Thats a great point. Thanks Rider. I’d say from memory, yes smooth. What would be possible cause(s) from motor then? I will take another closer look at that to confirm though.
Alternator nut can come loose, which initially causes misfiring as the flywheel floats around. Water in the fuel. Rust/debris in the fuel. Air leaks where the carbs mount??
Carb icing - these bikes are very prone to carb icing, as the intake tubes are so long. Anything below 10 degrees or so and the right amount of humidity will provoke it.
All checked. Tank was cleaned out thoroughly, and rechecked/emptied and rinsed. Carbs stripped and rebuilt. Could be water in the fuel now. I’ll clean it out but pretty sure it was good when this first occurred. There was that ringing sound - put down to horizontal piston slap - though i have my doubts....I wonder, could it be domething to do with gear selector mechanism? I had turned the engine by turning wheel with gear engaged, the wrong way by hand when inspecting/refitting the Alternator, and it made a ratcheting sound which worried me.
What do you reckon? Confirmation: 1. Coasting in neutral, and in gear with clutch pulled in and riding short distance with clutch slipping, no snatching symptoms. The snatching stalls the bike upon fully engaging gear immediately (its unrideable) - all final drive from sprocket to chain to rear procket and cush drive, wheel bearings and alignment is fine and freshly serviced, renewed. 2. Rode in temp of 11 C with warm engine , carb heater on, no difference: - problem not symptom of carb icing 3. Dismantled carbs agin; found to be completely clean. Checked and cleaned out/ poked pilot jet just in case. checked pilot jet screws. - problem not due to dirty fuel etc. Speculative Thoughts: .............................. I can only conclude with my brain, that this is a mechanical problem due somehow to clutch drive at engagement, gear engagement, or bearings. The plates and tab wear are fine. Springs are on the weak side (at service limit). i would tend to doubt gear shafts being out of true. How about primary drive gear or driven plate bearings? Also, perhaps I ought to look at the gear selector fork alignment / upper return spring action....
It's really hard to make sense of this. The drive train is smooth when coasting but try and engage the clutch and the engine stalls. Is it because the clutch take up is not smooth? Does the clutch drag? Does the bike stall when you put it on gear? Exactly what do you mean by snatching? Please try to describe exactly what happens.
Many Thanks. Engage the clutch and it stalls ... (no brake) where the chain 'snatches'.... I would perhaps better describe it now as 'binding' at the time it stalls (now just about immediately) - with a crunch at the front sprocket as the chain binds....See the video above for a very clear visual of the problem ( rear wheel off ground). It binds mediately with wheel on the ground under normal clutch operation, unless I slip the clutch in order to just be able to move off; I cannot fully engage the clutch without a stall. Clutch take up appears to be smooth... no judder, hesitation, clunkiness at the clutch - simply binding at the front sprocket, with powerful, smooth, insistent (not hesitant) transfer of power when engaging clutch. The binding/crunch/ is as if something is interrupting smooth power at the output shaft... a pulse of power starts the chain but is then interrupted, I fancy, as if the output shaft is vacillating in speed, and the chain therefore is going faster than the output shaft. Plenty of power there at output when engaging, not dying due to spark or fuel. Bear mind, I did notice some early indication of this beginning to happen before it became so bad, on a few short outings. I had wondered if it was due to town riding and revs... it started happening on switching from de-acceleration to acceleration whilst on the move in traffic. Then, finally it kind of 'went' - all the way suddenly on fast acceleration over a half-mile. I had to limp home slipping the clutch.
Are you sure it’s running on both cylinders?? That would explain snatchiness and needing to slip the clutch. To check, remove one plug lead at a time and see if it makes a difference
Enables me to get moving without stalling - i cant let clutch fully out without stalling due to chain bind. Is not due to lack of power, which i have experience of in past life, which stops the engine without chain bind. Motor starts and revs well in neutral without missing. No missing as I engage clutch. Spark tester shows two fat sparks, runs at idle on each cylinder with opposite plug disconnected. The almost new plugs now need replacing i think... deteriorated in getting it running at time of pickup coil swap. Occurs to me the symptom of binding wouldn’t occur with one cylinder down - hadn’t before on same machine when a plug died out. Would you not concur with that?
Sorry don’t understand last paragraph. Chain bind. Doesn’t the chain run smoothly in neutral when turned by hand on the stand and doesn’t it run smoothly when clutch-in coasting? Why would it stall the engine?
If the chain really is binding, could you have the sprocket on the wrong way, so the chain is out of line ??
I’m going back 39 years now to when I was seventeen but I had a DT175 that developed a fault that was vaguely similar, when the back wheel was off the ground the rear wheel would spin in gear smoothly with the engine running, with the bike on the ground you could pull away with the clutch slightly engaged, as soon as I let the clutch out further the chain would jump and whip as though it was slipping over the sprocket teeth, but it wasn’t, (your first video reminds me of it, although it was more severe on my DT) eventually on dismantling the gearbox I found that the end of the layshaft was ground away making it about 5mm smaller diameter than it should have been , so the whole shaft was able to move out of position causing the gear teeth to slip over each other and come out of mesh, a friend turned up a bush and repaired the shaft, it was fine for a few weeks then went again as I guess the lubrication to that end of the shaft had failed in some way which is what led to the failure in the first place, it seems that it would cope with the worn shaft whilst it was under a small amount of load, ie not much power was being transmitted into the gearbox due to the clutch being largely disengaged, but as the clutch was let out and more power transferred into the gearbox the layshaft moved due to its reduced diameter where it sat in its bearing and allowed the gears to unmesh , It’s not identical to what you are experiencing but there are some similarities, is it possible that a gearbox bearing has failed?, any metal particles in your oil?, I hope it’s not this but thought I’d throw it in there as a possibility?.
Yes (to qns 1 and 2). It stalls when engaging engaging clutch in gear. The last paragraph: i mean to say i never before experinced a reaction of chain binding the sprocket when power was lost due to a cylinder going down. If it does stall as a result, the engine just cuts out, and that is unless more revs are used to move off.
Interesting... this sounds like the sort of thing - something to do with the meshing. Answers to your queries: Not sure that a shaft bearing would cause this in a supersport... i dont know though. i imagine id hear indicative noise in neutral; perhaps not. Perhaps the Clutch driven gear bearings could cause whipping of shaft upon near-full engagement, but seems more like going out of mesh. Notice i could run it without chain on in gear. Of course then it has almost no work to do.... i think i’ll run it again like that and really watch, listen and feel the clutch and mesh action. I had been hoping perhaps the selector fork alignments could affect it- though its probably just wishful thinking. Ill take a look tomorrow. Im not really seeing metal in the oil. I’ll take another careful look with a lens and hold it to light. My symptoms may be as bad as your case - in the video i had to slip the clutch to keep it running long enough to film it and then I gingerly let it engage. Thanks for tour kind reply.
Have to confess I've been beginning to wonder if there's something amiss in he gearbox. Could there be some teeth missing somewhere that will run reasonably smoothly under no load but as soon as load is applied it locks.
I haven't read the whole thread, just bits, I have just watched your video, it looks like a new chain, is it possibly the wrong pitch chain? is seems to be riding up the teeth. I might be talking rubbish also. Steve
Its the right chain. Yep it looks like its ‘riding up the teeth’ - what im calling binding. Thats leading to thinking its gears ....binding under load.
Seems to me we could do with someone in the Middlesex area taking a look to see if they can make any sense out of this.
