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jetting

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Guest

Guest
GS 1000 with 29mm smoothbores individual k&N pods and a Kerker 4 into 1. Installed main jets are 137.5 in 1 & 4 carbs and 135 in 2 & 3. Plugs 1 & 4 are black and sooty. Should I go to a 120 main jet in all carbs inorder to correct the fouling? The mixture is so rich I never have to use the choke to start it.:confused:
 
Just a guess but I think you should go to a 130 on all FOUR of them...
 
Why not do a series of plug chops and you will KNOW what size jets it needs.
 
plug chop? running the bike at wot pulling in the clutch, kill the engine then look at the plugs?How can this tell me which jets to use?
 
Youre close. You need to run the bike at differnt points in the carb circuits. What it will tell you is WHERE you are rich or lean. I would suggest that you, based on my limited knowlege, are still WAY rich on your jet sizes. You may try the 130s, i would bet 120s are too small..
 
Running rich will not hurt the bike.
What are the stock jet sizes?
 
With the 4-1 you don't need to run the different size main jets.
If the stock size is 95 120 sounds like a good start.
Is there a baffle in the pipe?
 
Well guys, hopefully I can help as I currently have a set of the same carbs on my Frankencycle! 1085 Wisco pistons, .394/.394 Andrews cams, Yoshi headers into 3" into 2.5" glass-pack.
They had 115 main jets in them out of the box. I dropped to 112.5 mains and it still did not need a choke at all. I currently have 110 main jets in it and it runs MUCH better at half to full
throttle! I still have a slight bog in the needle jets, so I am going to drop them 1 notch when my O-rings show up in the mail.

Hope, that this gives you a better idea of what you need to do...

Eric
 
67fire said:
Well guys, hopefully I can help as I currently have a set of the same carbs on my Frankencycle! 1085 Wisco pistons, .394/.394 Andrews cams, Yoshi headers into 3" into 2.5" glass-pack.
They had 115 main jets in them out of the box. I dropped to 112.5 mains and it still did not need a choke at all. I currently have 110 main jets in it and it runs MUCH better at half to full
throttle! I still have a slight bog in the needle jets, so I am going to drop them 1 notch when my O-rings show up in the mail.

Hope, that this gives you a better idea of what you need to do...

Eric
Click to expand...
Did you raise compression to drop jet size?
 
ok here we go
i just finished tuning my new set of 29MM smoothies and i have the following settings
pilots #25
pilot air screws set to highest RPM
throttle valve cutaway 2.0
jet needle on P3
needle jet O-6
main jet #115
float height 24MM

i also have a 78 GS100 with a ported head cams that are degreed
29MM smoothies hindle 4 into 1 race pipe
so your close to me in set up (not as radical)
only difference is your at 585ft ASL and I'm at 3500 ft ASL
more info would be good
like
pilot jet size
throttle valve cutaway 1.5. 2.0 ????
position of the clip on your jet needle
(farthest from the point of the needle is P1 closest to the point is P5)
needle jet
main jet size
float height



here's what i suggest you start with
#115 main jets
#20 pilot jets
needle on P3
adjust the air screws for highest RPM
set the float height at 24MM

some basics on tuning
remember that each circuit corresponds to a throttle opening (not RPM)
idle to 1/4 pilot
1/4 to 3/4 jet needle
3/4 to WOT main jet
don't forget that each circuit overlaps the previous one
and float height affects all circuits
if your mains are too rich then your jet needle will also be too rich as the fuel is coming in though the main jet and is then metered by the needle to be correct

start with the main jet and work down to the pilot
this will be a trial and error effort you need to start with what i outlined first
start with the main jet
then the needle clip position (if you change the clip position then you have to re sync your carbs)
then the pilot circuit

you have to ride it and see what it does and do a plug chop
then come home make a change and ride it see what difference that made and do a plug chop see what the plugs tell you
then go home make another change and ride it again do this till you get it right
here is a plug chart to help you in reading your plugs
http://www.dansmc.com/Spark_Plugs/Sp...s_catalog.html
you can print this and have a hard copy to use when checking your plugs

i hope i have shed some light on this for you and helped you out a bit or at least put you on the right track to getting your bike running correctly
 
My head was milled a little (forgot the exact amount as it was over 15 years ago :o) the intake and exhaust valves are 2mm larger, I ported the head a little,
the valve reliefs were cut .020 deeper and wider. I am at 4,500-8,700 feet. I have not touched any other parts, yet. Getting closer. (wink)

Eric
 
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