Vapor lock, hot fuel, etc questions???

[Dan Sherwood]

I recently made a few changes on my 69 camaro in search of better drivability and mpg.

I had been running a single elec fuel pump for the 406 and small dose of nos. Fuel supply had not been an issue, but the ungodly noise of the fuel pump made it unbearble to drive unless at the track.

I switched over to a manual pump for street driving and the elec pump to only operate with the nos. I also replaced the older holley 3310 750 vac sec carb with a brand new one (only available in shiny chrome finish).

Now I seem to be having an issue with vapor lock and heating up the fuel that was not present previously, and my dakota digital fuel pressure gauge starts blinking showing the fuel pressure dropping from 5 to 0.(of course it shows 3 lbs less than a manual gauge-another product that I'm irritated with).

Of course this makes the car undrivable in the summertime, and at 7000ft elevation, it has this issue when it's in the mid 80's.

We have also gone from a dual plane air gap intake to a victor junior.

Suggestions on solving this issue would be appreciated!

[Bigblue73]

I experienced the same issue with "heat soak" into the carb. Are you running a phenolic spacer under your carb to isolate it from the intake? I added one under mine and it helped.

[Dan Sherwood]

I am, thx!

[paul67]

How far is the fuel line from the headers now that your using the mech pump instead of elect

[Dan Sherwood]

I don't think the line is any closer to the headers than before, but I'll have to take a look when I pick it up next week. It's been in the shop trying to solve this and a few other problems for the last week now.

Where the fuel line comes in was originally going to a mech pump a few years ago, so I'm not sure it's any closer than it was, but it's worth a look. I'm more inclined to believe the victor junior intake vs the air gap, the chrome carb vs the older gold plated one, or the biggest culprit might very well be the mech pump vs the elec pump. Or a combnation of all 3 ????

[paul67]

It could be the pump as its now drawing fuel not pushing from the rear does the fuel come out the top or bottom of the tank.

[Dan Sherwood]

Top

[68Formula]

Well low fuel pressure can affect vapor lock and vapor lock can affect fuel pressure. Like was said before, need to look at the routing. If you changed a bunch of things at the same time it's hard to say what the culprit is. Just make sure your lines are away from heat sources as much as possible and if that doesn't cure it, try swapping back individual parts to see if it goes away.

Also, check your filters to make sure when you changed things over something didn't get dislodged and is now plugging one of them.I know the 600s (I think the 750s do also) have one in the primary bowl and you should have one in the line between your pump and carb

[Dan Sherwood]

I do , and I did. Thx!

[68Formula]

So what exactly was the final fix that worked?

[Dan Sherwood]

Well we changed all the filters, and the shop fabbed some funky looking plate under the carb for a heat break, and although not needing alot of work we adjusted any fuel lines that looked even close to a heat source.
I'm not sure which one was the answer, but it seems to have solved it. Now if I could just get the carb to work better.