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Spark Plug Question

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22 hours ago, johnnyjazz said:

wowsers guys, you are all the best!  coming here is like going to school for me so thank you :)

senor feetupfun, thank you always for such valuable chunks of knowledge and experience.  i totally understand now how the choke would help cool the engine by letting in more air.  however, after much trial and error, at your recommendation i stuck with the original 12/53 gearing and just working on super slow stuff. trials all the way! i have the carby set to all the correct specs as are in my manual, 114 main, clip position 4 etc.  she's running a beaut now after replacing that o-ring, i feel so lucky and pleased to have her in my care for a while. Trials is so great and just as in music, the slowest stuff is the hardest and most challenging.  im utterly rubbish mind you, but getting better in the empty parking lots and industrial estates around Brooklyn!  the cops haven't been best pleased at times, but having it all street legal w/ insurance etc really helps.

but wow, good to know potentially with right jetting and gearing a ty250 motor could do 80mph

and one question, hypothetically, if i were to be riding on a highway at 60mph what size main jet would i need? bigger yeah to let more fuel through? and presumably at higher speeds 40/1 is a much better choice than 50/1 pre mix?

not that i'd run her like that, but great to know just in case...

really inspired to be learning so much about something new.  thanks again to all.

best wishes, johnny

re main jet size for highway use:

Test ride with bigger and bigger main jets one size at a time until it four strokes at full throttle, then go down one size. This can be done on the road or on a dyno.

The reason why you need to do this is that because the engine produces so much more heat at sustained full or near full power than it does when ridden with a variable load, the engine temperature will go too high if the fuel/air ratio is even slightly lean. 

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On 21/12/2017 at 3:12 AM, tony27 said:


It sounds wrong but more oil means larger jets are needed as every extra oil molecule means 1 less fuel molecule getting to the motor

Glad someone else thinks this lol 

When I said the Opposite (ie less oil means more fuel going in) on another forum I got laughed at. 

To me it makes perfect sense, to some so called experts is bull lol. 

Edited by shakennstirred
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I agree. It makes perfect sense to me too. People who don’t get it still think adding extra oil to the tank is a good idea, and I try to talk them out of it.

If i feel i want to add extra oil i take the plug out and put a few drops in the plug hole and leave it a while to work its way down.

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