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Anyone good with a dirt bike?

black rust

black rust

1/2 ton status
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Jun 29, 2007
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Beecher, IL
I'm having a couple issues with my dirt bike carb that I can't figure out. Basically it idles high, but I can't find a vacuum leak. I even tried sealing up everything between the carb and the engine intake with rtv, still idling high. Is there anything else that causes this? It doesn't do it all the time either, usually when warm. Sometimes if I drag the engine down with the clutch, it idles where it should, sometimes it just goes back up. Any ideas?
 
Stupid question here, but have you checked or messed with the IDLE control?

Also could be something with the CHOKE circuit on the bike (if it has one).

I would take the carb out and then dissasemble it. Take the bottom bowl off, becareful not to muck up the floats. I would pull the pilot jet (itll be a jet off set from the main) and then id pull the main jet and check to see if they are clogged, I would then inspect the Float to make sure there arent any holes in and take a measurement to make sure its at the right height. I would give the carb a good cleaing. I would also pull the top off of the carb and make sure the needle is seating all the way and there isnt anything in there keeping it from lowering. ALso check on the needle to makes sure the lil C clip didnt come off (if your bike has this style).

After re-reading, id say you have a float sticking. Make sure it moves freely and isnt all tarnished and the bowl isnt all tarnish. Becareful when cleaning the floats they are very thin brass or plastic in some cases, so dont go scrubbing on them. The bowls are fine, just not the floats

I would clean the carb really good, dry it out and then put it back together. I would put all the jets and needles back to factory settings.

Also make sure you dont have an exhaust leak, esp. at the headpipe.

When / if you take the top off, because of the rubber diaphram that they usually have (if you have this style carb). Jus be easy with it and make sure the top goes down all the way and seals up properly, dont over tighten the bolts.
 
That is what I thought too, but when he says it changes when it gets hot, that makes me think either something with the CHOKE circuit or the FLOATS are getting warm/hot and expanding causing them to close hence lowering idle.

I dunno.

HOnestly we need to know what year, make and model of motorcycle we are dealing with it. Too many variables, some have flat slide carbs, some are CV, etc etc etc.
 
Okay, guess I should have put more info in the first post. 1989 Honda nx125, 4 stroke. I did try to clean the carb out, but didn't mess with and settings because I couldn't find the factory ones, since this isn't the most common bike. I did try to adjust the idle control, but I would have to lower it so much that the bike would start to die, then when I brought it back up slowly, it would go back to where it was. It has electric start, not kick, but it starts easily with the choke.

IIRC, the float wasn't sticking when I cleaned it. I'm also having another possibly unrelated problem. If I open the throttle too quickly, it bogs down, but only in a low gear. At first I thought I has an accelerator pump problem, but it looked fine to me. It also skips around a little at high rpm sometime, not sure if that is an ignition miss or something clogged in the carb.

As I'm writing this, I'm realizing it probably something that is still clogged in the carb. I'm leaving tomorrow, but when I get back I'll clean it out again and if I still have this problem, I'll ressurect the thread and ask more questions.

Thanks for the help
 
Im still going to with dirty carb and improper adjustments. When you wack the throttle, if its bogging, your not getting enuff fuel. Id also check look at your spark plug. If its black than your running to rich, if its white its too lean. your plug should be a slight grayish color.
 
Most likely a needle sticking open a bit. Only takes a very small amount of dust or dirt to get into the slide and cause this condition. I have seen this way too many times.
 
Idle jet i work on bikes all the time remove carb or turn it side ways if room alows remove float bowl and unscrew the the smaller of the jets it is usually tucked in a tube.It probably has three jets center jet is main needel goes ito it the second in the idle and the third is the choke jet or enrichment jet. Make sure you remove them the hole is so small on the pilot a sewing needle wont go through it, remove it i usually have to grind the edges off my smallest flat head to get it into the tube and spray the crap out of it with brake kleen and try to blow through it.
I make $50.00 bucks a pop for doing this and 99.9 percent of the time that what it is, a shop will charge you 110 or more.
 
I worked on it again today, with little success. I took the carb off again and tried blowing out all the jets with compressed air, they didn't looked clogged though. Put it back on, and now I'm having accelerator pump problems, which I had before the first cleaning and went away until now. One thing I did notice though when I had it back together, I managed to get the idle down where it should be, then if I rocked the bike back and forth, it went back to it's high idle. So is this a float issue? It looked fine to me, but it may be set wrong, and can't figure out when the level should be.
 
Once again i have seen this over and over i cleaned the carb and it still does it i remove the jets clean it properly and wow majic it runs great Ppeople shake there heads i did that. Unless you phisically REMOVE THE PILOT JET AND BLOW AIR THROUGH YOURE MOUTH OR LOOK THROUGH IT IN TO THE SUN ITS NOT CLEAN.blowing compressed air will not do it you HAVE TO REMOVE IT spray carb cleaner and use a sewing needle to break loose the gas film they sell a special toool i have them but for you're case a needle will work. or replace the pilot jet with a new one.
to set float height remove carb turn it up side down and set the float lvel with the float flange or mating surface. be care full because it spring loaded on the needle so it can give a false reading. I set them with the spring compressed level with flange so when you look at it normal spring not compressed is a litte low carb up side down.
I see this all day long twice on sundays over and over.
If everything was in working order parked bike some time went buy now this 100% pilot cloged you will not belive how small the hole in the jet is. Like a human hair compressed air into the jet from the bottom only lodges it tighter < thats why you have to remove it and blow cleaner the opposite way.
Not trying to sound like an ass here but try it.
Also how old is the gas drain the tank and replace the fuel. always leave the gas valve on or shut it off and run the bike till empty if its going to sit or same thingn will happen.
Once agian tell people this and get the biked tuned up running great, get a call 4 months later its doing the same thing(did you leave the gas on NO did you run it out of gas after switching the valve off NO well then.
Its going to cost ya more money then
PM me you're number i will walk you through it
 
Alright, I pulled it apart again and cleaned all the jets with a needle and carb cleaner, and blew everything out again, and for now it seems to run good. Thanks for the offer
 
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