Replacement Gas Cap Concerns

[Stuart F.]

This morning I drove down to my local Ethanol free gas station (about 12 miles) to fill up for the fall Vettefest show coming up in a few weeks. I had not run my car for about 4 weeks due to some vacation travels and the extreme hot weather. It started up fairly normal, but was stumbling and hesitating from stop lights along the way (very un-characteristic). When I arrived and removed the gas cap, I got a fairly strong "whoosh" of air suction relief. I am currently using the replacement gas cap that has both a suction valve and a pressure relief valve (the GM cap currently still available).

After filling the tank, my restart was very good and it ran very smooth and responsive on the way home.

I question now whether I may have a faulty cap, and whether that was causing the rough running.

Stu Fox

[Joe R.]

Re: Replacement Gas Cap Concerns

Stu,

C2's have vented caps and you should have no air suction or pressure when the cap is removed. You certainly need a new cap. Just might be the problem with your running rough. Try that first.

JR

[Stuart F.]

Re: Replacement Gas Cap Concerns

Joe;

Thanks for the response.

This replacement cap was put on new a few years back when I was searching for ways to reduce the gas smell in our attached garage. Up until now, it had been working well. Perhaps I should at least give it another chance as it may just have stuck due to sitting, and the extreme heat we've had this summer. However, I could go back to my 63 cap which has just a clean vent hole if the problem continues.

I'm not sure, but isn't the dual valve cap standard from 64 on up until they went to the closed system? I believe the vented cap (with just a small hole) is an exclusive 63 animal, but I may be wrong.

Stu Fox

[Joe L.]

Re: Replacement Gas Cap Concerns

Joe;

Thanks for the response.

This replacement cap was put on new a few years back when I was searching for ways to reduce the gas smell in our attached garage. Up until now, it had been working well. Perhaps I should at least give it another chance as it may just have stuck due to sitting, and the extreme heat we've had this summer. However, I could go back to my 63 cap which has just a clean vent hole if the problem continues.

I'm not sure, but isn't the dual valve cap standard from 64 on up until they went to the closed system? I believe the vented cap (with just a small hole) is an exclusive 63 animal, but I may be wrong.

Stu Fox

Stu------


Yes, the cap with the vent hole was 1963-only. The caps with the integral pressure/vacuum valve were used from 1964-69. They are also SERVICE for 1963.

My late 1969 had both an integral pressure/vacuum valve mounted in the tank AND the vented style cap for MANY years. I ALMOST ALWAYS experienced the "whoosh" you describe when removing the fuel cap. Neither the integral pressure/vacuum valve nor the vented cap are designed to relieve pressure or vacuum to ambient conditions.

[Joe R.]

Re: Replacement Gas Cap Concerns

Joe;

Thanks for the response.

This replacement cap was put on new a few years back when I was searching for ways to reduce the gas smell in our attached garage. Up until now, it had been working well. Perhaps I should at least give it another chance as it may just have stuck due to sitting, and the extreme heat we've had this summer. However, I could go back to my 63 cap which has just a clean vent hole if the problem continues.

I'm not sure, but isn't the dual valve cap standard from 64 on up until they went to the closed system? I believe the vented cap (with just a small hole) is an exclusive 63 animal, but I may be wrong.

Stu Fox

Stu,

The cap for the C-2's is even stamped "Vented" on the cap itself. As gas is removed from the tank it allows air to replace the space. If it were not vented in some fashion the vacuum created would not allow the pump to supply the engine with gas. Original tanks for C-2 don't have a vent but replacement tanks have the valve assembly built into the tank.

JR

[Stuart F.]

Re: Replacement Gas Cap Concerns

Thanks for the information guys. Guess I'll just monitor this situation for awhile. Two conditions I noticed this morning that may have contributed to my experience; I had let my tank run lower than usual (it took 15.9 gal.), and the ambient conditions here was that we had nearly 100% humidity.

Well, whatever, I should know by now that these SHP engines can be temperamental, i.e. One day they will run real good and the next they are bucking like a bronco. Down here in Florida these things are magnified.

Stu Fox