Mikuni carb help

[Terramoto123]

I bought a pit bike and it didnt work til i cleand the carb then when i started it it start but after some time it died then i saw that the last owner had turned the mixture screw so my question is how much turn suit it be is it 1,5 or 2 turn or something.


Sent from my iPod touch using Tapatalk

 

[my67xr]

It need's to be adjusted to suit your bike but start the bike with it at 1.5 turn's out so it start's easy then tune it from there

 

[Terramoto123]

It need's to be adjusted to suit your bike but start the bike with it at 1.5 turn's out so it start's easy then tune it from there

Okay i'll try that thank you

 

[my67xr]

When you set up the carby and adjust the mixture,
Warm the bike up, then turn the idle speed screw in to raise the rev's another 800 rpm's or so
Now adjust the mixture screw in or out 1/4 turn at a time and let it settle for 10 second's
Listen the the way the engine is running, you want it running at the smoothest/fastest rev.
Once you think it's close then turn the idle speed screw back out till it's back to a normal idle speed.
Try the bike out after adjusting it.
That should be pretty close to spot on mixture's
Take note of what the bike is doing and at what throttle position if you need to adjust something.
EG, hesitate's off idle, stumble's at 1/4 throttle, feel's sluggish at wide open throttle

If after a ride and you want to adjust the mixture's a bit more, you may need to turn the mixture screw a tiny bit, only about 1/16 of a turn to adjust it from there


Is the carby one of these ?
If so it probably has a too small pilot jet. they come with a #15 but really like a #20 pilot jet

 

[Terramoto123]

When you set up the carby and adjust the mixture,
Warm the bike up, then turn the idle speed screw in to raise the rev's another 800 rpm's or so
Now adjust the mixture screw in or out 1/4 turn at a time and let it settle for 10 second's
Listen the the way the engine is running, you want it running at the smoothest/fastest rev.
Once you think it's close then turn the idle speed screw back out till it's back to a normal idle speed.
Try the bike out after adjusting it.
That should be pretty close to spot on mixture's
Take note of what the bike is doing and at what throttle position if you need to adjust something.
EG, hesitate's off idle, stumble's at 1/4 throttle, feel's sluggish at wide open throttle

If after a ride and you want to adjust the mixture's a bit more, you may need to turn the mixture screw a tiny bit, only about 1/16 of a turn to adjust it from there


Is the carby one of these ?
If so it probably has a too small pilot jet. they come with a #15 but really like a #20 pilot jet

Yeah it is the same carb. Ok thanks for information i'll try that and see what happens

 

[jev]

Hi Craig,

I have that carby on my TDR-PRO 125, has a Ducar engine.
There doesn't seem to be much adjustment, the screw is pretty much screwed all the way in, but small 1 degree turns makes a hell of a difference as you describe above.
It hesitates from 1/2 to 3/4 throttle then when wide open doesn't feel like much power.

I dont recall the jet sizing but will dismantle again sometime and check.


TIA

 

[my67xr]

I think it sound's like your carby might need a good clean out
Clean both the jet's including the hole's across them, check the hole at the bottom of the thread's in the base of the carby for the pilot jet is open and not partly gummed up.
Poke a strand of copper automotive wire through the hole's a few time's to make sure it isn't restricted.
Also blow compressed air in the through the 2 small hole's on the air filter side of the carb, with the mixture screw in and then take it out (with spring) and blow through it again
Refit the mixture screw and spring and have it 1.5 turn's out
Set it as above, and start it up let it warm then tune it
Most of that style carby's come with a #15 pilot jet which is a bit small for them, try a #20 pilot jet and tune it to suit
Slow/Pilot jet's here- Mikuni Carburetor Slow / Main Jets | Buy Online Australia at DHZ

 

[jev]

Carby was gummed up and some tubes were blocked with dirt and rubbish, it was soaked in petrol then carby was thoroughly cleaned out, air blasted.Made sure it was totally cleaned out before reassembling.

Ahh just found something while googling closeups of the carb, what is the screw at the very bottom of the float bowl?
Cause a slight adjustment (1 degree turn CCW)is whats making the difference between stuttering off idle, popping and farting to being able to ride with no top end.

Think I have been playing with the wrong screw, oops


i remember a while ago you had posted a link to TB with a remote adjustable mixture screw, I saved it but then lost it.

 

[my67xr]

Mixture screw is here.
You are best off making a tool to adjust it yourself, cheaper and easier

You need some 5mm pvc tubing and a small flat headed screwdriver bit.
Heat up the tube and push the bit in, let it cool and your done



With the Flex Jet, for the amount of time's you need to adjust your mixture's it's not worth it imo
Flex Jet, mixture screw
Flex Jet - W-59-12 - Carbs and Jets - Pit Bike Engine Parts - TBolt USA, LLC

 

[Terramoto123]

One question the o ring on the main jet broke off how portent is the o ring. Can i ride my bike or not.


Sent from my iPod touch using Tapatalk

 

[my67xr]

None of my Mikuni copy's have ever had them



See how it goes without it and if you find it run's strange and that you do need one, any auto part's place should keep a o'ring that size in stock
It would be a 6mm i/d, 9mm o/d, 1.5mm diameter, Viton O'ring
Don't just use a plain rubber o'ring as it will expand with the petrol and fall apart, most likely block your jet's and port's inside the carb

 

[Terramoto123]

None of my Mikuni copy's have ever had them

http://s598.photobucket.com/user/xrfairmont67/media/mini bike/Carby/20130515_105106-Copy.jpg.html

See how it goes without it and if you find it run's strange and that you do need one, any auto part's place should keep a o'ring that size in stock
It would be a 6mm i/d, 9mm o/d, 1.5mm diameter, Viton O'ring
Don't just use a plain rubber o'ring as it will expand with the petrol and fall apart, most likely block your jet's and port's inside the carb

Okay thanks

 

[jev]

Mixture screw is here.
You are best off making a tool to adjust it yourself, cheaper and easier

You need some 5mm pvc tubing and a small flat headed screwdriver bit.
Heat up the tube and push the bit in, let it cool and your done

http://s598.photobucket.com/user/xrfairmont67/media/tools custom tools home made/003_1.jpg.html

With the Flex Jet, for the amount of time's you need to adjust your mixture's it's not worth it imo
Flex Jet, mixture screw
Flex Jet - W-59-12 - Carbs and Jets - Pit Bike Engine Parts - TBolt USA, LLC

Great idea, you're a legend!