South West Bikers | Motorcycle Forum

Hi, my name is Dave and I live on the outskirts of Exeter. I'm not a biker but the frustrated father of a biker. I have joined this forum at the suggestion of my mate and your site administrator, Dave, in the hope that someone may be able to help. I have some knowledge of car engines picked up from 30 yrs of driving but the only things I know about 2 stroke comes from experience with chainsaws.

My son has a Yamaha TZR 125 (unrestricted with powervalve) that we are having trouble with. It was running ok until he got near the powerband then it started running really roughly.

So far I have stripped and cleaned the carb, changed the plug, cleaned the fuel filter and flushed the tank. The piston and gaskets were changed a few months ago. None of this seemed to make much difference (a little but nothing significant.) Yesterday he took it into Exeter and it broke down. Eventually someone else managed to get it started and he rode it about 500 yds and it conked out again!

I guess this latest problem may have something to do with crap stirred up when we swilled petrol through the tank but even if this is sorted we are left with the original problem.

The only thing left that occurs to me is possibly the HT lead breaking down. Beyond this I think it may be something to do with the powervalve.

What I need (apart from some mechanical god to sort it out) is someone with knowledge and experience to say it's this problem or that problem.
Then we can make an informed decision about which way to go next - whether we can do it ourselves or put it into a garage. We have a limited budget but also time pressures as he needs the bike to get to college daily at Bicton as he is nearing the end of his course.

Has anyone got any bright ideas - I would be very grateful for any help and of course am prepared to pay for time if anyone is prepared get it running again quickly but even just sensible advise would be hugely helpful.

Thanks for you time.

Dave
PS I did put this info on my first 'introduce yourself' posting in a rush and then realised this is where this info should have been

Hmmmm....I know a little about 2-strokes having owned a few....including the yamaha DTR125 which is almost exactly the same motor as the TZR..if u cleaned the carbs,changed the plug,unless there is crap in the tank......it's sounds like the problem is electrical....if it's the ht then it's cheap to fix - just hope it ain't the cdi box playing up 'cuz thats bad news......

Cheers,CBR_LOVER

Thanks - I will look at the HT lead as I know thats cheap. I have just had to do so many little things which all mount up in time and money I was trying to avoid running through the whole gamut of options on an elimination basis.

Cheers
Dave

if its just the higher rev range thats affected i'd suggest its prob more likely a carburration problem - more specifically the bit controlled by the needle/main jet or fuel level OR faulty power valve - is it opening/closing ok?

when they changed the piston/rings did they check the crank seal too? if this is leaking it will affect performance, any sign of fuel in the engine oil?

as you say for the sake of a couple of quid may as well eliminate plug cap and ht lead - lead should unscrew from the coil easy enough.

when you cleaned carb did you check float levels? worth doing this, along with condition of all o-rings diaphragms if its a cv carb, along with condition of needle in slide and emulsion tube it runs in. If theres any adjustment in needle height (ie circlip at the top of the needle and notches that you can move circlip up/down in) then it might be worth playing round with the mixture through the needle height to see if you can improve it - moving the circlip up will drop the needle and lean out the mixture, and lowering the clip raises the needle and richens it. just a case of trial and error.

got to ssay i think if its just higher up the rev range then the first call has to be ht lead, cap and spark plug (check the gap).

Also i know the DTR's can run of the engine with the main fuse blown -but they tend to run rough like this, are there any other electrical problems??

After the electrics u should look at fuel and anything that could cause starvation. After that your getting into the carbs and powervalve, but most likely something simple.

I'm getting rid of my greenlaner DTR this weekend - if you want the workshop manual you're welcome. From what you've explained my first suspect would be the ignition coil breaking down under load (probably the LT side), alternatively you could have an short to earth on the LT wiring to the coil or a generator pick up problem. It's very unlikely to be powervalve or CDI and you seem to have addressed any likely fuel issues. My suggestion would be to get the motor to fail to run again and then check for a spark by putting the HT lead & plug cap on a spare plug held against earth to totally eliminate any fuel side suspicions. You can check the coil windings with a multimeter to confirm those.

Good luck and let me know if you want the manual.

check your float level.if its to low,it ll run for 500 yds as you say,cut out,the carb refills and it ll start again,does it cut out.or splutter to a stop?
oh and check your cut out switch,if it has one,had the same probs on my rd 125,and it was the cut out switch,clean :]
hope this helps