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Hello All,

1983 FSB. 4.9l Six, NP435 tranny, MC2100 (2bbl) carburetor. Stock fuel delivery (mechanical pump).

I had some vapor lock last weekend that I'd like to sort out. In my mind I was being pretty hard on the truck. I may be expecting a lot.

I had my truck up to Big Bear, Ca last weekend for Forest Fest a yearly run through the San Bernardino Mountains. Temps were in the 90's and at an altitude of about 6000'. My truck lives at sea-level. I was running the AC, I do have two 12" auxiliary electric fans. Coolant temps were in the middle of the gauge (normal to a little high) on my factory temp gauge.

I had the truck in 4-low, 1st gear and had been idling around for a couple hours when it quit on me. Took me a minute to sort it out. I have an additional in-line fuel filter with a sight glass on it on the suction side of the pump and there was little to no fuel in the filter there. I cracked the fuel line at the carb and no fuel there either. I let the truck cool off with the hood open, cranked it till I got fuel up to the carb and went on my way. I left the AC off and the auxiliary fans on for the rest of the day and did not have a problem for the rest of the run.

A few things I'm thinking of doing....

1) Add an insulator spacer for the swapped carb. Ford had them from the factory for the 2bbl. I went ahead and ordered one for ~$15. Its easy and cheap and I don't see any negatives. It should have probably been there in the first place.

2) Insulate the fuel line. I can insulate the fuel line running from the pump to the carb going over the valve cover. The line from the tank to the pump seems like it shouldn't need it. On my six there is no header or anything really hot on the suction side of pump in the engine bay.

3) Add some hood vents. I'm not trying to really reduce coolant temps but this should let some of the radiant heat leave through the top of the hood and cool the engine bay down a little. I'm probably going to try options 1) and 2) before I cut up my hood.

4) Swap to an electric fuel pump. I already have an Airtex pump that is new that I keep as a spare in my parts box when I'm on trips. I think this is the real answer but other than this issue my mechanical pump has been very reliable.

Comments/Suggestions?

Thanks,
Dan
 

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I had to change to an electric fuel pump on my Jeep, never had any vapor lock issues again. This would be my first step.
 

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Yes, an electric fuel pump makes a big difference simply based on how it works. An electric pump pushes the fuel whereas a mechanical pulls. Pushing is a much easier process than pulling.

If the fuel up near the engine where it's hotter turns to vapor, the electric will still move it to the carb because it's pushing with liquid gas back at the tank. The mechanical one, on the other hand, is now pulling on vapor, which doesn't create the vacuum needed to pull fuel from the tank.

I've dealt with this issue a number of times, and it's always at the worst time. I can go for months without an issue, but as soon as it's 90+ degrees out and I'm climbing some twisty, winding, steep road in the middle of nowhere, sputter... sputter... stall. No gas in the fuel line all the way back to the tank.

I've tried lots of remedies, and none really fix the issue (only help a little), so it's time to switch to an electric fuel pump myself.
 
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