Vapor lock???

[yellow8882]

Sent: 6/28/2007 3:38 PM

Hi everyone, We just took our 77 Minnie Winnie "Turtle" on her first real voyage. Huntington Beach Ca. all the way across the Mojave desert to Williams Az. (Grand Canyon). She ran Beautiful until the last 15 miles and konked out 5 miles from town (7500 ft elevation). Had her towed in because I destroyed the rubber fuel line trying to "McGyver" a bypass of the fuel filter and didn't figure it out.

Anyway, after a nice four day visit we got a late start home and had to drive through the desert in 110 weather. Once the engine completely heated up (much higher than normal but still in the safe zone) the engine began to sputter on up hill grades and eventually much more often.   If I completely took my foot off the the accelerator for a couple seconds and then pushed it back to where it was, it would smooth out for a few seconds and then sputter again. I was able to maintain a steady uphill speed of 40-45 mph that way for about 4 hrs. I stopped at a town to fill and replaced the air filter and added higher octane fuel. It helped for a short while. Next fill I replaced the ignition modual. Didn't help long. At the last fill the air temp had cooled, I added higher octane gas, removed the fuel cap , let her cool for a while and didn't climb quite as much. One of these things did the trick!!!

So I guess I have two questions. Is this vapor lock?? and did any of these things help to fix it?

Thanks Everyone.

Chris

[RU70x7]

Sent: 6/28/2007 3:59 PM

One way to fix vapor lock is to buy real cold gas.  Well that works for a few miles anyway.  I have put clothes pins or tinfoil on the fuel line to dissapate the heat from the gas line.  I had a simular problem with a 1979 Brave.  I could only trave about 35 or 40 miles an hour.  I discovered my fuel tank switching valve had a small chunk of rubber it from the fuel line.  It wouldn't switch completely to one tank or the other and wasn't getting enough fuel to run the speed up.  I put a new valve on and everything ran smoothly.  With the heat you described it is likely your gas was vaporizing before it got to the carb.  Sometimes a new feul pump and help prevent vapor lock.  Perhaps an electric fuel pump would do the trink.
Bob

[Slantsixness]

Sent: 6/28/2007 5:34 PM

From whart you describe, it probably is not vapor lock.

Fuel filter clogged, rotted fuel lines to the pickup tube, bad fuel pump.
(if there are ANY cracks in the rubber fuel lines, or they are 20-30 years old, don't trust them, replace them!).

All of this matters if the original fuel supply including the mechanical pump, is still intact as supplied by Dodge (or GM if it's a Chevy chassis).

Also, I'll assume that you're confident that it isn't a carburator, or tune up / maintenance issue. (bad cap, rotor, wires, coil, a leaking carb, sludge in the carb will also produce these symptoms.)

Common mistakes:
Rubber fuel line all the way to the Carb, laying on the engine block.

Electric fuel pump or fuel selector solenoid mounted too close to the exhaust.

Dirt/ rust/ sludge / water in fuel tank.

Clogged Tank vent/ breather or Improper gas cap.

"Vapor locking", although common, is easily prevented, by keeping the steel fuel line and carb in the airflow of the radiator fan. (a common thing is to bring the fuel lines in from the rear of the engine. Well, that's where all the heat is, and virtually no airflow to keep it cool!) Especially in a class C or Van chassis.
With that in mind, Iv'e found that more than 90% of "Vapor Locking" vehicles do not actually turn out to be fuel perculation (vapor locking).

Rule of thumb: keep the fuel line at least a thumb's width away from the engine block at all times, and DO NOT put a fuel filter on top of the engine (it pretty much ends up like a coffee pot.... perculating al the time.)

You can put insulation (split a 3/8" rubber hose) around areas that come too close to the exhaust manifolds or block. In particular, this is a good idea behind the alternator (dodge chassis) for the line from the fuel pump.

The old "coil of fuel line in a coffee can full of ice trick works", but in 100+ degree weather, it doesn't work for very long, and isn't worth the effort.

Last but not least, please check your Fan clutch (you DO have one, right?? In general, clutchless Flex fans DO NOT WORK on motorhomes.) So it's possible that the engine is running too hot, and it might be ingition breakdown, rather than a fuel delivery issue. After all, you did say it made it to 45mph... if you were really vapor locking, unless it was straight downhill, I doubt you would have gotten the rig to maintain 45mph.

[ClydesdaleKevin]

Sent: 6/29/2007 8:40 AM

Tom has the right of it, so I don't have to repeat what he said...just make sure you check those things he told you to check.

We had vapor lock on the Ark, and it turned out to be the wrong gas caps...my old system called for vented gas caps, and the ones I bought in error were non-vented.

Also, you are quite LUCKY you mangled the rubber fuel line when trying to bypass the fuel filter.  NEVER bypass the fuel filter for any reason on an old RV, not unless you have just reconditioned your tanks and you are SURE there isn't a bunch of dirt and rust floating around in it!  We learned this the hard way:  We were driving on I-40 in Tennessee and the fuel filter got clogged from the rust being shaken up from the old fuel tank.  We were far from the nearest exit or Walmart, so I decided to bypass the fuel filter for a "short trip to Wallyworld."  The rust particles poured into the carburator, and we were dead on the side of the highway!  I tried to rebuild the carb roadside, at least clean it out, but the rust was so jammed into the ports I couldn't make it work, and I didn't have an air compressor with me.  I could see an Autozone from the the highway , so I unloading my bicycle, road down to the exit with cars honking at me, and went to Autozone.  They had 1 650 cfm Holly carb in stock, polished, and it cost me over 200 bucks.  It fixed the problem, but it was a LOT more expensive than a 3 dollar fuel filter...lol!

Kev

[yellow8882]

Sent: 6/30/2007 4:57 AM

WOW Guys, Thanks for such quick and thorough responces.
I am going through the fuel line now and just replaced cap rotor etc. because it has been running a bit rough since we've been home. While going over the motor yesterday I noticed a second fuel filter between the intake and the air filter so I will replace and get a couple extra to keep in "Turtle" just incase. (like I said I just got it and know almost nothing at this point) Also like the idea of putting an electric fuel pump on, so I'll be doing some home work.
Again thanks everyone and I am sure you will be hearing from me again.

Chris

[Wyoharris]

Sent: 6/30/2007 5:20 PM

For what its worth, a quart or so of diesel poured in gas tank first, then fill up with gas will delay vapor locking.  Not the best deal, but will get you home in the heat!

[Slantsixness]

Sent: 7/2/2007 9:13 AM

An electric fuel pump IS NOT A NECESSITY, nor is it desireable. It's just a waste of money and an annoying thumping or clatter under the coach. You will NEVER run out of fuel, fuel pressure or volume with a properly operating OEM mechanical fuel pump.

But if you do it anyway, buy an adjustable regulator for it.

Tom

[denisondc]

Sent: 7/2/2007 12:10 PM

I agree with Tom that an electric fuel pump is not necessary as a solution to fuel delivery problems with a dodge based Winnebago. A fuel system that is in decent condition will work without vapor lock in most places, and with rudimentary heat shielding, will work fine in places like Las Cruces NM in July, at 108° (thats the temperature in the shade, it was hotter on the pavement) nor at altitudes like Vail CO (8200 ft) when its 100° in the shade. I added aluminum heat shielding in places where the fuel lines were 'in sight of' the exhaust pipes and muffler. Not only did the vapor lock end, but the fuel line going into the pump & the auxilliary fuel tank was cool enough that I could keep my hand on it comfortably. (Before I added the heat shields, the tank and the fuel line would get hotter than a wrench left lying on the sun). My heat shields were lengths of scrap aluminum roofing from behind a gas station. Three pieces 4 ft by 8 inches did the job, suspended from steel utility wire.

I know that some folks have installed electric pumps, in order to allow priming the carburetor of an RV that has been sitting for weeks or months, and have the motor start right away - without prolonged cranking. I solve that by priming the float bowl of my Holley carburetor before starting - if its been sitting a long time. This also gives me the chance to observe the motor on first start-up. I do this with a fire extinguisher right next to me.

[yellow8882]

Sent: 7/6/2007 9:54 AM

Thanks Guys, I like the heat shield idea but the exhaust is routed real well almost down the center and splits left and right about half way down the coach and out. I think the only places that it may be a problem are where the exhaust and fuel lines cross. Probably wont do a fuel pump unless there is some reason at a later time.

However "TURTLE" has been running rougher since our trip. I checked the plugs, changed the roter and cap, and relplaced both fuel filters. It also has a gassy smelling exhaust. Don't know if it always ran like this and now I'm paranoid or what. but it definetly is running rougher. Thanks Again guys.
Chris

[Slantsixness]

Sent: 7/6/2007 11:17 AM

Your latest reply is starting to sound to me like your Carb Float or needle/seat is failing. Pickup a rebuild kit and new Float(s). Even a sticking needle and seat could cause excessive fuel and runing rich... which.... without enough air flow through the carburator, duplicates the vapor lock symptoms...
(I'm assuming This is a stock or the original carb?)

Tom

[yellow8882]

Sent: 7/6/2007 12:26 PM

I believe it is the original Carb but I really don't know. Rebuiling the carb sounds a bit scary!!! Are we talking a few parts and gaskets? or pulling every nut and screw out? Is it something that can wait a couple months? We use it heavily in the summer, back and forth to the beach (5 miles round trip max. 5 or 6 times a week) and no current plans for anything longer than an hour or two from home. I'd like to wait until Sept. or so if it is a big project. I think TURTLE is in good shape but that last trip was a bit tough on her! and I'm trying to work through everything to keep her in great running order.

Thanks for the help!
Chris

[DaveVA78Chieftain]

Sent: 7/6/2007 12:41 PM

A stock 77 miniwinnie is most likely a 440-3 with a Thermoquad carb.  You can rebuild it in a day.  Be careful though, they have a plastic base which can crack.  Also, there are a couple of o-rings in the base that can leak fuel resulting in rich running.  Rebuild kits are easily obtainable but you will have to dig deep for the floats.  Get the metal floats as the plastic ones start soaking up the gas in time resulting in improper float level.  Most people replace a Thermoquad with an Edlebrock. 


Use the search message feature for more info.

Dave

[yellow8882]

Sent: 7/6/2007 12:50 PM

Thanks. Actually its the Dodge 360 but I don't know what carb it is. Is this something that needs to be done right away? Is there danger is letting it go for a couple months?

[Slantsixness]

Sent: 7/7/2007 6:03 AM

The only real danger is a continuation of the flooding or "vapor locking" problem. If the carb is at fault, and it is flooding, it will be a noticeable fuel smell when you take the dogbox and the air cleaner off. The whole thing will reek of fuel. And the MPG will be really bad, like 5mpg... owww!

If the carb is flooding due to a sticking float, or a bad needle and seat, leaving it this way for too long could cause a fire. (well, it is gasoline, after all!)

(and I'm sayng this only if the carb is actually flooding or the root problem)

If it's a 360, you have two choices. the carb is either a 4 barrel carter thermoquad or very large looking two barrel holley. Either way, the rebuild is simply disassembly, cleaning and replacement of some small key components included in the kit. The float would have to be purchased separately. The float is about the only thing you have to adjust, but the rebuild kits come with cardboard gauges to do this. If you're the least bit handy with a screwdriver, you can rebuild the carb in a couple hours.The kits also come with fairly detailed instructions, although sometimes the exploded views of the carb are hard to read. If it's the first time you're trying this yourself, then document what you take out of where in the carb. there are a couple small ball bearings, clips and lever arms that need to be put back in the same places, or replaced with parts from the kit. Just make sure the same stuff goes back into the same holes and you'll be alright.

There are numbers on the carb, sometimes on a purple or blue metal tag under one screw in the carb body. write all these numbers down... like "7750-7"  "8955-1" or "6982353" (these are not your real part numbers, just similar to them). Sometimes there are a whole list of patent numbers on the carb...where it says "Pat. Pending" or "US Patents" ....ignore them, they won't do you any good at the parts counter.

If you have a parts manual for the Dodge chassis, the Carb part number should be listed there, and you will find the same number on your carb, or it's tag. (if it's original).

Either way, we'll be glad to help get you fixed up, so if you have any trouble identifying the carb, or getting it back together, and you know how to get a hold of us!

Tom