New toy and a few q's

[pyromaniac]

I was slightly impressed by the low end torque. The engine pulls very good on the low rpms, then continues up the rpm in a electric feel manner without the hit in the mid and does not rev very much, atleast it doest pull in the high rpm.

Sure lowend is nice but it seriously lacks any type of top end. Its jetted too rich(probably alot) so jett it correct should make it rev better.

Also i noticed it have a 34mm carb. As i have understand it, smaller carbs makes good lowend and bigger good topend. Can i just buy a bigger carb for any 2-stroke dirtbike and jet it correct and expect it to run as it should?

Another thing not very serious but anyway. If i ride and pull the clutch and stop the bike and try to put in 1'st gear to go away again it will stay in the gear i had when i pulled the clutch. So the issue is i cant change gears as im used to when its standing still. If i slip the clutch a little or have a little roll on the bike then there is no problem. Any ideas?

 

[Studboy]

What Year/Make/Model is this?

 

[Faded]

If I guess right do I get the prize money? :yeehaw:

How about a double-0 RM125....


The whole smaller carb/bigger carb deal is a fine line between attaining the required intake velocity while not being a 'bottle neck' in the upper rpm range where the motor's breathing requirements are the greatest.

 

[pyromaniac]

Does it really matters? Well i guiss i have to say it, its a '86 suzuki LT250. I know they arnt popular on this forum but my questions are really just 2-stroke related. I rejetted it today all the way to lean and it didnt rev much better if any.

So it should work to try a bigger carb and expect it to run simular to a normal 250? I know this model doesnt have a powervavle but as i understand it makes a better low-end and im not missing anything of that for sure.


faded: very bad guissed, i have never heard of a 125 with good bottom and no top :)

 

[pyromaniac]

I forgot, it also have steel reeds wich may also affect the top or how does it affect the engine?

 

[pyromaniac]

This was what i was afraid off, just bacuse it have 2 more wheels its ignored. Man its still 2-stroke off-road racing toy and they are fun too!

Well i hope someone show intrest anyway. I put on the 38mm carb from my 00rm125 and was suprised it even started and ran fairly good. Took it for a little run and it seemed to have all that bottom still but still not pulling in the revs as i want, it revs but not pulling and fluttering as the very toprpm. However it ran rich so maybe leaning it out helps. I noticed the intake on the engine is only 36mm so i guiss it wont take advantage of the 38mm carb more rather acting like a 36 but should be better than the 34mm carb. The intake is not square as most engines but round and very small. Maybe bore it out to 38mm can help aswell.

However looks like this engine is designed for bottom from top to toe. I think i have to do radical mods to make the engine as i want it.

 

[Faded]

Pyro, don't get so down brother! The 34mm carb for that model should work just fine, switching to the 38 w/out mods won't really help that much. When you say you jetted it all the way lean, what jets did you change and to what value? Just trying to get an idea of what you're doing here. Have you check the pipe/silencer for any obstructions like blown packing etc.? I'm not sure what material type the 'steel' reads are made of, or what thickness they are, but I would imagine that they would have a higher reed tension than fiberglass (or carbon fiber) that would help top end, not hurt it. The only other thing that may help is to check the adjustment on your throttle cable and make sure that when it's fully open the slack is taken up so that your slide is all the way up in the carb body.

 

[pyromaniac]

I changed the main jet, was 210 from the beginning then i have tried 200,190,180,160 with the 160 it began to do the BOO sound. The throttle cable was a good idea actually since i have modified it to work with a twist throttle but i think it opens all the way but sure check that. Even if it didnt open all the way i think it should pull better cause it revs alot but really dosent pull much. The pipe and silencer doesnt have any dents of leaks but the silencer is stock and non-rebuildable so it could be bad packing but the bike is not loud.

Its bore is 70mm thats the onlything that goes against the low'end trend. However i think it works as i should its just made to be a low'end machine. Its far away from any other 2-stroke i have ever ridden. Its decates from my 93cr250 i had. I cant have it this way, im seriusly thinking about putting another motocross engine in it or sell it and get another that have some top'end power in it.

 

[atc3434`]

Is it built with a power valve? Its possible its just built to be a low end machine. Probably carries more flywheel weight than a bike does as well. Make that torque work for ya. My IROC-Z Camaro only makes power to 4500 rpm, but it'll smoke a Honda turning 7500!

 

[pyromaniac]

Na it doesnt have a powervavle. As i understand that affects the botttom'end but i guiss they have built it to have good bottom anyway, of the cost of no top'end :(

I rather have no bottom'end but alot of top'end than the opposit. My type of riding its not very important with bottom end or torque cause i ride flat, high speed, good traction terrain so its its easy keeping the engine in the peakrpm.

 

[atc3434`]

Well, a powervalve doesn't really after low end or high end, it just serves to widen the powerband by altering port timing and the returning pulse wave from the expansion chamber. A different pipe, silencer, and porting combination would probably help to get the power where you want it.

 

[pyromaniac]

Yeah im afraid that's what i have to do. That will cost me about $400-500 including shipping and all. For that kind of money i can probably get my hands on a much newer engine and put in and be the way i want it without mods.