xeonzero Posted September 21, 2012 Share Posted September 21, 2012 hello there, im a proud owner of a 1990 yamaha tzr125 which i recently built up, the problem i am having is that somthing is wrong in 1st and 2nd gear the power valve will kick in around 8K RPM, (2nd splutters unless i let off the throttle a tad) 3rd 4th 5th and 6th all have now low end power ( expected) but wont reach 8k rpm, and wont take off, top speed reached is about 50mph on a flat, it has no yvps control servo, and i have no idea what the problem could be, i took the carb off and cleaned, all seemed fine, engine is a 2RH need any more info let me know and i will post, would love to get her back to her former glory and be able to keep up with traffic =) Link to comment Share on other sites More sharing options...
Moderator Cynic Posted September 21, 2012 Moderator Share Posted September 21, 2012 Try this....... Link to comment Share on other sites More sharing options...
xeonzero Posted September 23, 2012 Author Share Posted September 23, 2012 I do apologise sir, bit ahead of myself there, as I'm sure are many people, let me intro myself I'm Gareth, 21 , been riding for 3 years, and own, 4 bikes, my beloved tzr, BSA bantam d7, honda sky, and a chinaeese bike Hope I can help out on here as I hope to get some help Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 23, 2012 Moderator Share Posted September 23, 2012 Greetings Gareth and 1: Try it briefly without the air filter fitted 2:This doesnt make sense "in 1st and 2nd gear the power valve will kick in around 8K RPM, (2nd splutters unless i let off the throttle a tad) 3rd 4th 5th and 6th all have now low end power ( expected) but wont reach 8k rpm, and wont take off, top speed reached is about 50mph on a flat, it has no yvps control servo, and i have no idea what the problem could be, i took the carb off and cleaned, all seemed fine," I assume the power valve will never kick in because it's not functional...you mean it will take off in 1st and 2nd (Hit a power band) ? Link to comment Share on other sites More sharing options...
xeonzero Posted September 23, 2012 Author Share Posted September 23, 2012 in 1st gear when i reach 8000 Rpm the bike will take off like a rocket, because of the power valve. the same will happen in 2nd gear when it hits 8000 rpm but if i have the throttle fully open it will not take off like in first gear, it will splutter i only said it to see if anyone could make sence of it as i cant, sorry for confusing, im not sure what the proper name for the power: band / valve etc.. the thing that makes the bike go really fast when you get to a certain point of high rpm, and will try without the air filter and let you know results, if you need any info let me know, and if im still talking gibberish i can allways upload a video onto youtuebe and show you what i mean thanks Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 23, 2012 Moderator Share Posted September 23, 2012 It sounds like the power valve is 'Pinned open' Perhaps you will see some evidence of this if you look at the pulley attached to it. If it is 'Pinned' fully open then performance will be poor until a certain point in the rev band and when it hits that it will go like stink, could it be this you are experiencing. Having a working powevalve will help this situation because it will pull better with lower revs The 'power valve' is a mechanical rotating device that will alter the position of the top of the exhaust port for best performance throughout the rev range The 'power band' is the rush of power some 2 strokes exibit when they hit a certain rev range Link to comment Share on other sites More sharing options...
AndyDtr08 Posted September 23, 2012 Share Posted September 23, 2012 The problem you're having is the same alot of people have. The confusion between powerbands and the power valve. Powerband - If you looked at a graph of bhp vs rpm the powerband would be the section of the rev range that provides the most power so on yours it will start at 8krpm and maybe end around 11k rpm. Powervalve - A system that many 2 stroke bikes use to close the exhaust port off or "lower it" which smooths the power out and gives more power lower in the rev range. If the servo is not controlling the powervalve it is effectivly irrelevant as it won't be closing the port off and so the engine wil run as it wasnt there at all. Link to comment Share on other sites More sharing options...
AndyDtr08 Posted September 23, 2012 Share Posted September 23, 2012 It sounds like the power valve is 'Pinned open' Perhaps you will see some evidence of this if you look at the pulley attached to it. If it is 'Pinned' fully open then performance will be poor until a certain point in the rev band and when it hits that it will go like stink, could it be this you are experiencing. Having a working powevalve will help this situation because it will pull better with lower revs I would imagine it wont have the pulley fitted and will just have the holder so the only way to check would be to have the exhaust off and feel up the port to see if the valve is flush with the rest of the port. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 23, 2012 Moderator Share Posted September 23, 2012 I would imagine it wont have the pulley fitted and will just have the holder so the only way to check would be to have the exhaust off and feel up the port to see if the valve is flush with the rest of the port. Andy I always though that they had the valve and pulley fitted and simply pegged the U slot in the pulley through to the blind 4mm hole in the cyl head, therefore wide open...not talking through experience though...just what I imagined would be the method Link to comment Share on other sites More sharing options...
xeonzero Posted September 23, 2012 Author Share Posted September 23, 2012 Good to know the difference so I can explain without confusing, I don't have the servo attached so I assume the valve is pinned open, but would thats not the entire problem, but my be a contributeing factor, my local mechanic says the servo is not worth it as it won't effect the speed, but I don't know why it splutters, and why it won't speed up in 3rd gear and up? I will take the air filter off tomorrow and see what happens, but I'm curious of the piston is shot or something, I'm not really mechanically minded, If I was I could explain the problem more I will record me riding the bike tomorrow and then you might know what I blabber on about, sorry i can't help out much 1st gear is fine, will not splutter when hits power band 2nd will hit power band and will splutter if throttle is open fully ( I will let off a tiny bit) 3rd 4th 5th 6th, no low end power, won't hit powerband, and if I do manage to hit 8k rpm in 3rd gear it will splutter the moment the engine hits 8krpm Link to comment Share on other sites More sharing options...
AndyDtr08 Posted September 23, 2012 Share Posted September 23, 2012 Andy I always though that they had the valve and pulley fitted and simply pegged the U slot in the pulley through to the blind 4mm hole in the cyl head, therefore wide open...not talking through experience though...just what I imagined would be the method Before they started fitting the servos and "pinning" them to restrict, they just didnt fit anything. The L/H side just had a holder that blocked it off and the valve was held in place by this. They often turned it 180 degress to restrict it for learner legals. when they did fit the powervalve, it could be restricted by pinning the pulley wheel to the cylinder as you say but then the servo would be attached and cables too. Otherwise water could easily get in the holes in the pulley housing where the cables would thread into. The image I've linked shows the blocked off side with no pulley from an earlier DTR model but its the same idea. If the bikes got a good powerband from 8krpm then it suggests that the powervalve is the right way round and just acting as the exhaust port would normally. Sounds more like a carb problem if it's to do with the throttle position, very strange though as you say it spluttering the moment it hits 8krpm in 3rd+. Your mechanic is right, the servo won't affect the top speed but will give you better performance lower down. I'd take the exhaust off and check the powervalve position just tor rule that out, then give the carb a good clean, cleaning all jets inside and doing the standard checks whilst it is apart (haynes manual will be useful there). A compression test might be a good idea too. If it seems low, try putting some 2 stroke oil down the plug hole and doing a test again, if it comes up dramatically it could suggest piston ring/ bore issues. Link to comment Share on other sites More sharing options...
xeonzero Posted September 23, 2012 Author Share Posted September 23, 2012 I'm sorry to ask this and people here will want to shoot me but how do I do a compression test? And thanks for info, will post a vid and some pics of her soon Link to comment Share on other sites More sharing options...
AndyDtr08 Posted September 23, 2012 Share Posted September 23, 2012 You'll need a compression tester which is a tool. It has a thread section that fits into the whole where the spark plug goes, you then turn the engine over and the guage shows what compression is inside. It should be somewhere around 100psi i believe. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted September 23, 2012 Moderator Share Posted September 23, 2012 The TZR's have always had a powervalve, the very first of them had no pully assembly at all but the valve was there and pinned at an ambiguous mid point to give all round performance. Together with knocking out a washer in the pipe, a 240 main (250 if you like flat out) and trimming some webbing in the inlet you got proper full power (albeit a big fkin wheel lifting kick up the arse at 7000rpm and cock all below it , felt great), full power was also available as an option at purchace if you produced a full uk bike licence. Then they fitted the ypvs controler near the tailight at the back of the bike and the pully system. Some people had conned full power bikes, some like an electronics student i knew built his own controller and used a 350 pully/motor combo, others pulled the cap from the rhs and removed the pin and turned it to their preference, be that wheelies or 90mph. Problem was that ment the valve was loose and would rotate back to the closed position, gravity is a bitch right. That sounds like part of the problem here. You need to take off the exhaust and see how the valve is positioned, no other way on these motors i'm afraid. They generally leak at the powervalve too if they have been done. Link to comment Share on other sites More sharing options...
xeonzero Posted September 24, 2012 Author Share Posted September 24, 2012 took off exhaust and put my fingers up there, could feel the top ,rough (possably rusty piston ????) which didnt seem right, and nothing else, if im corect in saying that the valve is fully open as far as i can tell, im gona take off air filter and see take her for a ride, so will edit a update later, would have done it sooner but rain here is terrible Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 24, 2012 Moderator Share Posted September 24, 2012 took off exhaust and put my fingers up there, could feel the top ,rough (possably rusty piston ????) which didnt seem right, and nothing else, if im corect in saying that the valve is fully open as far as i can tell, im gona take off air filter and see take her for a ride, so will edit a update later, would have done it sooner but rain here is terrible Dont go too far without the filter, I meant try it a short ride 2 - 3 miles is plenty...just in case it makes it lean Link to comment Share on other sites More sharing options...
xeonzero Posted September 24, 2012 Author Share Posted September 24, 2012 right then, after a little learning experience, turns out that the piston has a bit of play in the barrel, rings are good, and compression is fair, have been told either i have a wrong sized piston or a re-bore is in order =( but can that really kill the power that much, and make the engine splutter and keep my top speed at 50 ish ???? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 24, 2012 Moderator Share Posted September 24, 2012 so the filter made no difference? Link to comment Share on other sites More sharing options...
xeonzero Posted November 10, 2012 Author Share Posted November 10, 2012 Sorry for a late reply, after taking off the head, it's been recently rebored to .75 oversize and the barrel looks good, the air filter made no difference, she stutters in all gears except 1st and 2nd, now gona try a new reed valve tomorrow, in no luck nes carb and jets, just can't pinpoint the problem, I have a hunch it's the wording but can't say for sure and the wires are cut and chopped , will try to get a video up with the problem, I have seen so many things on the Internet that say its cause by. Eg statis plate, spark plug, I have a feeling I will end up replacing the whole bike soon, haha just want to get her going again Link to comment Share on other sites More sharing options...
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