Hey guys I have a echo cs5500. Should the fuel tank pressurize and push fuel out of line when I tighten the gas cap. Saw will idle 20 second and go dead and when I pull fuel line off no fuel. I can tighten the crap out of cap and fuel comes out few seconds. Other saws I work on fuel won't stop coming out until I Crack open gas cap. Vent seems ok gas cap is sealing and gas line grommets are new and tight. What's really getting me is if I pepper throttle and get it to Rev up it will keep going until I let off then dies immediately. I pull line off no fuelor no pressure. Am I on the right track guys any help is appreciated?
Fuel tank pressure
- Thread starter Besawin
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Yes, with fresh gas it should initially pee out a stream if you agitate or heat up the fuel tank with the cap screwed on, usually up to 7.4 Psig is the standard vapor on gasoline. Totally changes with temperatures & if summer or winter gas blends…that’s why you pressure test a chainsaw carb inlet to hold 8# all day long.
Think they call it Reid vapor pressure or RVP. Once the pressure equalizes, it will only dribble. The carb’s diaphragm fuel pump & gravity will help pull fuel out, then the tank vent breaks the vacuum inside at about 1-2” Hg or 1/2 a psig.
Googled - “Depending on the state and month, gasoline RVP may not exceed 9.0 psi or 7.8 psi. EPA provides a 1.0 psi RVP allowance for gasoline containing 10 percent ethanol.”
If your tank vent “seemed”/tested ok as you stated, then just change the fuel filter & do a visual for a kinked line. Next step I’d do is to clean out & put new diaphragms in the carb.
Think they call it Reid vapor pressure or RVP. Once the pressure equalizes, it will only dribble. The carb’s diaphragm fuel pump & gravity will help pull fuel out, then the tank vent breaks the vacuum inside at about 1-2” Hg or 1/2 a psig.
Googled - “Depending on the state and month, gasoline RVP may not exceed 9.0 psi or 7.8 psi. EPA provides a 1.0 psi RVP allowance for gasoline containing 10 percent ethanol.”
If your tank vent “seemed”/tested ok as you stated, then just change the fuel filter & do a visual for a kinked line. Next step I’d do is to clean out & put new diaphragms in the carb.
Depends on the era. Older pre epa tank vents vented both ways. Anything in the last 20 years or so is only supposed to vent air into the tank to replace fuel as it’s used and not allow any air or vapor out, which is why the line may or may not be under pressure,, depending on the circumstances
Thanks for responding guys. As far as vent goes I just gave a visual by pulling the little white cap off and looking at rubber Part inside. Should I replace it for good measure ? Diaphram is only a few months old and soft . Lines where replaced for good measure. I will replace vent and report back. Thanks guys
I may have misunderstood what you meant. The diaphram metering side is soft but could the impulse/pump side cause this?
Yes.
It sounds like the carb is struggling to draw enough fuel to maintain the saw at idle.
The diaphragm on the opposite side to the metering diaphragm has a section that oscillates due to the impulse being fed to one side. Fuel is on the other side & the oscillation causes it to pump as there are a couple of one way valves created by little flaps on the same diaphragm.
It is likely either the diaphragm has gone stiff, there is an air leak on the carb or fuel line, one of the little valve flaps isn't sealing properly, or the gasket/diaphragm(s) have been put on in the wrong order.
Also possibly a weak impulse
Your 20 second start/stop & fail to idle issue with no fuel coming from the tank line needs fixed first. Grab a new fuel filter, the Echo CS-5500 owners manual states to clean them but I’ve had no luck using carb cleaner…just replace it.
Stiff petals on the pump side diaphragm or a weak impulse could cause a running problem, but they’ll normally idle fine.
The fuel flow issue from the tank to the carb is a separate issue, likely a plugged tank vent, connector, pigtail line is kinked, or a restricted in-tank fuel filter.
Do you have a vacuum/pressure tester for checking the tank vent & carb inlet?
I assume it has a Walbro HDA-53 carb?
Thanks I will get a tester from work. I have a walbro hda kit ordered. Also I don't know know if it matters but I went ahead and got some crank seals coming as well. Cause it's a older saw. Thanks guys I will try all these things and report back. I have rebuilt 8 or 9 saws but just kinda replacing most stuff been lucky flying by the seat of my pants. I'm learning there's more to a chainsaw than I could ever imagine. This old saw is heavy but a favorite of mine. Kinda like my 028
You’re on the right track & will get it figured out.
You can use the vac/pressure tester on the carb too... it should hold about 12psi on the fuel inlet all day. If it leaks down dunk it in a jar of water & look for where the bubbles are coming from
If you’re picking up a pressure tester, remove the fuel line from the carburetor and put pressure to it. If it holds, everything is good. If it won’t build pressure, crimp the filter end of the line and see if it holds. If so, your line doesn’t have any pinholes and the tank vent vents both ways. Same thing applies to vacuum.
