Boiling gas??

upnover

upnover

Grumpy, decrepit Old Man
Moderator
Joined
Mar 20, 2005
Location
Morganton NC
Here's the scenario:

Driving back from Tn Sunday in the Hillbilly Hilton(RV for those who do not know about it) I am towing my Jeep and trailer. In the past I have kept the engine down to the 3K RPM mark, this day I bumped it up a bit, and found that my power curve was great at 3.5K range. It was driving great and seemed to really come alive. This was the hottest day I have ever drove the Hilton, but my engine temp stayed in an area I was comfortable with. I first noticed it bubbling after I filled up with gas. I used 93 octane, but the sign on the pump did say it "could" contain as much as 10% ethanol. When I was in a hard pull it would bubble. I could feather the pedal and it would mostly clear up. From there, it got worse. The last hard pull coming out of Asheville up to the top of Old Fort Mountain, it all but fell on it's face.
Once at the top, I pulled over and let it run for 20 mins or so, then cut it off. I had been flagged down by an old friend and was just sitting up there chit chatting.
After I cranked back up, headed down the mountain in second gear, using the brakes intermittently to maintain a safe speed, the engine cooled down to the cold start area. Once underway on the flats, it warmed back up to normal. I again stayed in the throttle all the way back home. Never another issue.
My thinking is that I was having vapor locking or gas boiling issue. Somewhere in the past I saw an older engine like I have, and there was a shield that was between the carb and the intake. I assumed it was to shield the carb from the engine temps. I haven't had the chance yet, but thought I might ought to check out the fuel line route and make sure it isn't too close to the exhaust manifold or engine block it's self.

Any other thoughts? Please give me ideas.

1973 Dodge RV with a 440, 727 tranny, and 4.56 gears
 
Bubbling in the gas tank? Or from the carb.

I'm sure you meant carb or it would just be an exhaust issue? Aluminum Intakes do a good job along with carb spacers in dissipating some heat. Carb spacers add to bottom end anyways where you need it for the Hilton. The "air gap" intakes look promising? I'm a big fan in venting the engine bay though. Heat is the killer of everything. As heat rises in the engine bay, usually it has nowhere to go. I like vents towards the rear hood area while putting a scoop at the front bottom. You can place a thermometer or temperature gage for just the engine bay to compare? A before-after comparison is always good to see if an idea works?
Just like anything, trial and error. But having a record of some kind for comparison is golden.
 
I burned a chainsaw up with enhanol gas. I mix everything on the heavy side now.
 
very common issue with 4bbl small and big block mopars alike due to the fuel line routing from the pump to the carb. it can usually be remedied just by shielding the line or moving it away from heat sources an inch or two.

however, there is also an inherent flaw in the carb/intake design, and many of them will actually boil the fuel in the bowl of the carb. the choking down/leaning out/detuning with emissions regulations in the 70's/early 80's just magnified the issue. doesn't usually show any problem under normal cruising, but it cripples the functioning of the accelerator pump and secondaries when you get into it. it makes them temperamental on hot starts too.

anyway, if fiddling with the fuel lines doesn't work, switch out to a lower temp thermostat. it's probably got a 195 in it, try a 180. a 160 is an option also, but you'd probably find yourself having to swap it back out in the winter to get decent heat.

if that still doesn't work, you're last resort and ultimate "sure" fix is a decent aftermarket aluminum intake/carb.
 
Thanks Ivan, that's the type of info I was needing. I am looking at some fuel line insulation. Also looking at a spacer of some type. I have found polymer, and aluminum types. Have also considered making one out of aluminum. Something like 3/8" thick and a good bit bigger than the base to add some side insulation from the intake as well.
Whatcha think?
 
Just get a phenolic spacer. If you go to a decent parts store they will have on in stock. A lot of vehicles came with them stock. Just take your old gasket so they have something to match it up to.

You might also want to check and see if there is another fuel filter under the hilton somewhere. My friend just had the same problem with the 440 in his challenger. After checking the pump, and lines and everything else he could think of.... it turned out to be a clogged filter back at the gas tank.
 
Yes definitely use the phenolic (plastic) spacer. Either buy some fuel line heat wrap (summit or jegs) or you can use alum. duct tape. And make some tin/alum. shields anywhere near the manifolds. As far as the manifold... I'd get an alum. if you can find one used.

Also check where the supply line is routed, sometimes they are too close to the exhaust and pickup heat there.

Performance - IMHO your just coming into peek hp at ~3500-4k granted it probably doesn't have a whole lot more above that without a different cam and/or intake, but it will run like that WOT all day long and be happy. Just keep good oil in the engine to combat the sustained heat.
 
Chip,
I've recanted this numerous times, but can't find it on this site. Anyways, (very long story short) my folks had a motorhome with your combo (440/727) and along with numerous friends w/ the same setup... spent lots of time roadside fighting vapor lock. It was a given that at least 1 would have fuel issues on every trip!

The only common between them was the engine. After years of troubleshooting by numerous dealers (even the late '70s factory wrench team, the "Dodge Boys"), wholesale part replacement of the entire fuel system, and many other mods like fans/insulation/heat shields... they couldn't stop it from happening.

On one trip (to VA IIRC), the usual suspects pulled over to let it cool down. An old toofless hillbilly came by and asked if they needed help. The men filed over to explain the problem/history to this guy. He said he was familiar with it and asked for clothespins (of course, everyone HAD them)... he added about 50+ WOODEN clothespins around the fuel lines (supply & return) feeding the carb on that particular engine. After a few minutes, it fired up and proceeded to run fine for the remainder of the trip & the return home. Clothespins were added to each rig that died along the way until ALL of them were "modified". To the best of my knowledge (actually confirmed w/ my Dad a few years back), there was never another case of vapor lock in the bunch and trips became "uneventful". They were still installed when most of them were sold! :lol:

A bag of clothespins from DollarGeneral won't set you back much and should take care of the problem.
 
Dave, believe it or not, I have heard of that myself. The only explanation I could think of was that it helped to dissipate the heat kinda like the fins on some smaller type coolers.
My issue has shown it's self a time or two, but never to this extent. As I said, it was the hottest day outside that I had driven it.
With a trip coming up to Harlan, I want to rid myself of the issue. I am adding the spacer and the insulation to the line, but may stop by and get a bag of clothespins as well!
 
Gee Mike, thanks for stopping to help! LOL, J/K
Yeah I was there for a while just jawing with a friend I hadn't seen in a long time.

OH and for the record, and many people make the mistake, It's Old Fort Mnt, not Black Mnt. It's actually almost entirely in McDowell County
 
upnover said:
Gee Mike, thanks for stopping to help! LOL, J/K
Yeah I was there for a while just jawing with a friend I hadn't seen in a long time.
OH and for the record, and many people make the mistake, It's Old Fort Mnt, not Black Mnt. It's actually almost entirely in McDowell County
Click to expand...

Looked like you guys had it under control

Plus you don't want to have to entertain my 3 and 5 year sons while I helped out, Oh course we were in the wifes van, not much for tools in there.
 
x2 in the closepin's iv seen that done..work's like a heat sink, well kinda lol..cheaper and a one off look haha
 
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