Yamaha JT1 Starting and running problem

[@kxdude4]

Hey guys! I did everything suggested and was at my wits-end! I finally found the solution: I had purchased a tune up kit off of eBay with points and a new plug. I installed it as I rebuilt the engine. Turns out that the spark plug was incorrect. I don't know the correct terminology, but the base of the plug was longer than the original! Aarrgghhh!!!! I bought a new plug and it now runs fine!!! THANK YOU for all your help!!!!!!!!!!!!

[@EarthSurferUSA]

Because of growing up in this grass roots industry, I port and stroke smaller 2-stroke engines for a living today, (over 10 years now), and have won championships all around the world, and I think you are talking about what is called a "protruding nose plug", which would extend a bit further into the combustion chamber. I find it hard to believe that plug would cause what I thought was a rich needle jet (if that had a adjustable needle jet), and was just going to advise lowering the needle one notch, (and or a smaller pilot jet, if the carb had one that is replaceable). But I have been wrong before. :) Another thing to look at, especially with small bore cylinders, is the compression ratio. Those cylinders were not plated, and wore out faster, causing low compression, and it effected the power on the small bores the most. I would not be surprised if you can get 3 more hp out of a fresh top end if you can get one done, (depending on how "out of round" your cylinder is, and how worn out the ring is), and that is a pretty big increase for that small bore. You will notice the difference in power. "LA sleeve" in CA. might be a great place to start looking.

[@eschrader]

What is the correct spark plug info?

[@PULSEXBillionzz]

My 1st bike in 76 was a jt1.. great little bike to learn on. I just bought one at auction. cant wait to get it back together after tearing her down and making sure everything is correct., 1st off when u shut off ur choke and it died, it tells me ur either not getting enough air or too much gas and since u have gas dripping , ur getting too much gas so when u put ur carb back together did u put the needle valve ass. back in correctly? it can go in 2 ways but only one way is the correct way. pin down check it 1st

[@Lipelouco]

my first bike was one of those.... had it for maybe 15 years... I used to ride it to college and everywhere... good times

[@Driftdavillian]

Man what memories.. Had one when I was 12. Beautiful!

[@klockwerken]

Hi kxdude4: There are a few things to check. 1) Spark. Are you getting a good hot BLUE spark; not yellow? If Spark is good and blue then the next item to check is 2) Compression. Compression should be no lower than 75lbs. A fully rebuilt fresh upper half is close to the 90lbs range. 3) Fuel quality--Use FRESH GAS by dumping out the fuel tank and purging the fuel line and carb bowl. 4) Carb bowl--one of the most neglected maintenance items ever. Bad Spark is usually points (not so much condenser but they sell a tune-up kit with all of that stuff so use the new components and be VERY careful how the condenser wire(s) are attached with the tiny Bake-A-Lite plastic washers and fasteners making sure none of the contacts are accidentally touching the case, or "grounding" Next while the flywheel is off the bike, inspect the condition of the inner flywheel--no rust? Good; Rust, LIGHTLY sand away the rust using like a 200# sandpaper, wipe clean as a whistle and a super light coating of Vaseline to prevent further oxidation. Check for spark improvement. Not improved? Move on to the wiring itself and check the kill switch contacts. Also clean the spark plug. Often times it is NOT necessary to replace the spark plug but rather, clean it of all carbon and confirm plug gap using a feeler gauge. Fuel Quality: Thanks to the Draconian EPA and the effing Tree Huggers, much of the gas is E85 and has a short shelf life. Replace gas and purge the fuel line, and carb bowl of all fuel. Carb Bowl: unscrew the carb bowl and flush it out with kerosene and a dental pick to remove ALL crusty crap caught in the carb bowl trap. Re-attach It all of this does not work and you have given up, I take donations of all naughty motorcycles--simply give it to me!! Hope this helps!

[@NGC2392Eskimo]

Nice. Had the same bike back in the early 70s. Thanks for the memory.

[@powerwagon3731]

I too had the same bike as a kid of the 70s, problem is mine never ran but it started me on a life long love of dirtbikes and I have several now that I ride often.

[@mikerafonemusic6177]

thats cool, i havent seen one for a long time..i had one n raced desert on it when was 9..im 53 now..only problem that it had a hard time in sand..then my dad bought me an xr75, cured the sand problem. but then came the yz 80, i got one of those n smoked the xr's..lol. i love all vintage bikes..thanks for posting that!

[@kxdude4]

Thanks for the comment! I have you by 1 year so we prolly lived the same GOOD stuff back in the day! I lived thru the XR and YZ, too, but don't forget the Yami going to the GT80 in '73 before the XR in '74... We didn't have much money so I hadda ride against what basically looked like my JT1 - just with 25% more cc's (and a different color scheme..._. :-) Best times of my life!!! :-) Take care!!!

[@mikerafonemusic6177]

me too! for sure! thanks keep ridin!✊👍

[@TylerProvines]

Also I replaced the air filter, and that helped as well.

[@TylerProvines]

I had a similar problem with mine. I replaced the spark plug and it ran a whole lot better afterwards.

[@nathantimothycelestino]

hey can you check what kind of spark plug it needs

[@johnmcgee1860]

Mine had the same problem, the idle jet is plugged or close to it, the idle jet is a #38mm that's around .015 thousandths it's in the carb bowl, small screwdriver takes it out then soak in some carb cleaner then run a .011 thousandths guitar string through it to clean it out, and that solves the problem, if you have a torch tip cleaner that has a .015 thousandths wire on it that will surfice, mine idles perfect now with no bogging

[@Sertao2013]

You said you tested the float in water but you didn't say you removed the needle valve or cleaned it .

[@kevintreece62]

Did you ever get it worked out? Sounds like the Exhuast is plugged to me and not getting enough air through the carb.. Pull the pipe off and start it... I bet it will run really good with the pipe off! if so.. cook and clean out the pipe!

[@PeteS528]

It's a 2 stroke, it is not going to run well or at all with the pipe off. There is no back pressure in the exhaust without the pipe.

[@soltri3287]

may be many things, I have two JT1 and I are a couple of tips, my facebook page is FITO TWISTED CREATIONS, I can give you a list of steps for you to check, I'm motorcycle mechanic and my first bike was JT1

[@cynthiaadkins7313]

Any tips would be appreciated I have a 71 Jt1 and can’t get it to run for no longer than 30sec it ran once for a few hrs great and now it acts like it’s not getting enough gas or something I have to make it run with it being fully choked and sometimes it doesn’t run even doing that any ideas