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94 jr50

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Still new to bikes and I was given a 94 JR50 for my sons. It's in pretty rough shape and was told it dies once put in gear and you start to take off. Just picked it up today, and I thought it was 2t but there is an oil tank on it? Are you not supposed to mix gas in these? I'm looking forward to the project and getting it cleaned up and running. If anyone could tell me a bit about these bikes I would appreciate it.

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Ok so fresh gas, oil, cleaned air filter and bike starts first kick cold with choke fully on and will idle with choke on. Once you shut the choke off though it dies unless giving it throttle and it would not hot start.

Am I right to believe its a carb issue? It appears someone was messing with the screws on the carb. Also someone told me it may need rings? I don't know much about bikes but I am willing to learn and do any repairs if someone can point me in a direction to start trouble shooting this. My kids really want to ride it! I will pick up the service manual for it in the next few days.

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Hey Mountainbum,

Sorry I didn't pay to much attention and did not see the post. Granted now it has been years since I had my sons' KDX50(same as a jr50). The bike is a direct injection bike ie it takes straight gas and injects oil into the carb mixing in the cycle before combustion. Honestly you would be better off finding a specialty forum dealing with jr's than on here. KTM guys have ktm talk. Not sure about the jr as I sold it before I tore to deep into it.

I definately would recommend blocking off the oil injection and running your own pre-mix oil as the bike will run better. The problem you described is being caused by the pilot circuit in your carb. You need to pull and completely strip and clean you carb, blow out (with compressed air) every passage. Put it back together and set the air/fuel screw and idle screw to factory setting. It will run good again. Last thing look for an air leak. A bike with as much age may have a torn boot causing to much air to get in which is why it will start good and run with choke, but as soon as you crack the throttle (more air) it dies. Again sorry for the late post.

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Pre-mix is a bad idea and is completely unrelated to your carb likely being really gunked up. That's why it runs with the choke on and dies when you shut the choke off.

Elpato is right about that.

Here's instructions with photos for cleaning your carb: http://articles.superhunky.com/4/21

Good luck.

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Thanks for the help. I couldnt help myself late last night and started taking it apart. I just unscrewed the throttle cable/choke assembly from the top of the carb and left it hanging there to remove the carb from the bike and covered the carb to block hole with duck tape so nothing could fall down there. I hope that was ok....

I took the 4 screws out that seperated the top and bottom of the carb and stopped there as I had no idea what I was doing so thanks for the link Smacaroni that is just what I was looking for. I could already see gunk in there and what almost looked like a piece of glass that kind of deterieated in my fingers. I will get the carb all cleaned up in the next few days and see if that fixes the issue. The bottom air filter box screw to carb was too long (i added washers) so the whole assembly was loose, between that and the duct tape on the gas cap who knows what could have gotten into that carb.....

The bike was not maintained at all and I am assuming the dirty carb lead to someone messing with the pilot/idle screws. I will do some searching but if anybody knows the factory settings for air/idle and pilot screws that would be great.

The more I took it apart last night the more I dont want to put any considerable money into this bike as its in bad shape. Lots of rust and missing/mismatched scews and bolts. I might even skip buying a manual for now. If I can get it running for cheap so my boys can learn on it and my youngest who is 3 could ride it for a few years that would be great, otherwise I would probably by a different 50 in better shape. I'll be buying 2 more bikes next month for my boys 3 years, 6 years, and 7 years old so I will make another post in a bit after my wife measures them to get your guys opinions on what I should get them. I just got my first bike this summer and had a blast, this is a great sport.

Thanks

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These kiddie 50s (as opposed to the "fast 50s") are tough little pieces and will take quite a beating. While I wouldn't advise you to put a bunch of money in it, the simple fact that it runs with the carb gummed up is a good sign: the ignition system "works", the crank and connecting rod are "ok" (notice the quotation marks) and it has enough compression to run so the rings and piston aren't total crap. That's more than half the things that can be totally messed up and expensive checked off the list.

It sounds to me like you're probably going to have a future in mini/peewee purchase and maintenance. I highly suggest buying a can of GUNK brand parts cleaner. It comes in a gallon can. Any decent auto parts store should have it. I bought one about two years ago for $25 give or take. It'll probably last another three or so years for me if not more.

It comes with a parts basket and is only 3/4ths full so you have room to put your parts in.

Be very careful of the small parts, even the big carbs have tiny parts, so make sure your work area is CLEAN.

Now that you've got that and you've got your carb, take everything apart. Do not put any plastic or rubber pieces in the cleaner, it will be ruined. Only metal goes in.

There are two or three screws on each carb that you need to remember their position. One is the idle speed screw, and the other one or two are the mixture screws. The idle speed screw is usually in the middle of the carb, on the side and it lines up almost perfectly with the center of the slide.

Turn it in until it stops (snug, do not crank!) counting the number of turns in. Write this down.

The mixture screws are also usually on the side, but may be on the bottom. Position varies, but they almost always look like they're not holding anything in. Again, turn the screws in counting the number of turns. Usually this is between 1.5 and 3.5 turns "2 - 2.5" turns is your general setting that should be good enough to get any bike started.

Write this down as well.

When you reassemble, you'll turn those screws in till they bottom and then turn them back the same number of turns you just wrote down. You'll still need to adjust them, but not much. Unless of course the PO screwed with them in which case who knows?

The other screws just take them out and put them in the carb cleaner basket. The mixture screws if they have rubber caps or points, do not put them in the cleaner, otherwise they'll be fine. Do the same for every other part of the carb and since this is the first time, it's probably not a bad idea to take pictures so you have a visual paper trail to reassemble the carb when you're done.

I usually soak my stuff for 1/2 an hour but if it's really crapped up, it may take over night.

That's about all I have to add to the article I linked to above, SuperHunky knows his stuff and he's a pretty decent writer too.

The good news, when you're done the next carb you do will be a whole lot easier. I would suggest that cleaning the carb is the first thing you do to any newly acquired bike even if it runs right when you bring it home. Also, when you shut them off for the day, turn the petcock off, let the bike run till it starts idling high before you shut it off. Most carb "gunk" is from the fuel in the bowl evaporating.

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Great advice thanks! I will pick up some of that parts cleaner for sure, I was going to get carb cleaner on the way home anyways. Along with your link I found the complete carb diagram with parts list on bikebandit so I should be good. I have a call into the local shop to see how much a carb rebuild kit is if they can get one and service manual are.

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One last thing I forgot, you're probably going to find at least one O-ring is shot,

If you have any O-rings that are junk, head down to the hardware store plumbing section and find the nearest size SAE O-ring and try it. Most of the time it'll work just as well as the metric ones for a quarter and not needing to wait a week to get one from the dealer.

But a rebuild kit isn't a bad idea and should have the O-rings you'll need too, the kits often have replacement pilot and main jets.

I would suggest keeping any usable parts from the rebuilt kit that you don't use. Nothing sucks more than dropping a float needle and it bounces into a black hole.

Edited by Smacaroni

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If I can get it running for cheap so my boys can learn on it and my youngest who is 3 could ride it for a few years that would be great, otherwise I would probably by a different 50 in better shape. I'll be buying 2 more bikes next month for my boys 3 years, 6 years, and 7 years old so I will make another post in a bit after my wife measures them to get your guys opinions on what I should get them. I just got my first bike this summer and had a blast, this is a great sport.

Thanks

I see KTM in your future... Absolutely this is a great sport and you are going about it in the right way. You have to be a sponge and learn as much as you can and do 90% of the maintenance on these little bikes to keep yourself from going broke. But as Smacaroni said once you've done one carb they are all the same from here on out (more or less)... I am a fan of KTM as I feel they have good suspension and although require some maintenance parts are readily available. Of course ask 10 different people you get 10 different answers. Welcome to the world of mini's there is no looking back now. Your kids will be happy, you will be broke.:bonk:

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Well I got the carb all cleaned up good, that gunk parts cleaner made it nice and easy. I believe I did it right and the bike fired first kick cold again and will idle all day with the choke on but still wants to die once you turn the choke off and will not hot start. One thing im unsure of is the idle screw?

Its a milken (or something like that) carb, and there are 2 screws for adjustment that I see, both are on the side of the carb and I know that the screw to the right is the pilot air, and the one in the middle in line with the throttle valve is the fuel screw? Anyways the pilot was out 3 1/2 turns before i started, and the fuel screw was out 2 1/2. I could not find factory settings anywhere so I turned them both out 2 1/4 after cleaning but since the bike will not idle with choke off im just guessing with trying to adjust them. Should there be a 3rd "idle" screw on the carb or is idle adjusted on the throttle cable itself up by the handle bars?

The shop i talked to could not find a rebuild kit or service manual anywhere, even through the dealer, only individual carb parts. I think I did see a manual online but it was $78 and im not dropping that much right now for this bike. If it were just a carb issue the bike should still hot start just fine like it cold starts yes? Could the rings be shot or some other major issue? Ill try calling around tomorrow to dealer or shops to see if someone can tell me the factory screw settings for the carb, without a manual though id hate to rip into a 2 stroke motor for the very first time to do any major work but i may try. Rusty/stripping and breaking bolts is one of my worries, i went to pull the limiter out of the exahust manifold but 1 bolt was already completely stripped and rusted so I left it alone.

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One thing at a time my friend. Don't mess with the almost broken stuff as you know, but there's easier ways to check if you're looking at a top end rebuild than tearing it apart. Not exactly definitive methods, but definitely easier.

I'm not familiar with that carb, but it's unlikely that the handle bar throttle assembly adjustment is the idle speed adjuster. That's just there to remove slack from the cable.

As far as the other two screws, I'd suggest turning them one at a time while the bike is running. If it increases the idle speed, keep going until the engine is either screaming or it gets worse. If it gets to the point where it's screaming, take the choke off and see if it still runs. That one is probably the idle speed screw, turn it back to a reasonable idle.

If turning the screw in reaches a point where it starts getting worse, turn it back to where it idles best and then try turning off the choke. If it dies, turn the choke on, restart the bike and try the other screw.

If this still fails, I'd suggest looking at the gaskets which connect the carb or carb boot to the crank case - you may have an intake leak and these are easier and less expensive to replace than base gaskets.

Failing replacing intake gaskets, then you're probably looking at a top-end rebuild OR a dry-side crank case seal. Again, the dry-side crank case seal is usually cheaper and easier especially considering you've got broken exhaust studs.

Hopefully someone can give you more information whom is familiar with these carbs. Unfortunately, I'm not.

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Hey Mountainbum,

You need to pull and completely strip and clean you carb, blow out (with compressed air) every passage. . Last thing look for an air leak. A bike with as much age may have a torn boot causing to much air to get in which is why it will start good and run with choke, but as soon as you crack the throttle (more air) it dies.

There has to be an air leak. Did you use compressed air to blow out the passages in the carb? Just cleaning it will not clear the passages in the carb. If the bike runs with choke on but dies with it off, then you either have an airleak or a junk in the pilot circuit. Your bike "should" be warm and idling to adjust your air/fuel and idle screw off choke!!!! You have to get the bike to run off choke first. Even if that means it is idling super high. I'm thinking you have an air leak though...

At any rate welcome to the world of 50's they will make you :bonk::banghead:

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Thanks again. I just got some of the same advice from a coworker, first thing he said was crank seal or gaskets. I will try to get it idling today and mess with the adjustment screws a bit more, and no i do not have compressed air.......I had to resort to a can of compressed air which is not even close but all I had. My buddy has a compressor so I may take it over there in a few days and re-due the carb. Will update when/if I figuring it out.

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