fuel boiling out of carb?

[Zipperfish]

I'm running a stock savage 21 engine. Having a hard time keeping fuel going into the carb. When the enging is cold I have a hard time getting fuel to the carb in the first place, however once in the carb it will start and run a bit until it warms up and that's when it dies. Once warmed up it sound like fuel is boiling back into the fuel line as I can see bubbles and hear a percolating sound from the carb. I've checked for air leaks in the tank and lines an they seem fine. I removed the carb and cleaned it up as best as I could and still the same problem.

Any suggestions?

 

[2Savages]

Not sure but have you try opening your HSN and LSN, to make sure that you are not running extra lean. As I have had boiling in the carb do to being to lean. Just a thought.

 

[Zipperfish]

After I posted this thread I realized I may be too lean, so I richened up the LSN and HSN just a bit and that seems to keep the fuel flowing, thanks.

 

[olds97_lss]

It sounds like you may also have an air leak somwhere. Check the header gasket and replace the fuel lines. I also seal the carb neck and backplate on the engine with sensor safe silicone. A crack in the fuel tank, leaking inline filter or a bad coupler from the exhaust to the header could also be a source of an air leak.

If you having a hard time getting fuel to the carb for starting, the engine is more than likely having a hard time getting enough fuel for running as well. You should be able to plug the stinger on the pipe and with a couple quick tugs on the pullstart or a quick blip of the roto-start should get fuel to the carb. If not, you are loosing air pressure somwhere and this will give you a false lean situation. Regardless how much your richen the needles, fuel may not be making it to the engine anyway.

Or... like 2Savages said, your HSN may be set almost to the point that it's shut(way to lean). Most engines range from 3-5 turns from the bottom on the HSN. Check your manual or ask others what the factory settings are for your engine.

Also, do you have a temp gun? If so, what temp is the engine at the glowplug when it's boiling fuel in the carb? Anything over 270 isn't good in most cases. Anything under 200 isn't very good either, but that's for a different reason...

 

[Koobs120]

I hear that sound only after I've ran it a while..... is this bad??

 

[olds97_lss]

It probably means your running too hot.

 

[jon2]

I had that on my Old 2.5 when I didn't retune for the hotter temos. The fuel actually boiled when it got too hot.

 

[Zipperfish]

What is "sensor safe silicone" and where can I get it?

Also, I am running an RB Concepts tuned racing pipe with the stock header and coupler. They all don't fit very well together and there may be a leak there I suspect. Any suggestions on an air tight coupler/header set-up with this pipe?

 

[olds97_lss]

Sensor Safe Silicone Safe for temps up to 700F. Non-sensor safe silicone emits an acidic gas as it cures. Not good for nitro engines... Sensor safe doesn't emit the gas.