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Discussion Starter #1
Do any of you guys have any experience in setting up a Mikuni VM26 carb?
My sons Yamaha DT 125 LC3 does not want to tick over without cutting out.
On further inspection of the carb we have different jets in it. and I think that might be the problem.

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As you can see in the photo its supposed to have a 200 main jet and a 25 pilot jet...
It is fitted with a 195 main jet and a 27.5 pilot jet...
The needle clip was supposed to be set up as it shows in the photo but it was set on the 2nd from bottom.
Would these different settings be our problem.
He has tried a colourtune plug on the bike which i bought him for christmas and it shows a very yellow flame at 2000 rpm which is the slowest my son can get his bike to tick over and at those revs there should be a totally blue flame...
Should we try to re-jet the carb like the photo shows or do you guys have any other suggestions.:(:(:(
Float height and air mixture screw are set as it shows in the photo.
Any help or advice would be great because my blood pressure has gone way up and I want to fix this bike before it kills me:thumbup:
 

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the carb specs says needle clip 4th from the top , you say yours is 2nd from the bottom , is that not the same thing ? for future reference clip position is always counted from the top,
main jet wont make any difference to how it performs at 2000 rpm,
yellow flame would indicate rich , try unscrewing the mixture screw and see if it gets more bluish , on a 2 smoker the mixture screw lets in more air the more you unscrew it making it leaner, opposite of a 4 banger
 

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Discussion Starter #3
Dont we need to get it ticking over normally before we start adjusting the mixture?
I cant keep up with what he is doing because he has taken the bike home with him to work on it and I cant keep my eye on what he is doing.:mad::mad::mad:
He has reached the stage where he aint afraid to take things apart but dont have the experience to put it back together correctly..
I have told him to back off the throttle idle screw to slow the engine down but he says it makes no difference.
Maybe the throttle cable needs winding off a bit ,its a bit of a pain when his bike is 20 miles away at his mums place.:rolleyes::rolleyes::rolleyes:
 

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Discussion Starter #4
Have a look at the video and see what happens to the engine when Jnr turns the lights on ,I have no idea why this would happen and what to do about it.


Any suggestions chaps?
 

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Dont we need to get it ticking over normally before we start adjusting the mixture?
...........
Maybe the throttle cable needs winding off a bit ......
I agree it probably is just the cable needs slackening off, does the bike respond as it should to throttle openings above 2000 rpm ?

I assumed you hooked up the colourtune so you could dial in the pilot mixture,

as for the stalling issue try connecting a volt meter across the battery terminals when the bike is running and get a reading before and after switching the lights on
 

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Discussion Starter #6 (Edited)
Adjusting the air mixture screw does nothing to the colour of the flame as it still revs lowest at 2000 rpm.
I have a spare 200 main jet and we bought a smaller size idle jet..
We need now to find a P2 needle jet because it was fitted with a P4 and I have had a look at Allens Performance but I dont understand the serial numbers he uses on the different models.
The P2 that we have is stamped with the number 469 but I cant figure out how we go about ordering one....
Anyone have any suggestions to help us out?
 

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Discussion Starter #8
I know mate , thats why I am getting so stressed over it because it ran fine and we stored it over winter with an empty petrol tank just to make sure it didnt go off over winter..
The good thing about this is he is learning a lot about how his bike should run and when its finally sussed out he will forget about the cost and hassle and get on with thrashing the titties out of it...:D:D:D
I will probably save a fortune on high blood pressure pills....;););)
I also told him to check to see if his carb boot has any cracks in it and to spray his carb boot with easy start to see if the revs increase...
It feels like we are so close to having it sussed.

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This is the wrong needle jet for the needle that is fitted...
Some bloke offered him this for a straight swap including a brand new zorst but I told him to forget it.

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I dont fancy any more projects for now , I need to get out riding the ones i got.:thumbup:
 
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