fuel tank vent--both ways?

[purdyite]

My Poulan 2450 saw (I know, it's a Poulan...but it runs and cuts) seems to pressure up the fuel tank as I work the saw, then it gets hard to re-start after a bit. When I opened the fuel cap, there was pressure in the tank. If the vent works properly, is it supposed to prevent pressure buildup as well as preventing vacuum in the tank?
I have gone through the saw--carb, fuel lines, etc.

Thanks for any replies.

 

[xtremez]

Yes that’s how the tank vent works. Sounds like it’s time for a new one.

 

[Old2stroke]

My Poulan 2450 saw (I know, it's a Poulan...but it runs and cuts) seems to pressure up the fuel tank as I work the saw, then it gets hard to re-start after a bit. When I opened the fuel cap, there was pressure in the tank. If the vent works properly, is it supposed to prevent pressure buildup as well as preventing vacuum in the tank?
I have gone through the saw--carb, fuel lines, etc.

Thanks for any replies.N

My Poulan 2450 saw (I know, it's a Poulan...but it runs and cuts) seems to pressure up the fuel tank as I work the saw, then it gets hard to re-start after a bit. When I opened the fuel cap, there was pressure in the tank. If the vent works properly, is it supposed to prevent pressure buildup as well as preventing vacuum in the tank?
I have gone through the saw--carb, fuel lines, etc.

Thanks for any replies.

No, it should only let air in. The pop-off pressure of the carb should be high enough to prevent tank pressure from forcing fuel into the carb.

 

[ZeroJunk]

Yeah, it's a one way street unfortunately maybe. One common problem I have is hydra-locked motors, particularly 2 cycle blowers end up full of fuel after sitting. Seems the only solution is replacing the carb.

It won't let the tank pull a vacuum, but it will build pressure.

 

[SteveSr]

My Poulan 2450 saw (I know, it's a Poulan...but it runs and cuts) seems to pressure up the fuel tank as I work the saw, then it gets hard to re-start after a bit. When I opened the fuel cap, there was pressure in the tank. If the vent works properly, is it supposed to prevent pressure buildup as well as preventing vacuum in the tank?
I have gone through the saw--carb, fuel lines, etc.

Thanks for any replies.

This sounds like vapor lock. Are you still using winter blended fuel in hotter temperatures? Leaving the saw sit in the sun?

 

[Okie]

I've been refurbishing an old Poulan Super 25DA lately. Looking at it I don't know how they could have built a saw much more solid that that one. Just it's age should tell you how well the old saw lasted and appears to have several years left.

No, it should only let air in. The pop-off pressure of the carb should be high enough to prevent tank pressure from forcing fuel into the carb.

As Old2stroke says:

This is part of the going green thing. Also lots of small engine are designed now days that if the carb needle/seat leaks by the fuel (grain alcohol) don't leak onto the ground, it goes into the engine.
Very few updraft carbs on later model small engines.

I would just loosen the cap, since you know it's an issue with re-starting the Poulan saw when it's been run awhile and keep on working so as to keep the tree huggers and going green people happy. Do not get caught spilling/dribbling any gas or oil on the ground when re-filling your saw. Fossil fuels are a bad thing.
You might consider a ES saw. (battery operated saw)

 

[lone wolf]

This sounds like vapor lock. Are you still using winter blended fuel in hotter temperatures? Leaving the saw sit in the sun?

This happens every year around this time, a lot of guys think it's the vent, but I think it's winter fuel. I keep a couple of gallons of canned gas on the truck for when this happens.

 

[sonny580]

I agree with Lone Wolf!! Bad fuel!!!

 

[stihltech]

One of the first things to do in the shop is dump fuel from saw into a glass jar. 3/4 will have water in the fuel (ethanol or non doesn't matter. Next take a wiff. If you don't get a good vapor smell (not old smell), it may be the fuel. Remember, liquid fuel don't burn, vapors do. 90 days and it is garbage.

 

[lone wolf]

One of the first things to do in the shop is dump fuel from saw into a glass jar. 3/4 will have water in the fuel (ethanol or non doesn't matter. Next take a wiff. If you don't get a good vapor smell (not old smell), it may be the fuel. Remember, liquid fuel don't burn, vapors do. 90 days and it is garbage.

Most of the pump gas around here always lacks the smell.

 

[PV Hiker]

@lone wolf @stihltech is it my understanding that ethanol free fuel is not effected by winter grade blend of fuel? It is not mixed for winter use to burn hotter and cleaner?

 

[Okie]

If you cannot live with just loosening the gas cap every once in awhile on that POULAN go to tractor supply and for $3 you can get a NEW replacement gas cap.
Do not be surprised if it still does the same thing.

 

[lone wolf]

@lone wolf @stihltech is it my understanding that ethanol free fuel is not effected by winter grade blend of fuel? It is not mixed for winter use to burn hotter and cleaner?

“Winter Gasoline​

In winter, gasoline blends have a higher Reid vapor pressure, meaning they evaporate more easily and allow gasoline to ignite more easily to start your car in cold temperatures. This blend is cheaper to produce, which results in lower gas prices at the pumps from late September through late April.

Cost for your wallet: Prices typically fall 10-30c/gal starting in mid/ late September through late November as gas stations switch to winter gasoline and demand for gasoline falls seasonally as we start to stay closer to home. Many retailers continue to sell summer gas until their inventories run out, before then selling winter gasoline. Hurricane season can also affect prices before the switch, ending in a squeeze just before the switch since refiners don’t want excess expensive summer gasoline sitting around and especially if refineries are in the path of a major storm. “

 

[purdyite]

haven't checked this thread in a while...

I use 91 octane no-ethanol gas mixed 40:1. New gas. The carb has been through the ultrasonic cleaner. On startup, it idles great, runs wide open great, and after most of the tank is gone (saw good and warm) I'll kill it and then it doesn't want to start. That's when I noticed the pressure buildup and am thinking it's pushing fuel and flooding it. I could loosen the cap when I kill it, but of course I don't think of it then. And, I don't think I should have to.

So...the cap is one-way vent, is that what I'm hearing? (That make sense so fuel doesn't run out the vent) Then it's a type of check valve? Lets air in, not out?

 

[Mad Professor]

the old Stihl ones, that were just a hose with grub screws, were two way