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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 15 Nov 2008
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Successful sprag clutch repair?

Has anyone ever had any success in repairing their sprag/one way clutch on the starter system? I have removed mine from the bike altogether due to it locking up on the sprag clutch.
My 1VJ is really starting to annoy me with not kick starting when hot.It'll start fine when cold,fine when ridden to work.But as soon as I do a trail ride or ride a decent distance....Good luck trying to start it again.The last straw was yesterday,nice ride through back country NZ roads,waited for the other rider to cross a (very shallow) river,went to take off again and the bike stalled.Kicked the damn thing for near 30 mins,fuel on,fuel off,full throttle,no throttle,wound the mixture screw both ways from where it was set but nothing worked.So we sat down and let it cool off.After 30 mins,it starts 2nd kick!

Now the day before I had the same problem....I had a guy come and ask if everything was ok and did I need a push.Long story short,he said he had problems with his Ducati's sprag clutch doing what mine did and locking on and driving the starter motor while the engine is turning.He said you can replace the spring/s on the clutch to put tension back on the locking pins or whatever they have.Looking at the XT design,it looks to have one big spring round the outside.Is that correct? I didn't manage to get my flywheel off last time I tried to fix this,so haven't seen one other than a microfishe part pic.

If I can repair it for a few $ I'll be happy as Yamaha NZ want $352 for the unit ex Japan.
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  #2  
Old 16 Nov 2008
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I know it's a different model to yours but there's lots of information about sprag clutches on here so hopefully it will be of use - YAMAHA TTR250 TRAIL and OFFROAD MOTORCYCLE FAQ.
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  #3  
Old 16 Nov 2008
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Thanks for that,but I found that link before I posted.Thought I'd try the net before I asked the question.
Only thing with that write up is they didn't say what they did,so I'd imagine they've replaced the unit itself.I followed another link to a UK TTR site about replacing the starter motor and gears.It showed very worn sprag clutch teeth...It gives me an idea of maybe turning the teeth around which may work for a while.
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  #4  
Old 16 Nov 2008
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Idle setting

Stating the obvious of course, but shouldn't you also set everything so that the bike starts easily. This problem is usually caused by the idle mixture setting. In your case too rich, I would guess ...

Idle mix to standard setting. Idle speed to at least 1200 rpm.
Warm up engine. Turn out the idle mix screw till engine speed increases. Go on till speed starts to decrease again. Half a turn back.
Set idel speed 2 - 300 rpm about factory standard - this makes for easier starting; you do not have to touch the throttle during the starting process. You get used to the higher idle speed.

Good luck!
Auke
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Old 16 Nov 2008
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Only other thing I can think of, which you may have done already, is to run a search on the associated TTR yahoo group - TTR250 : TTR250
although I suspect there will be something similar for your model but don't know where it is I'm afraid.
Good luck.
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  #6  
Old 16 Nov 2008
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Quote:
Originally Posted by aukeboss View Post
Stating the obvious of course, but shouldn't you also set everything so that the bike starts easily. This problem is usually caused by the idle mixture setting. In your case too rich, I would guess ...

Idle mix to standard setting. Idle speed to at least 1200 rpm.
Warm up engine. Turn out the idle mix screw till engine speed increases. Go on till speed starts to decrease again. Half a turn back.
Set idel speed 2 - 300 rpm about factory standard - this makes for easier starting; you do not have to touch the throttle during the starting process. You get used to the higher idle speed.

Good luck!
Auke
Trust me Auke,I've been there many times with you on the subject of idle mixture
It's lean on overrun,popping and banging.Sometimes does it between gear changes.I've gone through adjusting the mixture screw till it sounds nice at idle.Starts fine when cold,starts fine when warmed up to "normal" temp,but when it's been pushed,like I say tight trails,open road 100km/h cruising,come to a stop or stall it,you'll be working up a massive sweat kicking it for no result.Leave it till it's cooled down again,around 30 mins,and it starts usually first or second kick no problem.
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Old 16 Nov 2008
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Quote:
Originally Posted by Hustler View Post
Only other thing I can think of, which you may have done already, is to run a search on the associated TTR yahoo group - TTR250 : TTR250
although I suspect there will be something similar for your model but don't know where it is I'm afraid.
Good luck.
Cheers,having a look at that now.
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Old 16 Nov 2008
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Whatever the engine is doing on the over-run, it sounds like it is giving you too much fuel at start-up. I had the same problem (exactly the same as you describe) on an old two-stroke many moons ago, and the only cure was to turn off the fuel 300-400m before stopping, so the float chamber was empty when you came to rest.

At the risk of stating the obvious, have you stripped the carb and made sure the choke is closing, the float needle is seating, the floats are undamaged and the levels are correct? That's the first place I would be looking. Also air leaks in the carb rubbers, from experience. Apologies if that is too basic.

I had two kickstart XT350s, and both were buggers to start when hot. The 600E seems to start first time, hot or cold, but the electric foot helps.
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Old 16 Nov 2008
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I have drained the float bowl in one of many attempts to start the bike.That didn't help unfortunatly.But I have also tried your trick of turning the fuel off before shutting the bike down.Didn't help either.
Carbs have been apart (numerous times) also had it looked at by a bike mechanic who said there was nothing wrong in there.
Needle and seat valve has been replaced recently,didn't help.
Float level is fine,fuel level is within specs.
There are no air leaks,I checked that a few weeks ago also.
How about the pulse coil inside the stator? Could be braking down when hot? Or would that show up when riding by cutting out etc?
If I can get the electric leg sorted cheap enough,I'll be happy

Quote:
Originally Posted by BlackDogZulu View Post
Whatever the engine is doing on the over-run, it sounds like it is giving you too much fuel at start-up. I had the same problem (exactly the same as you describe) on an old two-stroke many moons ago, and the only cure was to turn off the fuel 300-400m before stopping, so the float chamber was empty when you came to rest.

At the risk of stating the obvious, have you stripped the carb and made sure the choke is closing, the float needle is seating, the floats are undamaged and the levels are correct? That's the first place I would be looking. Also air leaks in the carb rubbers, from experience. Apologies if that is too basic.

I had two kickstart XT350s, and both were buggers to start when hot. The 600E seems to start first time, hot or cold, but the electric foot helps.
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Old 17 Nov 2008
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I thought you might have tried all of those, but they were worth mentioning. On the basis that once you are *certain* it's a fuel problem, it is *always* electrical I think you may be looking in the right place. I'm not familiar with the exact system on your bike, but I have known ignition coils that appear 100% fine, test 100% fine and work 100% fine until they get hot - and then they cause all sorts of poor running symptoms. The only solution is to swap with known good components until the problem goes away.

Good luck with the search.
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Old 19 Nov 2008
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Well I can safely tell you all,an XT400 pulse/pickup coil doesn't work on a 600.The mountings are of a different shape so makes one of the little magnets sit too far away from the pickups on the flywheel.
But I did find something interesting and that is that someone in the last 22 years has modified a pickup to suit mine.It's the same shape as the XT400 one,but just mounts where it should.The giveaway was the two locating bits that lock it onto that casing had been ground down.Every aftermarket one I've looked at only has one magnet for it's signal,not two like the XT has,so seems it's going to be fun finding a new one that's not a complete genuine stator assembly.

Also,since this pickup has 3 wires that are not standard colours,I have hooked the back into where I originally had them.I thought for shits and giggles,I'd changed the two green wires (using the cdi for reference) around and see what happend.It made the idle go up to around 3200rpm,but didn't seem to have any bad effect other than that.
Could my hard starting be due to having the two wires round the wrong way? Making it try to start at 36degrees rather 12degrees advance? It may be something I can try if it doesn't fire again when hot,just for experimental purposes.
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Old 19 Nov 2008
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Ignition / fuel

If your bike ran fine with the pickup wires connected as they were, changing them will probably not help. Otherwise, they were connected wrong all the time but that would make the bike loose a lot of top end power. But try anyway!

Another one; you said the carb has been checked and rechecked often. Did you also check the "overrun enricher", on the left-hand side. There's a membrane there that opens up another fuel channel to enrich when the slide is closed at higher revs, which should avoid too lean a mixture during overrun. Check that everything is clean, the channels open and the spring present and nothing stuck and everything moves freely ... Sorry for kicking in another open door ...

Would you be able to check the colour and size of the spark with cold engine and during one of your stalling moments ... ? Do not remove the plug from a hot engine, just take a spare plug and make sure the ambient light conditions are the same when checking.

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Old 19 Nov 2008
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I have pulled the coasting enricher apart a while ago to check if everything was ok in there,it looked fine.
The spark plug trick is my next thing to try,only thing it'll be a bit difficult to do if I'm out by myself,but I can try.

One thing that has got me curious,the bike kick backs on the kickstart like a bitch now.It never did that before I pulled the pickup out of it.Maybe it had a faulty wire on the 12 degree timing point?
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  #14  
Old 20 Nov 2008
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Kickback etc

At least your problems are new and interesting ...

I cannot explain why the bike should suddenly start kicking back when the low speed sensor is connected correctly. In fact, when all is in order, they should not kick back ...

You could check the ignition timing, at least the idle timing, with a strobe lamp - there is an idle ignition timing mark on the flywheel. Make sure to do this when the engine is warm and most oil is in the oiltank, otherwise you'll be quite dirty afterwards ...

Another thing to easily check: the adjustment of the autodecompressor mechanism - maybe too tight, so that it just opens the ex valve when hot?

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