82 GS750EZ carb tuning issues

[redruM69]

Back to stock pilots, screws 2 turns out, needles back down 3 notches, and up to 120's on the mains.

Things are running better now, Still maybe a TINY bit lean near 3/4 throttle. Carb's still load up and studder for a moment between shifts on hard runs.

Im getting closer!

[redruM69]

I FINALLY have it all figured out! I have pulled these carbs probably 30-40 times now, and finally its running smooth as silk!

It ended up being the slide SPRINGS.. I cut about an inch off the springs and WOW what a difference! No more hesitation off the line, or between shifts. Final numbers below for those that need em:

Stock Pilots
Pilot screw 1.5 turns out
117.5 mains
Unknown aftermarket needles, clip set one notch richer from the center notch.
Slide holes drilled bigger (Cant remember the size, wasnt that much bigger)
1" cut off the springs.

[chef1366]

I bet those are Factory needles. They come with a shorter spring.

[redruM69]

I bet those are Factory needles. They come with a shorter spring.

Nope, stock are mikuni branded brass needles, marked 5C28, with very little taper. Stock also are not adjustable without shims.

The needles I am using are unmarked, aluminum, and have adjustment notches.

[chef1366]

Factory is a brand like Dynojet. Well actually Factor Pro. (embarassed red faced emoticon)

http://www.factorypro.com/

[redruM69]

Ahh OK, I thought by factory you meant factory stock.

Yea, I figured the needles are something like these guys.

[trippivot]

how is the tune on those carbs? I noticed a PM for some advice.


I see some bad information here turning you in the wrong direction.


I also see some beliefs that are hindering you from a true scientific approach to get the proper stoichiometric ratio on your fuel system.

summer I am very busy in my motorcycle shop and drag racing my gs1000 2V


trippivot@hotmail

[redruM69]

how is the tune on those carbs? I noticed a PM for some advice.
I see some bad information here turning you in the wrong direction.
I also see some beliefs that are hindering you from a true scientific approach to get the proper stoichiometric ratio on your fuel system.
summer I am very busy in my motorcycle shop and drag racing my gs1000 2V
trippivot@hotmail

You know, I spoke too soon earlier, it still isnt quite right...
Once fully warmed up, it seems lean on high RPM 6k+rpm cruise (slight choke helps), and rich on rolling on the throttle a little from low RPM (runs OK when cold). Idle is smooth, WOT is strong.

I now have a suspicion I may need to get the correct longer/softer aftermarket springs. I think cutting the stock springs makes them too soft when the slide is closed, and too stiff when open. Thus making it rich when cracking the throttle, and lean on higher RPM's

Please correct my beliefs if you feel Im heading in the wrong direction!

[chef1366]

Factory Pro sells them

[trippivot]

First of all.. cutting ANY spring shorter makes it STIFFER!!

next I want to know#1 pilot jets size
#2 main jets
#3 needle setting clip groove
#4 air box or not?
#5 what exhaust ?
what spark plug do you run?

I want to know where (approx) you live altitude is a big factor
trippivot@hotmail.com

[redruM69]

I do have a set of stock springs to put back in if thats what you recommend.

Pilots are stock, 42.5.
Mains are 117.5 right now, I have a set of 112.5, 115, and 120's also to play with.
Needle is in the middle, or one richer from the middle, cant remember.
No air box, running mid quality XS oval pods.
Exhaust, unknown brand 4-1. Probably MAC or V&H. Loud "Gemini" can on the back.
Plugs are NGK D8EA.

Altitude is a bit higher here in Utah, approx 3500ft

[trippivot]

3500 feet is a challenge, I used to live in SLC. and raced at bonneville flats and the drag strip out west of town.

start at the pilot and get it lean enough it needs to respond to each idle screw. perform a lean idle adjustment test. to achieve the highest idle.
the bike will need choke to start when cold. always! if it doesn't lean it out more with a pilot jet change. 1 size at a time. 40 maybe 38.5 ?? plug chop will tell


you say the mains feel good with a 117? ok for now (I think smaller but?)

and the idle is good? ok great 2 out of 3 you are nearly there

the needle is a tough one to adjust but I'd start at 1 clip above middle on all 4 carbs. keep them all the same. ride it normally and feel the 1/8 throttle to about 1/2throttle while gently rolling into the grip. no quick or abrupt throttle twisting. change clip position til you find the best one to live with. it is a true compromise and don't chase expectations, even new flatslides hesitate at massive throttle imput. so I hope you/we are not chasing improper throttle technique.

what color are the plugs? there are 3 chop areas to test pilot- needle- main. keep leaning out until all the black is gone and replaced with chocolate brown. new plugs or sand blast the old ones to get a good color reading. this is tedious but worth it. you 'll be on the better side of 40 mpg if you do.

in reality the spring is not a big deal but you can swap them around if you like.

I want to make it clear- you cannot just stab a set of CV carbs and expect your engine to jump. you need to gently(semi quickly) roll into the throttle and allow the vacuum to build for smooth acceleration. no closed - WOT stab all at once.

no matter what if you just mash the throttle all at once most all bikes fall on their face for a millisecond until the intake velocity catches up with the butterfly input.

[redruM69]

Excellent info so far. Im not stabbing the throttle btw, but that does make sense.

I do have another question though. What differences do the idle mixture screw vs. the pilot jet have on low end/slight throttle? Does one affect mixture more in a different range than the other? Or are they the exact same circuit, and one just compensates for the other?

WOT chop test may be difficult where I live. However, just looking at the plugs after a ride show some black soot on the outer ring, and tan on the electrode/tip.

Also, a little more info that may help determine something. If I ride WOT for more than a moment, and then roll the throttle back down a bit to cruise (not closing the throttle), the carbs seem to lean out really bad, popping and hesitating, then clears up after about 2-3 seconds. Its almost like the slides close too far, then come back up..

Im going to play with clip positions more this eve if I get a chance.