[s4_250hp]

So I have a 84 GTI I have fitted a 32/36 carb with. I was able to get it pretty well tuned but I have a couple issues. The stock jets are making the car run a tad bit too rich. I have a air fuel mixture gauge that is helping me to conclude this. Also when you go full throttle it has a bit of a hesitation before it clears out. I have ordered leaner jets. This is not the real problem I am having however.

I have driven it about 400 miles with the carb. My real issue is that the car will run great but then I can hear the fuel pump knocking then shortly after this the car will die (starved for fuel). I have found out that if I go and relieve the pressure at the fuel cap this will fix the problem and the car will start right up. I made sure when I converted this over that I chose a good fuel pump. It is a FuelFlow 015 pump made in New Zealand.

Any insight on why when the tank builds too much pressure the pump fails to work properly?

 

[s4_250hp]

I think I figured out the problem. When I converted over to the carb I replaced the tank at the same time. I removed the "fuel tank breather gravity valve" at the rear of the car. I didn't think I needed this as I was converting to carb. Upon further investigating this is how the tank vents the pressure build up. I will be installing a universal breather valve this weekend to see if this fixes the problem. I am almost certain it will. I will post results.

 

[srgtlord]

Im going to bet its vapor lock. Search the carb forum for keeping an electric pump and using a bypass filter or fuel regulator.

 

[The Dubbernaut]

I nearly tore mine out too, yesterday! Took a look in the books and knew right away that’s how the tank breathes. Just replaced all the old brittle breather hoses to the filler neck and valve. When I was last driving the car in 2015 I couldn’t fill up more than 1/2 tank or gas would spill everywhere. Turns out the large 3/4 hose was split from a rock grinding a hole in it and it would spill out of the auxiliary hose to the filler neck spout. I dropped and R&R’d my tank because I thought I had a rust hole.