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1965 Fuel System - Pressurized?

I

Indycanard

Member
I went to fill my tank yesterday (65 Convertible), I was a few gallons from empty. The air temp was about 90 (HOT for Seattle), and I'm sure the tank was a bit warmer because the exhaust pipes are on each side. Anyway, when I twisted the gas cap to fill-up, a significant pressure released. Perhaps only a few PSI, no way to really know, but it was enough to concern me. The cap I have is a 1 year old Scott Drake reproduction. I thought the caps had vent holes?
Do I have anything to be concerned with?

Thanks
 
Yes. If the cap has a poor vent system, you can also cave in the tank as the engine pulls out the fuel. It can also cause the engine to stop running and cause fuel to overflow when parked with a full tank. Get the cap vented or a new cap.
 
"AzPete" said:
Yes. If the cap has a poor vent system, you can also cave in the tank as the engine pulls out the fuel. It can also cause the engine to stop running and cause fuel to overflow when parked with a full tank. Get the cap vented or a new cap.
Click to expand...

I haven't noticed any "vacuum" related hesitation or poor running so far. I'm not sure how this cap is constructed. I'm wondering if it may have a one-way vent or something, and the hot day increase in pressure could not release.
 
The only way you would notice a running problem is a long ride starting with a full tank, with no off time. It takes a lot for an engine to suck all the air from the tank and create that type vacuum but I have had it happen. The early signs are what has happened to you. If you had a full tank sitting on a hot day, you may have gas splash out if the cap was opened.
 
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