Possible vapor lock or ??? 454 / 496 GM motor

[jeff york]

I had an odd incident last night. I pulled my 1977 Airstream Argosy 454 / 496 GM powered coach out of storage. I ran it about 10 minutes before leaving and then drove about 25 miles and stopped for gas. I pumped about 22 gallons of regular gas into it. It sat maybe 20 more minutes running while I pumped the gas. Then, right after I pulled out, the motor shut down. I got it to restart and then as soon as I got through the intersection it shut down again. I could hit the key and it would sputter and fire up and quickly shut down. I had to pump the heck out of it to try and keep it running. But, it would quit. I took some starting fluid and got it to start again and it quickly shut down. On the second try with starting fluid it started and I drove it about a block to a Walmart parking lot. I shut it off I think. After a few minutes, I started it back up and decided to try and get it home about 4 miles away. It ran just fine the whole way. So, now I am wondering what happened. 

Back ground. I recently replaced my mechanical fuel pump with an electric fuel pump. I test drove it quite a bit before taking it out on the road so I thought everything was ok. I think after it shut off last night I checked the fuel pressure control valve and it may have been set as low as 2-2.5 PSI. It was dark so I am not sure. I pushed it up to 4 PSI and thats when I started it and it ran the rest of the way home. However, it ran fine for the first 20 plus miles and probably an hour. Its a Rochester Quadrajet carb. The fuel lines at the motor I changed to flexible neoprine ( I think) and on the mechanical pump it was a hard line from the mechanical to the carb. AS per electric fuel pump installation, I placed a pre filter in front of the pump to filter large particles and a new filter to filter small particles at the carb. 

There is no return line on the electric pump. 

So, did I get vapor lock ? Odd this happened right after re-fueling. Was my fuel pressure set to low ? Do I need to add something to insulate the gas lines from heat to prevent vapor lock ? Do I need to add stand offs on the fuel line to get them farther from the engine to stop heat soak ? The fuel line sits pretty close to the intake manifold and the valve cover. Sorry for the lenght. Just trying to throw out all the details.  

[jeff york]

Jack, The 12S was the only pump I could find locally and since it was a facet style pump and I use those in my airplane, I figured it was ok. I take no offense to any comments or remarks that recommend I take a particular action. In this case that I chose a bad pump. That is why I am here and thats why I am asking the questions. I learned long ago that you if you have resources. Be it engineering, flying, restoring a car or this Airstream. You are not the first to advise me of the quality issues with the Mr. Gasket 12S pump. It was more expensive then the mechanical pump so I thought it was ok based on that and the more expensive pumps all produced far to much pressure. They were fuel injection pumps. 

I am going to look at the canister fuel filter that is mounted on the frame under the engine and see if it has a tank return line. If it does I will incorporate it into the fuel system by putting it back into the fuel circuit. I took it out when I installed the 12S. I will look to see where I can get the Cater electric fuel pump and get that ordered. I like the idea of a Carter as I always had great luck with Carter carbs in the past. It was recommended that I get a Holly Blue electric pump but, in my past I always thought Holley carbs were junk because I could never get them to work correctly and always had to jerry rig them because their linkage was never correct for the applications I bought them specifically for. As far as the gas cap I bought yesterday,  had two choices. One said just gas cap and the other said emissions gas cap. The emissions cap had a lock on it and appeared much better built and seemed to have vent looking orifice. So , I bought it. Upon inspecting it and comparing it to my old gas cap, it is very simular but, the seal on the new one gives me the impression that the old one has a bad seal. The seal look the exact same but the old one looks like it was soaked in something that blew it up out of proportion.   

[Jack Wasmuth]

Good to hear from you Jeff. I read about the Mr. Gasket pump and sorry to say but it did not get very good reviews. It is on the low end line of pumps. Works for a while and then quits. It is not one that I would recommend. I have had excellent results with Carter pumps. If you wanted to step up there is the Competition series For about $70.00 that I highly recommend. I have had great results with this pump in many different applications Also this pump has twice the GPH that the 12s has. Carter #P4070
 Noting worse that breaking down on the road.
The gas cap emission test here in Washington says NO vented caps,as the fuel vapor is to be recovered in a vapor canister and then burnt by the engine.I am not sure but I don't believe that we can buy a vented cap here in Washington. I have not tried in many years as even most of the older cars and trucks had a vent line. My 1976 Dodge does, so I would think that your Airstream would also. But my MH was California emissions. My gas cap is not vented.
Any way let me know if I can help. I would change the pump and also install a return line if it were mins.
Take care Jeff.

[jeff york]

Jack, My Mr. Gasket is a 12 S. Tonight, my sons and I took the RV on pretty much the same route to drive it back to storage in my hanger at the airport. I started it. let it warm up for about 5 minutes, drove about a mile to pick up my other son, let it sit for about 10 minutes waiting on my son and then drove it the 20 miles back to the airport. Had several stop lights and stop signs on the way to the interstate, Then a beautiful drive along the winding Newtown Pike passing Thoroughbred horse farms all along the route. It was a driving leason for my son who wants to get practice driving the Airstream. He wants to take his friends camping in it so he wants time behind the wheel with me there in the co pilots seat. Not a hitch or issue. However, this was not a accurate test. Difference in precious tests, didnt fill up with gas and just before leaving, I installed a new emissions vented gas cap.  

[Jim Stoltz]

I'm not buying the vapor lock theory,,,,yet. I know they're prone to it, but the big question is: did this problem exist BEFORE the electric pump was installed? If not, the vapor lock theory doesn't hold up. Although sitting, idling and heat soaking for 15-20 minutes does point to heat build up BUT, GM installed the electric pumps to eliminate the vapor lock. If that pusher pump is maintaining constant pressure it shouldn't vapor lock. 

Disclaimer: My engineering degree is the wireless networking type.

[Jack Wasmuth]

Jeff is your fuel pump a Mr Gasket 12S?

[Jack Wasmuth]

Like I mentioned before a fuel filter with the return line coming from it back to the tank will also help a lot.

[Jack Wasmuth]

Because you have headers and an enclosed engine compartment and heat rises, we tend to build heat around the carb when stopped. The engine cover is insulated so we have a lot of heat trapped around the carb and and cleaner. I too had this problem with my class c with a rebuild 360 and headers. If you are still running the metal fuel line that came up the from of the engine from the mechanical pump, I would run the line up over the transmission and by the distributor over top of the vale cover being careful that the fuel line does not lay on any thing that gets hot like the valve covers or intake. A fuel line in the front of the engine gets heat from the radiator as the fan sucks the heat from the radiator.
 Another idea is to install a 12 volt fan that can blow across the carb. Also I don't like stock air cleaners. I have a 6" tall open side air cleaner. While on my race cars We always picked up air from the bottom of the windshield so that the engine gets cool air. Cool air equals more hp.
 I think that just rerouting the fuel line to come up over the transmission will reduce a lot of heat.

[jeff york]

Jack, are there ways, devices or coverings that I can out on the fuel lines to separate it from the heat ? I am concerned about adding anything on top of the engine and not being able to close the engine cover, its close. Funny you mention the alcohol. I didn't think we had it in our gas in Kentucky. yesterday, I noticed we do. ideas on pressure relief valves ????

No need to worry about pissing matches. I dont do them. Just trying to qualify I know a bit from engineering but, I count on resources like this.

[Jack Wasmuth]

One of two things is happening when you idle: 1) the carb is getting heat saturation and the fuel is boiling and the alcohol is turning to a vapor, thus loading up. Alcohol boils at 102 degrees, thus when you take off the engines stumbles. 2) the fuel lines are to close to heat and when the float stops the fuel from entering it backs up and heat on the fuel lines forms bubbles thus causing a stumble upon take of. If you baby it it usually will settle down.
 I too have a long and learned knowledge of fuel delivery as I have dealt with carburetors both on and off the race track. I have far too many trophy's to count after 40+ years of rebuilding carburetors for everything from Mom and Pops to NASCAR 850 hp engines.Your 496 is a strong runner but it is far from needing anything exotic as far as a fuel delivery system is concerned. I do not want to get into a pissing match but I always had a saying KISS . If you remove the heat from the carb. you will cure your problem. You carb needs a thick gasket between the manifold and the carb and you need a return line as ALL electric fuel pump delivery systems require the excess fuel to be returned to the tank UNLESS you have a very high dollar pressure relief high flow pump which I do not believe that you have and the system does not require one.
Any way I hope you can fix your problem.

[jeff york]

Jack, yes I understand pressure and volume. I have three engineering degrees including aviation engineering. I built my racing plane, 2 time national champion and its engine, its fuel systems and have no return lines on it. But, I have a vent line that sits in the air stream. I also rebuilt, bored stroke balanced and blueprinted my 454 to a 496 in the Airstream. feel free to turn up the volume on the replies. I appreciate them and can handle them . But, building a high torque thoroughbred motor motor makes me wonder if its bred may be a bit much for sitting idling for long periods of time. It acts like it loads up if I let it sit running as if the low idle is simply to low for an engine built this way. It does get incredible fuel MPG at 12 for a big rig. I am going to put on TBI fuel injection but want to iron this out first.

I know, my dad this weekend said I am putting way to much money in this thing. But, its stunning and actually can run with the cars on the interstate. LOL.