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vm26 Pilot fuel screw adjust

mvalenti

mvalenti

Forum Mentor
Maybe its old age creeping in.... I cleaned, rebuilt, and bench synched my carbs, and now I am in the process of tuning them on the bike. Having a hell of a time adjusting the pilot fuel screws.... I even made my own tool as I didnt have a short enough screw driver. How do you guys do it?
 
Typically, you set the fuel screws off the bike and don't touch them again. Adjustments are made with the side mounted air screws.
 
Nearly every seyt of VMs I have taken apart had the bottom pilot screws at around 3/4 turn out from gently seated....which was a tad lean from the factory. I just richen them up a tad and set them at 7/8 and walk away. Fine tune the fuel air mix with the side mixture screws. Typically they are called "air screws" as they meter the amount of air in the mixture. Turning them IN will cut the air down and RICHEN he mixture. OUT will add air a lean out the mixture.
 
Thanks all. I will pull the carbs off tonight and bench adjust to 7/8. Getting quite a bit of popping thru #1 last night and noticed (I must have missed it on the bench) it was " a bunch of turns out" from seated...
 
Chuck, the air screws, IIRC, start out at 1.5 turns out and then adjust per the high idle method? Follow up with a vac sync.
 
1 1/2 to 2 is a good start point. I dont high ilde method them. I use my colortune and then do a test ride under load. I adjust the flame color just past the spot where it shows a rich condition and micro adjust from there.
 
Good for VMs mostly. CVs not so good except to see when the mixture screws turn on and off the fuel at idle. Will also show if a CV carbs are rich when on the main circuit around normal crusing RPMs.
 
Make sure you get the new color tune version. The older one doesn’t have anything on the center of the plug to keep it from arcing across the glass. The newer model has a cover that looks like the porcelain on a regular spark plug in the center.
 
Good to hear there is an improved version for the CT.
Our Suzuki speced VM 26 carbs are very lean tuned from the facory. It appears the Kawasaki versions have a thicker tipped fuel screw, which allow a richer setting for idle and transition to the needle. Z1 Enterprises used to carry these screws and they work well on our 850 engines. Their slotted heads are longer than the Suzuki spec screws and extend further out of the bowl casting. I fashioned an adjusting tool out of a piece of hacksaw blade, 30mm long. Made a short narrow blade to fit the screw slot with enough left to grip between 2 fingers. You can adjust 1,2 & 4 carbs with ease, but #3 is a bit fiddly getting access along side the chain tensioner.
Some carbs get butchered by PO's trying to free broken fuel screw tips. The carb damage around the screw means you can't rely on the factory settings. Also, when you go with the thicker tipped screws, you need to be able to adjust them on the bike. I set my Kawasaki screws at 7/8 off seat. I needed to lean them further. An infared exhaust gas temperature gun works well for comfirming your fuel screw settings at idle. Just aim the red dot at each header pipe 25mm below the pipe flange. The temps should all be within 20 deg C of each other. If your air screws are all within cooee of each other and one pipe temp is significantly lower than the others, a leaner setting is required to that carbs fuel screw.
Our engines cold start easier, and transition better with these Kwaka fuel screws.
 
mattd1205 said:
Make sure you get the new color tune version. The older one doesn?t have anything on the center of the plug to keep it from arcing across the glass. The newer model has a cover that looks like the porcelain on a regular spark plug in the center.
Click to expand...

got a p/n for that new style? just want to be sure of what I'm getting. Thanks!
 
Tooknit forma ride today ran like crap. Came home and pulled plugs... i have not purchased colortune.

20180804_122019.jpgy
 
Sorry for the spelling mistakes.. i took the bike for a ride today. Didnt run well. Bogged when pulling away from a stop. Surging while riding. Poor acceleration. Popping on #2 at decel.

Just did valve shims. Cleaned carbs (soaked) each one overnight. Blew out with compressed air, chased ports with thin wire. New orings in carbs and intake manifolds. Going back into garage and going to adjust 2 and 3 as they look like they are running rich.
 
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