Just wanted to find out if anyone would know a possible solution to a problem im having, if I roll off the the throttle not even that quickly sometimes the bike seems to backfire a lot. Also im getting quite a bit of oil and smoke coming out of the exhaust. I have adjusted the screw on the bottom of the carby a little bit but seems to make no difference. I have a Pitpro 140cc bigfoot with the 30mm mikuni carb on it, anyone know how I could fix these problems.
backfiring and oil coming out of exhaust.
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my67xr
Miniriders Legend and Master Spanner Spinning Mode
yeah as above, try tightening the exhaust flange nuts at the head
if air is getting in past the gasket/copper o ring, it will pop out the exhaust on decell.
it could also be too rich ?
have you tuned the carby to suit the engine ? (rejetted it?)
and are you running a lightly oiled foam air filter ?
and check that the breather hose at the top/back of the engine isn't blocked up or kinked
if it is it could be forcing a bit of pressure back through the engine and past the rings
if air is getting in past the gasket/copper o ring, it will pop out the exhaust on decell.
it could also be too rich ?
have you tuned the carby to suit the engine ? (rejetted it?)
and are you running a lightly oiled foam air filter ?
and check that the breather hose at the top/back of the engine isn't blocked up or kinked
if it is it could be forcing a bit of pressure back through the engine and past the rings
the exhaust seems to be broken on one side when I do the bolts up that hold the exhaust to the engine one side of the exhaust can still be moved up and down a little bit like its broken a weld on one side. Haven't rejetted the engine yet still trying to tune it via the screw on the bottom of the carb but it doesn't seem to affect the engine much? I started two and half turns out, if I screw it in then I assume I am leaning the engine out and if I screw it out I assume I am richening the engine up is this correct? The filter is lighty oiled its just a stock airfilter that came with the engine. One more thing if the exhaust is broken at the flange where it bolts to the head would this affect my ablility to be able to tune the carb?
Blender
Well-Known Member
Screwing in the mixture screw will richen the mixture, un-screwing leans it out.
When you say a broken weld on your exhaust, do you mean the piece of tube that slips over the exhaust, the piece just at the tip of the header pipe ? That has happened to me, I just went and got it welded, it only cost around $20.
When you say a broken weld on your exhaust, do you mean the piece of tube that slips over the exhaust, the piece just at the tip of the header pipe ? That has happened to me, I just went and got it welded, it only cost around $20.
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my67xr
Miniriders Legend and Master Spanner Spinning Mode
the mixture screw wont really affect it if you are try to listen for a difference at idle speed.
you'd be lucky to pick a difference in sound/idle
does it hesitate at all when you blip rev it ? (engine warmed up)
if it does hesitate then the Pilot Jet is too small.
once you have the Pilot jet you need, turn the idle up to about 1800 rpm.
now you can adjust the mixture screw in or out 1/4 turn at a time, let it settle for a few seconds
you need to listen to the way it is running, you want to get it running at it's fastest/smoothest point
once it is close fine tune it and adjust the mixture screw a 1/8th turn, let it settle
once you are happy it's close, drop the idle speed back down to normal and give the bike a try
you'd be lucky to pick a difference in sound/idle
does it hesitate at all when you blip rev it ? (engine warmed up)
if it does hesitate then the Pilot Jet is too small.
once you have the Pilot jet you need, turn the idle up to about 1800 rpm.
now you can adjust the mixture screw in or out 1/4 turn at a time, let it settle for a few seconds
you need to listen to the way it is running, you want to get it running at it's fastest/smoothest point
once it is close fine tune it and adjust the mixture screw a 1/8th turn, let it settle
once you are happy it's close, drop the idle speed back down to normal and give the bike a try
Its broken where the header goes through the mount that attaches to the engine. I haven't taken it off but that's what it looks and feels like, if I move the header with my hand one side will move up and down but the other side of the pipe wont. When I turn the throttle its fine till about around half throttle I guess and then it seems to bog down when I go past half throttle to quickly, if I go slowly all the way to full throttle then it doesn't seem to be that bad.
so you would say cruzing down the road in 3rd you jump on the gass... And it hesitates for a moment than goes good?
Move your needle clip further down on the needle to ritchen up the 3/4 opening mixture
my67xr
Miniriders Legend and Master Spanner Spinning Mode
yeah that is what Zac meant.
so if you rev it quickly there is no hesitation at all ?
so if you rev it quickly there is no hesitation at all ?
my67xr
Miniriders Legend and Master Spanner Spinning Mode
yeah that's the only needle in the carby, it has 5 notches on the top of it
the clip should be in the centre notch now, move it to the bottom one to richen it up, then see how it goes
the clip should be in the centre notch now, move it to the bottom one to richen it up, then see how it goes
my67xr
Miniriders Legend and Master Spanner Spinning Mode
what carby is on it ?
normally you can just push the needle upwards into the slide, it will pop the retainer clip out the top of the slide.
then remove the needle, unclip the notch clip from the centre slot and refit it to the bottom slot.
then slip the needle back down through the top of the slide, refit the retainer clip,
refit the spring and cable and put it back on your bike and try it out
you will probably want to adjust your mixture screw again just to get it running sweet.
normally you can just push the needle upwards into the slide, it will pop the retainer clip out the top of the slide.
then remove the needle, unclip the notch clip from the centre slot and refit it to the bottom slot.
then slip the needle back down through the top of the slide, refit the retainer clip,
refit the spring and cable and put it back on your bike and try it out
you will probably want to adjust your mixture screw again just to get it running sweet.
Its a mikuni 30mm probably a copy mikuni I assume that comes on a 140cc Pitpro bigfoot. I figured out how to get the needle out by compressing the spring and pulling the throttle cable out through the slot in the side of the slide, I found the c clip on the needle and it was on the lowest setting on the needle I assume this is the richest setting is that correct? I moved it up one spot and it still hesitates a bit not sure if its any better than before, would setting being to rich cause the problem with hesitation at around half throttle? Also there was another clip in the slide that sat over the needle on the bottom of the slide and the spring pressed on top of that does anyone know what that's for and is the throttle cable supposed to go through it?
my67xr
Miniriders Legend and Master Spanner Spinning Mode
that other clip holds the needle into the slide
try the clip on the middle notch then see if thats any better.
you could even try the top 2 notches, a 30mnm is a bit too big for a 140cc
try the clip on the middle notch then see if thats any better.
you could even try the top 2 notches, a 30mnm is a bit too big for a 140cc
ok so I moved the clip to the second highest spot on the needle and now when I open the throttle it the engine dies unless I release the throttle back to idle? Is this now because its running to lean? I took the spark plug out and the end was all black which is to rich correct? I thought it was supposed to get whiter when I leaned the bike out.
