Vapor Lock Again On Mothers Day Cruise

Well it’s back I just don’t understand it. It was not really hot today in mid 80’s. We went for a long 35 mile drive with most of it along a paved river road at 20-30 mph. Some highway initially at 45 mph and temp was fine, just a tad above normal, which is normal when staying at 45 mph for extended time. But then in the river road just cruising the sights and temp goes right back to normal. After that got back to 40-45 for about a mile and loss of power and dies. Starts up but no power. Then won’t start. Fuel visible as normal in clear filter and in the fuel pump glass bowl. Been here before so we sit on side of road about 10-15 with hood up and wife not happy. She says call tow truck but then it starts and we head home.

I made this exact drive a week ago with grand boys, same temperature and no issue. I do not have electric pump but considering one now. The only thing I can think of different is I always run ethanol free gas in Willie, but I noticed the fuel gauge below half so I stopped and topped it off with pump gas just in case. Only took 3.5 gals so now I know gauge needs some calibration. But would that small percentage of ethanol gas have anything to do with it?

 

F-heads are not known for actual vapor locking in my experience. Possibly (?) it could happen if there was an aggravating condition such as a clogged filter or a suction leak? Fuel cap venting okay?

Once I was having weird power problems that resolved when I replaced the old float valve needle in my carb. I think the rubber tip was getting sticky.

 

I fought with a terrible vapor lock problem, electric pump, no return. I installed a regulator and pressure gage. Engine would go lean, pressure to zero and die when crawling due to vapor lock. I'd up the pressure on regulator and it would run then go rich at highway speed so I'd dial the regulator back. Chased my tail with this.

What worked for me is mechanical pump only with a return. Steel line from tank to pump and fuel filter after the pump. It now has been running perfect for a couple years highway and crawling. Stays perfectly at 3-4 psi and it's ejected carbon that was built up from running too rich from electric fuel pump. Heads are probably way cleaner now.

 

I'm thinking the same as Pete's post. You should plumb in a fuel pressure gauge between the carb and the filter so you can tell what is actually happening. My guess is there is some partial obstruction on the line from the pump to the tank, probably the pickup in the tank. When it's warm, that is just enough negative pressure to produce the vapor lock.

 

A step further,
If your tank has a return, you could install an I6 regulated filter and have your return.

You also get a steady regulated 6 or so PSI.

 

F-heads with YF carbs and mechanical pumps are set up for about 2.5 psi.

 

I was under the (perhaps erroneous) impression all Jeep three nipple filters had a restrictor in them. I've been through a number of newer Jeeps and have never noticed any orifices or restrictions downstream of the fuel filter on the return line or tank.
That being said, I'll rescind my earlier general comment on the filter being generically restricted.
Ya learn something new every day...........................

 

I have cut open these filters used on '70s Jeeps and they have always contained an orifice on the return line.
I also have not seen a Jeep fuel tank with fuel return and an orifice in the tank.
Fuel return is always seen as dumped into the fuel tank, with no restriction.
The TSM does not refer to an orifice, but it does imply some limiting of return - a "small amount of fuel."
In some cases the parts book shows a check valve in the return line, but no restriction as such.
Skeptical of the claims of a wide open return cited in the above video.

 

The orifice or restriction needs to be at the filter end of the line not the tank or it won't let the gasses escape the pressure line rapidly.

Once vapor hits the orifice it can pass a lot faster than liquid.

 

Possibly spark related? Coil or condenser getting hot and loosing spark.

 

First, a ‘58 does not have a return line, tank pickup line is clear and fan is not slipping. If it was spark related, it would be very regular. I’m going to go thru the gas in the tank close to home then fill with ethanol free like I normally do. I’m truly thinking that is related but time will tell.

 

I drilled and tapped my sender cover. No restrictor added.

http://www.earlycj5.com/xf_cj5/index.php?threads/155775/

 

I have been forced to use 10% ethanol fuels in my F-head for at least a decade, and understand your concern. They are a huge pain, mostly due to corrosion issues.

But a minor fraction of a tankfull, at only 10%, used one time, seems to me very unlikely to have such a dramatic effect.

 

I still think you need to at least temporarily install a fuel pressure gauge. That will for sure go a long ways towards isolating the problem. Get one of these:
https://www.summitracing.com/parts/sum-800135