# How are chainsaw gas tanks vented?



## Thunderglass (Dec 30, 2009)

I have a Poulan 2500 chain saw that has a fuel problem. I have replaced the carb already and checked engine compression which is @ 150psi. The saw will only run if spraying starting fluid into it. I have checked the condition of the rubber intake tube and it seems tight. I have also replaced the fuel cap with same result. Fuel line is new also. How are these fuel tanks vented? The new carb came pre-adjusted and said that only the idle may need adjusting for it to run properly. I've adjusted to no avail. Have not adjusted the high or low settings yet. I'm still suspecting a fuel delivery issue? Any thoughts?


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## Thunderglass (Dec 30, 2009)

Will I have found one thing that's not correct on it. It's missing the impulse seal. Not sure if this is going to get it running or not but I'll see if I have a small piece of tubing that will work in it's place until I get the correct seal. I also see in the parts breakdown a vent plug but it's not showing exactly where it is. Will look some more and play some more this weekend.


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## 30yearTech (Sep 14, 2006)

The fuel tanks can be vented through the fuel tank, or sometimes the little duck bill valve just presses into a small hole in the tank itself.


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## Thunderglass (Dec 30, 2009)

Thanks. I did find it. It was a pressed in mesh type filter under the mounting block for the carb going directly into the tank. I used some compressed air on the filter and fuel came out the disconnected fuel line, so no problem there. I replaced the impulse seal but with almost the same result. Engine starts on choke and even runs if you keep the RPM's up but let off the throttle and it will bog and then die. Will not restart unless it's choked even if engine is warm. Internal seal in crankcase maybe?


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## Thunderglass (Dec 30, 2009)

Also sorry, I should have posted this in the 2-stroke section.


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## 30yearTech (Sep 14, 2006)

Yes, it's possible you may have a small air leak into the crankcase somewhere. Check the crankcase bolts on the bottom of the engine. I have seen these come loose and fall out in the past.


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## Thunderglass (Dec 30, 2009)

I replaced the impulse seal with a small piece of tubing that fit pretty tight into the engine port but decided that a little dab of high temp 
RTV would make sure it stayed in place. Wrong move on my part. :drunk:

Saturday I started to disassemble the engine to check the bottom engine crank seal and found the problem. I had pushed the impulse tubing into the engine port after dabbing on the RTV so the tubing pushed the RTV into the engine port and did a very good job of sealing off the port. After cleaning out the RTV from the port and reinstalling the tubing (home made seal). It fired off on the third pull and ran like a top. Adjusted the idle down and it purrs like a kitten. Back in business now. Thanks for all the help and the search feature on this site provided tons of good information.


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