RD4ME

Project looks to be coming along nicely. I'm interested in hearing how you like that OKO carb when you get it all back together!

Thanks for sharing Jeff! Looks like we're having an early spring in Ontario - so timing is just about right to start thinking about getting my TY out of the shed! I'm glad I have this thread as it reminds me where I left off before winter hibernation!

Ok - many thanks. I guess I’ll start tracking down a seat cover for my 250. suggestions are welcome!

Looking for a new seat cover for my 1978 TY250. There seem to be more available for the TY175. I was wondering if anyone knew if they were interchangable? Thanks!

I've had the carb out again and there's no blockage in the jet or the passageways. But it does still require the Air screw to be in all the way to run right. Bmonk dropped a logic bomb which has me putting the brakes on my bigger jet order. I sprayed carb cleaner around the base gasket and intakes - nothing seems to get sucked in and the revs don't change. I've had the flywheel off and don't see any evidence of the seal leaking - although if air is being pulled in I don't knwo that I would. Haven't had the clutch side opened up yet - so I guess I could go there. Just wondering if I'd be doing any harm to it by riding with the Air screw all the way in? I guess if the issue got worse - there'd be no further adjustment - but at the same time it might conceivable work itself through. By the way - I had my first "off" yesterday when riding it in minus 11 degree weather. The grass was frozen and slick and I clutched-in and put the front brake on; due to my sticking clutch plates the back wheel kept turning so I pulled the brake harder - locked it and went over. I rolled off with nothing hurt by my dignity! I quickly got up before my wife noticed...she would have been concerned over the big skid mark I made on the grass!

OK - great - I'm going to order a #37.5 and a #40 jet. I've removed my stock #35 from my Mikuni VM26SS and have measured it. Pretty certain it's the M28/1001 series - but hoping someone might be able to confirm?

Thanks Feetupfun for the great explanation - I think I can follow those instructions. But the good news is - I may not need to! The Snap is Back!! It looks like I've made a break through. I pulled the carb off to install my new needle and seat - and pulled all of the jets and doo-dads out again and gave it full clean/blow out. Then when I was adjusting the Air screw - I noticed as I screwed it in further - it revved-up faster. So I screwed it all the way in and took it for a spin up the street - and it felt like a different bike. The front end came-up high with just a blip of the throttle without any pulling on the bars - it was amazing! But then when I screwed out the Air screw to the 1.5- 2.0 turns - it lost its snap again. So I'm not sure if when screwed-in all the way it gets more or less air - and why it needs it. But I guess that's what I need to figure out next - but pretty pleased that I've found the power again!

Thanks. I did try the Q-tip in the drill trick using some metal polish - but couldn't get it to stop leaking so I ordered a new needle and seat kit. I also spent the last weekend de-coking the exhaust. I filled the pipe with casutic soda and let it sit overnight. I wasn't that impressed with the result - particulalry since that chemical is so dangerous. So I used a blow torch to burn out the carbon and fed a steel cable through throught he pipe and hooked it up to a drill. That worked much better and removed a bunch of carbon deposits - pipe was quite clean afterwards. I really thought that would solve my power problem - it might of helped a touch but I'm convinced this bike isn't putting out anywhere close to what it should be for low-end power. So that's my list completed - the only thing I haven't done is the timing. I pulled the flywheel and the points looked new - and I have good spark. I haven't found a dumbed-down step-by step guide and I don't have a way to accurately measure the piston position for the advancing of the spark - and I'm concerned I'll do more damage than good! But any advice on where to go next is appreciated! 1) Spark Plug - done 2) New Gas/Oil mix - done 3) New Tranny oil - done used Rotella 15W40 4) Compression test to veriify my foot feel - done 5) Air box check - Done 6) Carb clean - done 7) Clutch adjustment - done 8 Exhaust check/de-coke - done

Thanks thai-ty. I don't fully blame the bike for the lousy wheelies - but I should be able to flip one of these over backwards - and I can't! Scifi also suggested to try a lower gear. If it ever stops raining I will try it this weekend!

Hi Guy53, I've got to do something with my cluthc - the pull is way to stiff. Can you let me know where I can buy the extended clutch arm (TY250) - I'm in Ontario. Thanks

Interesting - thanks. I'll give that a try before the snow hits the ground!!

We've had a fair amount of rain this week and the knobbies have being doing a number on the grass. Hoping the leaves fall soon so my wife doesn't notice the chunks missing from the lawn!

Too cold to do much today so painted the muffler. Zipped around yard with it out a couple of times. More noise - no extra power.

Thanks Scifi, Section and Tony - this has been so helpful! I swapped the o-ring on the main nozzle tonight - still leaks so that's off the list (and it did fit because I can feel the resistance when I put the bowl on). You can see the scoring on the needle - I'm really hoping that's the cause of my leak. I found a place in the US (jetsrus) that stocks parts for the Mikuni VM26SS - so might get lucky going that route. I'm fortunate that my bike came with a well used owners manual - it's quite detailed and ha been very helpful.

Thanks for the links and additional tips. I inspected the needle and seat and there's no obvious signs of wear - but given that the float does float - it's all I can think of. I believe my bike has the stock mikuni VM26SS which are not easy to get rebuild kits for. I did find a needle and seat at Yambits in the UK - so I have an option there. I will try replacing the the o-ring first - is it #4 below - the one that fits on the main nozzle? Thanks!

This is helpful to know - I guess I could be going down a rabbit hole trying to find additional power that isn't there. It does surprise me though how soft the power delivery is off the start. I guess maybe the best way to know for sure will be to go to a vintage event and ask someone more familiar with the power delivery to take it for a spin and get their impressions. In the meantime, I will go throug the additional clutch and timing adjustments (thanks Scifi) - to confirm everything is ok. I'll also order a new needle and seat for my carb - to see if that stops the leaking.

Trapezartist - I think you are right: while the throttle situation is way better - the bike is still missing its snap - and now it also leaks gas! So that's one step forward and two steps back!!! So, I've covered of: Throttle cable, carb clean & condition, compression, reed inspection, seat & air box, spark plug, fuel/oil. Exhause baffle is also clean. I did order a flywheel puller today so I will soon be able to check the timing and points - although the spark is strong. I also wonder if the clutch could be dragging somehow and preventing the power to be laid down? I'm not sure what else it could be that is preventing the bike from revving-up - and that's it for the weekend - so the msytery continues. If you have any other suggestions - please let me know.

OK - after about 8 hours of playing around - I think I have it sorted (mostly)! I think what had happened is the cable splitter section that is held by a bracket circled in the picture had pulled itself through the bracket. The standard cable adjustments at the top of the carb and by the throttle were maxed-out trying to compensate. They weren't quite enough and so there was a pile of additional slack in the cable. The combination of the slack and the standard slide length made for the huge throttle pull. I removed and bent the bracket a touch and then reinstalled so it now holds more snugly. Video below of the resulting throttle pull and super-fast return! Many thanks for pin-pointing the issue so quickly - I do think a Domino Throttle may be in my future! As with most of my projects - they tend to never end- and through this excercise I have somehow developed a carb leak. When I leave the petcock on, fuel will drip out - same when I lean the bike over. It's like the float is not closing-off the float needle/seat properly. I've checked the needle and float height and both look good. I was wondering if by pulling the slack out of the throttle cable, I might be opening the throttle a little and that might be letting gas through somehow? It does seem odd that all of a suddne the floats might have failed or the needle and seat got tweaked! Anyway - back to the garage there's still a few hours of daylight left!

Thanks again for the advice. The engine does rev-up when I move the throttle. It just has a really long pull before it reaches wide open - and a slow return. You can see this in the first video below. If I figure out how all the adjusments work on the cable and get it tightened-up - does it manke sense that it would make the bike idle higher? Would I then lower the idle screw? There's a second video which shows how the cable seems to pop-out at the top of the carb. Does that seem ok? Btw, my bike has the oil pump removed.

Thanks to everyone for their advice. My checklist doubled in size and I’ve been in the garage all morning trying all the tips. Section swept - thanks for all the detailed info. I have pulled the seat and it’s all intact. No real deterioration of the sponge although I see 2 small cracks in the pan. I have pulled and cleaned carbs and reeds - they are in great shape. Compression is about 115psi so all good. Points I haven’t checked but the bike does start and idle perfectly. I do think the issue may be related to the throttle cable. It has a huge rotation to full throttle and it doesn’t snap back well. There are so many adjustments I don’t really know where to start. The slide and spring seem to work perfectly - but above the cap where the cable ends there is some movement. I’m not sure which part to adjust or if it needs a new cable. I have taken a video and will post when I get home - hopefully it will help with diagnosis. Thanks again to all - I’m enjoying the mystery!

I just picked-up a really nice 1978 TY250E. It's in great cosmetic condition and it starts easily, idles well and has a ton of compression. However, for a 250cc 2-stroke trials bike it seems to be a bit lacking in low end power. I figured that a bike would loop itself in first gear if it was given full gas and a good pull on the bars. On my bike - it takes a lot of effort to get the wheel just a foot off the ground. Part of this is poor rider technique, but I have other 2 stroke bikes and when they are in the power band - they rev-up like crazy! I posted a couple of videos below so you can see what I mean. It might be my expectations are too high for a bike with a heavy flywheel - but when I see videos of other TY250s - they seem much more snappy. I do know that the clutch needs adjusting - when it's cold and I put it in gear witht he clutch in - it starts to drive away. It's ok when the trannny warms up. Here's my approach to fix. It's based on easy to harder work effort but any advice appreciated: 1) Spark Plug - done 2) New Gas/Oil mix - done 3) New Tranny oil - done used Rotella 15W40 4) Compression test to veriify my foot feel 5) Air box check 6) Carb clean 7) Clutch adjustment 8) Exhaust check/de-coke Open to suggestions for anything else. Thanks. Throttle response

I've been fortunate to have fulfilled a long time goal having recently picked-up a really nice twin-shock TY250. I grew up in England in the early 80's with with friends who had a TY80 and TY175. They were beautful bikes and I tried everything to convince my folks to buy one! Instead, I got to ride my Dad's Honda PC50 moped - not quite as cool - but still much better than walking. Well now I'm in the club and I'm really pleased with my new ride. It's not perfect (what is after 40 years) and it's running a bit rough - so my next post will be in the Yamaha section! Would be great to hear from anyone in the Toronto area who rides vintage trials. I'm thinking I might see if I can ride in a few fun events and maybe pick-up some tips from members.