Mark71

I've read a lot of threads on the board here about gas boiling in the carb, spacers to solve the problem and so forth. I used a Mr. Gasket spacer and that seems to have solved my problem - for the carb.

BUT - I still have a hot-start issue. I could hear fuel percolating somewhere in the engine bay and I put a stethoscope on the pump. It's boiling in there, alright. To confirm, I put a clear fuel filter between the pump and when the engine is cool (shortly after starting) the filter is completely full. After driving a while, at idle, the gas in the filter is bubbling like crazy. After stopping the engine, the fuel in the filter bubbles away completely. Restarting at that point is difficult... After sitting overnight, the filter is full again (!!!) and starting is super easy.

My pump is a mechanical pump with input and output only(no return line). Has anyone had a similar problem? Did the original pumps all have return lines?

Is there a decent solution, maybe a spacer or some sort of pump mounted ice cube tray (anyone still reading)?

Just for info, 71 SBO 350, newly rebuilt Q-Jet, A/C...

MDchanic

How hot does it get down there ?!?

I've personally never heard of fuel actually boiling inside the fuel pump, but vapor lock is an age-old problem in all cars, and you've described it pretty well.

No, not all '71s came with return lines, and yes, a return line would probably help, or at least reduce your problem.

A rear-mounted electric fuel pump might also do the trick.

So, I'd suggest either running a return line, and changing the fuel pump and the fuel sender unit (to one with the extra nipple), OR installing an electric fuel pump and seeing whether that helps.
Installing a fuel pump would probably be easier.

- Eric

Rickman48

I also have never heard of this symptom - but todays fuel has so much crap in it, wouldn't surprise me!
What temp is this thing running at?

Lady72nRob71

Lady (a 72) has this same issue. It is more like a soft percolating sound (heard only in the quiet garage), but that still meets the term boiling. She has no return line and I am guessing this is why the factory moved to a return line setup later that year.
Her issue occures after a nice long drive, when the whole engine bay is hot. I can hear it during any time of the year, whether she is at 180* or 195*. She has factory A/C as well.
She had came with a dead electric fuel pump over the rear axle, a horrible installation, and I guess this was a lame attempt to have reduced this issue. I took it off and had no big problems. Sometimes she takes a few seconds of extra cranking but thats it.
I accept it as partially a design issue and more of a crappy gas issue.

joe_padavano

This has become a much greater problem due to the alcohol in gasoline. Cars expected to have high underhood temps (hi-perf and A/C cars) came with fuel return lines specifically to combat this. Recirculating the hot fuel back to the tank cooled it off.

Run to Rund

You can't space the pump away from the engine as the actuating arm would no longer contact the ecccentric properly. In addition to the above posts, make sure the fuel line is not near the exhaust system.

Mark71

Well, it gets pretty warm down there. I installed headers (unwrapped) from Hedman, but it had this issue back with the manifolds, too. I am running a 180* thermostat and even in heavy traffic and hot weather, it never really moves too far above that, but of course that is just the coolant temp - exhaust will be a bit warmer.

Everything I've read about the electric (not in-tank) pumps is that I need a regulator up in the engine bay. I think you have to have a return line for the regulator as well, so maybe it is the same work either way. Plus, won't the regulator get just as hot?

Assuming the pump has no return line, where does the excess pressure bleed off from the fuel pump when the float closes the valve in my carb?

MDchanic

It doesn't. There is no excess pressure. The pump pumps up to about 6 psi and that's it.

- Eric

Run to Rund

Some electric pumps don't need regulators. I mounted a Holley red pump near and just in front of the gas tank, a small screen-type filter from Jegs or Summit, and run the line forward. I made up a longer steel line from the fuel pump area to the carb, and use a stud-on-the-head bolt to hold the Caddy Seville block off plate to the block, and for an adel clamp to stabilize the line.