WHERE DOES IT GO???

[yoodoo]

Right, still getting flat spots on my EN 125 and have tried eveything apart from valve clearerances.I will be doing these though. When i bought thr bike this tube in the oicture waas blanked off with a small rubber pipe and a zip tie around it.I think this may be a contributor in the flat spot situation.Can anyone tell me where this goes ?

Gracias.

J

 

[Tamiyacowboy]

twostroke its the oil injection site from the oil pump. 

 

fourstroke (scooters) its the vacuum line nipple feeding a vacuum to the fuel petcock.  on a fourstroke motorcycle they tend to be gravity feed so this nipple is blanked off to stop any tuning issues with air leaks.

 

flat spot: 

 

0-1/4 throttle is the idle and mixture screw ( can also be pilot jet but rare )  

1/4 to 3/4 throttle is the slide needle 

3/4 to wide open throttle is the main jet 

 

i would say your flat spot is around the mid range so it could be a needle setting maybe a tad to rich/lean in that midrange area, most think you just chuck on a carb and it works but they have to be retuned

Edited August 16, 2017 by Tamiyacowboy

[yoodoo]

I think its a sealed carb Tam?

J

[Tamiyacowboy]

negative its a vacuum diaphram carb , mikuni . that carb has a butterfly valve that opens and closes and the negative pressure created by the engine opens the diapham allowing it to raise up and lift needle in the jet port. very common on fourstrokes these days

 

sealed carbs are one sthat have taper proof screws on the float bowl and the mixture screw so you cant adjust them or even swap out jetting nozzles , very rare mikuni's are sealed units tend to find them on the scooters rather than bikes. 

 

the top cap (black) is held on with a screw or two, undo them but keep pressure on the cap as under it is a spring if you just unzip those screws the spring goes awol and zips across the room lik a rocket.

 

 

ok once you got the top cap off your gonna see the diaphram and in the center a little white cap holding the needle down, lift it out and on the needles should be some rings and a little C clip take note of where the C clip is placed  , from bottom of needle , ie second grove up from bottom. write that needle clip setting down somewhere.

SO that needle has settings ie those rings on the needle on the higher up the clip is on the needle the leaner the mixture is and the lower the needle clip is the richer the mixture is. 
raising the needle clip upwards means less of the needle is exposed when the throttle is hammered open , this means the needle only travels up the jet port so much and hinders the flow of fuel.

lowering the needle raises it up in the jet port and that means when you on the throttle more of the needle is drawn out of the jetting port so we get more fuel flowing to the motor. 

 

what your looking to do is see if your running lean or rich mid range, so you would drop it down one notch and give it a test run. if there is a marked difference in the flat spot you can leave it at that new setting and be done. IF you notice it runs worse you unbotton the carb again and raise the needle clip to the original setting then rasie it one notch up again and then retest to see what the difference is. 

 

ok so the needle settings failed and even raising or lowering showed no improvement ? well next we will look at the mixture screw, count how many turns it takes to seat the mixture screw fuly in and record this in writing ie 2 - 3/4 turns in. now back the screw out 2-3/4 turns out and then give it an extra 1/4 turn out. start bike have a test run see if the flat spot comes away , if its worse reset it to stock value, then screw it in 1/4 turn and retest. this is going to see if the mixture screw is the cause of the flat area just as the throttle bypasses the miture setting and starts to draw on the main jetting . 

 

carb tuning is more about tweeking than all out rehashing, so always write down what you do to each of the settings and how the outcome was ie 

 

needle setting third notch from bottom : runs with a slight bog 

needle setting one notch up from bottom : runs without bog and a nice snappy throttle . 

 

mixture screw 3 turns out : bogs down on throttle up

mixture screw 2-1/2 turns out : sweet as a nut idle smooth throttle pick up smooth no bogging at 1-4 to wide open on throttle range . 

knowing exactly what you have tweeked and by how much is a godsend and helps you revert back to current stock setting or tweek up and or down to required running your happy with. 

Remember shove a new sparkplug in and do a plugchop to see what the colour of plug is thats a good show on what the engine is doing and how its burning fuel. 

 

white tip on plug = to lean 

black tip on plug = to rich 

chocoalte brown on tip = perfect ratio on fuel and air with clean burning 
 

Edited August 16, 2017 by Tamiyacowboy

[yoodoo]

cracking answer, thanks Tam.

J

[yoodoo]

YAAAAAAAAAAAAY Finally got the flat spot out of my bike.As Tam said , I altered the needle to one notch from the top.Jobs a guddun. Runs fekkin perfect.

J

[Fly In My Soup]

On 16/08/2017 at 20:26, Tamiyacowboy said:

negative its a vacuum diaphram carb , mikuni . that carb has a butterfly valve that opens and closes and the negative pressure created by the engine opens the diapham allowing it to raise up and lift needle in the jet port. very common on fourstrokes these days

 

sealed carbs are one sthat have taper proof screws on the float bowl and the mixture screw so you cant adjust them or even swap out jetting nozzles , very rare mikuni's are sealed units tend to find them on the scooters rather than bikes. 

 

the top cap (black) is held on with a screw or two, undo them but keep pressure on the cap as under it is a spring if you just unzip those screws the spring goes awol and zips across the room lik a rocket.

 

 

ok once you got the top cap off your gonna see the diaphram and in the center a little white cap holding the needle down, lift it out and on the needles should be some rings and a little C clip take note of where the C clip is placed  , from bottom of needle , ie second grove up from bottom. write that needle clip setting down somewhere.

SO that needle has settings ie those rings on the needle on the higher up the clip is on the needle the leaner the mixture is and the lower the needle clip is the richer the mixture is. 
raising the needle clip upwards means less of the needle is exposed when the throttle is hammered open , this means the needle only travels up the jet port so much and hinders the flow of fuel.

lowering the needle raises it up in the jet port and that means when you on the throttle more of the needle is drawn out of the jetting port so we get more fuel flowing to the motor. 

 

what your looking to do is see if your running lean or rich mid range, so you would drop it down one notch and give it a test run. if there is a marked difference in the flat spot you can leave it at that new setting and be done. IF you notice it runs worse you unbotton the carb again and raise the needle clip to the original setting then rasie it one notch up again and then retest to see what the difference is. 

 

ok so the needle settings failed and even raising or lowering showed no improvement ? well next we will look at the mixture screw, count how many turns it takes to seat the mixture screw fuly in and record this in writing ie 2 - 3/4 turns in. now back the screw out 2-3/4 turns out and then give it an extra 1/4 turn out. start bike have a test run see if the flat spot comes away , if its worse reset it to stock value, then screw it in 1/4 turn and retest. this is going to see if the mixture screw is the cause of the flat area just as the throttle bypasses the miture setting and starts to draw on the main jetting . 

 

carb tuning is more about tweeking than all out rehashing, so always write down what you do to each of the settings and how the outcome was ie 

 

needle setting third notch from bottom : runs with a slight bog 

needle setting one notch up from bottom : runs without bog and a nice snappy throttle . 

 

mixture screw 3 turns out : bogs down on throttle up

mixture screw 2-1/2 turns out : sweet as a nut idle smooth throttle pick up smooth no bogging at 1-4 to wide open on throttle range . 

knowing exactly what you have tweeked and by how much is a godsend and helps you revert back to current stock setting or tweek up and or down to required running your happy with. 

Remember shove a new sparkplug in and do a plugchop to see what the colour of plug is thats a good show on what the engine is doing and how its burning fuel. 

 

white tip on plug = to lean 

black tip on plug = to rich 

chocoalte brown on tip = perfect ratio on fuel and air with clean burning 
 

 

Now THAT is how to post...

 

 

[Tamiyacowboy]

no worrys just glad yoodoo is back on the road again. 

 

most folks stop at the carb thinking is like some techincal rocket science stuff , but one its explained how they are tweeked its  a fairly simple affair. 
now if yoodoo would have taken it to a bike shop he could have well been looking at around a £50 bill for a hours labour. he fixed the problem in under an hour saved £50 and is proud his tinkering worked , and thats good enough for me