Fuel Lean- Raise Needle or Larger Jets?

[scott0757]

I recently purchased a used XS and need to adjust the carbs as they appear to run very lean, especially on cylinders 1 & 4 which unfortunately turned my new headers blue pretty quickly.
I dropped the heat range of all the plugs 1 step, but was wondering if I would be better off increasing the jet size or merely raising the main needle?.

Opinions?

I also have a leaking gas diaphragm and wondered if anyone else just bypassed it and connected the two petcock lines together on each side and ran it to the gas filters? As long as the float needles work properly, what does this hurt?

[MAXIMAN]

If you are running stock exhaust and airbox you should be able to jet the carbs to stock and set the floats at stock height and be fine. There are several threads that deal with this issue here in the forums.

What model 11 do you have?

[scott0757]

It's an 1980 XS1100SG with OEM airbox, but replaced rusted out mufflers with MAC 4-2 mufflers. The OEM headers were already blue when I got the bike and it appeared to be in OEM condition. Plug insulators were white in cyls. 1 &4 so dropped a heat range on all 4. I think it needs adjusting richer. I also get a backfire when I back off throttle until the bike warms up. Almost chokes out when I use even the lowest setting of the choke.

I plan to try the pin height adjustment first.

[mro]

Spec for 80 carbs float height 23mm (+ - 0.5mm)
No needle adjustment but can use a washer???
Will still run good with float set just over 22mm.
(currently trying that on my stock 80G)

main jets can range 110 (specials) 1 and 4 cylinders with 120's in 2 and 3, to 115 1&4 (standard model) and 120's 2&3, or 110's across the board like mine which is a CA. bike.

If you have adjustable needles may have 78/79 carbs.


mro

[scott0757]

From what I saw in the other threads, I probably have the washer set up (bummer). Also it appears the 1980 SG jets are all the same and smaller where other models had larger jets with richer jets in cyls. 2&3 for cooler running.

Guess I'll see what I can get to with the needles. I hate taking the carbs off this bike with the upper airbox clearance and bracket that goes OVER the tank mount flange. What a design..

Thanks...

[mro]

What a design..

Once you get it running where you want it and have done all the "old bike" maintenance, seldom have to delve back into the carbs. Last 18,000 miles or so have had the carbs off twice and both times were my fault. Once because didn't replace some original fuel line and it flaked some off into the carbs and once some rust from the tank did same.


mro

[underdog57]

How about turning out the Idle mixture screw ??

Bob

[TopCatGr58]

Hey Scott,

Aftermarket pipes will make it run a bit leaner, but like MRO said, a cheap way is to raise the floats a mm. Dog mentioned the pilot jets screws, hopefully your brass caps on top of them have been removed, if not, just need to drill thru them GENTLY with a small bit, then screw a sheet metal screw into them, and then use pliers to remove and throw away....then you can adjust the screws a 1/2 or so turn out to richen....there's a guide in the tech tips for tuning the idle circuit by ear!!!

The aftermarket pipes are single walled and usually blue or gold depending on your jetting, they won't stay nice chrome! Popping on decel is commong with aftermarket pipes, but you may be able to reduce it with adjustments to the pilot screws. You did use NEW exhaust gaskets when you put the new pipes on didn't you?! A small leak can also cause it to run leaner, pop more, etc.!

Also, with modern fuel, it's a bit more difficult to gauge air/fuel mixture with the color of the insulator. It's been suggested to look at the round base of the plug that the electrode is attached to....a light dark/black coating/film is good, but should not be flaky or wet. IF you find that the float adjustment doesn't get you what you want, while you've got the bowls off, make note of your main jet sizes, then you can order them from MikesXS fairly cheaply and should be able to follow the jetting guide in the tech tips!
T.C.

[underdog57]

One more thing to add is ,,,,
you mention 1 and 4 are lean/hot . If all jets are the same , you should have hotter 2 and 3 cyl ....
Might help to clean , verify floats and needle setting ...
I really doubt you need to jet at all .
My 79 special has 4 into 1 plus stock filter/airbox . And is scary as is ....

On the fuel hoses , I just use prime and one line from the petcock.
bypassed the works and t'd to plumb the carbs in ....
A lawn mover inline shut off for a positive closeing off the fuel ...
Put the filter inline also ...
The line goes from the front right petcock , down to the shut-off then filter . Then looped the line up by the bracket for the airbox .
And into a T that goes down to the carb T's ...
Have to shut it off or the float valves seep over time ...
easy to remember ...

your in the right place for chat like help !!


Bob

[scott0757]

Excellent threads. Really appreciate the feedback. I'll do exploratory surgery and adjustments this weekend.
Yes I has new exhaust gaskets. (I did use old ones temporarily when I was putting these pipes on. MAC had shipped two for the left side!! I reinstalled the OEMs for another week!)

From what I'm reading, not all carbs had the idle air settings adjustable..Some are capped like was mentioned, but I had no idea you could pop the caps out and get to the screws! Sweet!
Love those EPA regs. trying to squeak out one or maybe two MPGs from a 40+ mpg bike when we have trucks and semis and SUVs sucking down 13 MPG....
Life in America! Gotta love it.
I'll let you know how I make out. Thanks again

[scott0757]

Update. Was setting float heights when I saw 3 of 4 carbs had repairs where the float pin locations (had been rewelded). The 4th stud was cracked at the pin and had been epoxied and that gave up.... Made a steel post stud and machined/drilled for the new post in the carb body. JB welded in place...looks like new! We'll see how it holds up. Should be OK for some time or else I'll need a new carb body.
Rest all bowl heights a on the rich side of OEM specs. Were all set really rich, (probably explains the easy flooding.)

Balanced butterflies on all for per forum tip (wire method).

Took the caps off the idle jet screws and opened each 1/4 turn.

Ordered 120 jets for 1&4 and 125's for 2 &3 as the bike has all 110's. New 4-2 headers drive that change. Will update once they are installed.

Test run tomorrow..weather permitting