Fuel Caps/vaporlock

[PreddyFast]

I have a 1973 Indian with a 413, drove it 2 hours in 90 degree heat with no problems, then the engine started to stumble and could not maintain 60+ mph. I have read that my Winne needs vented gas caps, I found that the ones that were on it were non-vented. Here is my situation, I changed the non-vented to Vented caps and drove it till it was up to temp and parked it, when I went to show the wife the caps I almost had the cap blow off in my hands there was so much pressure in the tank!!! Please let me know if I need to go back to the old cap or if anyone has had this problem. Thanks

[Stripe]

This is a toughie, your fuel system may or may NOT have a evap system that returns your gas fumes back into the fuel system. If it DOES then a vented gas cap is NOT called for as the solenoid for the evap solenoid is what allows the vapor to vent into the intake.  If this solenoid fails it can cause the problems you describe.  BTW, the vented gas caps are a one way deal, they let air in only. The mass expression of air could be the from the fuel system constantly taking in too much air during operation and it's not having anywhere to go when you end a long driving trip.
If you do NOT have this system, then I would check to see if your fuel pickup in your tank is getting clogged by debris. What could be happening is that when you stop, the debris falls back into the tank until you start driving again and re clogs, but I could be wrong.

If the power loss happens in the same amount of time I would try driving with the gas cap a little loose and see if it happens again. Careful not to lose the cap.

The old style vent caps were done away with because gas vapors are considered pollution.

I hope this gives you some ideas where to start.

CMM500

[Oz]

The evaporator system is what we commonly call the "cookie jar".  It's located on the outside of the frame, on the passenger side, just behind the front wheel well (or close to that).

Why do you believe it's vapor lock associated with the fuel caps?

This could be totally unrelated to the fuel caps and evaporator system.  What is common is overheating of the gas in the fuel line near the engine which causes the vapor lock.


Hm?

[ClydesdaleKevin]

I could be wrong, but on our old 72 with a 413, The Ark, it required VENTED caps...so I'm pretty sure you were misinformed and that you need to go back to the vented style cap.

We also had vapor lock problems with the Ark...changed to vented caps and it helped...then a new fuel pump, and it helped a little more...then a new Holley carb, and it helped even more...finally some sheet metal heat shields around the fuel lines where they get near the manifold, and the problem went away completely.

Kev

[brians69d24]

Coachmann are sure about the vent being a one way deal?  What about when the tank gets hot? There will be liquid/ vapor expansion and no where for the displaced air to go at least in the pre-emissions vehicles.
brian

[Oz]

It does make sense to start with the easiest, least expensive approach to the troubleshooting.  I learned that just from being here in the community many times and it definitely saved me a ton of money as, very often, the fix is an easy one.

Vented gas caps first.   If that doesn't do the trick, on to the next option.

[PreddyFast]

Update... I drove 133 miles with the so called Vented caps... The tanks built so much pressure that fuel was leaking out a connection and dripping on the hot exhaust. I went back to the non-vented old caps, and the problem cleared up, no leaks. Seems to me that this is a fuel boiling issue. The Motorhome ran like a dream this weekend, but also never got into the 90's while we were driving. Thanks for the replies to my issues, I will be back to update when I get more info from my father-in-law (owner) about what he has done to it and after i get more seat time. I still love the looks ya get when ya pull into the campground with this old Beast!!!