390xp

[huskyboy]

The function of a tank vent is so that when you leave the saw in the hot sun... the fuel tank does not balloon up like a fuel can without a vent. If it is building too much pressure the needle/spring in the carb will be overran and flood the saw. If the vent is too restrictive, it won’t let enough air in and the saw will starve for fuel.

 

[Dub11]

I thought the tank vent was to let air in to keep it from vaper locking while running?

 

[redlight066]

The white stick recessed in the tank is the actual vent. Yes your saw will run with less than optimum fuel pressure. It would be hard to start with a lack of fuel pressure. Poor fuel supply will also cause a lean condition and possible failure.
That diaphragm can only pump what is supplied. It is not going to draw fuel from the tank. The vent does exactly that. Allows pressure to build to 5PSI and bleeds off excess pressure. So the carb can have a consistent fuel supply.

 

[huskyboy]

The white stick recessed in the tank is the actual vent. Yes your saw will run with less than optimum fuel pressure. It would be hard to start with a lack of fuel pressure. Poor fuel supply will also cause a lean condition and possible failure.
That diaphragm can only pump what is supplied. It is not going to draw fuel from the tank. The vent does exactly that. Allows pressure to build to 5PSI and bleeds off excess pressure. So the carb can have a consistent fuel supply.

The impulse of the saw provides pressure/vac for the diaphragm to draw fuel. No impulse, no fuel. If your theory was right then the saw would run without impulse.

 

[redlight066]

Mason I’m not going to continue this.

 

[NPKenny]

Mason I’m not going to continue this.

I would like to hear this out a bit more. I have been of the thought that Huskyboy is correct, but would really like to understand the tank vent. If tank pressure is what is necessary, it does change my understanding.

I’m certainly not reading this as a pissing match, but as an actual discussion. Especially since I respect your opinions.

 

[huskihl]

I would like to hear this out a bit more. I have been of the thought that Huskyboy is correct, but would really like to understand the tank vent. If tank pressure is what is necessary, it does change my understanding.

I’m certainly not reading this as a pissing match, but as an actual discussion. Especially since I respect your opinions.

It’s my understanding that tank pressure is not necessary, but it certainly aids in starting the saw. Problems occur when pop off pressure isn’t high enough or a dirty needle could bypass some of that pressurized fuel and flood the saw while not in use. Vents used to pass air each way, but I believe they aren’t supposed to allow air out now due to an EPA mandate. I’m not certain if there’s an upper limit as to how much pressure they will hold before bleeding off though.

 

[Nutball]

Yea, I didn't know if there was a max pressure limit, but the vent must let air in as fuel is consumed. I've always assumed the carb pressurized the tank somehow since tank pressure can be beneficial, and a puff of air exits when the tank has been opened after the saw has been run, and considering how saws tend to run lean sometimes when started right after having let the pressure out of the tank. I guess the gas itself could be the pressurizing mechanism as it likes to evaporate even at low temperatures.

 

[Huskyrunner76]

The tank vent not building pressure doesn’t affect the saw, just leaks fuel. I used 3 bond to hold in the last 385 tank vent that kept falling out. On the other hand... the tank vent building too much pressure is what affects running.

The saws run fine , just seem cold natured when starting . I can pull my 390 1 or 2 times on choke , she hits ! Have never pulled on her more than 4 times total ! The 395's all 6 of them have always taken a dozen or so pulls ! I simply hate these 395 saws ( so glad I no longer own any ) ! I've never had a tree that my 390 can't handle with ease . She's got the best power to weight ratio and balance of any saw I've ever ran . Any logger that I know (around here ) that has ran a 390 for at least half a day , all say it's the best balanced and just good natural feeling saw that they too have run ! So yes I'll take a 390 over any other ! I don't mill with saws so no need for a 395 as some have suggested . Heck if I want to mill then I'll do just as I've done with saws ....... Not try to use a darn toy and get the right tool which would be an actual saw mill !

 

[huskyboy]

https://www.tanksinc.com/index.cfm/page/ptype=results/category_id=160/mode=cat/cat160.htm Older saws were just the same way as a older car with a simple hole with a sintered breather to keep sawdust out. They’ve gotten more complex because the epa doesn’t want gas splashing out or vapors. It’s the same story if you read anywhere on the internet from credible sources, tank vents purpose isn’t to supply the engine with fuel pressure. That’s the job of the diaphragm and impulse in a saw or the fuel pump on a car. Tank vent allows the tank to breathe, can’t get air out if you can’t get air in. Look at your coffee cup from dunkin donuts. There is a little hole on the opposite end of the lid to allow air in while you drink it. Tank vent does same thing. Don’t overthink this guys. Lol

 

[Nutball]

You can have a one way valve to let air in, but not out. I remember a Stohl 015 didn't have that, just a tiny tube that was pinched down to barely let any air pass.

My 2188 would leak fuel of let sit on the starter cover side based on the location of the brass bead vent.