Enlarged carburetor diaphragm?

[dexameth]

Well this is weurd. New carb, only pulled apart to adjust needle clip 4 times and now it's almost too big to fit anymore. I gotta get the cap to hold it in place while I wedge my key or something in between the cap and the carb to force the diaphragm into its groove. Very frustrating. Happens on all of my carbs but I didnt think it would happen this quick on this carb...

[knobby]

Set it on a table over night to air out the fuel fumes in the rubber.. have seen this before with certain rubber parts.

Not an ideal solution for tuning but it should save frustration. Maybe save the clip changes for last thing in the evening, then pop it in there first thing when you wake up.

[FrankenMech]

Ethanol in the fuel can also cause rubber parts to swell like that. Letting them dry out will sometimes help but the swelling can also be permanent. Microscopic examination will reveal tiny square or cubical cracks in the rubber surface caused by the swelling. Eventually those cracks will produce holes or fractures all the way through. The fracturing also produces little cubicle particles of rubber that break off and can clog passages. Asia does not have to deal with ethanol fuel so a lot of their parts are not made of the better and more expensive rubber/elastomers that are more resistant to the ethanol mix. Ethanol and gasoline are a bad mix...

[lostforawhile]

Did you get carb cleaner on it? This will cause it to do this,it eventually revert back to shape

[dexameth]

Dec 21, 2017 22:06:17 GMT -5 lostforawhile said:

Did you get carb cleaner on it? This will cause it to do this,it eventually revert back to shape

Not at all, I never clean the slide or needle with carb cleaner... ever. I feared it would harm the rubber more than just expand it.

[dexameth]

I had to readjust the needle again today, it was too rich at mid throttle causing me to sputter around 30mph cruising, so I went up one notch this morning and fought the diaphragm again, but got it. Runs way smoother cruising now.

I need to get this intake tube I found on Amazon, so I can mount up my slide carb and be done with this mess. I did fit the carb on before, but it would only go facing forward and to the left, bumping my leg when I rode. Can't face backwards, the bowl sits too low and hit my case. The intake linked above should be the perfect problem solver here.

[lilpinny]

Try a combo of the intake you mention and a clocking flange to turn the carb up to 45 degrees sideways. Some combination of that should get it out of the way.

[lilpinny]

Something like this... but the right size for you bike.

www.composimo.com/GY6-Flat-Clocking-Flange_p_36.html

So it would go engine -> clocking flange -> intake -> carb

Check out my bikes pic in the intro section of the forum. You can see the red air filter sticking out a little from under the front seat. That’s how I did that. Your mileage my vary.

[tocoo]

I put carb cleaner on my diaphragm while each time I cleaned the carb... CAn I rub silicon oil on my diaphragm to prevent holes ?

[lilpinny]

Technically you aren’t supposed to put silicon based stuff (like Ultra black RTV gasket maker, etc) where it might come in contact with gas. The gas will eat it away.

Having said that people use ultra black as a gasket maker on intake manifolds all the time. But it’s exposure to gas is pretty limited in that application. I think on the carb diaphragm it would be in constant contact with gas, so I don’t think it would be a good idea. I think it would do more harm than good.

[lilpinny]

You could try a non silicone based sealant, but you don’t want to smear it and coat it on the diaphragm, that just gum everything up and get it your fuel... id be nasty.

If your putting it around the edges to make a seal between the carb and the outside world, that might help. Haven’t really seen that done before though. Usually you just tighten the carb bolts down it’s it’s airtight.

[FrankenMech]

Silicone oil will not prevent holes in the diaphragm. Gasket sealers of any kind are not to be used with carbs. RTV swells badly when exposed to gasoline. I use permatex aviation form-a-gasket on manifold seals since it is hot fuel proof, but do NOT use it on carb gaskets.

[lilpinny]

huh... aviation permatex. No wonder they don't have that at the auto parts store.

I might have to try that next time i'm in there and have the engine apart... I used RTV Ultra Black between my intake and engine. It was either that or making my own paper gasket. I know you're not supposed to, and when I called permatex they said don't do it, but a couple of garages say that's whey they use and it's fine so I went and did it. I really can't complain, no problems. But it's one of those things that I have in the back of my mind. Next time i'm in there I might scrape the old stuff out and put that on.

I've seen more people mess things up with gasket maker and that permatex copper stuff than just using the paper gasket and the right torque. Never seen any kind of sealant in a carb.

[FrankenMech]

Aviation permatex has been available at all the auto parts stores around here. It comes in a bottle with a brush in the cap. Usually on a shelf below all the tubes of RTV crap. I use it with paper gaskets on some parts with surface defects, never on a carb. Sealants in carbs can squeeze out and block passages, -a major No-No...

I make paper gaskets all the time for old engine and machine parts.

I also use spray adhesive for securing a gasket to a part, like a car water pump, then use grease on the other gasket surface facing the block. It makes part removal and engine surface cleanup easy.

People seem to love RTV and that yellow 'monkey snot' automotive contact cement to make 'gaskets'. You will avoid using them if you ever check out the inside of a radiator, heater core, or the intake screen on an engine oil pump. The accumulation of gasket maker squeeze-out is horrendous.

[90GTVert]

There's also a Permatex MotoSeal Grey that many here use on 2T cases and intakes that parts stores may carry.
www.permatex.com/products/uncategorized/permatex-motoseal-1-ultimate-gasket-maker-grey/