butterfly shaft

I am having the high idle problem and I read some stuff in an earlier forum that I have some questions about.... here is part of that forum....


If the problem is not the seals themselves, then it could be that one or more of the butterfly valves are not fully closing - and thusly would also let too much air in, and cause a lean mixture - which would cause the engine idle to race. You can test this theory by pushing down on the synch screws with a screwdriver or your finger while at idle. If the idle speed suddenly drops to a normal idle speed (appx 1050 rpm) then it's likely that a butterfly valve needs some fine adjustment - so that they all close off at the same time (and completely close off), and open up at the same time.

Rex S.
_________________
Rex S.
Richardson, Tx


....First of all I am going to order the new shaft seals and wanted to make sure that the right part for a '81 XJ750 is "32: O-RING part #35360-001" and is it 8 that I need to order?

.... Secondly pushing down on the screws does bring the RPMs back down to normal idle on my bike. My seals don't look bad but I am going to change them just to be sure. But I was wondering how do you adjust your butterfly valves like Rex mentioned above?

 

Well bruin, that is where the syncronizing screws come in. Drop by, I'll point them out to you. PM me with your contact info, I'd be glad to get you set up.

 

Bruin, part # 32 is the o-rings for the fuel line distribution fittings.
Yamaha does not list the shaft seals in question.

 

The butterflys can also be staticly adjusted by measuring the distance between the bottom of the butterfly and the carb throat. The screws that hold them in place on the shaft can be loosened and their position moved somewhat. It is a limited movement but it is effective. The distance between the bottom of the butterfly and the carb throat can be set with a .20 inch feeler gauge.

 

the only problem with static balanced carbs, is that it doesnt account for any diffrence in performance of each cylinder. i would still balance it running.

 

Correct Brian. The static balance is done to help the dynamic balance. If the static is way out then the sync screws may not be able to compensate.

 

ahhh i see what your getting at. Good point!

 

wow, i know this post is old, but... i need some help please. i have spent a lot of time trying to get my 82 xj750 to idle properly. I have thoroughly cleaned my carbs and bench synched them using a paperclip. i then measured the exact distance from the top of the butterfly to the first little hole in the top of the opening of each carb.they are the same. the idle mixture screws are 3 turns out. my bike starts up instantly with no choke. it shoots up to 6000 rpms and stays there. if i loosen up the throttle cable via the handlebar adjustment i can get it to lower the rpms, but only down to 4000. if i screw out (unscrew?) the idle screw so it is not touching the throttle, it stays the same.(4000rpm). if i push down on the synch screw, the idle will go down from 4000 to 900rpm. if i let it idle at 900 rpms after a few minutes it slowly drops down to 0 and dies. but starts right up instantly every time. if i start it up with the throttle cable loose, idling @4000 and push down on the synch screws as b4 to get to 900 rpms, i can screw in the idle screw a little to get it to come up to 1100 rpms, but as soon as i twist throttle, it shoots up to 4000-5000 rpms again. i dont see a binded cable anywhere, i passed the clunk test. my throttle snaps closed when i let off. anyone know what i am overlooking here?i have a couple tiny cracks on the engine side of my number 1 rubber carb boot, but could that cause such erradic behavior? any help would be awesome. thanks

 

oh yeah, the "choke" is definitely not on also, as i have disconnected it to be sure. thank again for any help.

 

It sound to me like you need to "Lube" the Butterfly Shaft Seals and clean the linkage springs and washers.

You can't expect moving parts to move without some lube. Varb Cleaner dries-out and makes the parts so clean they are begging for some lubricant.

Go get some Marvel Mystery Oil.
Get an Artists Paint Brush; too.

Put some Marvel in a clean container and start "Painting" all the moving parts and springs on the carb rack.

You can use a small Syringe to squirt some Marvel Mystery Oil into the Butterfly Shaft Seals and loosen-up the Butterfly Shafts so they DO come closes under the pressure of the return springs.

Lube everything that moves of has a bearing surface that you can paint some lube on to.

 

i will do. thanks


thanks for responding so fast too.
~zw

 

I'd think seriously about syncronizing the carbs. A bench sync is a fine place to start out in but you need to get it dialed in. This might also help get your idle where it needs to be.

 

ok, here is an update. i removed the carbs. untightened all brace screws and straightened out the rack b4 retightening.i then bench synched and reset all idle mix screws to 3 turns out. i lubed up all the springs and sprongs. ready to go. i then started the bike and it started instantly, as usual, and lo and behold, it idled at 1000 rpm. so i decided to go for a ride. here's where it gets strange. when i twist the throttle wide open, the rpms shoot straight up to 7000 and only actually start pulling the bike from 7 to 9 before i have to shift. there is no acceleration from 1 to 7. if i twist open in 2nd gear, it shoots up instantly to 7000 and if i keep going it "slips" the clutch into neutral before it gets to 8500 rpms! third to fifth act like gear one, but 2 is the only one that actually changes gears on me. always back to neutral. if i hold the throttle open and slowly accelerate i can reach 60 mph without slipping the clutch. only when i crank it open and it starts losing power to the wheel, but not the tach. i have put oil in with no protectants in it and have tried adjusting the clutch cable but i don't think it did anything. it has had the energy saving oil in it before, but not anymore. could that have permantly damaged it?

 

Adjust the Clutch Cable to put slack in the Cable and test the Clutch with a slackened Cable.

If the Clutch acts normally with the slackened Cable you can prioritize your maintenance and work on tuning.

If the Clutch still slips after you have slackened the Cable and slipped the Clutch at 6,000 -to- 7,000 rpm's ... I'd just figure on replacing the whole deal and not even bother to look and see if the Drivers were Blued and Burnt.

There ain't a lot of ways to kill a Clutch but riding at the High-end of the Tach with the Clutch Slipping like mad is known to be one of them.

Your best bet is to throw a whole Clutch Kit in there and start enjoying a New Clutch from Day One on it.
There's no sense of trying to salvage a burned-up Clutch and Drivers.

When you have to start pushing the Bike rather than riding it ... it gets real annoying!

 

i have tried to slacken the clutch cable but can't figure it out. there are two nuts on the top side of the cable holder, and one on the bottom, then a little rubber cap. i can screw the bottom nut down the thread, but the two on top i can't figure out witch way to turn them. also, have you heard of that happening before? (slipping into neutral from 2nd gear. and only does it in 2nd)

 

also, when i lube the cable, do i just put some wd40 at the top and bottom of the cable and moved it back and forth? or is there more to it than that? thanks

 

Up at the Lever ... there is an Adjustment Knurl. Loosen the "Wheel" and turn the Thumb Slack Adjustment until the Lever has some Play in it.

For the moment ... Let's all hope that you have a tight Clutch and see what adjusting it will do.

Yes. I have heard of Bikes jumping out of Gear. Generally, it is NOT good news. But, before we go there ... lets settle the issue of your Clutch Adjustment.

 

You need to get the top nut loose. First loosen the lower nut. Then, while releasing tension on the cable by levering the clutch arm with a pair of pliers or like device, lift the cable housing up out of the adjuster bracket. There is a small dog on the top of the bracket that rides against the nut to keep it from loosening.
May I take this moment to highly recommend the purchase and review of a maintenance manual. It will pay for itself, I promise!

 

ok, i have completely taken the cable off the bottom lever and made it loose. then i tightened it up so that there is a little slack in the cable at the bottom. the little lever is able to go all the way down that it can go.when i pull the hand lever, the cable pulls the lever up about an inch.but i can still move the lever up further than the cable can pull it up. is that normal? the bike seems to run awesomely now, aside from this new problem. oh well