Vexing starting problem?.....

Nickathome · Post by **Nickathome** » Sun Jun 15, 2008 1:08 pm

Scenario;

Truck starts cold, runs fine. I go to the gas station(6 miles away) get gas, no big deal, engine starts again no problem. I then drive to the local pool (about 6 miles the other way) to let my kids see the truck out and about. I stop to talk to them for a while. Upon gettin gback into the truck to restart, it cranks and acts like its struggling a little, but would not start. I checked fuel filter, I see no fuel. I turn on the electric pump(which I have kept in line even though I run a mechanical) for a few seconds to pump some fuel into filter and carb. Crank engine again, nothing. Wait a few minutes, then remember the trick I tried last time with some starter fluid, so I remove air filter and spray a doze of ether (I know not good for carb etc) into carb throat. I get in and truck starts right up, and I drive home without another incident. What is going on here? Am I getting vapor lock? Why does it run fine and will stay running but not want to restart? Any info appreciated.

Carter · Post by **Carter** » Mon Jun 16, 2008 5:00 am

Nick, I don't have an answer to your problem, however, yrs. ago one of my runner Ms would develope the same trouble after a warm shutdown and turning the gas off at the shutoff next to the fuel pump worked. I'd crank it 'till it fired and ran ok then make a mad dash to open the shutoff while it ran on the gas in the carb. bowl. I'm not saying it was flooded but shutting the gas off worked for that trucks engine. FWIW, Carter

MSeriesRebuild · Post by **MSeriesRebuild** » Mon Jun 16, 2008 6:14 pm

Sounds like vapor lock is the deal. Typically the way it works is as long as you are moving faster than crawl speed there is enough cool air reaching the engine compartment to hold it at bay. Once you stop, so does fresh air. The engine is hot & that temp surges for a while after shut down with no air circulation The cure is simply figuring out how to keep the heat away from the small fuel lines. It doesn't take much to vaporize gas in small amounts such as in the 5/16" fuel line.

Nickathome · Post by **Nickathome** » Tue Jun 17, 2008 2:20 am

Charles;

I do think I am getting vapor lock. I am trying to figure out a way to install a heat shield around my fuel pump. My engine has the fuel pump placed aft, real close to the downtube of the exhaust. I wrapped the tube with that asbestos type stuff thinking that would help to keep it cool. but it doesn't seem to help much. I have an idea for a shield that I think will work, plus I was thinking of buying some of that fuel line heat shroud that I saw on the summit racing website.

knattrass · Post by **knattrass** » Tue Jun 17, 2008 3:10 am

That air gap is key to cooling and any light gauge metal would work. The fuel line jackets perform the same function with the outer coating acting as deflecting the radiant heat. Wrapping the manifold is probably marginal since they are primarily done to prevent the wild expansion/contraction of the metal under exhaust loads and flatten out the temp curve to avoid cracks.

Nickathome · Post by **Nickathome** » Tue Jun 17, 2008 5:08 am

A guy here at work told me that even wrapping aluminum foil around the fuel lines will also work. I don't know if I want to go to that low tech of an approach just yet though.

Drew M. · Post by **Drew M.** » Tue Jun 17, 2008 7:12 am

Nick,

Take the mechanical pump out of the picture. Run the electric pump (located near tank) to regulator if pump is over ~5psi to the fuel filter and then the carb. The mech f/p is redundant - and if if fails, the elect pump will fill your engine w/ gas. The mech f/p is hot from being bolted to the engine and close to the exhaust and ratiates heats into the gas in and near it contributing to the vapor lock problem.

I used to have vapor lock problems. Now, I run the elect at the tank and bypass the mechanical f/p. The truck starts much easie (1-2 seconds of cranking).
-Drew M.

knattrass · Post by **knattrass** » Wed Jun 18, 2008 3:39 am

If you're changing over to electric - don't forget the safety interlock of having a oil pressure sensor installed in the circuit to ensure that when the engine quits, the fuel is automatically shut off! Charles also recommended a neat idea to install a momentary push button into the circuit that allows an electric priming function.

Nickathome · Post by **Nickathome** » Wed Jun 18, 2008 5:30 am

I actually went the other way. My truck was purchased with an electric pump already installed. It seemed to be dumping excess fuel into the carb and over powering the float even after I rebuilt the carb and readjusted everything. I installed a cheap pressure regulator but I still seemed to be getting fuel overflow into the intake manifold. So I installed a mechanical and that went away, but just kept the electric in the line as a backup. I guess the reason the person who owned the truck before me was having vapor lock problems hence the installation of the electric pump. The mechanical works fine otherwise and I'd like to keep it, so I am figuring out ways to shield the pump and lines from the exhaust heat. I'm not ready to give up on that yet. I will be ordering some fuel line heat shrouds from Summit racing tonight, and am planning on making an aluminum shield for the fuel pump this weekend. To me its worth spending $20.00-$25.00 to learn something. And if it doesn't work out, then I'm not out all that much.....I think it will work though.

Vexing starting problem?.....

Vexing starting problem?.....

Vapor lock

Wrapping..

Why run the mechanical pump?

Not changing to electric....