Vapor Lock or ???

[truckster]

I have a 72 Blazer with a 5.7 L31 Vortec, Performer intake, Quadrajet, rams horn exhaust, and mechanical fuel pump. Occasionally it will die on me (especially on left-hand turns, it seems) and I can tell it's fuel starvation. It only happens when the underhood temps get high, but it can happen when the engine temp is moderate. I thought it might be vapor locking in the fuel pump, so I installed a fuel pump with a return line (to keep cool fuel flowing through). Now I suspect it could be fuel boiling in the carb. Do I need a phenolic spacer, and which one should I get?

[memo43]

I had something similar happen to me on my k5.
For me it was the distributor rotor, the rubber bushing was so worn out that when I would make turns left or right it would stall.
I went as far as replacing the fuel pump and even adding an electric pump just to try and cure my issue.
Check out the distributor and make sure nothing internal is worn out or burnt up.

[jeffahart]

I had this happening to me also, swore it was the carb. I'm a pretty big q-jet fan so I didn't give up and yank the card. And, I swore it happened when the secondaries were opening.. just like you feel it's when hot or making a left. What it was... distributor power wire. The wire had worn from the throttle linkage rubbing. At just the right amount of throttle the metal linkage would touch the bare wire and stutter due to disruption in spark. How I found it. I got fed up and started smacking wires around in the engine bay with a wood doweling, and it happened... the stutter. The wear on the wire was so slight and in an obscure location I could never see it on a visual inspection. But the wire smacking lead me to the general area. Still not sure what made me do the wire smacking with that dowel, but it ferreted out the problem, and did cause me to smarten up on my wire routing.
Good luck!
j

[jeffahart]

Oh, I forget a really important point. When evaluating the problem, I always took the air cleaner off. The distributor wire was in a different position with air cleaner off. Which was the whole problem. Air cleaner was pushing the distributor wire into a location closer to the throttle linkage when installed.
Good luck.
j

[The Rocknrod]

Interesting, I would have never thought about the distributor. I was thinking there might be something floating around in the fuel tank.

[AcampoDave]

Living in a hot climate, I'm a fan of phenolic spacers. I have 1 inch 4 hole black plastic Summit branded one and my engine starts easier when hot, and throttle response of idle is improved too. I never had vapor lock but my fuel would boil in my carb and flood my engine after a hot shutdown.

[truckster]

I ordered the 1" spacer from Summit and installed it this morning. I went out and ran it as hard as I could for a while with the A/C on the whole time. There was no stumbling and no stalling. I think that solved it.

The distributor suggestion was a good one; I've had that happen before. I replaced the distributor when I installed the engine (6k miles ago) so I didn't think that would be the problem. You never now, though...

[The Rocknrod]

Good to hear and thanks for the follow up.
Now that I think of it I had a 56 big window with a 502 in it and had to do the same thing.

[AcampoDave]

That's great that the Summit spacer worked. Those things are a bargain. Glad you could get o e for a Quadrajet.

[tdangle]

any thoughts on if a 1" works better than a thinner spacer for isolating the heat. I had the same issue and pretty much solved it with a 1/4" spacer. Wondering if more is better

[truckster]

Mine had a 1/4" composite (cardboard) spacer and was having problems. The 1" phenolic spacer seemed to do the trick. It makes sense - more insulation means less heat transfer.

[AcampoDave]

I started using a 4 hole spacer after I read this tech article http://garage.grumpysperformance.com...fication.1038/ and later started this thread http://67-72chevytrucks.com/vboard/s...d.php?t=747364 I've since swapped the one in the thread for the Summit plastic one and find it to be better phenolically (hey, is that even a word?).

[truckster]

It makes sense. I rarely open the throttle all the way, so low- and mid-range torque is more important to me.

[burnin oil]

I have played with them all and the wood ones are the best. Phenolic tend to warp and have vacuum leaks. Aluminum just raises the carb up. I have also stacked them. Even tried 4 hole into an open adapter. This works also for a higher HP build.