VonR

I had similar but not exact problems with a YB100 that I aquired last year - in fact I posted the problem on this site. Again, I started with the baffle - but made no difference. It was a combination of things in the end: a) Rust inside fuel tank internittently blocking fuel tap, pilot & main jets - the solution was to use a tank lining kit - I used the POR15 kit from the FROST auto restorer's catalogue. Also fitted an in-line feul filter. Float height was wrong - in my case, allowing too much fuel in (on the occasions when tap and jets weren't blocked) c) Changed grade of spark plug to NGK B7HS - it was running a B7RS (or something with an R in - chucked it away, so can't confirm) d) Ignition timing was slightly out - so corrected that e) Exhaust was blowing slightly through both of the joints - so sealed those up with exhaust putty. Now pulls hard and revs well in all gears (bit tinny when cold but I suppose that's normal) Brgds, Ian

Jim, Might well enlist your services if you are up and running businesswise as I could easily spend another 20 years messing around with this (in fact I'd only spend another couple of months before setting fire to it at the bottom of the garden) - if you email me your details to [email protected], I'll arrange to trailer it up sometime. Thanks

Jim, Latest on this one! - Replacement Exhaust made no difference at all. Weight was almost identical anyway. As often the case, looks like multiple factors at work. Oil pump setting slightly out. An adjustment means that bike pulls much better until it gets hot then it exhibits the same symptoms (nevertheless, a step in the right direction). Took it to a local bke specialist. They have re-checked timing/tuning. They suspect a faulty magneto winding and/or condenser but it's a bit trial and error - and of course no spare parts readily available. Do you know of anyone that stocks these items or suitable replacements? Thanks Ian

OK Jim, thanks again for the advice. Have just ordered a new silencer on Ebay anyway for a reasonable price but will try a quick blast up the road with just the down-pipe - didn't realise you could do this in my ignorance of 2-strokes (thought the engine needed the back-pressure). At least it might prove the point before I fit the new silencer. Air filter looks very clean -presumably previous owner has already taken the obvious measures. It will be intereting to compare the weight of old and new silencers based upon what you have said - will let you know. Regards, Ian

Thanks Jim - will continue with diagnosis this coming weekend. I still have the silencer off so will weigh it. It did feel heavy, come to think of it. It also appeared to have been patched up with gun gum around the fixing bracket, so investment in a new silencer might be worthwhile. Looked into exhaust port with torch and felt around - all felt clear but will double check. Will then proceed to look at oil pump. Have been turning off petrol tap in between running. Always starts first kick with no choke. Brgds, Ian

OK - I've done the exhaust (obviously been recently cleaned), checked the carb settings and ignition timing and all OK - so I'm suspecting the adjustment of the oil pump. Will gladly take your follow-up advice on offer. Thanks, Ian

Thanks Jim, appreciate all of these points and clarification. Work has stopped play until later on this week - will feedback then. Brgds

OK thanks all for the advice. The choke does have 2 definite positions. You can pull it upabout 1cm and it does stay there. In it's fully down position, however, you can still see about 10mm of bronze stem above the black plastic base - just doesn't look right. It also occurred to me that exhaust baffle may be coked up - so I will look at that first and then, when my Haynes Manual arrives, I will venture into the carb. Brgds

Hello, I'm looking for some advice and best plan of attack Bought a 1981 YB100 today. It starts first kick every time (without pulling the choke knob) and idles really nicely with about 10K miles on the clock. When you try and ride it, the engine struggles as if it's all clogged up. You can go through the gearbox but 20mph is about the best it will do. I know nothing about small Yamaha 2 strokes (Haynes Manual on Order). However, notices that the choke knob stands about 10mm proud of the carb cover - is this normal? Just wondering if the carb has been assembled wrongly and the engine is flooding. Examined the plug (which previous owner said was new). It was a bit dark around the electrode and a bit wet around the perimeter but nothing too drastic (possibly because the bike hasn't been very far). Can anyone offer advice on sequence of checks: a) Should I go for the carb/choke first? Ignition timing - too far advanced maybe? c) Oil pump requires adjustment? d) Check state of air filter? e) Anything else? Many Thanks