuly in 2 to 3 kicks cold 1 or 2 hot

thanks

 

A 500 is going to be hard to kick.They have alot of compression in a single cylinder with a long stroke. I would check the carb to make sure you are not sucking the bowl dry. Check the float level and the jetting.

 

a 'properly' ported motor with good mods should chew up a CR250 pretty easily, but there is a great number of variables here... rider, etc.

If it 'falls off' about 6500 rpm, your pipe is probably doing that. (probably not a mid/top end pipe)
So much depends on where, how, and what the pipe was designed for, and also how the porting was intended to run and if the ports 'compliment' the pipe, carb., etc...(There's much more going on than one realizes.. All the pieces to the puzzle need to match in order for the machine to perform well)

the best way to figure out what's going on here is to ask the motor builder what it was designed to do.

 

does anyone have a link to see how the power valve working. and are they supposed to move when they are just reved or do they have be under a load. also do they push tword the top of the moter or is it pulled to the bottom

 

It is suppose to open at around 5500 RPM (or so) with or without load.
Look in the little window... rev the motor, if you dont clearly see that valve open, then there is your problem. Take the jug off and clean it, its all gummed up.

-Matt

 

the valve doesnt open at all if i take the preload off it will try but it dont want to eaither rev high enough to open it or it is broken inside but it will try to open if there isnt a preload on it. when i got the bike it was adjusted open and never shut if up is open. has anyone else had this problem. but the motor only has about 6 or 7 hours on it and it moves very easy by hand

 

that right big bore 2 stroke didn't rev as quick like other models,the stroke lenght mean how up the rpm will rev,like a banshee with 54mm stroke can easily rev 9000 rpm,mine big bore scrambler 400 rev at 7200 rpm but not power valved,the pipe and porting decide how fast the engine will spin.