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NEED HELP ON GS650 CARB SPECS - JETS, THROTTLE PLATE, etc

  • Thread starter Thread starter Suzuki_Don
  • Start date Start date
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Suzuki_Don

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Hi Guys I need some help on CV carbs I am putting together for the 650 top end conversion on my GS550B. The carbs are off a 1983 GS650L which I believe was shaft drive. They are Mikuni BS32SS type carbs.

Now there seems to be some difference in the setting between the 650E models (chain drive) and the G & L models (shaft drive) as far as the carb parts and settings go. Can anyone tell me why there is a difference in these setting when it is essentially the same motor.

The differences that I have found so far are as follows:
"G" MODEL:
MAIN JET 110
PILOT AIR JET 160
STARTER JET 45
THROTTLE VALVE 135

"E" MODEL:
MAIN JET 97.5
PILOT AIR JET 175
STARTER JET 47.5
THROTTLE VALVE 125


There are different diaphragm springs as well with the "G" models having part number 13503-47070 and the "E" model having 13503-44080. What is the effect of having differing diaphragm springs.

The parts that seem to be the same on both models are as follows:
PILOT JET 42.5
NEEDLE JET Y-7
JET NEEDLE 5C45

Can anyone explain to me why the differences between the chain drive and shaft drive carb settings.
What differences exist between the throttle valve butterfly, 125 compared to 135.
Why does the "E" model have such a large air jet (175).

Having said all this there is not a lot of info on the GS650E carb specs. Plenty of stuff on the "G" model. Any "E" model specs that are available seem to be missing vital data.

On another point is there anyone out there that would have the Canadian carb specs for the "E" model as this seems the way to richen up the intake system to make the bike run better.

Hoping someone can help in all of this nightmare.

P.S. I obtained a lot of the data on springs, jets sizes etc from the Suzuki fiches on line.

SORRY IF THIS IS A BIT LONG WINDED.
 
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Sorry. Forgot to mention that the carbs I purchased have all the same parts as the "G" model as stated above except it has #150 pilot air jets instead of the #160 pilot air jets.

Thanks.
 
Can anyone give me a clue on where to locate the model number on my carbs. I have looked all over and cannot see any numbering.
Thanks
 
Are there any GS650 CV carb Gurus out there to help out. Please.
 
Suzuki_Don said:
Are there any GS650 CV carb Gurus out there to help out. Please.
Click to expand...

I am definitively not a guru but I do have a few 650 carbs around. As to your questions about why the differences, not a clue. I really fine it strange that for two motor so close in displacement such different carb setups.

Part of my thinking is that the 650e was built from a 550 motor and the carbs were tweaked to make it go. The g models were built different from the ground up and have a much different head than the 550 hemispherical combustion chambers.

Back to your questions. I do know the carb bodies were dye stamped with a model number. This is below the diaphragm cap on the outside. I have seen this on unmolested, virgin carb sets. Usually it doesn't last through the carb cleanup. I have also noticed that the float bowls are letter stamped, not sure of significance, possibly based on year.

As for the other differences, not sure of anything. My thoughts are that the g should be a lot richer on the mains and leaner towards pilots compared to e model.

I am currently trying to sort out my 550 with the guts of a 650e carbs stuffed into 550 carb bodies. I do know that the 550 carbs needles have a lot more taper than 650. Unfortunately, I have been swamped with work and family and haven't had time to mess with it other than around block. It definitively runs better at startup and seems to pull more smoothly than before.

I think I know where you are going with this. Would try to put 650 carbs with your 650/550 mill. Get prepared to do plug chops and go from there. I will try to find some more info on these also:idea:. Good luck with build.
 
Thanks Ed. Your encouragement is appreciated. I have also noticed looking up fiches and part numbers that for '82 both the "G" and "E" heads have the same part number, so it would appear the heads are the same for both models for this year.
 
the differences you found in the carb setup may be also due to different years of manufacture and/or different intended markets
usa models generally seem to have a leaner setup

so, in your case, i'd go with whatever you have and worry about the fine tuning later

regards the carb body part #, mine became visible only after the cleaning

different springs would i guess give different resistance to the lifting of the needles

my haynes manual for 850 lists carbs specs for usa and for other markets, so if you can find that manual for a 650 maybe it would shed more light on the differences you mention
 
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Thanks PSYGUY. I did purchase the carbs from the US. So think they would be on the lean side. That's why in my earlier comments I was asking if anyone knew the Canadian settings on the 650E's carbs so I could richen things up a bit.

You see I am not sure how to make them richer exactly. There is a huge variety of air jets. I have some ranging from #145 to #175, these are pilot air jets. I'm not sure if I make these smaller or make the fuel pilot jet larger. You don't have this option on VMs which I am more familiar with. Any help and advice appreciated.

I want to get the settings as close as I can because I am using the original air box and it's a pain to get the carbs on and off and I don't want to remove them any more times than I absolutely have to.
 
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I'm looking at the numbers you've posted and two things come to mind as "possibilities" as far as the jetting is concerned, though this is only speculation.

1) Air filter and air box shape-length-placement; exhaust shape and size; would be different between the models and may require different jetting as a result. (pilot air jets)

2) There may have been different springs used in the G-models (and again this is only speculation) to slow the rate of deceleration when rolling off the throttle which would lessen the back-lash effect of the direct drive shafties.

As the jet needles and needle jets along with the piolt jets are the same, I would assume that we're only looking at the "fine tuning" of the different bikes........

As everyone knows...when intake and exhaust rates change (even slightly) there is a difference in how things run in relation to their fuel ratio. That being said, when these bikes were imported back in the 80's, the factory had to meet very strict emissions requirements without killing their performance and as a result, MY GUESS is that each bike was set up to optimize it's performance while still meeting the regulations. This is/was true for the US market...not sure on the rest of the world.
 
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