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RD4ME

No Snap!

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56 minutes ago, RD4ME said:

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.

The last video looks like how a standard Ty250BCDE in good condition responds. The standard motor has a strong flywheel effect that most people didin't like when they were new and the same sentiment applies even more nowadays with grippy tyres and good rear suspension. Lightening the flywheel is a very common mod to these engines. Another beneficial mod to make them more snappy is to fit a good modern ignition.

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Have you checked the ignition timing...?   If it is retarded, then the response could be slow.   Also if the points gap is on the small side, it will retard the ignition.

The TY175 has Contact Breaker gap = 0.35 mm (0.014 in.) and Piston BTDC 1.80mm (0.070 in.)  I suspect the 250 is similar.

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4 hours ago, feetupfun said:

The last video looks like how a standard Ty250BCDE in good condition responds. The standard motor has a strong flywheel effect that most people didin't like when they were new and the same sentiment applies even more nowadays with grippy tyres and good rear suspension. Lightening the flywheel is a very common mod to these engines. Another beneficial mod to make them more snappy is to fit a good modern ignition.

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.

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 The 74/75 models had lighter flywheels, I ran one on my 77 model. I don't think it helped my scores but it made the bike more fun to ride. Get your bike in good working order before making any changes though.

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My C model definitely has a lot more snap than that but it has no flywheel band & runs electrexworld electronic ignition on a freshly built motor. 

Seeing as you're in Canada the best place for a new throttle cable is B&J Racing, they should be able to supply a domino throttle as well. Don't worry about the listing saying 74-77 as the 78 is the same apart from colour scheme. I've heard that Bob's TY motors are amazing, if postage wasn't so expensive I would have sent my cylinder to him for the porting work

http://www.bjracing.com/id115.html

If you want to use the standard throttle then TY trials has this cable & is 1 of the best source for parts around. I bought all the bearings, seals, gaskets etc for the rebuilt from them & had the parts in New Zealand in around a week. John is great to deal with & knows his stuff

https://www.tytrials.co.uk/trailandtrialsuk/prod_43441-24-Throttle-Cable-TY250-Twinshock.html

When you are changing the needle & seat pay attention to the condition of the o-ring that fits into the float bowl, when these get damaged it allows fuel to bypass the main jet

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2 hours ago, tony27 said:

When you are changing the needle & seat pay attention to the condition of the o-ring that fits into the float bowl, when these get damaged it allows fuel to bypass the main jet

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!  

image.png.ad80a1dba2ae859b2b47e76b81ed111b.png

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Yes it is number 4, but it is a very odd size, not often found in O Ring Kits.   ( from memory maybe 4 x 1.5..?)

To tell if the O ring is worn, it should be a squeeze to put the float bowl on.  If the float bowl just drops off the o ring, then it is too slack.  You can use a smear of silicon grease to lubricate the fit.

.

Edited by scifi

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On 28/10/2018 at 5:33 PM, RD4ME said:

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!

InkedIMG_3328_LI.thumb.jpg.59dac18970bbed138e3513da5ea65b81.jpg

 

You still have the original oil pump control throttle cable. If the oil pump cables are removed the action can still be a bit sluggish. I would be going with a new one piece throttle cable. The TY has a heavy flywheel, Yamahas first attempt with the wide cased TY 250 A had people complaining that the engine was too ‘zappy’! So they tried to tame it and thus you ended up with a slow revving but torquey engine that pulled very well. Another thing to look at is that grip it could be binding on the end of the handlebar and against the throttle body, silicon spray should prove it. Your engine sounds nice, but as I said get the contacts checked. I am assuming your bike is de-oil pumped. 

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14 hours ago, RD4ME said:

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!  

image.png.ad80a1dba2ae859b2b47e76b81ed111b.png

#4 is the part. Here is the kit for replacing all the o-rings & bowl gasket, definitely worth doing for the price & should get rid of most carb problems

https://www.tytrials.co.uk/trailandtrialsuk/prod_189299-4-9-14-24-Carb-Repair-Kit-TY250-Twinshock.html

Could be worth ordering either the ignition tune up kit at the same time unless you plan on upgrading to electronic ignition

https://www.tytrials.co.uk/trailandtrialsuk/prod_147767-911-Ignition-Tune-Up-Kit-TY250-Twinshock.html

Do you have a manual for the bike, the only 1 for 250s that seems to be easily gotten is from cycleserv for the B model but it works for the later bikes as well. I can check with a guy here in New Zealand who sells copies of manuals to see if he has ever copied the genuine Yamaha manual if you need 1

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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.

image.png.a1050f21b633b0c5199194ed493211ae.pngimage.png.47aa39ffeedc774d57d2c075824439da.png

 

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That grooving would definitely cause your leaking issues, new valve & needle will seal & lower the fuel level to where it should be

The o-ring wouldn't be the cause of the overflowing but may help with the lack of snap if you're getting main jet bypass

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Just noticed something else that will prevent a wheelie...  You ought to try 2nd or 3rd gear, not 1st.   The camera's wide angle view makes it look as if you are going faster than you really are.

I can generally get my 175 up to my ears, and straight back down in less than 8 feet, in 2nd gear.

.

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On 11/4/2018 at 7:18 AM, scifi said:

Just noticed something else that will prevent a wheelie...  You ought to try 2nd or 3rd gear, not 1st.   The camera's wide angle view makes it look as if you are going faster than you really are.

I can generally get my 175 up to my ears, and straight back down in less than 8 feet, in 2nd gear.

.

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

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On 10/29/2018 at 11:09 PM, RD4ME said:

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.

image.png.a1050f21b633b0c5199194ed493211ae.pngimage.png.47aa39ffeedc774d57d2c075824439da.png

 

I am new to the TY, but not to old bikes. The needle seat will often build up a coat of varnish. Try cleaning it up with a "Q"tip and a small dab of toothpaste. Swirl it around and wash it up before assemble. Usually works. 

 

28279691_10155953121965803_2061531376689837503_n.jpg

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20 hours ago, sbest said:

I am new to the TY, but not to old bikes. The needle seat will often build up a coat of varnish. Try cleaning it up with a "Q"tip and a small dab of toothpaste. Swirl it around and wash it up before assemble. Usually works. 

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

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