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Vent gas cap or not

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J

jbuffalo

Senior Member
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1978 Mg Midget, Weber carb , no smog equipment, electric fuel pump, weber and fuel pump are new. The car seems to be starving for gas, I went about 1 mile and it stalled, waited 30 seconds and it started up. Do I need to vent the gas cap-it is not vented? Just took off cap and it runs real well-I think? thanks Jim
 
Excellent question, I eagerly await the answer! Although my "sealed" gas cap couldn't seal much these days, the seal has completely disintegrated...

Jim, is it a HVLP pump? (approx. 4 PSI, but high volume?)
 
Try this, a peice of plastic wrap or alum foil over the tank cap inlet with a rubber band around it. Poke a small hole in the plastic or alum. Give it a go. If it solves the problem you know the cause.

Now me I would just take the cap off and drive it around some.
 
If the cap is old, they get condensation inside the vent and rust closed. A quick cure is to slice a Vee out of the rubber seal. If you hear a rush of air when you remove the cap, the vent is clogged.
I am not sure about the 1500s but all other Spridgets used a vented cap.
You might have a float adjustment problem on the Weber too.
 
some of the decision will depend on the gas tank itself. Smog equipped cars have gas tanks with a vent hole that vents through the vent/filter mounted inside the trunk next to the passenger rear fender. (It's the piece that looks like a large tuna can - sort of) this is then hooked up back to the engine somehow (I have no plans to reinstall so I haven't learned where). Anyway, if like me, you buy a new tank, there is no vent hole for a vent line, thus the need for a cap with a hole in it. I know some have had the fitting for the vent sweated in but I have no plans to.

Hope this helps
 
That pressure is too high for a Weber. Just a matter of time before it overpowers the needle and seat. Wanna get one with under 2 psi.
 
So, did removeing the cap fix the problem?
 
Its great to see a person with focus. No, I did not try a drive with out the cap-I did find that the vent hose from the fuel tank was broken-I fixed it-work is getting in the way of my hobby. Now I am going to look at the cannisters and all the hoses. Found and replaced the brake switch-have lights.thanks Jim
 
Cap is vented and all vent hoses are off. Car runs great. Check classified for fuel pump block off plates for 1500-cheap. thanks Jim
 
Do be aware of the vent hose in the trunk; I had mine break and it started leaking gas into the trunk after a fill up. I hope you didn't remove the vent hose completely; you don't really need gas fumes permeating the trunk. The only thing I might mention is I had a similar problem to yours which ended up being the fuel pump having a small air leak that would eventually make the engine start stalling.
 
RE: the fuel pump. webercarbs.com suggests the use of a Carter "green" electric fuel pump, which is similar to earlier Sprite fuel pumps in that it should be set up as a "pusher" low down, close to the gas tank. I'll find a part number. I can't comment on it personally, I'm still using the stock mech fuel pump, with a regulator.

Edit - P/N is Carter 4070
 
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