1979 XS1100 Special carb spring lengths?

[delray4468]

Hello. new member here and my first post, though I have been using the archives from xs11.com for 3-4 years. I inherited my dad's 79 xs1100 special. in very good condition right down to the original exhaust pipes, which i guess are hard to find. been fiddling with this project for years...

my nemesis is the carbs. have read a lot of tech data herein and i am hung up on two points that I hope the brain trust here can opine on.

Symptom is off idle complete stall. warm up on choke ok, off choke idle ok. add any throttle. engine dies.

Carbs have been cleaned at least 5 or 6 times, including professionally. has crossover tube as a 79 carb should, brass floats, all jetting is new and per Clymer manual specs. original airbox, though for the constant carb off and on, airbox is off for the moment, so I AM trying to solve the off idle stall w/out pods or the stock airbox. Also the Octopus has been permanently removed.

1. i've read some archive posts about the springs wearing' out over time. but could not find the stock height of a new spring. the springs I sampled from carbs 1 and 2 are both under 4". which makes me wonder if I should stretch them? again trying to confirm what the length was new. And could this contribute to my off idle stall?

2. float level. assuming the carbs are not overflowing, i not clear how the fuel level in the carb affects performance. I THINK the fuel pickup for the pilot jet and main jet is from the bottom of the float bowl, as long as the fuel level is higher than the pickup point, why does having a fuel level say.... 5mm versus 3 mm above the pickup point make a difference? feels like i am missing an important subtlety.

BTW, love the bread tie solution to pre-syncing the carbs.

Hope these questions make sense. Many Thanks in advance for any and all input.

Delray Dobbins
Dallas, TX
1966 Beechcraft V35 Bonanza
1974 Yamaha Trials TY80
1979 Yamaha XS1100 Special
2009 Honda CR125
2021 Kayo 230

[dpotter58]

Have you checked the diaphragms for pinholes?

[red bandit]

Your symptoms sounds like the carbs need cleaning but sounds like maybe they are. Did you use Mikuni jets? That is a must. Are any idle mixture screw tips broken off? I would sync them and go from there. No air cleaner for now is fine. The springs in pic are for WOT and do not come into play until about 4000 rpm. I would leave them alone, for now anyway.

[delray4468]

Have you checked the diaphragms for pinholes?

All the diaphragms passed a general visual look over, put i have not, like with a flashlight behind, looked for pinholes. will do that to try an eliminate one more factor. Thanks!

[delray4468]

Your symptoms sounds like the carbs need cleaning but sounds like maybe they are. Did you use Mikuni jets? That is a must. Are any idle mixture screw tips broken off? I would sync them and go from there. No air cleaner for now is fine. The springs in pic are for WOT and do not come into play until about 4000 rpm. I would leave them alone, for now anyway.

Thanks. i'll leave the springs alone for the time being then. I am also using a laser thermometer on the exhaust pipes to find carbs that are way out of alignment. 2-3-4 were around 190 deg at idle, # 1 was 120. found the tiny hold in the tip of the idle jet was clogged. so one more little item fixed, though I doubt that it was the cause of my main symptom. All idle mixture tips are new and check good. not sure about the brand of jets. will check that. Thanks!!

[LAB3]

How are your spark plugs and caps? Removing the wires from the caps and clipping a 1/4" off the end and cleaning the contact inside the cap often does wonders.

[bikerphil]

Check all the pilot jets and make sure you can see light thru the tiny nozzle hole. If they are obstructed, you will have no throttle response.

[jkorn]

There are several extremely small paths in the carbs from one part to another. Make sure they are clean an open. Squirt carb cleaner then compressed air thru them. Otherwise some jets just don’t get fuel.

[delray4468]

I found ONE pinhole in diaphragm #1, #2 was all good. hate to mess with trying to cut the ring and replace the whole thing for one pinhole. currently going through the archives to see what others have done. a spot of superglue looks like it may have yielded ok results...in the meantime, have pre-syned the carbs using the bread tie method and also tested the vacuum advance. book calls for full advance by 5.9, mine is closer to 7. have opted to defer that till a later time as I don't think that is part of my off idle complete die symptom.

[DiverRay]

A little bit of black silicon seal, just a smear, should fix the pin hole. Put it on the TOP of the diaphragm, the vacuum side, then let it cure for 24 hours before doing anything else with it. I actually smeared ALL of the diaphragms with it when I found a problem with one. Ran those carbs for about four years, then sold the bike still running well.