jet size thread

[adam79]

I could of sworn I have read a post or faq about the difference in carburetor jet sizes, and it lists them in a grid for all the different years and models of XS1100. I can't seem to find it. Does anyone know where it is?

[MrOzz]

Adam,

Do you mean this thread?

http://www.xs11.com/forum/showthread.php?t=382


Ozz

[randy]

I think this is the one you're looking for:

http://www.xs11.com/forum/showthread.php?t=73

[adam79]

this last one was it. Now Im confused, cause my jets for my xs1100sf dont match up with the info from the thread

[randy]

Hence the disclaimer:

"NOTE- many bikes have been equipped with high velocity exhausts and accordingly will have larger pilot and/or main jets installed."

[adam79]

How do I tell if my exhaust is high velocity?

[randy]

The point of it is, your bike is either stock or not, those jet listings are the stock sizes. If any exhaust or intake changes have been made, chances are the PO changed jets to compensate.

Is your exhaust stock?

Is your intake stock?

If you can answer both questions yes, then you should (probably) (YMMV)have stock jets.

BTW, what is the reason for your original question, is it not running right?

[adam79]

this is the thing: I have absolutely no idea what the PO did to the bike, or how many PO there were. So, I cannot answer the first 2 questions. I also dont know what to compare to my parts to, cause this is my first bike. I had backfire problems, and while riding the bike stumbled/bogged down when I hit the throttle. So I read some forums, talk to some people, and followed a faq in the maintainence tech tip forum area and cleaned my carbs out. So I buy a rebuild kit for a few parts I needed, and noticed that the main jet in the kit is 137.5 while ALL of my main jets are 140. Another thing, my needle jets on carbs 1 & 3 read 266 x-2, and #'s 2 & 4 read 301 x-2.

So, basically, Im stumped.

[TopCatGr58]

Hey Adam,

In the "TECH" forum..., there's a recent thread about seeking the truth about Emulsion tubes, will help you with yours, but essentially, the tubes have a different number of aeration holes in their sides. Yamaha attempted to provide richer fuel ratios for the inner 2 cylinders, 2-3 since they don't get as much air flow, to help them run cooler so that they would be even with the outer 2 which get more air flow!

SO...the tube with less holes in them go into the middle 2-3 carbs, the nozzles with more holes go into the outer 2 carbs, and yours sound mixed up!

As for the jet size, the 137.5 you got in the kit was stock, so 140 is only 1 size up from that.

You didn't answer the previous questions, are you running stock intake/airbox and stock exhaust pipes, or aftermarket...individual air pods and pipes, either 4-1 or 4-1 WITHOUT a crossover!?

Having either ONE can call for a slight increase in jet size, but having both usually requires a few sizes up!

Backfiring and stumbling when opening the throttle are signs that it's possibly a bit too lean, what do the plugs look like..bleach white or black sooty, or somewhere in between?
T.C.

[adam79]

I couldnt answer the question because I dont know what a stock exhaust looks like.

I am running the stock airbox. As for the exhaust, it is 2 pipes converging to 1 on each side of the bike, I think it's stock. The spark plugs are black and evenly covered with a dark black suit. It's not clumpy or goey.

Here is a picture of the pipes and the spark plug. It it from my cell phone, and it is night here, so it's not great quality.

[prometheus578]

Haven't seen a stock exhaust in years...
If I'm not sadly misshapen... there's a cross over pipe underneath the bike that joins the two pipes together.
It's been thirty years..
Chances are your pipes are aftermarket "MAC' pipes.
Macs are freer flowing, and some people go up a jet size to compensate for that, which might explain you having larger jets.
(I've got the same pipes.. went up one jet size)
Black plugs mean too much fuel.
But before ya run off on that tangent... hey, maybe someone left the choke on for too long. (or a combination of other things)
Hard to say.
Pick up a fresh set o' plugs and we'll sort it out.

[adam79]

as for the intake, I think it is stock also.

[psycoreefer]

Yeah, looks like the stock intake. If you do a search you will find hundreds of threads on rebuilding/cleaning/jetting carbs. A few seem to have mastered the process and gotten perfectly running bikes, a few have given up, and a few (like me) are still making regular changes in search of the perfect setup.

Carbs are tricky to tune as there is lots of variables and a significant amount of overlap between circuits. It often takes time, trial and error, and patience, but you can do it. If you want useful help you need to provide as much information as possible.

I had backfire problems, and while riding the bike stumbled/bogged down when I hit the throttle

What RPM did you experience the stumble/bog? Low like just above idle, in the middle or up near red line?

Was the backfire only when slowing/closing the throttle or was it constant?

What carb kits (brand) did you buy and what parts did you use from them? Did you carefully compare the new parts to your old ones?

Were these problems before or after the rebuild, or both?

Did you check the float level height and what was it?

Did you set your idle mixture and balance the carbs after the rebuild?

Are you absolutely positive with out a doubt that you got all the crud out of the carbs when you cleaned them? Did you remove the idle mix screws, idle jets main jets, etc.. when you cleaned?

The pictured plug is really black and indicates very rich, what RPM was the bike run at before you pulled the plug? Was it at full operating temperature? Choke in?

Give us some more info and all the friendly folks here will be able to provide more information then you ever even thought you wanted to know.

[egsols]

and noticed that the main jet in the kit is 137.5 while ALL of my main jets are 140

Some of jets that come with the cheaper rebuild kits are not precisely 137.5's See if you can compare them against the 140's you have, to make the sure the hole is indeed smaller.

Like others have said, it appears that you are running on the rich side but we would need to know at what rev's you are encountering your stumbles. Also when did you pull the plugs? To get a true read of the plugs you have to do a chop (search for this and you will find the explanation) Pulling the plugs after the bike has been idling will only tell you how it is running on the idle circuit.

[adam79]

the bike, when not in gear, warmed up, would rev up fine, with just a bit of stumble and sometimes backfire. If reved it up while it was warming up, there was almost always backfire. While cruising, if I punched the throttle, the bike would go to about 5000rpms then stumble (the bike wouldn't die, it just bogs down and the rpm's wont climb any higher). Slowly accelerating through all the gears (matching my twist of the throttle with the climbing speed of the bike) worked, but I couldnt get the bike over 90mph.

The backfire was mostly on acceleration, or cruising on the highway at higher speeds. In fact the loudest backfire I experienced was cruising on the highway.

The backfire gradually got worse, and the bike seemed to get more sluggish and less responsive over time. So I lightly seated all the mixture screws and then turned them out 2 1/2 turns. (i did not know much about the bike at the time or how it worked). After that, when I push the ignition button,,, BAM BANG! Nothing but loudest backfire I had ever heard from the bike. Wont start.

So, the last thing the spark plugs experienced was the choke on and this horrid backfire.

After that, I took the carbs off, disassembled, cleaned. There really wasnt much varnish. There was no hefty amount that could be scaped off with a toothpick and have a visible thickness. Most of the holes in the jets were open and clean. Carb #2 had the most gunk (which again, really wasnt much), but it was the only carb that had something obviously wrong with it. The reddish fiber gasket on the float needle valve had disintegrated. I bought the rebuild kit for this reason, and because the head of the #3 pilot jet was stripped and I had to extract it.

It is my first rebuild. I followed a faq from the tech tips: Removing and Cleaning your XS11 Carburators. The small parts I soaked for 20hrs in carb cleaner, then blew them out w/compressed air. Many times I sprayed the passages through w/carb cleaner, then doused them as heavily as possible, let it soak, and blew them out with compressed air. They all seem to be flowing and clean.

The carb kit is from K&L, part # K - 622

The bike has not been started since I took the carbs off. The carbs are still off the bike.