1980 Suzuki JR50....carb settings?


9 replies to this topic
  • zephyr338

Posted November 28, 2010 - 12:57 PM

#1

Im working on a JR50 and it wasnt running when i got it. I have since cleaned the carb(removed all jets, etc and soaked in cleaner, blew out, etc) raplaced fuel lines and inline filter. With the bike in neatral the throttle range is nice and smooth from idle to full throttle. When i put it in gear its slow out of the hole and anything over 3/4 throttle it bogs. I cant seem to get the carb settings right. Im not super familiar with bikes. Can anyone tell me what the two screw settings on the side of the carb are for? is one high and one idle?
right now the bike starts fine, if i put the choke on......the bike still runs.
my mid range is ok. my low and high end arent right. Help?
i removed the exhaust.....actually very clean. not much carbon build up at all on the jug end. im getting nice blow out from the other end. any ideas? i dont think its a dirty carb issue but how i have it set on the needles.

  • bronc3

Posted November 28, 2010 - 03:02 PM

#2

The carb adjustments should be for idle speed and pilot mixture adjustment, and the pilot adjustment is usually recessed. Once past 3/4 throttle or so the pilot mixture isn't really a big determining factor as to how the bike runs. Then it is primarily the main and slide needle that determine the mixture, the pilot just contributes slightly. Make sure the main is clean and also check for a plugged exhaust.

  • zephyr338

Posted November 28, 2010 - 03:41 PM

#3

bear with me im a rookie...................

when you say "main" do you mean the thing with the 4 or 6 little holes in the end of it? its clean as a whistle. i made sure the little holes were clear, it got a bath in carb cleaner and blow out. I can see through every orfice in it. is that what you mean by the "main"? the exhaust is clean. pulled it off the jug.
check out the pictures...................
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hows the plug look? it was installed yesterday..........rich or lean?
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is this normal? every once in awhile the breather tube from the carb pukes some fuel then stops. seems when i put the bike on the stand or something?
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and here is a picture of the bike.......not bad shape at all!
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  • bronc3

Posted November 28, 2010 - 04:43 PM

#4

The main jet is the largest jet in the carb, and the needle in the center of the throttle slide pokes down into it when the throttle is closed. As the throttle opens the needle rises out of the main and allows more fuel to flow through the main jet, relative to throttle position. The size of the single hole in the main jet and the profile of the needle determine how much fuel passes through the emulsion tube and into the intake.

Puking fuel is not normal, it shows that the fuel level in the carb is too high for some reason, such as float level adjustment. It could also be due to the float pivot binding or a faulty fuel needle and seat which are not sealing properly. It seem s as though you have probably found your problem, you just need to find out what is causing it.

Strange, the plug looks good, but if the fuel level is too high the mixture will be rich and the plug will generally be black or dark in color.

The exhaust might look acceptable at the exhaust port, but still could be restricted somewhere down the line, like where the expansion chamber chokes down to go into the silencer.

  • zephyr338

Posted November 28, 2010 - 05:11 PM

#5

do you know what model carb this is and where i can get parts for it?
any idea what the correct spark plug is for this year bike?

  • bronc3

Posted November 28, 2010 - 05:27 PM

#6

Carb should be a Mikuni VM12, plug should be an NGK BPR4HS.

Plug gap is .028

Parts should still be readily available.

  • zephyr338

Posted November 30, 2010 - 05:56 PM

#7

thanks for the help. so i have spent alittle more time tinkering with the settings on the carb. got home from work tonight and threw the newly fixed rear brake pedal back on and fired her up. love that this little baby. fires on the first or second kick and idles great. so i took her for a spin to test the brakes and low and behold maybe i got the settings right? shes topping out smoothly now. now hesitation from 3/4 to full throttle and it isnt "skipping" like it was. i am not touching that carb again! she is officially back from years of sitting in a shed along side some quads that also didnt run. they are next on the list. my buddy should be happy and his kids even happier. cant wait to see them get to ride them again. thanks bud. i appreciate the lesson.:thumbsup:

  • bronc3

Posted November 30, 2010 - 06:04 PM

#8

I am not a JR expert, but there are some other tricks for this bike.

If you search here in the peewee section you will find a relatively simple mod that will give your bike a two speed tranny. The gears are already in there, you just have to modify the bike to enable first gear.

There is an extra pilot jet in the carb to tame the bike for newbies; yours may have already been removed.

  • zephyr338

Posted December 01, 2010 - 12:15 PM

#9

are those the little tiny things i removed? one on top of the other? the bottom one ws longer then the top......what one do you remove? you have to remove the top one to get the bottom one out.

  • bronc3

Posted December 01, 2010 - 05:38 PM

#10

are those the little tiny things i removed? one on top of the other? the bottom one ws longer then the top......what one do you remove? you have to remove the top one to get the bottom one out.



Yup, the 2 small jets, stacked on top of one another. I believe you remove the first/long one.




 
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