2009 affirmatron
2007 negatron

Interestingly, there is a companion thread on Vapor Lock on the SDC forum. Saw mentioned there and have seen it elsewhere numerous times that 1 gallon of diesel fuel to 20 gallons of gas will work well. Since until just recently I have not encountered the problem for several years, I used to add 8 oz. of Marvel Mystery Oil to a tank of gas as that is also seen recommended many times. After several years with no problem, now it's occurred on three of my cars and one is a V-8. The last occurence was on an inline six and when I lifted the hood, the inlet bowl filter gas was bubbling.

I try to keep my tanks close to full, use the STABIL if not driven frequently in instances where the car is down for some reason. The '55 Clipper Super is the only V-8 I've experienced the "apparent" vapor lock on. Since the car exhibited what I had experienced previously on a number of occassions and flipping on the electric pump smoothed it out, I assumed it to be vapor lock given the new tank, blown out lines, and filter at the back.

I have observed those fuel filter bowls on my cars and really have never seen one go down that way. The one on the Kaiser I drove home yesterday (40 miles) was bubbling at the top with about 1/8-1/4" space at the top. I have at least 2 or 3 6V electric pumps that have quit on me but they are the bellows type. On the other hand the electric bellows pump on my '53 Hudson has been on it about 11 years. I'm only using the solid state type now. But even a couple of those have failed on my brother's cars over the last 3-4 years.

Not sure why some cars are more subject to vapor lock than others. It was surprsing on the '55 Clipper Super. My '53 Hudson has the problem even with the lines insulated; but the electric pump way back at the tank clears it up. My '54 Kaiser had it big time EVEN with the electric pump working full time until I rerouted the fuel line well away from the exhaust manifold. I drove another '54 Kaiser home today from an engine shop about 40 miles and it was ok until a mile from home. But fortunately it recovered. I have no electric pump on that car yet. But vapor lock is a fairly common thing. I never heard of it until 1994.

When I finally made it home yesterday I should have (always 20-20 hindsite) raised the hood and checked the bowl filter at the carburetor inlet to verify it was boiling. I am going to remove the extra filter screwed into the electric pump since it is the most restrictive and I have the clear filter ahead of it and the original bowl filter at the carb. inlet. With clean gas tank and lines, I don't need all that filtration anymore.
Also I have seen it recommended numerous times and have done that in my Hudsons of adding ~ 8 oz. of Marvel Mystery Oil to the gas tank to help alleviate the problem. Some say a little diesuel fuel will help, but I'll just go with the MMO.

Well, since the original intent of this add-on electric pump was just for priming after long sits, the pump is not at the extreme rear, but alongside the left frame member but still within a couple-three feet of the gas tank; so it is back pretty far. I'll check the heat riser for funstionality. I'm inclined to eliminate the smaller screw-in filter from the electric pump inlet at this point. And the reason for the clear filter close to the tank was originally before I had the gas tank renued with the coating, so for sure one filter can come out and the screw-in is the most restrictive. In fact I had one on my '54 Hollywood years ago and it plugged up on a trip, but you had to unscrew it and saw it apart to know that.

But I will check the fuel pump although it is fairly new and try to check all the hose clamps for tightness. It is possible, too, that I need to remove one of the filters for less restriction. I have a transparent filter at the back near the tank plus another screw-in type that goes into electric pump and that perhaps could be impeding flow a little although I use these filters on the cars and have for many years.

This is the first time for this on this car and the tank was over 3/4 full. It will probably be awhile before I get it back out on the road for any appreciable distance as most of the drives in the car are just a few miles every 3-4 weeks. Checking web searches and as earlier above posting, a return line to the tank seems to be a route recommended, but I sure hate to get into that and it would be a chore to do it on every car.

Keith, I thought of the gas cap when after I changed out the filters I had one small backfire and it shut down on me twice. I took the cap off and there was no air or rushing sound at all. But then it fired up and idled ok for awhile. The gas cap scenario may indeed be the culprit on my brother's Lincoln as he changed it ouy and hasn't had the trouble again at least not yet. Don't know what's going on here with these gas caps. I had to get a new one for my Studebaker about a month ago.