Carby Tuning Problems!

[johnnie5]

 

[Cactus Jack]

Well it's quite obvious from the graph above posted by Johnnie5 that at full throttle you're NOT fully on the main jet just as I had envisioned - there's an overlapping effect between jets so the needle shape and position affects top end mixture to some degree - most probably only minor . I checked in a "30" mm Mikuni I have here and the needle is still 5 mm in the emulsion tube at full slide lift with the "E" clip at the lowest groove - so that means the needle can be set to as much as 10 mm into the emulsion tube.


Taken from a link : One final note on jets. All of them and the carburetion functions then perform tend to overlap into some other jet's territory. If you mess with one jet, you may have to mess with a few of the others.My best advice is to not change more than one jet at a time. Slowly work out the correct jetting and keep notes on what you are doing. If you get totally fouled up at least you can go back to where you started.

Rocky Mountain ATV Club

 

[cass38a]

To set the idle mixture . You turn the idle up - then turn the mixture screw in until the engine revs drop - then (counting the number of turns) turn it out until the revs drop - then turn it back in half way . Lower the idle speed and repeat the procedure until you get the engine plonking nice and smoothly just short of stalling - then you can turn the idle screw back up to get the best idle speed to suit how you ride . Then , if you want , you can screw the screw right back in - counting the number of turns , write it down somewhere for future reference , then screw it back out by the same number of turns . Once you know where the neutral mixture setting is between rich and lean , you can go either side to suit different temperatures etc .

This works really good and is how Mikuni recomend it is done, however you need fingers made from asbestos to be able to do it (or a right angle screwdriver) at operating temprature which most of us dont have.

To overcome this problem I ran my screw all the way in and came out half a turn and test ran the bike then I kept making a quarter turn adjustments and test riding the bike after each adjustment until the bike ran well with no flat spots.

For the pilot system to operate well the mixture screw needs to be between one and two revolutions from closed so once the bike running well (regardless if you use cactus jacks method or the more hit and miss method that I just pointed out) and you count the revoultions if the number of revolutions is greater than 2 1/4 you need go down a jet size and if the revolutions is less than 3/4 go up a jet size.

I hope this makes sense and link in the sticky thread on Mikuni carbs says it all if you can be bothered to read and understand it.

 

[Cactus Jack]

This works really good and is how Mikuni recomend it is done, however you need fingers made from asbestos to be able to do it (or a right angle screwdriver) at operating temprature which most of us dont have.

LOL - Yes - whatever works for you . What I do is get rid of the dopey stock carbs and replace them with a Keihin , OKO or proper Mikuni VM with the mixture screw on the side .

Come on , get the McGyver in you going . You could probably make an angled screwdriver with some wire bent at an angle and the end flattened into the shape of a screw driver head with a hammer ~ or use a small spanner and a 5 mm impact driver flat head bit jammed into it - you can also buy cheap angled screwdrivers from Super Cheap autos ~ then slap a small sheet of leather , fibro , or masonite over the cylinder to prevent melting your fingers . But once you have a fair idea of where the mixture screw should be - it's a lot simpler .

 

[cass38a]

I actually made one by cutting the tip off a cheap screwdriver and rejoining it with a small length of tight fitting rubber hose. It could flex into the right position but the hose melted before the carby was tuned. It only worked on my 125 as the cooling fins run across the cylinder but wouldnt work with a 140 as the fins get in the way.

 

[themountain]

LOL - Yes - whatever works for you . What I do is get rid of the dopey stock carbs and replace them with a Keihin , OKO or proper Mikuni VM QUOTE]


....first true word I see on this thread!!! ...why joking around with a piece of crap , when you can do it easily??

 

[darb110]

umm i dont really kno but surly it would be out to make it leaner and in to make richer?? sound logical?? =P well try one way screw it a fair way out and try that if its good run with it if its not go the other way? just remember how far u twist the screw =P