almost there! final carb tuning. need advice

[aslsmm]

So..... i have been banging my head against a wall trying to get this gt750 road worthy.

its a 73, it has the tall mukini carbs that are stock. so the arent CV carbs. i got it firing on all 3.

L= pop,pop,pop,pop
C=nothing unless i cover the mouth of the carb then it sucks gas and goes =pop,pop,-,pop,pop,-,pop
R=pop,-,-,pop,-,-,pop,-,-,pop
pop=fire
-=no fire

what needs adjusted? the jets are stock, i got a new keyster rebuild kit for all the carbs and i put the larger jet in the middle and two smaller jets on the outter.

the R cyl seems to need the air screw adjusted cause i got reaction when messing with it, would i need to adjust anything else to get it to fire when it should?

the C cyl im lost. i cleaned the carbs and derusted the gas tank. the tank isnt even hooked up right now, i have a clean plastic container that is holding the gas so the fuel isnt clogging anything that i can see.

do the needles need adjusted? the jets that were in it when i got it were 125,125, 130 i believe. the keyster jets were 112.5,112.5,115. the larger being in the middle. the old jets were good so i can swap em back if i need i just dont want to take the carbs apart AGAIN with out direction. and they are synched. i had a shop synch em. they were rather upset that i would dare to only have them synch em and not do 3k worth of "ABSOLUTELY NECESSARY" work. any way any help will be appreciated. you guys have kicked ass so far.

[aslsmm]

what about float level adjustment?

[pearljam724]

what about float level adjustment?

It's vey important to have a good set of somewhat soft boots. If yours are original, most likely they are junk due to hardening with age, heat and cooling cycles, etc. Otherwise, it will create a lean running condition. Equally as important, to have a very good battery. Unlike, modern bikes. These bikes will not run properly with anything less than a battery in very good condition. As a result of it not being so. It often leads one to think there are other mechanical problems. Your descriptions to your problems are a little vague. What exactly is your problem ? It won't idle ? Difficult starts ? It stalls ? One cylinder will not fire ? The float levels must be adjusted equally on each carb to factory specifications for your model. Very easy to check and adjust. I like to use a metric rule I have purchased for a few bucks when doing so.

[tz375]

You have probably heard this elsewhere, but keyster carb kits are not very good. Typically the jets are not the same as stock Mikuni parts and needles are rarely the same taper as stock.

Main jets are not in play at idle, but why did yours have 125s? Does it have an aftermarket exhaust and pods? If so, I'd put those larger main jets back. Stock should be 102.5-100-102.5 in N100/604 Large Round main jets. GT750 uses a SMALLER center main jet not richer and goes to all three the same with chambers and pods.

Your intermittent miss could be weak ignition, over rich mixture, partially clogged pilot jets or partially clogged pilot fuel outlet. How were the carbs cleaned and did you/they test each and every drilling?

[aslsmm]

the middle has a larger. and i thught keyster was a god kit. oops. i paid nearly 100 for the carb kits. any way i will take em apart and mess em up again. lol.

[Alan H]

Specs as follows from the service manual. I suggest you find/download one quick!!

Triples are always smaller main jet on the centre AFAIK.
I reckon you need to set up the tickovers all the same too on separate carbs they have tickover screws on each carb. Make sure the jets are correct and clean. Make sure that the carbs are seated properly and the rubbers from carb to engine aren't cracked and are tightened up properly. Clean filter. Check float levels (see pic). Sounds like the centre carb is either; tickover screw almost out or slow running jet blocked. Left not too far out, right needs tweaking a tad to lift tickover. That should give you a start point.

The fun's just starting!!!

[aslsmm]

thanks guys. i will dive into this tomorrow. the pic looks like it will help

[Vintageman]

There were at least three jettings offered for GT750. The CVs were very different than VM round slides. The 74 CV was different than 75-77.

My issue with Keyster is they tend to make one kit and it is only for one of the jettings. Next, they don’t mark there parts the same as Mikuni. For example the Keyster Jet Needle may say Y32. You need to cross what that is supposed to be for a Mikuni number to know if that kit is for your year bike.

So you may purchased a kit for wrong model year? I may be blowing hot air for maybe Keyster does have various kits for GT750 models. They don’t do for T500 or T350 which underwent changes as time went along. Only first generation offered for those bikes

[aslsmm]

GREAT NEWS!! there is a guy about 30 miles away from me that has a collection of gt750s and knows the 73 in and out.

he bought the rear grab bar from me for 25 bucks and we started chatting. any way i am going to his house next sater day and he is going to help me get the bike in order. im freakin stoked.

1 i get my bike running FINALLY

2 i get to see an awesome collection of gt750's and an re5 wich i have yet to see in person. can't wait.

[aslsmm]

finished. i didnt even have to go to bernies house. i opened the bottom of the carbs and saw that i had installed the corerct jets.

L=102.5
C=100
R=102.5

but i have pods and expansion pipes so i put the old jets back in

L=112.5
C=110
R=112.5

then i adjusted the float level and voila!

the middle cyl was firing every time. then the r cyl would fire intermittenly so i adjusted the air screw and it picked up, then the l cyl wouldnt fire so i fiddled with the fuel mix screw and air screw and no its running on all 3. it idels at 2500 but i know how to tune it down to 1500.

thanks for all the help guys. i am going to do a video on wiring the boyer brandsen kit, rebuilding the 73 carbs and how to tune it so that people can just watch the vids in the future. thanx again.

[aslsmm]

took my first ride today. she bogs out till 3500 rpms then she takes off.

she is totally out of tune, but at least she is ridable. now i can tune her here and ther and ride her short distances till i get her nailed down. many thanx to everyone here that helped.