Carb Help! Is my diaphram working? Pics

[gotsm]

I am having trouble with driveability issues with my super nice XS1100.

Here is a pic of my diaphrams.



My problem, a serious off throttle stumble.

Seems this is due to perforated diaphrams, I removed them, and could find no holes.

These carbs have been apart, by me and someone before me because there were replacement float valve and aftermarket gaskets on the bowls. The mains, pilots were clear, so I just reassembled.

I am stumped now.

Can I have you all look at these diaphrams to tell me if they are original yamaha, or replacement ones.

I dont know the difference.

Can anyone give me some things to try here, I am stumped.

Mike

[DiverRay]

Mike;
If someone has been through the carbs, you NEED to check the jets!!
The diaphrams can be checked with a light bulb. Just look for light (pinholes) as you spread out the diaphram. You may be running a little rich or lean on the pilot jets, and that my be the problem as well.
What do the spark plugs look like? are they a nice tan color, or are the ceramic centers white or dark brown to black? as you have the problem at the bottom end, you could probably put new plugs in and ride it at low RPM's for a few miles. Then pull and check the color of the plugs.
If you are running lean, the exhaust pipes should be turning blue or bronze close to the head.

[gotsm]

Help again!

I have installed brand new plugs, and havent ridden the bike much due to the huge stumble off idle.

Needs to be ridden WFO, and that makes it a dangerous beast.

I can pull some plugs and look, even post a pic, but that will be later.

dont know the jet numbers, and shudder at the thought of taking the carbs off again, so much work. But if I have to I will.

Are these bikes ThAT sensitive on jet sizes? It has stock pipes, airbox, everything else short of a K&N airfilter.

This hole in the powerband is deep and wide.

Mike

[DiverRay]

The bike IS that sensitive. If someone put in K&L jets, the numbers look correct, but the jets are WAY to large. As it runs at WOF, and not well anyplace else, I would suspect the jets, or possibly the float level.
Check the Tech Tips on the left, and pull the carbs. IF you pull the bottom off the airbox, loosen the throttle cable, and loosen all the clamps, you should be able to get the carbs out in about 10 minuites.
Once off, pull the float bowls on all 4 carbs and start with the float level.
The Tech Tips can help from here, but it isn't that hard, and well worth the time spent. Set up correctly, you should have tourque and horsepower all over the RPM range, and get about 35 to 45 MPG!!
Ray

[skids]

Just off idle means cracking the throttle a little? At resting idle, your carbs are using the pilot screw holes the most and maybe just a little bit of the three pin holes near the throttle plate of each carb. As you open the throttle plate, the three holes inject gasoline with the position of the throttle plate. Open it a little more and the diaphragms begin to lift the main jets. If you can make it stumble in the garage while on the centerstand, keep it stumbling (if you can) so that you can color the plugs and affect the temperature of the header pipes. Then shut it off and immediately spray the header pipes with water to see any differences. Then check out the plugs (should have been new to start with...sorry.)

[strom]

Wow... my diapharms are waaaay worse... and it runs OK.

LP

[randy]

Sounds like you have pilot jet problems. Did you remove each jet and clean it? There area lot of fine holes in each jet that can get clogged. And, it's not only the jets, but the passages in the carb beyond each jet that need to be clear.

I had a similar problem right after a re-build with K&L jets. Found out that the K&L pilot jets didn't have any emulsion holes! The original jets had four holes each! Go figure.

I replaced the original (cleaned) pilot jets and no problems since!

Keep us informed of your progress.

[gotsm]

You guys are awesome!

Thanks for all the tips, its good to know I am not losing my mind here.

The removal and installation of the carbs is such a pain, but a shared pain with all that have gone before me!

Good to know my diaphrams look good, they must be replacements?????

So, I will take them apart, and check the pilots, when I get them apart I will post a photo to see what you all think.

Other than this little carb detail, the bike really drives and operates like a fine tuned watch.

Mike

[Winterhawk]

If someone put in K&L jets, the numbers look correct, but the jets are WAY to large

Bingo, I bet they used K@L's pilot jets.

[gotsm]

Here are the pilots!

Got the carbs off today, and there are the pictures.

Can you all help?

Mains 142.5
Pilots 42.5

Pilots looked to be clear, except one pilot might have have some crud in it. Cleared it with a small brass brush from a solvent brush.

My question is, for the crew here is, what is the purpose of the caps over the pilot jets? Do they need to be there? I have never seen cap screws over the pilot jets before, but re-installed them anyway because they were there already.

Is my jetting correct for the stock pipe setup that I am runnning?

The pilot jets are Yamaha/Mikuni because they have the 4 holes in the emulsion tubes.








Mike Berg

[prometheus578]

caps over the pilot jets

Some carbs don't have the caps, and the pilot jets get their juice from the fuel in the bowl. Other carbs have the pilot jet tower plugged (like yours), and get their juice via a passage from the main jet tower. Other carb setups(Kawasaki, etc) use a rubber plug instead of a screw.

[John]

Like Prom said, the older carbs, 78-79 had the pilot jets capped off because they get their fuel fron the main jet. The newer carbs do not get the fuel from the main jet, so there for the hole that the pilot jet sits in is left open. The main jet size you have is actually one size too large for a totally stock set up. They should be 137.5 for the older bikes. The pilots are correct.

[skids]

Re: Here are the pilots!

You have older style carbs, therefore: Stock mains should be 137.5 for stock pipes and regular airbox. Your pilots are of course fed by the cross-over passage from the mains and should be capped as shown. AND...like Diverray said, these bikes are affected by the jet sizes. I am not too sure how you can confirm that pilot jets are Mic's be seeing 4 holes in the "emulsion tubes."

Originally posted by gotsm
Got the carbs off today, and there are the pictures.

Can you all help?

Mains 142.5
Pilots 42.5

Pilots looked to be clear, except one pilot might have have some crud in it. Cleared it with a small brass brush from a solvent brush.

My question is, for the crew here is, what is the purpose of the caps over the pilot jets? Do they need to be there? I have never seen cap screws over the pilot jets before, but re-installed them anyway because they were there already.

Is my jetting correct for the stock pipe setup that I am runnning?

The pilot jets are Yamaha/Mikuni because they have the 4 holes in the emulsion tubes.

Mike Berg

[John]

Pehaps he meant the pilot jet and not the emulsion tube, as the E tube should have a lot more than just four holes. There should be, what, 14-16 holes in the E tube?

[gotsm]

This isnt good news!

None of this is giving me any idea how to solve my driveability issuse.

Was hoping to actually find a blockage or incorrect jetting, but so far only a one size larger main jet.

The pilot jet has 4 holes, did not remove the e tube yet, should this be done to verify it has holes? And replace with original Mikuni parts?

Mike