Project 74 GT550

[r3tro74]

OK so I’m still fine tuning the carbs. The float gauge shown here is helpful. http://kawtriple.com/mraxl/tips/floatgage.htm" onclick="window.open(this.href);return false; (Measurements adjusted for my application)
It showed that 2 of my floats were twisted slightly- high on one side and low on the other.
When I first got it running I had 30 pilots, 105 mains, stock needle jet and needle. Needle clip position in the lowest groove and Uni pods. This seemed way rich and did not want to hold a steady speed.
I found a 27.5 pilot worked well (1 ¼ out air screw). Raising the needle clip position up 1 (to stock position) helped the mid throttle, but still did not pick up well- as I roll the throttle from ¾ back to ¼ or so, the power would increase. I moved the clip up one more (3rd groove up) and the mid range got better, but still a little weak feeling. Going to a leaner position than stock does not make sense to me, so I was thinking the bigger main jet is supplying more fuel to the needle jet? Also at WOT in higher gears I occasionally got a slight surge feeling like a slipping clutch- (not the clutch, RPMs hold steady).
I thought maybe the main jets were too big so I put in 102.5. That was unacceptable because it would quit pulling at 6500 to 7000 RPM.
Currently I have 107.5 main and the WOT surge is gone. 27.5 pilots have good feedback from the tach at idle when adjusting in or out from 1 ¼ turns. 3rd groove up for the needle clip. Slowly rolling the throttle from closed to WOT in high gear yields a steady increase in power, slowly rolling back from WOT to closed yields a steady decrease in power. I’m pretty close. I still get a bit of rumbling holding steady speeds at ¼ throttle or so. I’m thinking of changing the needle position but not sure up or down- Maybee I should leave well enough alone- won’t get a chance until tomorrow.
Also some of the Mikuni exploded parts diagrams show an Air jet installed- Mine seems not to have an Air jet and I don’t see one in the Suzuki Parts catalog. Are these supposed to have an air jet?
Thanks for any suggestions or comments.
Bryan

[Coyote]

Also some of the Mikuni exploded parts diagrams show an Air jet installed- Mine seems not to have an Air jet and I don’t see one in the Suzuki Parts catalog. Are these supposed to have an air jet?

No. That was a cure for the 750 with surging problems. BA40 carbs. Mine sounds the same at 1/4 throttle. Almost sounds like it's 4 stroking, but it doesn't surge. Apply a little load and it' goes away. I think that is caused by the chambers as there are no cross overs. Sounds to me like you have it spot on. Leave it alone and ride it a while.
By the way, how can you easily change the needle clips so quickly? I always find that to be about a 4 hour job. And nearly impossible to do without throwing the carbs out of sync.

[r3tro74]

It is a job to change the needle clips. With the pod filters at least I don’t have the factory air box and all its parts- bolts under the tank and all. However that may be a “catch 22” because pods probably make it harder to tune.

I pull the filters off, disconnect the fuel petcock lines, loosen the rear spigot clamps, and pull the carb assy back away from the engine. That gives enough room to remove the throttle cable bracket from the front of the carb assy (10mm ratchet wrench). A jersey glove helps so waiting time for the engine to cool off is eliminated. With the bracket disconnected, moving the bracket with cables still attached in the forward and down direction allows the front cable to be removed from the throttle cam, then move the bracket to the rear and disconnect the rear throttle cable from the cam. Doing it like this, with the cables still attached to the bracket, I don’t need to pull the gas tank or readjust the throttle cables/oil pump cable. (still check)

Once the assy is on the bench remove 6 bolts securing the individual carbs to the main bracket. A little finesse is required to clear the 2 choke plungers when removing the bodies off of the bracket. I leave all the bodies still connected to each other by the hoses and set aside.
A narrow screwdriver works good to spin the adjusting rods down through the adjusting nuts. Compress the slide spring down to the slide and hold it in the palm of my hand, leaving my thumb and forefinger free to spin the rod while holding the adjuster nut stationary with the other hand gets it the rest of the way apart. This way I don’t need to take the bellows boot off- the lower adjusting nut just stays connected to the boot.

To synchronize going back together, thread the rods back up into the nuts and get it all back together with about 1-2 threads showing above the upper adjusting nut. With 2 ½ turns out on the common idle screw, check the openings with a .020” wire. I can adjust the common idle screw a little to get a light drag on the wire on the closest to .020” carb. I set the other 2 to match using the individual adjusters at each carb- this way I only have to adjust 2 carbs. The easiest way to adjust is loosen the 14mm lower nut a little, hold the 10mm upper nut stationary with a finger and then use a screwdriver to turn the rod (slide) up or down. Hold the screwdriver stationary and snug up the bottom nut. Snap the throttle cam and recheck. Repeat a few times, I can get a close as a 1/16 turn and feel a difference on the wire. The first time I set it up with only 1 ½ turns out on the idle screw and ended up with too high of an idle with the screw bottomed out, so now I use 2 ½ turns. This usually ends up with about 2000 rpm idle when firts starting, but plenty of "room" on the idle adjuster to idle down.
I have never gone as far as to ground out individual cylinders with it running and all that.

I just make this stuff up as I go, so this may or may not work for someone else.

[bill in okc]

I raised my clips to the middle position from the lowest/richest position and noticed an improvement today as well. My next step will be going from the 30 pilot jet to the 27.5 - it is a bit rich right off-idle and I've got the screws out 2.5 turns. We might end up with pretty much the same jetting. I went overboard with the rich and am slowly leaning things back down - but that is what I've read you are supposed to do

[Alan H]

Yes. don't do it lean and richen up as new pistons come expensive.