jetting opinion

[jetmechmarty]

I hope this isn't like opening up about oil or tires, but.....

When I went through my carburetors last year they were jetted 110-120-120-110 when it was done. I have only the Clymer book and the '78 FSM.

My SG is running the stock airbox with a K&N filter in it. I have 4 into 1 exhaust. It has been running well. The plugs look more gray than brown, but who knows with this blended fuel.

I have to take the carbs off again and replace the float valves due to chronic leaking. I have the K&L kits from George Fix. Should I use the jets in the kit to go 120 across, or "don't fix what ain't broke"? Or?

[crazy steve]

Marty, if it were my bike I'd go to 115s across. 120s are 4 sizes up and a bit much IMO, but every bike is different....

[jetmechmarty]

Thank you, Steve. If I have those in the kit, I'll take that advice.

Where would you go if the kits have only 110 & 120?

I'm going to have a close look at the plugs. I don't know if I'll be able to see a difference between inside and outside plugs as it ran a bit at idle before I parked it, combined with my 15 mph speed in the neighborhood.

[GLoweVA]

After you put new/different jets in, you'll obviously re-sync to get everything balanced again.
Then you can look at the trend that the new jets give you.
Look of the plugs, performance, gas milage, etc.
Compare these to what you had before and decide if you want to stay with those jets or not.


I think it's funny & ironic that 'JET' Marty is messin' with his jets!

[jetmechmarty]

I think it's funny & ironic that 'JET' Marty is messin' with his jets!

How about that! The jets I'm usually messing with are of a much grander scale!

[crazy steve]

Where would you go if the kits have only 110 & 120?

Your local metric bike dealer should have or be able to get genuine Mikuni jets; they're not much money, less than $5 each IIRC...

[jetmechmarty]

Your local metric bike dealer should have or be able to get genuine Mikuni jets; they're not much money, less than $5 each IIRC...

Excellent!

[ViperRon]

Marty I agree with Steve on the jetting but given that you have some color on your plugs you are definately not running lean like I was. My plugs were bright white and my pipes blued all the way back to the joining point. I went one step up from 120 to 122.5 and now have a litle yellowish brown and the pipes and cylinders are not running as hot as before. If you need 2 115s I can send them to you if you PM me an address. I have a 1980G so you can cross reference the parts for fit. really you need to get on the road and run it a little before you can count on the color of the plugs for setting jetting. Idling it typically can give you very misleading results as it primarily uses the idle mixture when idling.

[motoman]

I have a 1980G so you can cross reference the parts for fit.

If original model year carbs on both bikes, The metering rods are different size/configuration between the 80-81 Special and Standard.

[ViperRon]

If original model year carbs on both bikes, The metering rods are different size/configuration between the 80-81 Special and Standard.

Moto man


Main jet (115) 620 14231 23 A0 for G and SG

G and SG are both 1980 models just different jet size recomended as SG is 120 and 125 and G model is 115 and 120

620 14231 23 A0=115
620 14231 24 A0=120
620 14231 25 A0=125

Yamaha part numbers that is what I found.

[81xsproject]

Marty, before the FI, I had 4-1 with pods and with the wideband O2 sensor, found that 117.5's where just right. So, with your setup Steve should be right on with 115's.

[jetmechmarty]

I'm into this job now. My camera is MIA.

Jetting is 110-120-120-110. The plugs are light gray to white. 2 & 3 are whiter than 1 & 4. What gives?

For the time being I'm stuck with no transportation. Any suggestions?

I have verified the jetting. Carbs are open and I'll have to look at spare XS650 carbs to see if they have anything to offer.

[jetmechmarty]

I have four main jets that are 132.5. Too big?

[jetmechmarty]

My K&L kits did not come as advertised. I have 120 & 125 available.

Should I be thinking about moving the needles? The bike is runnig very well, but I don't like the white plugs.

[jjz28]

I just got my first 79 xs1100sf special, what size are the factory jets? Mine has 137.5's in it and it runs good. I know it has different pipes.