Chuck84TA

Noticed when temps were high last summer that I noticed moderate hesitation at 3000-4000 RPM during WOT operations.

Stock L69 and q-jet...


Looked at the vapor lock bulletin sticky and it mentioned something about a electric pump at the tank..(I don't think my car participated in that recall, unfortunately).

What if I installed a high perf mechanical pump replacing the OEM style pump?

To combat the vapor lock issue,it would make sense to me to have more fuel pressure and flow to minimize vapor lock.

Does this make sense?

bestracing

You don't want too much pressure because you can overcome the float/needle seat and over fill the fuel bowl which will flood the motor.

First thing is check your fuel pressure. Maybe your stock pump is starting to die and is not delivering enough fuel in the first place.

Check the fuel lines and see if the heater hoses, or exhaust is coming too close to the fuel line or is sitting on the fuel lines. Header installations can be a cause of vapor lock where they are heating the fuel up before it ever gets to the carb.

naf

iTrader: (7)

Vapor lock occurs when fuel in the lines BEFORE the pump vaporizes. More pump won't help.

A more likely issue is fuel boiling in the carb due to heat it picks up and the drop in pressure.

L69s should have the in-tank pump in addition to the mechanical. Check for the fuel pump relay near the booster and you can verify it's working by jumping the terminals.

The in-tank prevents vapor lock by pushing fuel vs. the 'pulling' action of the mechanical. Fuel flowing through the return line helps prevent fuel boiling by keeping it cooler...

I had never experienced either condition in 6 years and +100K miles on my 85 until this past Summer, but close inspection of my fuel pump showed that the lever fulcrum was loose in the body and likely reduced it's efficiency. I'll have to wait until warmer weather to be entirely confident that my new pump solved the issue.

You can also install a phenolic spacer between the pump and the block that should reduce heat transfer. I've also had to insulate the fuel lines on my '87 due to the heat transfer off of the adjacent hedders.