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View Full Version : VAPOR LOCK - 76 MIDGET



Alvin
03-16-2010, 09:51 PM
I think I have classic "vapor lock". My 76 1500 (recently rebuilt) starts right up on cold starts all the time. But if I drive it for 10 - 15 minutes and then try to start it again after it sits for 5 - 10 minutes it is a problem. I checked and I have good spark, but no gas. If I squirt a small amount of gas in the carb it starts up but runs rough for 20 sec or so but is then OK. I have an electric fan on the front of the radiator that kicks on at 170 degrees. The mechanical fuel pump is new. If the car is run and then sits for 20 minutes or so it starts up fine. I live in Miami, FL but it is not hot yet here. Do I insulate the fuel line leading from the steel line on the frame to the fuel pump or what? What should I use to insulate it? Thanks .......AL

Billm
03-16-2010, 10:43 PM
Does your fuel line from the tank to the pump run as original from the factory or is it possibly rerouted so that the exhaust heats the fuel too much? That line (from the tank to the pump) is where I would concentrate my investigation first.
BillM

Sarastro
03-16-2010, 10:55 PM
Here (https://www.nonlintec.com/sprite/fuel/) is the story of my problems with vapor lock--or perhaps a similar problem--and what fixed it. I've found that fuel doesn't move well through the modern paper fuel filters that are often added to our cars. A vapor bubble forms, and it's difficult to force fuel through it at the pressures we use. Part of the problem may be modern fuel--unleaded fuel uses more volatile substances to provide anti-knock capability than the stuff in the 60s and 70s.

I remember that my old TR4A from the 60s had a sediment bowl instead of a filter. So, maybe the problem with filters existed then, too.

sparkydave
03-17-2010, 07:52 AM
Hi Alvin, I have a '77 and I had some vapor locking, though not quite the way you desribe. Mine would usually stall on the road, but it got to where I couldn't drive it more than 15-20 minutes. My fuel pump was getting hot enough that I could take the cover off the pump and hear fuel boiling inside it. I ended up putting a Facet pump at the tank, and bypassed the mechanical pump completely.

JPSmit
03-17-2010, 09:49 AM
I switched to an SU - and have had no problems. The only other thing I did do was route the fuel line behind the heater box to get to the carb.

bigjones
03-17-2010, 09:59 AM
Alvin,

Do you have the heat shield in place?

The original heat shield is NLA so I made one from some aluminum flashing material and screwed it to the fender under the carb. Doesn't look pretty but it solved the vapor lock on my Midget.

Cheers

Alvin
03-17-2010, 03:28 PM
Thanks for all your input. I have the original fuel line and the original metal tube that goes over the trans and then into the fuel pump. I do not have the heat shield. If someone could Email me a pic of where it goes and what it looks like I could fabricate one. As you can see from the attached pic, I do have the paper filter that Steve mentioned that could be a problem. I will remove it tomorrow and see if it makes a difference. I have the fuel line from the fuel pump to the carb away from the engine to reduce heat, but possibly it is still getting too hot. Is the vapor lock issue created before the fuel pump or after it?? Thanks ........AL

Guest
03-17-2010, 03:50 PM
You have the stock carb, SU or Weber?

Guest
03-17-2010, 03:54 PM
I've never had problems fuel or vapor going through a paper filters. I have a huge "bubble" in mine. The only problem I had with them is exposing the fuel to more engine heat than a rubber line and vapor locking. I use an extra bit of radiator hose that was trimmed off as a cover to insulate my filter and no more problems. I slpit it down the side and wrap it around the filter.

Alvin
03-17-2010, 04:19 PM
I have the original ZS carb. Sorry, but can't attach my pic. I guess the file is too big ....AL

JPSmit
03-17-2010, 07:03 PM
Alvin, the pics need to be less than 100 kb in size - I can adjust the size of mine with microsoft office picture manager - or just about any other picture software. I'd love to see it too, so, if you can't email it to me at johnpetersmit"at"yahoo.com and I'll resize and post. Oh, and if you do it, don't save the smaller picture over the larger unless you mean to - don't ask me how I know.

bigjones
03-17-2010, 07:33 PM
Alvin,
As far as the heat shield, I would recommend viewing Moss Motors and Victoria British sites online for their parts catalogs.
The diagrams are very useful, even if some of the parts are NLA.
Cheers

JPSmit
03-18-2010, 08:52 AM
Here are Al's pictures - FWIW my fuel filter was next to the pump not the carb.

JPSmit
03-18-2010, 08:52 AM
and

Alvin
03-18-2010, 10:59 PM
I removed my fuel filter that was before the carb and all was well today. I drove it all around with many stops in between that would normally cause a problem, but no problem today with the fuel filter off. I will keep it off and see what happens. Thanks for the tip Steve ........AL