Re-installing slightly shrunken vacuum slide diaphragms?

rick1956

rick1956

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Hi all,

I figured I'd toss this question out there to the masses. I'm sure several people have had to deal with it already and may be able lend me a tip or trick.

The carbs on my '81 are likely all original. Everything I've been exposed to has been cracked or otherwise in need of typical kit items and rebuild, and I'm in the middle of reassembly. Everything is going well except the vacuum slide diaphragms. They're in good, clean shape with no visible flaws of any kind except a teeny bit of shrinkage. By teeny I mean just enough that the ring won't stay seated on its own to allow me to smack the cover on without it moving.

The information I have gleaned tells me that the only replacement diaphragms these days are "non cloth-layered," and because I'm a quality-oriented realistic guy I'd rather keep the originals.

Any thoughts?
 
rick1956 said:
that the ring won't stay seated on its own to allow me to smack the cover on without it moving.
Click to expand...
Use a thin layer of a "thick" grease on the carb mating surface. Should hold the diaphragm in place long enough to get the cover on.... if that's what you're askin'?
 
JimD54 said:
Use a thin layer of a "thick" grease on the carb mating surface. Should hold the diaphragm in place long enough to get the cover on.... if that's what you're askin'?
Click to expand...

That is, indeed, what I'm asking, thanks. I'm thinking I need some thicker stuff than what I've got. I tried old black, fibrous wheel bearing grease, but it didn't quite do the job. I'm trying not to resort to a couple increments of silicone... :unsure:
 
I have found plumbers silicone or even Dielectric grease will hold them in place. Strong enough to do a diaphragm drop test without the covers installed.
 
Be careful what kind of grease you use. Petroleum based stuff can do bad things to some rubber. Ive used a 'red rubber grease' before. I read a post somewhere recommending Dielectric silicone. He said coat the diaphragms with Dielectric silicone one both sides and then close them individually in zip lock bag and let them sit for a day or two sealed in the bags at room temperature. Wipe off and fit.
 
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wherearewe said:
....Petroleum based stuff can do bad things to some rubber.....
Click to expand...

That diaphragm is in a carburetor that uses "petroleum based" gasoline.... It's compatible.
 
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JimD54 said:
That diaphragm is in a carburetor that uses "petroleum" based gasoline.... It's compatible.
Click to expand...

Yeah thats a good point. I did say 'some rubber' though, which is why products like red rubber grease exist. In any case it's still not a bad idea to use something designed to be safe purely out of good practice when you have it on hand.:bike:
 
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wherearewe said:
Yeah thats a good point. I did say 'some rubber' though, which is why products like red rubber grease exist. In any case it's still not a bad idea to use something designed to be safe purely out of good practice when you have it on hand.:bike:
Click to expand...
And that's damn good advice. Always use compatible fluids and materiel's. I've a horror story on what my step son did to his Jeep brakes that I won't go into here. It was a thousand bucks lesson on compatible fluids.... :(
 
 
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You're mistaken about a couple of things. There are good cloth-inner replacements and they are about the least expensive alternative. 2M didn't include my review of them in his anthology :) Second, you don't slap the top on. Massage the diaphragm into the groove, take your time and it will stay there, and gently put the top on. The deliberate slow movements required is good for you. If you just can;t manage that, use scotch tape in three or four positions to hold the diaphragm down and then after the top is on pull it loose.
 
Like XJ sez, been around this many times; it's a kind of slide the cap around and capture the diaphragm into the groove technique. I've gotten a couple of pretty well shrunken ones back in service. Learned to always store em in place with the caps screwed down, :eek: :whistle:
Yes always check you have it right with a slide drop test. (that test only works with the choke plunger installed and on the seat.) Bought a Royal Star Venture, 4 carbs, that was only running on 3, a shop didn't get one diaphragm in right.
 
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A top install technique that often helps is to slide the top over and into place from the side. You can work the diaphragm lip into the carb body groove as you progress. It's easier than trying to get the whole lip to stay in place as you plot the top on from above. I use the red rubber grease mentioned for lube, wonderful stuff.
 
Thanks so much for everyone that replied with their helpful tips!

I was able to get them both together using the "slide from the side" method. That method was actually the first idea that popped into my head when I first started reassembly, but I dismissed it because I figured the spring and its perch would get in the way and it wouldn't work. I was wrong, luckily. One side went in on its second try, where the other side was a bit more stubborn, taking about 6 tries. I also pre-warmed them gently with a heat gun to help them with pliability.

The bottom line: I got 'er done, and thanks to all you guys also gained more insight and ideas! :cheers:
 

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