tuning info needed

[Anonymous]

hi

i hope there is someone in this group who have experience with tuning
those old bike
i need help with a gs1100et 1980

i just put a new 1166cc wiseco piston kit 10.25:1
new valve job
original carburator are check and cleaned . vacuum balance check for each test (test with main jet 107.5, 112.5, 120)
k&n pods
new spark plug and wire ,timing check
original exhaust system (quiet ride)

now there is the problem: it start and idle perfectly but as soon i twist
more than 1/8 throttle as it reach around 4000 rpm it start to lose rpm and power at the same time carb 2 and 3 spray back some gasoline

if i hold the throttle it die

if i release the throttle before it die it go back to a perfect idle

if i try to twist it again rapidly it die and if i wait 5 seconds it climb again to 4000 rpm and it start to lose rpm at the same time carb 2 and 3 spray back some gasoline again and again

doe's someone have some suggestion to help me?



as it affect cyl 2-3 (carb 2 and 3 spray back some gasoline )
i look for electrical , i try another (2-3) ignition coil ,cdi box and pulser
not better


p.s: just to make a test i installed 33mm smoothbore carburators with main jet 120 and it give power rigth away even with rough jetting

could it be a good idea to run 33mm smoothbore on that bike with original exhaust system ( i just want to have a good running bike no race)?

do you have some starting point for jet selection?


i want to thank you for taking the time to share the help and information you accumulate over the years

claude

[lhanscom]

Here's a guess, not sure if it's a valid statement or not. I think having K&N's and a valve job, but the stock exhaust may be your problem. I'm thinking that you're loading up the cylendars with great flow on the intake, but restricted flow on the exhaust. When you start getting into higher rpms the exhaust can't handle it any more, and you start getting mixture back thru the intake.

[Anonymous]

thank you luke for your fast answer

but when you say

"When you start getting into higher rpms the exhaust can't handle it any more, and you start getting mixture back thru the intake"

it could make sense if i could get over 4000 rpm (redline around 9500 rpm )
and if all (4) carb get mixture back thru the intake
only cyl 2 and 3 do it

i apreciate your help

[lhanscom]

Ok, here's another stretch, and I do mean stretch. What if one of your coils was dieing when your ignition advanced? Not sure how this would happen, possibly a bad ignition box. Kills the 2 cylenders and therefore doesn't burn the fuel, some of which comes back out the intake.

Told you it was a stretch. :?

[Billy Ricks]

One place to start is you say the carbs spray back. This means you're running without any filters. This is screwing up the mixture from the get go. Try with either an airbox and filter or pods. Did you install a jet kit? Coming off idle the slide needles come into play. If you didn't do a jet kit the needles are non adjustable. At this point you're basically screwed without one. If you have adjustable needles try raising them a notch and see what happens. If the smoothbores are available to you run them.

[Anonymous]

hi luke
i already check electrical for ignition problemt affecting cyl 2-3
(carb 2 and 3 spray back some gasoline )
i install another (2-3) ignition coil , a cdi box and pulser coil


not better


hi billy welcome to brainstorming session

you are rigth for running without filter is no good for the mixture
it was only for troubleshoot that's how i notice carb2 and 3 spray back

no i don't have jet kit but i raise the needle one notch with the mainjet 107.5 not better

i have a set of mikuni 33mm smoothbore (main jet 120) rough jetting
that i put on for a test

it definitively run better good acceleration but rpm hang around 5000 and the carb slide look to be held by vacuum force then close after few seconds to return to idle (still have to be jet properly)

before trying to work on re-jetting i just want to make sure that smoothbore can be use on a ligthly modified motor i always hear that you need a good 4/1 exhaust to run them

finally what is bugging me is that only carb2 and 3 spray back
why only them

[SqDancerLynn1]

FIRST thing I would do is go back and check the valve clearances.

[Anonymous]

It sounds like you've had the tank on and off a bunch of times but whenever this happens to me it's because I pinched the gas line.

Steve

[Anonymous]

FIRST thing I would do is go back and check the valve clearances.

also make sure your exhaust isnt clogged by mudwasps or other critters. I had to clean out my old 4-2 factory after removing my 4-1 exhaust.
good luck.

[KEITH KRAUSE]

Are you absolutely sure the valve clearances are within spec' for #2 and 3? Also, are you sure the carbs have been synched as closely as possible?All the jets are tight?
I assume the ignition timing is correct?
For a bore kit and pods, stock exhaust, my guess for jetting would be 3 full sizes up on the mains (15 higher than whatever is stock), raise the needles 2 positions by lowering the e-clip 2 positions, (OR) 4 full sizes up on the mains and raise the needles 1 1/2 positions by using jetting spacers. Turn your mixture screws out 1/2 turn more or maybe 1 full turn.
You may have to go up 1/2 size on your pilot jets if the mixture screw adjustments don't help enough. REMOVE the 2 floatbowl vent lines if they are still on.

[Anonymous]

tuning info needed

hi gang

i read your answer and

1) valve clearance check and double check

2) tank and hose ok

3) exhaust ok

4) i keep working on jetting

it is more like some kind of mismatch with original carb and my new set-up

because when i install mikuni 33mm smoothbore it run a lot better
but still have to be jetted and i am not sure it could be use with stock exhaust

[Billy Ricks]

One reason 2 & 3 might be spitting back is the stock exhaust. If the carbs have been synched to all match the other it could be the problem. With a stock exhaust Suzuki recommends setting the two center cylinders something like 1/2 ball lower than the outside two. Has something to do with the crossover of the exhaust.

[Anonymous]

tuning info needed

hi

it look like billy got the answer for carb spray back

i use to set the carb to get four vacuum reading the same
(very accurate vacuum guage)


for this test i am working with 33mm smoothbore (they had less spray back then the original carb but they still spray back

i set 1 and 4 carb around 3/4" Hg higher than 2 and 3 carb

and guess what ?

no more spray back

how much vacuum difference (inch Hg ) is need to set carb properly?

now i can concentrate on jetting
there's nothing like brainstorming

by the way i notice a significant increase in vacuum as i put bigger main jet

could it be another way to help find the better jet size ?
try bigger jet to get the highest vacuum value
until you reach an over rich situation (reduce vacuum value ) then back-up

i know that vacuum is a good way to mesure good running condition and adjustement of a motor


i don't know if i am rigth or not but i let you know either way

[Billy Ricks]

Claude,

I would just guess they need to be about 1/2"Hg lower. Suzuki manuals show the use of a ball type guage. They tell you to drop the two center cylinders by about 1/2 of a ball.

Since you have adjustable slide needles someone must have installed a jet kit. You're just going to have to ride it and do plug readings to check your jetting efforts. You can probably trust the increase in vacuum to a certain point for selecting the mains. Trouble is at idle you're not really on the mains.

[Don Lobacz]

Go up to 120 mains, test run and check the plugs.