Gen1 Carby Jet's

[rocket]

Hi All,


I just wanted some info on carby jets.


My 1989 Gen1 VMAX is chewing too much fuel, almost 11 Liters to 60 Kilometers travel but that is in peak hour traffic no highway cruising

I ordered a 6 Sigma Jet kit (Stage 1-2-3) but the main jets supplied are a 160 or 170 to choose from.


I was assuming to get better fuel economy I would need to go to a 150 or less main jet?


Any help would be greatly appreciated.

 

[Fire-medic]

At lower altitudes above sea level, and if using a full aftermarket exhaust with larger header pipes, and a low-restriction canister (or canisters) which most designs use, then something like a Mikuni 150 or 147.5 is what most riders doing a re-jet have found to be a good match.

If you have a stock exhaust, you could try going one Mikuni size smaller, (increments are in units of 2.5) to 150 Mikuni and see how that works. What do the Sigma 6 directions say about the main jet sizing? Do they match Mikuni or are they a larger number for the same orifice main jet size, like Dynojet?

 

[rocket]

Thank you for your reply, 6Sigma says to use a 160 or 170 main jet, I am thinking this would not help fuel economy?
The exhaust is aftermarket, Inch and three quarter diameter pipes and the mufflers are Supertrapp with a 22mm diameter hole in the outlet they are not using the original stackable plates. I am 650 feet above sea level.

 

[rocket]

Here are the fitting instructions for the 6Sigma kit.

 

[Fire-medic]

The instructions, to my comprehension, do not specify which type of main jet sizing they are, Mikuni or someone else's. I suggest measuring the Mikuni size, and then the 6 sigma sizes, by numbered drill bits to find out what size the 6 sigma main jets are.

Two primary things for setting up your carburetors:
float height
main jet size

Other things to do/check:
shims on 1-slot jet needles. Canadian models I believe have multiple slots, USA models have 1 slot.
holes drilled in the throttle slide, where there is already a smaller hole (NOT the hole where the needle goes! The 6 sigma directions mention those too)
cutting-off 1 or more coils from the slide springs.

Another way to do the slide spring shortening, is to tie-back 1 or more coils, effectively shortening the springs. You do this with safety wire, be sure to place the twist of wire shortening the springs where it will-not interfere with the slide movement. I prefer this, as you can always return to the OEM spring length.

 

[rocket]

Thank you for the information, I will compare the 6Sigma jet bore sizes to the standard jets and see where that takes me.