Tuning in a set of rs 40s

[4cyl h2]

I've got these on a 1325 gs 1150 flat top piston web 370 lift cams 28-23 stock valve head with radius valve job and porting by star racing no air filters old style star pro sidewinder pipe Dyna s ignition stock coils with aftermarket wires. ( spark seems very strong on all 4 will easily fire an st 125 gm spark tester). Bike runs strong for throttle response and wide problem is idle and low drive ability. 17.5 pilots standard MIKUNI needles and needle jets tried at all positions idle fuel screws at various positions settled on 1/4 from seated. Engine won't stay smooth or consistent after synchronize Runs fine with a set of rs 38s. Don't think iTs an engine or ignition issue. Are these harder to dial in any suggestions??

 

[steve murdoch]

Personally never spent any time with the RS series.
Have a look at this thread from the Gixxer site. A couple things to check for proper running.
http://www.gixxer.com/forums/15-oil-cooled-gixxers/113984-tuning-mikuni-flatslides-vs-reg-carbs.html

 

[4cyl h2]

To anybody who has tuned on the 40s. What did you wind up with for pilot jets. Specs say 17.5 which is what I have but I'm beginning to think these things are lean on bottom

 

[GregT]

To anybody who has tuned on the 40s. What did you wind up with for pilot jets. Specs say 17.5 which is what I have but I'm beginning to think these things are lean on bottom

Biggest I've used personally is 38's - but on smaller motors which shows up similar problems.
Around idle, gas speed is low, They don't seem to get a good signal at the idle jets so I'd try something around 22 -25.

 

[4cyl h2]

Don't know how much change one size pilot will bring. But only have a set of 25s so I'll give them a try. Looks like the pilot feeds both the feed hole under the slide and the one in front of it Anybody know how the transition between the two feed holes and throttle position progresses

 

[4cyl h2]

Fix turned out to be 2.5 turns on the fuel screw stayed with 17.5 pilots at 1/4 turn idle was ok but off idle was no good turned out just lean. Put pilot at 2.5 turns fixed it. Didn't think it would be much different than 38s. They worked on same engine at 17.5 pilot and 1/4 turn

 

[londonboards]

Maybe the carbs are too big for that motor at slow revs. It's not getting enough flow through the carbs. 38s or even 36s would have been a better bet. Bigger carbs does not mean better performance unless you are drag racing at wide open throttle.

 

[4cyl h2]

Maybe the carbs are too big for that motor at slow revs. It's not getting enough flow through the carbs. 38s or even 36s would have been a better bet. Bigger carbs does not mean better performance unless you are drag racing at wide open throttle.

Honestly I always thought the same thing. But the throttle response with the 40s is a notable improvement over the 38s ( which wasn't bad) at any rpm in the range. Wide open seems better too