Excessive Air in Fuel Lines

[rndtrp]

I'm having some trouble with excessive air in my fuel line. I have an HPI RS4 3 with an HPI T-15 engine and a 75cc tank, it will only run for a few seconds because of the bubbles in the line to the carb. I have tried new lines and varied the lengths, but can't seem to eliminate them. When I put my finger over the carb opening and hit the Roto Start they disappear and the car starts, but as I release it the bubbles cause the engine to quit. I am running a Team Associated pipe that does not have a pressure nipple; just a hole to put the fuel line in. Any suggestions would be greatly appreciated.

 

[olds97_lss]

You may want to seal the neck on the carb itself where it mounts to the engine. Seal it with sensor safe sealant. This is a place that is typical for a lot of engines to get air leaks. Also, I'd check the banjo fitting on the high speed needle where the intake fuel line connects. Normally, I seal the carb neck, the banjo fitting and the backplate on an engine before I even install it into a truck the first time just to avoid any air leaks.

Are you certain that your tank isn't cracked? Or, if you have an inline filter, is it sealing well?

To reduce foam in the tank due to the vibration, spray one squirt of armor all into a gallon of fuel. I'm not sure why, but it makes the fuel not retain any bubbles.

 

[FRIDGE]

if your car is the hpi rs4 3 evo then it may be that it has a tank primer. another source for air leaks if thsi is the car in question.

 

[roundrocknitro]

I have an evo and I'm haveing the same problems. i think it may be the fuel line fitting seals.

 

[rndtrp]

Air

It started after I changed the fuel lines for the first time. I think the line to the tuned pipe needs checking. Thanks

 

[WA2FAST]

The line to the tuned pipe is only feeding pressure, that shouldn't have any effect on air in the actual fuel line at all. Do you have a fuel filter? If not, then it is more than likely the fitting on the exit side of the fuel tank or a filter if you have one inline. The seals on fuel filters quite often go bad. I know that my fuel filter took about 3 tanks to work out all of the air bubbles. It is a "stone" fuel filter. Works great, but there was a lot of air to be moved out.

 

[Rolex]

If you have a fuel filter, mount it up and down, not sideways. That way all the air gets out when you prime the engine.

 

[canadian-mgt]

you wouldn't have happened to install the lines in the wrong way would you?make sure the feed line isn't plugged into the pressure fitting in the tank.if not I would guess that you probably have a problem with the primer or maybe a leaking tank or filler neck o-ring.why don't you try unplugging the lines then (with the tank empty) blow into the pressure line while pinching off the feed line,use soapy water to spray down the tank and primer and see if you find any bubbles where air might be leaking.

 

[WA2FAST]

Originally posted by canadian-mgt
why don't you try unplugging the lines then (with the tank empty) blow into the pressure line while pinching off the feed line,use soapy water to spray down the tank and primer and see if you find any bubbles where air might be leaking.

This is your best bet. Give this a try, this will tell you if it has anything to do with a leak anywhere on your gas tank.