Author Topic: CB 750 A  (Read 2318 times)

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Offline Fran Fitzpatrick

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CB 750 A
« on: December 07, 2011, 11:41:32 AM »
Hello all,

     I have a 1978 CB 750 A in need of new / used Carburetor insulators / manifolds.  The ones that go from the carburetor to the engine.  Two of mine are sucking air and I can't get the bike to idle without the choke.  Or does anyone know of a heat resistance sealant I could coat the insulators with?

Thanks Fran

Offline raymond10078

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Re: CB 750 A
« Reply #1 on: December 07, 2011, 12:58:27 PM »
That is an interesting question.

Myself, I bought a re-pro set from a member on here - but he has stopped making them.  I haven't seen any other sources for these in quite a while.

Regardless, you'll get more responses by posting this question on the SOHC/4 Bikes forum, as we all use insulators (different part numbers, but the same materials).

The insulators do see a good deal of heat, but I don't personally know a value.  Wikipedia indicates that gasoline boils at high as 395 degrees F - and I know that the fuel in my carb doesn't boil.  So, using that as a guide, I'd say that any sealant good at 500 degrees should be good guess.

As you may know, finding these insulators can be tough, especially in good condition.  If you do find a set (without leaks), there is quite a bit of discussion (in the SOHC/4 Bikes) forum about what chemicals can be used to soften the old, hard rubber.

If you either can't find replacements, or are too impatient, I would personally try some sealant (like Permatex 1372 - rated for up to 600 degrees) and a tape overlay.  I couldn't find any black tape rated for over 200 degrees.  Lot's of silver tapes, though (flue tapes).  Being cheap, I'd probably try to use regular 3M 33+ electrical tape, and see if it stays in place.
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline Fran Fitzpatrick

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Re: CB 750 A
« Reply #2 on: December 07, 2011, 05:43:52 PM »
Thanks for the info.

Offline Chuck Hahn

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Re: CB 750 A
« Reply #3 on: December 08, 2011, 09:33:34 AM »
Could rub some Ultra Black RTV into the cracks and squish it deep in.  then wipe smooth and let them cure for a day or 2.

Offline Chuck Hahn

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Re: CB 750 A
« Reply #4 on: December 08, 2011, 11:49:17 AM »
Or maybe paint them with that liquid electrical tape. Check the temperature perameters on it though.

Offline raymond10078

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Re: CB 750 A
« Reply #5 on: December 08, 2011, 03:12:55 PM »
Good option - the Ultra Black RTV is good to 500 degrees.
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline Chuck Hahn

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Re: CB 750 A
« Reply #6 on: December 08, 2011, 04:27:36 PM »
And its Black!!!

Offline Trav-i

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Re: CB 750 A
« Reply #7 on: December 09, 2011, 09:22:49 AM »
Fran,

Also check these guys out, they might be able to help you.

http://www.classicmotorcyclesolution.com/1_7_Products.html
Forum member #9962

I don't know a lot about anything, but I know a little about practically everthing. 

If your not first, your last - Ricky Bobby

1992 GL1500 Interstate

73 CB750 Bobber Project (Always an on going project) Sold
71 CL350 Scrambler Project (Done and riding it) Sold
78 CB750 F3 Super Sport with F 0 engine (Current project)

Offline raymond10078

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Re: CB 750 A
« Reply #8 on: December 09, 2011, 11:24:00 AM »
I sent these guys an e-mail - asking about availability.

I have read prior statements about urethane materials degrading when exposed to ethanol - and that production had stopped.

I'll post an update when I get an e-mail reply.
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline raymond10078

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Re: CB 750 A
« Reply #9 on: December 12, 2011, 06:46:16 AM »
As promised, here is the e-mail reply from www.classicmotorcyclesolution.com:

Quote
Hi Rex, High concentrations of ethanol are causing some problems with the urethane and until I can find a reasonably priced product that will withstand the gasoline/gasohol I've stopped producing them. I have a couple compounds that I'll be trying soon and hope to start making the boots soon after. I'll keep you posted. Thanks.
 
..................Paul
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.