Primer Bulb Vacuum Issue

BrackishB · August 5

Have a re occurring issue where my primer bulb is getting a vacuum, sucking flat and starving the engine of fuel. I have replaced the fuel lines, filters and primer bulb. When I use an external tank I have zero issues, once I re connect to internal tank the issue continues. If I run 5-10mpg, it doesnt seem to happen, soon as throttle up to 20mpg it happens quickly. Any other ideas on what could be my issue? I have also tried unscrewing my fuel cap when the issue occurs and still nothing. I am open to any suggestions, thank you.
-Brackish_B

Salty Dawg44 · August 5

Could be trash partially blocking either the screen at the bottom of the pickup tube, or the antisiphon valve at the hose connection on top of the tank.

surfman · August 5

I vote anti siphon valve.

hhfisherman · August 6

you had eliminate the major parts
only the anti siphon valve and the screen on the pick up tube in the gas tank.

Tony Roma · August 6

Please keep us posted, an answer to this mystery will help plenty in the search option, good luck

BrackishB · August 7

Thank you all kindly, I will explore the possibilities of the anti siphon valve and the pick up tube in the gas tank tomorrow and will update with results

surfman · August 7

The anti-siphon valve is located on top of the tank right where the fuel line connects to the tank, usually.

Soda Popinski · August 7

had this issue it was the AS valve.

snookaffinity · August 7

Soda Popinski said:

had this issue it was the AS valve.

Same thing for me. Removed the ball and spring in the AS valve and cured the issue.

surfman · August 8

Is that thing really necessary?

Kokosing Lover · August 8

I don't think anyone has mentioned this, but it could be your gas tank vent as well. The vent works both ways; it releases pressure in the tank when the gas produces vapors and when you fill your tank, and it also allows air to enter the tank to replace the volume of gas pulled from the tank during running. If that line gets clogged, and this usually happens at the mesh covering the outer opening of the line, then you get a vacuum forming in your gas tank and eventually your motor won't be able to fight that vacuum and can't draw fuel.

bicyclist · August 8

Sounds like this problem is not related but I though I would post this as an FYI.

Email from a friend with the USGS. So there is an exotic beetle that eats into rubber.

Image: https://us.v-cdn.net/6030354/uploads/editor/xv/sau4w2nyueuy.png

Hi All,

Just last week while out in the field, one of our boats here in Gainesville started sputtering and quit running after 45 minutes of use. The crew was able to get back to the ramp safely by paddling but upon further inspection, they noticed the fuel line and primer bulb on the boat was filled with tiny, perfectly round little holes. Once back at the lab they started digging in those little holes and found tiny little beetles of all things! Thanks to Howard Jelks for finding a possible suspect. The Camphor Shoot Borer (CSB). Here is a little clip out of the article link that is attached below.

As happens too often these days, the CSB is yet another insect that’s not native to this country. It was first reported in the U.S. in 2004, and is now found throughout the Southeast from NC to TX. It normally feeds on a variety of hardwoods, especially sweetgum. In Texas it’s more likely to be found in the eastern part of the state.

One entomologist pointed out that he has noticed these beetles often come to his alcohol-baited traps used to collect other bark beetles. Most gasoline these days contains alcohol, so, putting two and two together, we can assume that alcohol is likely what’s attracting these little guys to lawn mowers.

https://citybugs.tamu.edu/2017/04/27/boozy-beetle-the-camphor-shoot-borer/

Soda Popinski · August 8

Kokosing Lover said:

I don't think anyone has mentioned this, but it could be your gas tank vent as well. The vent works both ways; it releases pressure in the tank when the gas produces vapors and when you fill your tank, and it also allows air to enter the tank to replace the volume of gas pulled from the tank during running. If that line gets clogged, and this usually happens at the mesh covering the outer opening of the line, then you get a vacuum forming in your gas tank and eventually your motor won't be able to fight that vacuum and can't draw fuel.

Done that one too! Like a fool i tightened it all the way down not knowing what it was when I first got my boat and then spent 3 days trying to figure out my fuel starvation problem. unscrewed the fuel cap and thing ran like normal, eventually someone clued me in probably on these boards. I have also had an issue where i was losing fuel in my carbs because the primer bulb went bad, it was collapsing in on itself. Replaced the bulb, thing went back to normal. Fuel issues can be frustrating.

finbully · August 8

bicyclist said:

Sounds like this problem is not related but I though I would post this as an FYI.

Email from a friend with the USGS. So there is an exotic beetle that eats into rubber.

Hi All,

Just last week while out in the field, one of our boats here in Gainesville started sputtering and quit running after 45 minutes of use. The crew was able to get back to the ramp safely by paddling but upon further inspection, they noticed the fuel line and primer bulb on the boat was filled with tiny, perfectly round little holes. Once back at the lab they started digging in those little holes and found tiny little beetles of all things! Thanks to Howard Jelks for finding a possible suspect. The Camphor Shoot Borer (CSB). Here is a little clip out of the article link that is attached below.

As happens too often these days, the CSB is yet another insect that’s not native to this country. It was first reported in the U.S. in 2004, and is now found throughout the Southeast from NC to TX. It normally feeds on a variety of hardwoods, especially sweetgum. In Texas it’s more likely to be found in the eastern part of the state.

One entomologist pointed out that he has noticed these beetles often come to his alcohol-baited traps used to collect other bark beetles. Most gasoline these days contains alcohol, so, putting two and two together, we can assume that alcohol is likely what’s attracting these little guys to lawn mowers.

https://citybugs.tamu.edu/2017/04/27/boozy-beetle-the-camphor-shoot-borer/