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johnnyjazz

TY250A original gearing question.

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hello friends, sorry to be a nuisance but was hoping if someone would confirm that the original gearing on a '74 ty250A is 14/53....i often see it said 13/53 was the original gearing?

the bike has 12/53 on it now.  my question is, if i put a 14 on the front how many link chain would i need..is it 110 or 114?  would the bike then suck at trials tho?  seeing as im going through the hassle of getting it road legal be good to keep up with traffic! 

many many thanks from an mechanically ignorant green horn in NYC!  :)

 

 

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Yes with a 14 it will be crap for trials competition.

The BCDE models had 13 as standard. I would need to look up a book to see what A model had.

No Idea about the number of links. I usually just buy a 120 link and shorten it to whatever is needed.

Going from 12 to 14 on the front makes very little difference to the chain length. If the axle is near the rear end of the slots with a 12, it should allow a 14 with no extra links.

You will need bigger than 14 to ride at highway speed.

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Don,t mean to high jack,but I have a sprocket/gearing question also.

Can you still get front and rear sprockets in the 428 chain?

If not is the 12/44 combo good in the 520 chain size?

Thanks, Scott

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Q1 yes you can buy 428 chain sprockets for Ty250

Q2 Chain size/type has nothing to do with gearing. It is the ratio of the sprocket sizes that determines gearing

14/53 ratio = 3.79 = too fast for trials

12/44 ratio = 3.67 = even faster!

12/53 ratio = 4.42 = good for trials - good choice for 428 chain

10/44 ratio = 4.4 = good for trials - good choice for 520 chain

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wow! thank you so much for all your awesome help and kind advice.  learning so much everyday and most grateful.

at your suggestion i will keep it at 12/53.  i only want to potter around the back streets of brooklyn where the average street speed is 25-35mph getting to some off road places i know to practice trials.  i have no intention of going on the expressway! it would seem 4th and 5th have enough go.

i like your shakespeare quote too.  Thanks again and best vibes, johnny

 

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14 hours ago, scot taco said:

Don,t mean to high jack,but I have a sprocket/gearing question also.

Can you still get front and rear sprockets in the 428 chain?

If not is the 12/44 combo good in the 520 chain size?

Thanks, Scott

 I think PBI is the only U.S.company making rear sprockets for the TYs, the fronts can be found from many sources.

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hello again my trials experts friends! as wondrous soothsayers of all things TY and this forum being a veritable grotto of educational engineering effervescence, would someone be as kind as to help me with my latest conundrum?

having just got my bike fully street legal (thanks Vermont!) i have found with the current gearing of 12/53 i really am struggling to keep up with traffic even on slower roads.  let me state that i am well aware this isn't a road bike and isn't geared as such and i am not a speed freak at all, id just like to not be a hazard to others!  im only riding 2-3 miles to get to a few industrial construction sites where i can practice trials.

so my question is, when i look in the manual (see attached pic) it says the original gearing is 14/53 and during break-in to avoid speeds in excess of 60mph!

i mean seriously, could a '74 TY actually go that fast or was that just a generic page from a book to cover all models like the DT/RD too?

i find with the 12/53 i am lucky to get maybe 35mph tops and if my sums are correct the difference between a 12 and a 14 front is 16.9% so that's nowhere near 60!   the bike seems to be running very well, alot of torque and smooth but just as slow as a steam roller.

seeing as i will have to do some road riding to get to my secret spots are there any mods i can do to help with overall top speed?  it currently has a #112 main jet and i remember 'mr feetupfun' saying somewhere if you were using it at more higher speeds, then the main jet size is of vital importance to avoid seizing the motor. 

any advice or guidance most welcome.  very best wishes from NYC.

johnny :)

(btw, if interested to get it road legal...$17 reg, $6 inspection, $99 year insurance! happy days)

 

3.jpg

Yammy 250..jpg

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Hi JohnnyJazz. 

 

That is a very pretty bike.  If you did the restore, great job!

A couple thoughts, facts, and questions.

Words in italics below are from your posts.

 

August 8.

 

I only want to potter around the back streets of Brooklyn where the average street speed is 25-35 mph getting to some off road places I know to practice trials. 


Sept 8

 

. . . have found with the current gearing of 12/53 I really am struggling to keep up with traffic even on slower roads.  let me state that I am well aware this isn't a road bike and isn't geared as such and I am not a speed freak at all, I’d just like to not be a hazard to others!  I’m only riding 2-3 miles to get to a few industrial construction sites where I can practice trials. . .

. . . I find with the 12/53 I am lucky to get maybe 35 mph tops and if my sums are correct the difference between a 12 and a 14 front is 16.9% so that's nowhere near 60!   The bike seems to be running very well, a lot of torque and smooth but just as slow as a steam roller. . .

 

According to the Yamaha ad material for the 1974 TY250, it has a top speed of 100 kph (62 mph) with 14/53 final gearing.  Going to 12/53 is 14% reduction (14-12, divided by 14) which should net you a top speed of 51.6 mph at redline (Yamaha did not post how many rpm that is but max torque is 15.2 Ft# at 5500 RPM so it should turn at least 5500).

 

First question: 

Are you getting into 5th gear?  Fifth gear is a 0.656 overdrive, where 4th gear is 1.0.  Fifth to 4th is about a 48% reduction which would net you top speed of about 32 mph. 

 

Second question:

Are you getting full opening of the slide in the carb?  If not, you will not get max power or rpm from the engine resulting in lower top speed.  Solution could be a simple as a throttle cable adjustment.

 

Meanwhile:

Learn to use that rear view mirror and move right to let faster vehicles pass.  At most it will delay your arrival to your riding location by a couple minutes.  Riding in and around Manhattan, you are probably spending more time than that sitting at stoplights.

 

Learn to pull away from lights in second or even third gear.  That will get you up to speed faster so less bothersome to cars behind you. 

 

Observations:

It looks like your levers are located fully out toward the ends of the bars.  You might try moving them further in toward the center of the bike.  This will increase the leverage you have on the clutch and brake, while also reducing the chance of breakage if/when the bike falls over. 

 

Is that a bulb horn I see in the picture just above the fuel cap?  It brings back decades old memories since I had one on my bike.  I suggest relocating it so you can honk it with your thumb without having to take your hand off the grips.  If you need to honk, you will probably also need to work the clutch, brake and or throttle at the same time while hanging onto the bars with both hands. 

 

Have fun! 

 

 

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One more comment.

FeetUpFun is correct that screaming the bike for long road runs will cause the top end to get hotter than desired.  Increasing the main jet will allow more fuel which will help cool it.  On the other hand, adding more fuel will reduce the relative amount of oil being injected (assuming you are still using the automatic oiling system) which will affect the lubrication of the bottom end.  So it is a trade-off depending on how you will be riding the bike.

A way to check:

After riding on the roads back home, shut the bike off, let it cool a bit (so you don’t have to deal with hot pipes and plugs) remove the plug and inspect the ceramic insulator by the spark tip.

Bright white = too lean.  Would benefit from bigger jet for more fuel and cooling

Black and oily = too rich.   Would benefit from smaller jet.

Light tan = Perfect. 

 

Do yourself a favor and always carry a spare plug and wrench to change it.  Even well jetted bikes will foul plugs from time to time (usually at a very inconvenient time).  Spare plug and you are back riding in 5 minutes.  No spare plug and you are pushing the bike 20 to 45 minutes for 2-3 miles.  Not fun.

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37 minutes ago, thats_a_five said:

One more comment.

FeetUpFun is correct that screaming the bike for long road runs will cause the top end to get hotter than desired.  Increasing the main jet will allow more fuel which will help cool it.  On the other hand, adding more fuel will reduce the relative amount of oil being injected (assuming you are still using the automatic oiling system) which will affect the lubrication of the bottom end.  So it is a trade-off depending on how you will be riding the bike.

A way to check:

After riding on the roads back home, shut the bike off, let it cool a bit (so you don’t have to deal with hot pipes and plugs) remove the plug and inspect the ceramic insulator by the spark tip.

Bright white = too lean.  Would benefit from bigger jet for more fuel and cooling

Black and oily = too rich.   Would benefit from smaller jet.

Light tan = Perfect. 

 

Do yourself a favor and always carry a spare plug and wrench to change it.  Even well jetted bikes will foul plugs from time to time (usually at a very inconvenient time).  Spare plug and you are back riding in 5 minutes.  No spare plug and you are pushing the bike 20 to 45 minutes for 2-3 miles.  Not fun.

I can't see from the photo,(If the throttle cable is the twin type,going down to the oil pump) but I think its fairly safe to assume that the original oil pump is no longer in use,most now use premix somewhere around 50-1.

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10 minutes ago, jon v8 said:

I can't see from the photo,(If the throttle cable is the twin type,going down to the oil pump) but I think its fairly safe to assume that the original oil pump is no longer in use,most now use premix somewhere around 50-1.

JonV8, true that many people have switched to pre-mix.  Like you, I can't tell from the pic if the cable is still in place but I think I can see the hose from the pump to the cylinder which is why I brought it up.  Between us, hopefully JohnnyJazz learned more about his bike and can make good decisions. 

FYI, my '74 TY250A still runs the oil injection pump.  That way I only have one fuel can for all the bikes. 

Cheers!

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Unfortunately Take_a_Five you might have to buy a new piston as a 40 year's old oil injection pump is very unreliable thing.

 

Guy

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Wowsers super exalted and revered internet buddies!!

thank you so much for the wonderful replies esp 'thats a five' for such a huge chunk of knowledge. its really appreciated as i embark on this new journey of 'vtg trials!'   sorry to be such a noob, i hope its not annoying u expert peeps!.....(remember, there's always a subject each of us knows nothing about....)

i guess im just having that 'mid life crisis' and didn't want a harley or a muscle car!

in answers to your questions, yes, i'm easily able to get into 5th...in fairness maybe its nearer 40mph tops than 35 and yes, while in NYC it would appear all one does is sit at the lights :(.  -and thank you very much for the suggestion about throttle slide.  i am planning a carb overhaul when i get my new single throttle cable. the oil pump has been disconnected but is still running both cables from the throttle at the moment.

thanks for all other great pointers about the plug.  i went for a blast earlier and took a pic on my return.  im pretty certain it looks how it should?

but ultimately, i realize this bike just wants to be off road and was never built for streets so i'll listen to what shes trying to tell me.   i'll put a 14 on the front and see how it goes from there.

also, if i can dare to impose with yet another question....as a novice clubman vtg trialer, am i best to keep the bike as original as possible for potential resale or should i just go for gold and start upgrading things like the rear shocks etc...

i didnt restore the bike myself, i believe its all original- but have been going over it and doing/learning about basic maintenance as it has sat for 30 years in someones static collection.   i had trials bikes as a kid in the 80s in the UK- and obviously don't come across too many in NYC, so i just bought this one on a whim!  i get good vibes from the bike so just want to treat her nicely and do her right :)

thanks again trials friends for all your time, knowledge and expertise. humbly yours, johnny

 

 

 

 

 

20170908_145627.jpg

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