[Manklemore]

Hi all, im new here and new to motorcycles so bear with me if im not being super intelligent about this lol, but uh, here goes

SO i bought a 1982 gn125 off someone who inherited it from his dad's storage facility left in a wil, blah blah, it was left in working condition but wasnt touched for about 19 years so i had to do some cleaning to it. from what ive read already, i cleaned out the carb all around where i could after taking off the bowl, couldnt find a way to get the whole carb off) added fresh oil and an oil filter since neither were there at the time of purchase, new gas, and thats all i did. So initially after doing all this i got it running, a little jerky because the bowl gasket was cracked in two spots, so i also replaced that. Was running rich as heck but ran totally fine from what i could tell except a gas leak out of the carb exhaust and air filter....

Jump to present; i cleaned the gumming off the pin the floats move, and the floats actually move now so theres no more gas flooding out. but now when i start up the bike, it runs for about, say, 10 seconds if i dont give it any throttle, maybe 4 if i do, then it dies and wont turn on unless (dont judge me i dont know where i got the idea from) I physically blow a little air into the carb via carb exhaust, then it repeats same as above. Im damn sure its an airflow issue but i cant figure out what to do about it...

(also i guess its worth noting im not sure what size Mikuni Carb i have, its between a 22mm and a 24mm but even the gasket i got to replace the old one fit, all the shapes, but looked way thinner than the original.)

 

[jag13]

You need to take the carb off the bike and clean it properly. (Youtube can show you how much easier than me trying to explain the procedure.) That means all the jets and ports. Also inspect the intake boot and all fuel and vacuum lines for cracks/leaks.

 

[Manklemore]

Okay ill try that, y brother is home from college for a bit and he knows carbs more than i do, so i'll give it a shot, thanks

 

[Manklemore]

Okay so i removed it, but im scared to break it down because i cant even find out what model Mikuni carb it is... doesnt look like any model i've found online and theres no ID # except on the slide that the throttle controls and it has the double square and a 125 next to it... would post pics but im pretty sure i cant do any of that yet

 

[Manklemore]

 

[jag13]

It's a Mikuni CV carb. They are all basically the same. Youtube Mikuni CV carb cleaning for basic instruction.

TIPS:

Be careful not to use carb cleaner on the rubber boot on top of the slide (or ant other gaskets) as it will expand the rubber and cause it to not want to seal upon re-assembly.
Keep track of which jets go where.
Before removing any adjustment screws, turn them IN and count the rotations. Write these down and use that info when re-assembly.

It is really quite easy. Just take your time and do it RIGHT. otherwise you may have to do it all over again.

 

[Manklemore]

Okay so fully broke down and cleaned every piece of the carb, it had no adjustment screws, and the only gummed up/stuck piece was the needle that goes in the jet, just finished reassembly this morning and i still have the same problem, but i dont need to blow air in anymore it handle it on its own, no vaccuum leaks or cracks on intakes... i dont understand...it ran just fine but blackened the hell out of my spark plug when the float needle was gummed up and stuck down, why would cleaning it cause all of this to start?

 

[Critter]

Put a new plug in it and see what happens

 

[jag13]

Maybe someone else can chime in with different experience, but I have never seen a Mikuni CV carb that didn't have an air mix adjustment screw. And air/ fuel mix seems to be where your problem lies. On some carbs it is hidden behind a factory installed metal cap.
can you show more pics of the carb from different angles?

If I remember correctly the air mix screw should be on the bottom on that carb.

 

[Manklemore]

found it under what i thought was just dirt/burnt gas, its on top towards the engine side, it was 3 turns screwed outwards, do i screw in more out or in for a more lean mix? i keep looking everywhere but i keep seeing different answers from "experienced" riders

 

[jag13]

All the way in, until it touches bottom (lightly). Then turn it out 1-1/2 turns. That is generally where those carbs are set from the manufacturer. From there you can fine adjust, usually between 3/4 (in) to 2 turns (out).

I am a little concerned about what kind of PROPER cleaning you gave the carb, that the mix screw was still hidden under dirt.

 

[Manklemore]

i cleaned everything else that used either screws or had a hose attached, adjustment screw was basically hiding in the open with all the other grooves to me... but again, screwing in will reduce fuel?

 

[hogcowboy]

I am a little concerned about what kind of PROPER cleaning you gave the carb, that the mix screw was still hidden under dirt.

i cleaned everything else that used either screws or had a hose attached, adjustment screw was basically hiding in the open with all the other grooves to me... but again, screwing in will reduce fuel?

What you are missing here Manklemore is if you missed that, what other areas did you miss that are equally important. Like the so many tiny passages. You may be creating a mess adjusting something that doesn't need it because a passage is blocked.

Proper cleaning would not have left anything hidden. Cleaning a carb correctly is critical. Just shooting carb cleaner around may or may not work is all I'm saying and why the concern. Hate to see your beat you head against the wall later on.

 

[Manklemore]

hogcowboy you're right... i just figured it'd be as simple as it looked but i guess not