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Carb jets!

  • Thread starter Thread starter DrSatan
  • Start date Start date
D

DrSatan

Guest
Well whilst waiting for my new o-rings for my carb rebuild i thought i would check out the jet sizes, this is what i found...

Pilot jet - 40
Main jet - 92.5
Pilot air jet - 120

I am wondering if these are stock sizes?
The bike has a 4 into 1 Motad exhaust and stock air box, i am wanting to put pod filters on so would like to know if these jets are sufficient or not and if not what size jets should i be looking for?

Thank you for your time,

The bike is a gs550 mx '82.
 
i dont know if they are stock jets but they probably are. if you want to fit pods you would need to up the mains to about 110's i would guess, just as a starting point
 
DrSatan said:
i thought i would check out the jet sizes, this is what i found...

Pilot jet - 40
Main jet - 92.5
Pilot air jet - 120

I am wondering if these are stock sizes?
Click to expand...
Yes, those are stock sizes.


DrSatan said:
The bike has a 4 into 1 Motad exhaust and stock air box, i am wanting to put pod filters on so would like to know if these jets are sufficient or not and if not what size jets should i be looking for?
Click to expand...
Depending on how free-flowing your exhaust is, you should already have 100 mains, maybe 102.5. Adding pods, you will need to go to something in the 110-115 range.

.
 
Thanks for the quick responses, si it's just the main jet that needs changing?

Thanks again.
 
Hi,

DrSatan said:
Thanks for the quick responses, [so] it's just the main jet that needs changing?
Click to expand...

For your configuration, probably. But you should perform "plug chops" to be certain. Since certain jets deliver fuel at certain throttle openings you need to make sure each throttle opening delivers an adequate air/fuel mixture. It is possible to be OK at one throttle opening but lean at a different throttle opening.

You may be OK with the pilot jet since you are using the stock airbox. But you may need to raise the jet needles a tad to make the mid-range a little richer. You can tell by doing the plug chops and reading the spark plugs.

You'll find a couple of procedures for figuring out jetting on my little website along with links to everything you ever wanted to know about reading your spark plugs.

Related links on my little website:

Plug Chop and
Idle Mixture Adjust Methods
(by Mr. koolaid_kid,Mr. tkent02, Mr. psyguy)

Spark Plugs, How to Read

CV Carb Jetting and Cleaning

Fine Points Of CV Carb Internals

Shimming The Needle

Suzuki GS Series Carb Specs

Mr. Matchless' "How To" Guides - carb info, wheel alignment, igniter repair, lighting/electrical upgrades, parts fabrication, etc.

Thank you for your indulgence,

BassCliff
 
Last edited:
DrSatan said:
Thanks for the quick responses, si it's just the main jet that needs changing?

Thanks again.
Click to expand...
Generally speaking, you only need to change the mains, but will also need to richen up the mid-range by lifting the needles a bit.

Are your needles adjustable? If so, move the clip down (toward the pointy end) one notch now, another notch when you add the pods.

If your needles only have one notch, like ours in the USA, you will need to remove the thick nylon spacer that is above the clip and replace it with a stack of washers that is about half as thick.

.
 
With a Motad and stock airbox no jetting changes are needed - it's a very 'benign' pipe.

If you want to go to pods (are you sure you do?) then you will have to up your mains - about 105s or thereabouts - and you will have to lift the needles. The pilot circuit will tune in easily on the mixture screws.
 
Winner

Winner

Benign ---? BINGO !
hurray.gif
 
I guess 'benign' is another of those British English words that didn't make it across the water with the same meaning (or range of meanings). Oscar Wilde (or was it GBS?) was right all those years ago.

In this sense it means 'having little or no effect'.
 
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