Jet sizes

[SanDiegoMike]

Why does the XS1100 G take #115/#120 main jets and the XS1100 SG takes #110/#120 jets?

This question was part of a reply posted by Prom in a different thread, but it has me wondering something about the sizing.
Does this mean that the stock configuration has carbs #2 & 3 being jetted 4 sizes bigger than #'s 1 & 4 if the jets are numbered in increments of 2.5? I understand that the larger jet size was to keep the middle cylinders cooler. I'm also wondering, since I believe I need to re-jet to (hopefully) make my bike run better, if my jets are the stock sizes, would it be too much of an increase if I just put the jets from 2 & 3 into 1 & 4 and went to 130's in 2 & 3 to keep the differential the same?

[egsols]

When I check the Yahama fiche it tells me,
115 on 1 and 4 and 120 on 2 and 3 for the G and
120 on 1 and 4 and 125 on 2 and 3 for the SG
and 110 for all on the LG

Thennnnnnnnn, when I check the 81's

The SH and LH both are shown as 110's across all four with the H
still using the 115/120 combo.

Almost looks like someone was still experimenting with jetting for the new emmissions standards of 1980!

Our maybe in 81 they decided to reduce the jet size in proportion to the fuel tank capacity?

[prometheus578]

"Once You're A Jet, You're A Jet All The Way..."

"...From your first cigarette till your last dying day..."
Anyway...
Jets... obviously, there's room to play there.
Yes, there's a difference between a #110 and a #112.5, but is it really that significant?
I mean... a carb with two #110's and two #120's...
Why aren't the spark plugs from the cylinders with the #120's darker that the other two?
Hard to see.. maybe they are.
Jets were decided upon the need for power, but also for emissions, etc.
That carb set-up with the #110's and the #120's... would run almost the same with all #110's or all #120's.
Well, close to the same... the difference you'd be hard to detect.
(unless one has an exhaust gas analyser)

I think #130's would be too much.
Try for all #120's first, Mike..

This is why I seldom discuss re-jetting issues.
Too many variables...
Hate to give advice... as I'm not the guy doing the labor nor spending the money.

Put it this way.
I may rejet my carbs for reasons of my own.
I understand that it's trial and error. Keep going up sizes till I've gone too far, and then back down.
Now, at what point do I stop going to larger jets, and instead, start raising the jet needle for mid-range?

I mean... here's a good site for carb tuning:
http://www.factorypro.com/tech/carbtun.html
Just remember... each re-tune you do requires pulling and reinstalling the carbs. (over and over)
I'm not particularly fond of doing this.
And as I've got a lead ass... I doubt that I'd recognize the intricate differences in performance.
I just read plugs and if they look OK, I'm OK.
Yes, we'd all like finely turned bikes...
But to me... when I go on a cigarette or beer run... getting from stoplight to stoplight .002 seconds quicker is of little consequence.

Plus, there's the cost of jets to consider.
What are they, about $2/3 a piece?
One jet size will cost you $12.
But suppose you do that, and it's not enoguh?
So you spend another $12.
Hmmm.. starting to look good, maybe up another size.. so there's another $12.
whoops... too much, go back down a size.
Now you've got the original four jets... plus four each of the two unneeded sizes rolling around your tool box....
And then comes....
"Damn that Prometheus... He really dicked up my bike now!"
(People hate me enough as it is... without me having to offer them more reasons.)

Why were you rejetting again, Mike?
New pipes or an airfilter change?

[SanDiegoMike]

Prom-
I'm trying to get rid of a really nasty mid-range flat spot/stumble/sputtering/(insert your own description here) that I didn't have until just a couple of months ago. Here's what I posted before:
-Replaced the spark plugs
-Trimmed the ends of the plug wires
-Checked for vacuum leaks at the manifolds. Didn't find any, but I wrapped the carb boots anyway and installed gaskets between them and the head.
-Replaced the vacuum caps
-Took the carbs off. Cleaned 'em. Set the floats to 23mm from 27mm. Reinstalled.
-Took carbs off again. Replaced all 4 o-rings for the float needle seat assemblies...no more leaking from #4. Removed all the jets again including the emulsion tubes this time. Cleaned 'em all again. Re checked float height again. Bench tested for leaks. Flipped 'em right side up before putting the bowls back on to make sure floats all hung at same level. Bench synched. Reinstalled. planedick and TheWiz came over and used planedick's carb sticks to sync.
-Pulled PUC assembly off to access and lube centrifugal assembly. Replaced PUC wires because PO wiring of same repair was brittle and cracked. Discovered flat spots in rotation of advance plate.
-Did resistance check of ballast resistor...1.5 ohms exactly.
-Did resistance check at TCI 4 prong plug...720 ohms both tests.
-Did voltage check to TCI...should be 12vdc, measured 11.37vdc.

I have the Jardine spaghetti pipes w/o the crossover, K&N air filter in the stock airbox. Denso W20EX-U plugs. I haven't checked the resistance across the primary coil windings yet...don't know why.

I don't have adjustable needles. I really don't know what else to try at this point.

[prometheus578]

I don't have adjustable needles.

Why, yes... yes you do.
What one does... (sometimes even "two" do this) is to place a thin washer underneath the needle. This raises it up... providing fuel earlier for the mid range, so to speak.
If I recall correctly on these models, at the end of the needles there is a plastic nub. Placing a washer underneath it moves the needle.
No, not a honkin' big washer like a flat washer... but about as thin as the washers used in the washer/o-ring combo that the pilot screw takes.
Where to get such a creature... who knows?
Then again... most shops have carb kit cases, jets and such.
Their carb part kits should also have little springs, O rings and those danged washers.
Take a needle to a shop and get four washers that fit nicely around the needle.

[egsols]

Took the carbs off. Cleaned 'em. Set the floats to 23mm from 27mm. Reinstalled

Did you check them with the clear tube method to ensure the fuel level in each bowl is the same?
At what rpm is your stumble, around 3500 or so?

[prometheus578]

Clear tube method is done because there's no float height data availabe for those carbs.

Floats and carb innerds are the same for all four carbs.
Instead of dickin' with each carb using the tube....
Use the tube method on one carb... open it up and measure the float height, and set all the other carbs to that height.

[egsols]

Hey Prom,

Don't mean to intrude on this thread but while we're talking about it, what's the best buoancy test for the floats? Just throwing them in a pail of water and making sure they all float the same.

Reason I'm asking is that I'm gonna tear my carbs back off because after carefully adjusting all floats to 25.7mm (79sf) I'm not convinced they are setting the same fuel level.

If I had a way of confirming that they all had the same buoancy then your method would be the cats rearend.

[prometheus578]

"No known bouyancy test that I know of."

In theory, all the floats should be equal.
"Oh, this one has a little more solder..."
"Oh, this on has a dent in the side..."
Variables, yes, but again, we're dealing with averages.
The bowl is constantly draining and refilling...
The bike(and carbs) are constantly leaning from side to side.
Then, with the tube method of fuel levelling.. there's the vagueness of the meniscus to consider.
Any "small" difference in bouyancy I wouldn't worry about.
If you can adjust for it, fine... but close is about as close as you're gonna get.

[egsols]

Works for me. I will still drop into some hot to ensure there are no leaks and if one sinks or hisses I know I have issues, other than that I will employ your method of setting up one with the tube and utilizing its calibration for the rest.

[egsols]

Works for me. I will still drop the floats into some hot waterto ensure there are no leaks and if one sinks or hisses I know I have issues, other than that I will employ your method of setting up one with the tube and utilizing its calibration for the rest.

(damn keyboards covered with apple fritter glazing)

[audio_mekanik]

Originally posted by prometheus578


Where to get such a creature... who knows?

I got a small pack of washers, i think 120 of them from radio shack. came in 4 different sizes; or was that 5? Was less than 2 bucks.

[SanDiegoMike]

Don't have the type of bowls to do a clear tube fuel level test...
Want to make sure I understand what's happening by changing jet sizes an/or adjusting needle depth...Bigger jets=more fuel available, raising needle allows more fuel sooner. Raise the needle too much and you're constantly rich, increase jet size too much and you're constantly rich as well...correct? Is there an order of doing these changes?

[psycoreefer]

Re: "Once You're A Jet, You're A Jet All The Way..."

Originally posted by prometheus578

I mean... here's a good site for carb tuning:
http://www.factorypro.com/tech/carbtun.html

Check out that link, it has some good info about what you should change first and how to test each range. I think it says the order should be mains, needles, float level. You should check it out to be sure.

[DiverRay]

Mike,
I always do the floats FIRST, as they have a LOT to do with how it runs. I would set your floats to 25mm, as that is just a little more fuel in the bowl. If it seems rich at idle and low RPM, set them up 1mm to 26 and try again.
Just my way of doing carbs....