slide diaphram

[thewiz]

Dawn found me looking in disgust at a puddle of gas underneath the bike that had formed overnight .... can't write what I said, but I'm sure some of you will understand.

Gas leaking was caused by me leaving the front screws loose on the fuel tap I had just rebuilt. My bad. Another quart of gas in the crankcase ... geez, if there were a carbuertor in there, my problems would be solved I hardly think the oil companies will even notice that I change the oil about every week. What's my three quarts in the overall scheme of things, anyway?

When I pulled the plugs, i was astonished that they all, for the very first time since I've been playin with this motor, were clean and the proper color. So I have been fixin' some things, needles in the center slot was the big thing .... but I ain't done yet.

Still will not pull much past 5500rpm. Feels like its starving. These are the first set of cv carbs I've messed with so I'm payin' the price of learning the nuances of them ... but ... when I re set the needle clips, I noticed that the diaphrams didn't really nest in the circular groove in the carb body very well at all. It looked a hair smaller in diameter ... like it had shrunk ...even the tabs fell short of their little half moon homes.

I thought perhaps that carefully putting the caps on might seal up the rubber .... but now I wonder? I have searched for info on diaphrams and not yet seen a pic .... but ... shouldn't the diaphrams nest easily and fully in the grove? AND could I use some from a spare set of carbs as long as they looked good? If the diaphrams weren't lifting the slides, could that be robbing upper rpm power?

[prometheus578]

Yeah, those diaphrams shrink over time.
Sometimes it's hard to know, once you have the caps on, whether the diaphram is still in it's groove, and not pinched.
Hard to get those buggers to lay flat during installation.
I've placed thin feeler gauges across the diaphram lips, set the cap on top of the gauges, and then carefully pulled the gauges out from the side.
Holds everything nicely in place.

[thewiz]

Good idea, Prom ..

I was actually just now looking over the diaphs from the carbs you took apart at my place nearly two years ago now. They ain't any better either. I have a third set in another carb stick still in the carb ... might be my best bet for a good fit. Just pulled one off the bike and it appears to have a little pinch mark in it, alright

Any reason I couldn't tack these puppies in place with a little snake snot sparingly applied? AND ... could that be the source of poor high rpm performance?

[TopCatGr58]

Hey Wiz,

They recommend NOT using any petroleum based stuff, was trying to remember something that wouldn't harm the rubber that you could use to temporarily stick them down into the groove until you put the cover on....K-Y jelly came to mind!

Need to know more about your setup...Indy filters?? Some brands=EMGO have a prominent lip that creates restriction in the inlet bell ports causing loss of power at the 5-6K+ rpm range!!

Have you checked your cent. adv. unit to make sure it's moving freely and that the timing plate can rotate? If it's stuck, you won't get the needed timing advance to move beyond the 5K point!!

What are you jet sizes, any other mods, exhaust?

Did you test the vacuum slides after assemblying by pushing it up to it's max travel, then put your thumb/finger over the arced opening to create a vacuum, and then release the slide and see IF it drops down quickly vs. slowly or if at all? IF drops quickly, then you have pinholes/leaks in the diaphragm. IF it holds or takes many seconds to slowly slide down, then it's okay. There's a small vent hole in the metal slide section, so it usually WILL drop, but should do so very slowly!!
T.C.

[Ivan]

If you want to tack them in place with some adhesive, Weather strip adhesive from 3M will not harm rubber. It is a pain in the butt to use though. not sure about how good it will hold up to gasoline fumes either. I considered using it on my carb rebuild, but after many many profanities I was able to get them to lay in the groove. I started with one edge and let my thumbs slide around the circle to meet on the other.

[thewiz]

OK, let's see ...

TC ... sorry, here's a recap: stock airbox, exhaust and carbs. Mains are, 137.5, can't see anything on any of the six or so pilots that I've been lookin' at, needle jets are x266, air jets and needles, don't remember.

Just replaced a jammed up cent. advance with a working one ... checked it with a strobe, installed: Mikes XS coils, a perfect set of used pu coils, an accurate timing wheel. As for the carbs this time? ... probably wasted fourty bucks on a ultra sonic douche. Turned out that only one of four needle clips were in the center and I should have checked in there earlier .... but "live and learn", right?... fixed that and it made a HUGE difference. But it ain't quite right ... far from it. I know for a fact it ain't ignition though.

Thanks for pointing out that test on the diaphrams too ... I'll check the two remaining on the bike to see if they're working before I pop the caps off. I know that I'm pretty close to bein' good to go on this one, I can tell by the plugs. Thx for the help.

Ivan ... that's exactly what I was thinkin' ... I keep black and yellow around Gas shouldn't be in the groove ... so no sweat there. Too funny the way you described getting them to lie flat in the grooves ... I tried that' for a half an hour but I'm now convinced that it's gonna' take some glue ....

[SFerinTEXAS]

I dont remember exactly what i used , been a couple of years ago.Had shrunk diaphrams from letting them stay out off the carbs too long. Found a paint can lid or maybe a glass from the kitchen, tried several different things just a hair larger than the diaphram, streched it over and wraped a big rubber band around it , let set a day or so then quickly put in the carbs. now I keep all my extras in carb bodies always. I just did my annual on the SF carbs 2 weeks ago and pulled the diaphams to remove the emulsion tubes amd immediatly put the diaphams back in the bodies with 2 screws until Im done with everything else and am ready to put the tubes back in.

[thewiz]

Right On, SFer ...

I'm glad I have another spare set still in the carb bodies to play with if I need 'em. Good idea with the stretch tactic too ... and also with the precaution when you remove 'em for service. Thx for the help .... really. I hate the thought of cementing these in there but I may anyway. I wouldn't do it on someone else's .... BUT ..... .... hard to justify the tariff on new ones.

[melbxs]

warm em up with the hair dryer before fitting. Soften them up.

[thewiz]

Thx, mate !!

I believe a little heat is definately called for in this case.

[thewiz]

epilogue ..

I am almost afraid to say this .... but .... I think it's fixed now. Just got back from a short ride and shut off the fuel taps.

This morinig I re installed the diaphrams using a tiny bit of 3M weather strip adhesive to tack 'em in place whilst I installed the caps. Only took a miniscule amount on a tootpick down in the groove. Stuck 'em right in place. The weatherstrip cement will peel off with a thumbnail or a little bit of release agent. It appeared that no diaphram had been sealing when I checked 'em all out too. When I took them apart on Saturday to clean ... was the first time I ever removed their diaphrams ....this was only one of a number of things that were wrong ... starting with coils and high tension leads, pu coil wires, cent. advance gov., timing plate, valve adjust, slide needle adjust .... whew!

Since I've had these carbs for a year and a half and never really had them running until now, I had no idea that they were gong to need so much attention. The seller said to check the float levels and stick 'em on and run 'em. Both of us should have known better. They were and are, especially now, still a beautiful set of pristine BS 34-IIs.

Gonna' ride it for a while and do a few things to my G ... then tear it back apart and paint it ... once I'm satisfied it's a good reliable runner.

Thx again to everyone for all their help and suggestions. You're awesome.

[scalded dog]

I place a 17 mm socket inside the intake under the slide body, it gives me plenty of rubber from the diaphram to work into the grove and it stays in place while I put the caps back on. Later 'Dog