Topic: 73 CB750 Carb gasket question

[asianq]

Hello all. Here is my delimma.

I tried to change my bowl gaskets after noticing a minor leak from one carb bowl. Upon taking it off I noticed there was what appeared to be a paper gasket. I decided to go ahead to pull all of the bowls down and found rubber gaskets in the remainder. I know...If the others weren't broke why fix it...

I had them all replaced with the carb still on the bike. Leak fixed until...about 6 hrs later I noticed 3 of the bowls leaking profusely. I turned off the petcock and decided to try to refit them myself. As I took off the bowls I noticed the gaskets had swelled to almost twice the size of original diameter.

So from a trick I learned, I had held them above the stove til they shrank back down....Presto! Whala!

I placed them back on thinking they were seated perfect since I applied a little adhesive on the bowl gasket and set it on the bowl as I placed it back on the carb. Leak solved....until once again about 6hrs later leaking started again. I noticed the gasket bulging out of the bowl. So I had riden my bike home turning petcock on and off all the way so I didn't spill to much petro.

This time I have decided to take carb completely off and try to set the gasket in the carb body first then carefully seat the bowl on top. Will have to wait til am to get gasket.

My question is this.... Is it the seating of the gasket causing the gasket to bulge out of the bowl or is it just the type of gas mix of alchohol and gas causing this??

I've read many threads on keeping the gasket there, but how am I to stop the extreme swelling of the gasket if possible to make sure the gasket doesn't bulge back out? Once again if it is just proper seating then enough said. If not then any other help will be much appreciated.

Sorry such long thread, but just had to make sure story was complete to understand steps done and possible areas of fixing to be indepth... Thanks in advance.

[dustyc]

I'm curious about this too.  Where did you get them/what brand are they?  My neighbor bought some and the same thing happened to him, so he robbed the gaskets off a set of my carbs(what are friends for?), so now I'm left with the dilemma of a new set for myself.

I assume Honda gaskets won't do it.

[mattcb350f]

Both K&L's and Keysters gasket/O-Rings did it on me. I think they're from the same manufacturer.

The gasket shouldn't bulge out between the bowl and the carb. I believe the bowl and the carb mate aluminum to aluminum here and there should be no room for said bulging gasket to escape.

The only way I can see that this happened is that either the bowl is not going on all the way or the gasket wasn't in the grove in the first place.

 Matt.

[dustyc]

Were you ever able to make them work Matt?

[mattcb350f]

Were you ever able to make them work Matt?

Well....sort of. I tried the freezer. shrank um a bit but not enough.

Waited a day and they went back to almost original size on their own. I didn't know heat would do the trick at the time.

When I got them close, I put the bowl up to the carb and with a tooth pic, I gently kept poking the gasket into the grove while I tightened the screws and voila. I had them back on.

 Matt.

[dustyc]

Good to know that once crammed in and tightened up they'll stay put.

[coyotecowboy]

" or is it just the type of gas mix of ALCHOHOL and gas causing this??"

You just answered your own question.

Alky makes regular rubber gaskets swell every freekin time.  Next time it might be the tips of your float needles.  Never use blended gas in something that isn't set up for it.

[Gordon]

It's the cheap aftermarket gaskets, not the type of gas that causes the swelling.  Honda gaskets don't swell like this even in gas with alcohol. 

[asianq]

Does Honda still sell oem gasket still?

[Gordon]

Does Honda still sell oem gasket still?

Yep.  I don't know if you can get just the bowl gasket, but they come with the carburetor gasket set.  Part #16010300305

[asianq]

Great... I guess nothing is better than the original parts for these bikes!

[Gordon]

Great... I guess nothing is better than the original parts for these bikes!

That's usually the case.  Of course while I sit here touting the benefits of stock Honda carb o-rings, all three of my bikes have the cheap, swell up with gas, aftermarket o-rings in them.  They work just fine as long as you employ the scotch tape trick when installing them, but that requires having the carbs off the bike. 

[ger87410]

What is 'the scotch tape trick'?

[Gordon]

What is 'the scotch tape trick'?

Look here:

http://forums.sohc4.net/index.php?topic=7480.0

Then see my post, the 6th one down. 

[asianq]

Just installed K&L float bowl gaskets. Woohooooooooooo! No leaks. I guess like everyone says if you are goint to do something, do it right the first time. Taking off the carbs and making sure the gaskets are set in perfect is better than guessing.

The guy at the parts store showed me a trick to make sure it's seated in there well. As you lay the bowl on the gasket thats already on the carb, he wiggled the bowl to make sure it's properly seated in the groove before clipping in the retainer to the bowl. Seated perfect.

Keeping fingers crossed that this did the trick.

Hey Gordon was that with the carbs off the bike or on??

[asianq]

Arghhhhhhhhhh!  Just woke up to the smell of gas and once again a puddle of gas. Immediately shut petcock off after noticing only the number 2 carb leaking. What do I do to stop this issue? Pulling my hair out trying to figure this out.

Didn't notice gaskets bulging out at all. Could it be the float? I believe these are adjusted to 27 mm as they should be.

I know I had these puppies seated in properly. Well I guess since only one is leaking as opposed to 3, I'm moving in some type of progress.

Any positive results are greatly appreciated!

[asianq]

Update.

Well I think I finally got the problem fixed. I took it back to the shop today. I didn't know that the needles get worn down to where there is a groove in them. So, they changed the needle and seats to factory oem ones and luckily they also had a real good set of used oem bowl gaskets that won't expand with gas touching them. No leaks all day.

They did tell me that I could eventually get the rubber tipped needles to place in the carbs that won't cause the wear nearly as bad. Definately if this problem arises again I will resort to those needles.

Got it home washed it and polished up everything. Looks great and runs great! Will post pics soon.

P.S. If you want you can upgrade the jets to 125 instead of 120 and wow, great get up! Highly recommend.

Well happy and safe riding. I hope if anyone has this type of problem this helps you. Lesson learned for me.

Rock on and ton up!