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TY250A minor resto help needed and a few other questions..

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Hello dear friends,

Johnny here in NYC hoping to get some advice from some of you super knowledgeable folk :)

few things if i may....

1, When i got the bike it had the long trail seat.  i recently scored a really nice original seat and pan which i'm super happy about.  however, i didn't realize there was such a big gap between the seat and the tank.  i think having the old trail seat sit flush with the tank has maybe discolored/chipped it.  Q/ what would be the easiest way for a novice to clean that bit up so it looks a little more aesthetically pleasing or would i need to really re do the whole tank? maybe there is a generic yamaha touch up white?  ive attached some pics so you can see what i'm talking about.

2, I am replacing the the top cylinder fins as the original has a cracked/broken fin.  Q/ other than a new copper gasket is there anything i should know or look out for. Is it pretty straightforward and i'm presuming it's ok to swap them between bikes?

3, Having set my bike up for more road gearing (at feetup funs suggestion 16/53) i can comfortably sit around 45mph now.  I use a pre mixed 50.1 synthetic husqvarna high octane ethanol free fuel (i can get it at work) and the original B7ES plug. Q/  For more of a road riding application should i be using 40.1 and a B8ES? or am i ok where i am...im terrified of blowing the engine up but also dont want to gunk it up with unnecessary oil....i know pre- mix ratios are highly controversial but i just don't feel i know enough myself to make an informed decision.

4, and lastly...Q/ correct/optimum tire pressures for street use?

any insights into any of these questions would be gratefully received.  Thanks so much for all your help.  i learn so much here at trials university.

many thanks in advance and bright moments!




Edited by johnnyjazz

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Well here goes, knowledge gained from having been a Yamaha Dealer and just recently restored a TY 250 E. Your bike looks really good and in complete condition. Yours has the wider engine cases and is heavier in build. The single seat that you have looks nice but is it located far enough forward, it looks as though it could go forward an inch or two. You’ve got to get the rear of the tank cleaned up and painted, looking at the pictures you have a dent in the top of the tank. To do justice a good body and paint shop should be able to sort it at a reasonable price. Once its done some clear  helicopter tape could be applied to protect the new finish. 

Geared for speed, it’s a Trials bike and the tyres are not nice to corner on at speed, they can have you off really easy. The steering angle is designed to be fairly quick and you may notice the front wobbles and feels dead. Unlike a proper road bike or Moto/cross bike which will have significantly more trail in the steering department. Then of course there are the brakes to consider, which for trials work are great...ish but for fast road work😳✋ Remember the faster the engine speed the faster the wear and this applies to all of the running gear.

You don’t mention the auto lube system, presumably this has been removed, you must check to make sure all,of the lube pipes are off and the oil entry points are blocked. The oil pump drive shaft hole needs to be correctly blanked off and sealed, check that this has been done. The oil mix ratio is ok but you may find going for 60:1 may give better running. 

The Yamaha owners manual contains tips for road and trials riding, with tyre pressures suggested at something like 28 psi front and 30 psi rear.....going from memory, but then my handbook is for the more modern 1978 E model. The carb mixture screw had a two position cap fitted which in position one was for trials work and position two was for road work....going between sections. However I don’t know if your early model had this. There’s nothing nicer than a gentle run at about 35mph on the road, taking in the scenery...carefully of course! 

When you take off the cylinder head slacken the head nuts a little at a time working first on the front centre nut then the middle rear and then diagonally to each nut, this procedure will help to prevent distortion. You may not need a new gasket if it is copper, you can anneal it to reuse if in good condition. With the head off you must check the cylinder bore for signs of seizure and scoring of the bore. You can also check for excess piston sideways movement. Pistons are not cheap and you may find that removal of the barrel gives you a better picture of the internal condition, you will be able to check for big end play and main bearing noise, you may find that the crank is reluctant to turn easily, this may indicate that the main bearings are cocked up due to age. The crankshaft oil seals may also be hard and leaking, these should be checked, leakage here will ruin a good engine. You may find everything is sound👍🙂 and usable, let’s hope your lucks in😉

Anyway it’s nice to see a good looking Trials bike like the TY being kept in nice condition, enjoy. 

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Thanks so much Section Swept! really appreciate your input :)

yeah, i took all the auto lube system off and blanked it properly etc  interesting for road use you recon 60.1? 

i know its a trials bike and not built for road use....but it kinda found me so we just coming to a compromise what with being in the city.  obviously brooklyn NY not best place to find many trials spots!  i had a few i used to use but the cops not so keen.  everything is suddenly 'private land'... so trying to make it more a green laner..  but yeah, i hear ya...brakes suck, geometry sucks...just re living my youth and trying to save a piece of history...

re the two position air screw you mentioned, the guys on here told me previously that the choke can be used in that way.  they would put it on during long road sections and ride through the 'burbles'...had the effect of cooling the engine i learnt.

and re the seat gap...i agree, it def seems like it wants to go an inch or two forward but on all the original photos i've seen they all seem to have that gap.  i enclose a pic here..unless im mistaken this is how they came?

and your bike looks beautiful sir, magnificent work!




Edited by johnnyjazz

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Yes your single seat looks to be in the normal position. The seat pad does shrink over time which makes that gap slightly bigger than the brochure photo. I assume you have tried buffing compound to get rid of the stain from the long seat touching the tank? My original TY250A model tank has some stains in that light colour area that I haven't been able to buff out, but I'm happy to just leave it alone. The world is full of repainted TY250A fuel tanks but there are not very many TY250As that have the original paint that still look as good overall as yours. I love the look of my original tank so much that when I ride the bike in trials, I fit a repainted tank, to avoid the risk of damaging the original tank.

It's good that you have fitted suitable gearing. Riding at a steady 45 MPH should not cause problems with engine heat because 45 MPH is below the speed where air drag ramps up dramatically, but if you were wanting to go for a brief blat along a freeway (maybe 30-60 seconds at 60 MPH), a B8ES would be more suitable and if you were going to run it at constant high speed for more than a minute, a B9ES would be more suitable. The middle electrode on a spark plug has an ideal temperature. Too cold and it will collect deposits which conduct electricity and too hot and it will lose metal quickly. The length of the metal part of the centre electrode determines how fast heat is conducted away from the tip. If you look in there you will see that there are different lengths for different plug numbers. If a plug tip is getting too hot, it not only disappears quickly, but also radiates heat which can overheat the crown of the piston. It's always safer to run a colder plug than a hotter plug for this reason. Before you fit a B8ES, go for what is a normal ride for you with the B7ES and then when it cools off a bit, take the plug out and have a look at the middle electrode. Then fit the B8ES and go for a similar ride and then inspect the centre electrode and you will probably see that the deposit on it is a slightly different colour. Fuels are different throughout the world and other bikes have different jetting and are ridden differently which means there is not much point looking at photos of other people's sparkplugs but there are generalisations you can use to know of everything is fine on your bike. Because you have told us the oil type, mix ratio and plug number you are using and that you ride it mostly on the road, I can say that your plug tip and the ceramic insulation around it should look totally dry and with a colour in the range from mid brown to light grey. When you fit the B8ES and do the same test, the colour will probably be a bit darker. Bear in mind that the plug tip colour shows the recent history of what was happening inside the motor so if you are interested in plug colour from riding at 45 MPH, do the inspection somewhere very close to the riding and don't let it idle for long.

For gentle road riding an air-cooled bike with correct air-fuel ratio, 50:1 synthetic oil is fine.

You can re-use the head gasket by annealing it.

Usually 14 PSI on a TY is enough to avoid having a tyre overheat or cause squirming on a road ride. The higher you go above that sort of pressure, the worse the ride on bumps.

As for those paint chips, you can probably find some nail polish to match the colour. Nail polish is chemically compatible with the paint on the tank and it's also good fun taking a fuel tank to a cosmetics counter.

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Thanks so much Feet up fun! :) you are the best as always.  Macy's here i come!  your kindness to share is always legendary.  very best wishes from NY! johnny

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