Hello! I'm trying to fix a gas leak in my carbs in a '99 CBR F4. It hemorrhages gas from carb 2 when the bike is not running but the fuel pump is powered.

I pulled them apart for the first time and noted that, in addition to every idle jet being clogged and the float valve in carb 2 being clogged, the bowl gaskets are all in poor condition, too.

I'd prefer not to pay $22 x 4 for some pieces of rubber. I read one guide for a different bike that recommended re-sealing with RTV. I have two types on hand: Sensor-Safe Ultra Copper High Temp RTV Silicone, which explicitly says "not for use on parts in contact with gasoline, and Black Silicone Adhesive Sealant, which does not say anything about gas.

Question 1: Can I use RTV? Can I use either of the ones I have, or is there another type I should buy?

Question 2: Is there anything other than the gaskets and clogs that could cause a leak like this?

Thanks!

 

My first guess would be your needle is not shutting off the flow of gas. If you look at the float, there is a needle and seat. There may be some dirt trapped in there, or the float may not be adjusted correctly.

How are you applying power to the pump? If its direct, that may be your issue. these pumps do not run all the time. Most are pressure sensitive. When the pressure builds, they stop pumping until its needed again. If you are apply direct power and the pump never shuts off, it is going to have to go somewhere and that one carb may just be the weakest link. is it pouring out of the overflow tubes?

Go to your local autoparts store and ask them for a sheet of gasket material that is the same thickness and type as your old gaskets. You can cut new ones if you want to save some money. I'd suggest against the silicone as it wont hold up well. Not to mention, your bound to get some inside the carb as you put the bowl back on. It will break loose and enter the carb and really plug things up.

Another option if your carbs are in really bad shape is to buy a used rack from ebay. You can usually find them for a decent price. A lot of times, they have been pulled from good running bikes that have been totalled. Its a quick and easy way to rid yourself of carb issues. Unless your knowledge is high, it can be a big PINA.

 

I'm applying power by turning the ignition switch on, but not starting the bike. The fuel pump starts going, the fuel filter bubbles, and gas comes out from... somewhere near carb 2.

The carbs were very clean, except for the clogs. Almost no varnish. Odd combination. It's possible that the old gasket was degrading and dropping little rubber bits.

I drained the bowls before opening them. A little bit came out of 1, 3, and 4, and nothing came out of 2. That supports the idea of either a clog or stuck float valve.

The float valve looks in good shape, but had a clog that I couldn't see that I blasted out with pressurized carb cleaner.

What worries me is that I think the fuel pump should have shut off if it was a full clog, not just pumped gas out of some unseen hole.

It had been sitting for an unknown number of years. It was stolen 4 years ago, and the police just recovered its beat-up corpse in a drug bust. Everything is broken, but I verified the motor and transmission are functional. I want to get it going again, but don't want to pour cash into it.

I read that Permatex makes a gas-safe gasket called MotoSeal, but that the copper stuff is fine for a float bowl because it doesn't make constant contact with fuel, and splashing is fine.

 

Photo of carb 1 is attached. This is after one quick spray of carb cleaner.



edit: I guess you can see carb 2 pretty well, too. That's the one I suspect is causing problems.

 

I'd say you should just suck it up and buy the proper gaskets.

 

Do not use rtv where it can come in contact with gas .. it will cause further clogging of the carbs. If you already have carbs off the bike then order the proper rebuild kits and rebuild them.This way you will know what you got if you cant afford to do that then gently clean them out and be sure not to let carb cleaner set on any gaskets or o rings for very long because it will eat them. good luck. Also check your rubber fuel line it tends to fall apart from the inside out and will clog the carbs aswell. make sure the floats move freely and that there is no junk on the needles or lodged in the seat holes. take your time and be thorough so you dont have to tear them back apart again right away.

 

I went to Ace Hardware today and found a liquid gasket that explicitly states it is safe for contact with gasoline.

Despite the recommendations, I'm going to try it. I know real replacements would be a safer bet, but I don't want to spend that much money on a bike that has a very slim chance of ever working again.

I looked at the clogged jets under a microscope, and it looks like they're clogged with pieces of very, very stubborn gasket. 4 hours in carb cleaner, scrubbing with a wire, and boiling for 45 minutes didn't clear them. A 30-second blast with Freeze Spray seems to have done the trick, though.

 

Maybe this stuff? My old Yamaha project has a petcock that is sealed up with what I think is this stuff:

http://www.permatex.com/products/aut...c_Compound.htm

 

this sealant is effective but very strong odour. make sure u put back the old gasket when u apply a sealant.
Eclectic Products, Inc. | Industrial Adhesives, Fillers, Coatings | Seal-All Gas & Oil Resistant Adhesive

 

You may regret using any type of sealant on those carb bowls . If all isn't well even after cleaning and readjusting the carbs ,, and it still leaks,,maybe worse this time ,, lets hope you can remove the fuel bowls again after that ace hardware glue drys . As for RTV sealant,, it turns to mush when it gets into contact with solvents or fuel ,, it liquefies then gets into your jets and passages ,, then your looking at a lot more than 88 bucks to fix them . Even gasket / jet rebuild kits can be had at 15 bucks a piece on Ebay. What your getting ready to do is just a band-aid ,,if it works . You don't wanna run down the road with that bike on fire ,, would you? I think your bike and your life is worth way more than 60-88 bucks .
Just my opinion bro .