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fuel boiling in carb?

Started by spencerhenry, April 26, 2012, 11:06:40 PM

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spencerhenry

one saw started leaning itself out the other day. i opened the tank, and bubbles were coming out of the fuel filter. lots of bubbles and it did it for probably close to a minute or more. i put that saw away and used a different one the next day. the second saw is a bone stock 361 that is like new, the first saw is a ported 036 with many hundreds of hours on it. the second day on the 361, i opened the tank to fill it before the tank was empty and there were bubbles coming out of the fuel filter.
all my saws of late are hard to start when warm, but run fine once started. my 044 likes full throttle to start when warm, if not it takes several pulls. the 361 is like new and it too needs several pulls when it is hot. it is not hot outside, today was in the 50's. i am running at about 8400' elevation.
only thing i can think of is that the fuel in the carb is boiling when the saw is shutoff. when running the new fuel coming in is cool. otherwise i have no idea where the bubbles are coming from.

joe_indi

A low pressure situation could cause the fuel to 'boil' at normal temperature.
There are three such possible situations.
A blocked air vent, but then the fuel in the tank would start 'boiling' when you remove the filler cap.
A blocked pickup body (fuel filter).
A blocked fuel strainer in the carb.
I would check the pickup body and strainer.

Joe

Al_Smith

You could possibley have a slight problem with the carb pressurizing the fuel tank .Because the pumping action of the carb is basically engine impulse through two check valves in the carb fuel pump section on occasion the sealing action, lack of rather  can cause a certain amount of reverse pressure on the tank often times you'll get bubbles .

Most likely if the carbs were fitted with new soft components the problem will go away .No amount of cleaning the carb,blowing the thing out with compressed air etc can over ride diaphgrams and check valves that have stiffen up .Yeah I know some people think it will but it really will not .Carb kits as general rule cost less than 10 dollars .Baileys sells them by the thousands no doubt .

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