Wb3a

John Mulvihill · Posted: Mon Oct 18, 2010 6:42 pm Post subject:

Hi,

For needle grease, try Dow Corning Silicon Vacuum Grease. Its a thick, non-hardening grease designed to plug vacuum leaks, etc, and is used on glass burette petcocks. Inert to 600 degrees and gas/fuel doesn't bother it. It doesn't evaporate or harden. Wipes off. I also use it to seal crankcases, etc, it doesn't move around and a glob will sit happily next to a crankshaft turning 15K.

As an alternative, try di-electric silicon grease, sold for car ignitions, looks to be the same stuff, albeit a little thinner in composition. Easier to find though.

(Sorry for the 'albeit', my wife taught remedial reading in High School).

John
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George Clausen · Posted: Tue Oct 19, 2010 2:32 pm Post subject:

John, I like your idea and will try it, I have both types of grease on hand. Perhaps this will be part of every rebuild from now on.
George

JIM SILVERHEELS · Posted: Wed Oct 20, 2010 3:01 pm Post subject: DID

Did a carb today and was amazed how much play there really was on the low speed needle. Not having the vacuum grease I used a dab of roofing tar. The piker in me had me do it.
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John Mulvihill · Posted: Wed Oct 20, 2010 8:24 pm Post subject:

Yah, Jim, but gasoline will dissolve it.

Pry that wallet apart, grab the Senior Citizen discount, and go for it!!!!!

Remind me and I'll give you a gob of the silicone stuff next time I see you.

John
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al nunley · Joined: 13 Nov 2006 Posts: 3037

John Mulvihill · Posted: Thu Oct 21, 2010 6:52 am Post subject:

Hi Al,

To do a vacuum check (AKA pressure differential<LOL> check) you'd probably have to pick up a Mity-Vac and try it. Autozone had the best price when I bought mine, but that was years ago. Good for bleeding brakes too. There are some cheap copies of the Mity-Vac but I understand they crap out fairly quickly.

Not sure how you'd find the exact site of a "vacuum" leak as there wouldn't be any tell-tale bubbles.

John
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al nunley · Joined: 13 Nov 2006 Posts: 3037

JIM SILVERHEELS · Posted: Thu Oct 21, 2010 7:55 am Post subject: HEY

Anyone ever machine an o ring groove for the low speed needle? Should I try it?
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Gordon Duax · Posted: Thu Oct 21, 2010 8:36 am Post subject:

One thing I just remembered doing to stop small air leaks around the throttle shaft on the snap-ring end.

Once the throttle shaft was in, and the snap ring was on, I would degrease that side of the carb, put a film of grease over the end of the shaft, and then completely cover the shaft, snap-ring, and the surounding aluminum with silicone sealant.
Once it set-up, the silicone 'cap' would keep any and all air from passing around the throttle shaft, but the shaft was still free to rotate.

Another way to tighten up the needle threads in the body is to strip the body, degrease it, put a drop of your favorite bake-on piston skirt coating on the needle threads, and run it in & out a few times.
Remobe the needle, and bake the coating in place.
Be careful, a little goes a long way.....
Get too much in the threads, and you will have a very difficult time getting the needle to screw in.

But I like John's vacuum grease idea better Smile

I'll have to order in a tube of it.

Walt Gifford · Posted: Thu Oct 21, 2010 9:33 am Post subject:

Is that the same grease they use on o-rings for water systems? There's a big o-ring on the head of my water softener that I have to lube to get it on and off with reasonable torque. If it is you can get little 1" blister packs from the plumbing store.

Gif Cool

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Gordon Duax · Posted: Thu Oct 21, 2010 9:53 am Post subject:

I doubt it.....
Dow Corning Silicon Vacuum Grease can be bought through McMaster-Carr, cat. # 2966k52
5oz tube is about $22 + shipping.

There number is 404-346-7000

The also have it in a gallon pail for really big bucks Wink

John Mulvihill · Posted: Thu Oct 21, 2010 8:29 pm Post subject:

Hi,

Jim: Re the Dow Corning High Vacuum Grease:

USE-ENCO.com has it for a few bucks less and industrial supply houses can get it (they won't know what it is, so bring the part number).

A tube of it will last most casual engine builders for 5 to 10 years. It never dries out, evaporates or deteriorates. Its also great for rubber seals on house plumbing, car radiator hoses, etc, etc.

Al, the Mity-Vac works just like our pop-off testers, but it creates a lower pressure. Its also really great for bleeding brakes. Hook it to a bleed screw on the caliper, create a lower pressure with the Mity-Vac and brake fluid flows so nicely from a reservoir hooked to the master cylinder. It makes life easy.

John
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al nunley · Joined: 13 Nov 2006 Posts: 3037

John Mulvihill · Posted: Fri Oct 22, 2010 5:39 am Post subject:

Good question. I've never "vacuum" tested one just pressure tested.

In pressure testing, I've not had a needle leak, but I've been using the vacuum grease...... Actually I started using it to help the carbs last longer, since we were using triggers, AND its not affected by gasoline. I also thought that it would help around the rubber o-ring that wears, gets hard, and/or makes the needle hard to turn.

BTW, When pressure testing, I also found a couple carbs that had bubbles coming out of the fitting where the pulse line hooks up. When I replaced the bottom plate on the pumper side of the carb, the leak went away and the carb was easier to tune. Probably warped the plate from overzealous screw tightening.

John
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al nunley · Joined: 13 Nov 2006 Posts: 3037