Need help with JR50 please!!

[Psychotic1]

I bought a 2003 JR 50 off of craigslist for my son for $600 with training wheels. Guy said it was in excellent condition. So I sent my wife to get it because I had to work. She gets it home and then I find out it had been sitting for a year. So I start checking it out. It will fire and start but then dies after few seconds. No biggie, I take the drain screw out of the float bowl and nothing comes out because it is all gunky. So I take the carb apart and it's pretty nasty, clean and blow out the jets, they were completely clogged. I cleaned the air filter and oiled it and put everything back together. Got it started and was like kool, job done. My son who is about 45lbs gets on to ride it and it won't hardly take off. Once it gets going its alright but it just has no ass to it, I have to give him a push to get him going if it isn't completely flat or downgrade. This is my first experience with a 50cc bike but this don't seem right. My wife messaged the guy and said it pulled him and he was 185lbs. Said the only thing that went wrong with these bikes was the needle usually needed cleaned or replaced. Maybe I need to reclean it and dip it in some ChemDip? I set the air screw at 1.5 turns out and played with the idle but it just don't wanna pull itself. Sit there giving it gas and it doesn't wanna take off? ANY HELP PLEASE?

[mwerling1212]

well i know pw50s have exhaust governors that limit the speed. its like a washer that restrics the flow. there is also a throttle governor, so those could be the problem.

[Psychotic1]

Yah, it has a throttle governor which is a screw by the throttle. I had it all the way out and still same thing. You can sit there revving it and it don't wanna pull unless your on completely flat ground and it is a slow pull. Don't make sense. I'm guessing it's carb related I dunno.

[driedupmotocrosser]

what does it do when your sitting there on the gas? does it rev up like the clutch is spining or does it bog? sounds like it could be a few things did you clean both pilot jets?stock carb has 2 pilots stacked on top of each other check that first. next check you main should be clean check to make sure you didnt put to much oil on the airfilter fresh gas?? check the silencer they get real gummed up very easy that would cause problems with low end as far as restrictors theres one in the exhaust at the flange to the motor and one at the carb flange but they're probably already out good luck Brad

[Psychotic1]

When he's sitting there it doesn't bog out it just revs. I did clean both pilots out. I oiled the air filter then squeezed the excess out. I will recheck that though. It does have fresh gas. I will check the exhaust restrictor at the exhaust as I didn't see one when I took the carb off. How do you get to the silencer?

[driedupmotocrosser]

the silencer is at the end of the exhaust there should be 2 phillips screws remove those and grab the end cap with a pair of channel locks and slide out the guts its a hokey design and gums up easy . do your self a favor take the carb apart and remove the top pilot jet bone stock the bike should pull your boy no problem when i bought mine it rode it down the street and i weighed 245 at the time try removing the air filter first and see if that helps if you oiled the filter and wrung out the excess you have waaaay to much oil on the filter

[Psychotic1]

I will be trying the above mentioned tomorrow. So will I have to repack the silencer or is it something I can just clean out? I greatly appreciate your help. Will post back tomorrow.

[driedupmotocrosser]

i was looking in some back posts and i'm 99% thats your problem pull the silencer off by removing the bolt that holds it to the frame and loosen the pinch clamp and pull the silencer off then ride it if it runs right your problem is solved all you have to do then is diassemble the silener clean it out and slap it back on and junior will be all smiles

[czkzaz]

I bought a 2000 and had the same problem, had to push my son to get him going. After many frustrated hours of research I found that there is a hidden 1st gear. I pulled the side cover and ground out the slot to allow the bike to use 1st gear. I have a pic that can be e-mailed.

Edited March 13, 2010 by czkzaz

[dustbowl]

drop a tooth on the front sprocket or 2.Grind the head,remove 1/8 ,3/16off the bottom.Stock these bikes are like 5:1,after head shave,grind you will be closer to 10:1..Major improvement over stock.

[Psychotic1]

I did pull the air filter and throttle was alot crisper. I still need to check the muffler then I think it will be fine.

[Psychotic1]

What is the factory specs on the idle screw and the air mixture screw?

[driedupmotocrosser]

idle should be around 1 1/2 idle has no spec screw head about flush with body

[CaptDan]

...said it pulled him and he was 185lbs.

Sit there giving it gas and it doesn't wanna take off?

Hmmm. 185lbs. adult riding a childs bike...

Could it be that the clutch plates are smoked?

For hop-ups, check...

https://www.thumpertalk.com/forum/showthread.php?t=206309&page=3

Edited March 18, 2010 by CaptDan
Fixed link.

[Psychotic1]

I don't think he meant he was riding it on a regular basis, just that it should pull a young child fine.

[CaptDan]

Okay, got it.

Still, if it revs without going awywhere...

When he's sitting there it doesn't bog out it just revs.

...it sounds like fried clutch plates.

[Psychotic1]

O.K. it isn't revving it just sits there while you give it the gas and doesn't move. It doesn't wind out or anything. I took the silencer off and that seems to help (a little). How do I take the silencer apart to clean? The 2 screws need removed? I hope not cuz there not coming off. How do I go about cleaning it?

[driedupmotocrosser]

sounds like yu need a piston and ring pull the plug and put your thumb or finger of the hole and kick the bike over and see how much compression you have or beter yet get a compresion gauge most say under 100 lbs needs a new piston i usually go by hours

[krusty1]

Hi, I am new to this forum. I just bought a 1979 JR50 two weeks ago for my kids and I liked it so much that I snagged another one up on craigslist (1992 JR50) yesterday. I had a similar problem with the new one today when we were tesing it out for the first time. I my case it turned out to only be the rear brake was engaging when you sat on it. Apparently when the swingarm flexed it would pull on the rear brake rod and bog everything down. I loosened the adjusting nut about 6 turns and everything ran great!

P.S. Both of my bike are currently running premix, one has a broken nipple on the injector banjo bolt. Does anyone know where I can ge a replacement for part for this so I can use the oil injection?

[krusty1]

drop a tooth on the front sprocket or 2.Grind the head,remove 1/8 ,3/16off the bottom.Stock these bikes are like 5:1,after head shave,grind you will be closer to 10:1..Major improvement over stock.

Do you grind off the base of the cylinder or the the headshell? If ou grind ff the base, wouldn"t his change the port timing?