Sometimes all carburetor problems ARE NOT ignition

All carburetor problems ARE NOT ignition
« on: August 26, 2019, 11:11:55 AM »

You know sometimes it’s real easy to overthink things. My motor (511 inch, roller cam, CNC heads, 10.2:1 compression) continued to run fantastic as long as it was moving at speed but once i slowed down it would cut out and stay “dead” for a while before I could start it again. It would cut out abruptly, so it MUST be ignition, right? Well I have gone through no fewer than 5 ignition systems ending up with an MSD. a-6. Same results.
Finally had eyeballs on my AFR meter when it cut out again and guess what? Not ignition, boiling fuel and vapor lock. Finally realized that running the 1/2 inch fuel line up the inside of the fender well about 5 inches from the headers and no thermal insulation under the carb might not be the best way to go, especially with 96+ degree days.
Not that I tend to overkill things but when I get back home (I’m cooling off in the Blue Ridge Mountains for a while) I’m going to re route the fuel line to a bypass regulator away from the aheaders and run a return line back to the tank. If that doesn’t do it, look for a 73 coupe de Ville in the for sale section.
Greg Surfas

 

Very interested in this. I’m wondering if I’ll be in the same boat.

 

As an installing dealer for the AirSensors brand of aftermarket electronic fuel injection I fitted these units to any number of vehicles and their engines. There was one customer, actually a senior couple, who was ready to pony up the cost of a F'I conversion to fix what sounded like a simple case of vapor lock, just like yours. The vehicle was a motor home with the engine setback into a doghouse which acted like "an oven designed to cook fuel."

This older couple ventured from Utah to portions of Canada every summer and they had tired of becoming stranded, most noticeably on the hills and mountains. Of course that was just when the engine was under the greatest load -- with less atmospheric pressure keeping the gasoline in a liquid state. I knew there was a simpler, cheaper solution than fuel injection. I asked if they would trust my suspicions and allow me to purchase and install a thermal barrier between the carb and intake manifold. They agreed and a couple of hours later I had made friends for life!

The trips to Canada were event free from that time forward - a point I was reminded of each and every Christmas by a card from that lovely couple. May they rest in peace.

bro. d

 

Bro D.
It was the suggestion that I install a carb insulator, and my actually doing it that brought my thinking around to the point where I actually started looking at what I had. 5 inches from the passenger side header is NOT where a 1/2 inch fuel line should be run. As usual don't ever stop at 100% so I'm going to re-run the supply line and insulate it, replace the pressure drop regulator with a bypass regulator and run a 1/2 inch return line back to the tank. I've jerked around with this for too long and still need to get 500 miles on the motor and rear end before I go back to the track.
Greg Surfas

 

Your observation sounds like the ticket.

Let me know what you use for insulation on that fuel line as I'm going to need some here as well.

Best,

bro. d

 

Bro. D
This is the stuff I used, both for the fuel lines and for my external oil bypass line. It comes in all sizes.
https://www.summitracing.com/parts/dei-010473
Greg Surfas

 

THANKS!

d

 

The larger 1/2" line is actually making the heat soak worse. The larger diameter = lower velocity of fuel through the hose at idle, and = more time in the engine bay to pick up heat.
A fuel return line is the ticket, keeps the fuel moving faster through the engine compartment by constant circulation. If you are running a mechanical fuel pump the Cad '77 and '78 425 fuel pumps have a return line on them to prevent vapor lock. Insulating the fuel line or adding a header heat shield will also help.

 

First of all I have been "nose blind" to even the thought of vapor lock as the cause of my engine crapping out, so I chased my tail through several ignition systems. Once I stopped running on the treadmill and stopped to think rationally the vapor lock was a no brainer. The 1/2 inch fuel line seems to be necessary as I "out ran" a 3/8 inch line with the same Holley "Blue" pump. A long time ago this motor out ran even the beefed up Pontiac HP pump so the mechanical pump was taken out of the circuit.
Plan (this week) is to replace the pressure regulator with a bypass regulator and run a 1/2 inch return line back to the tank. Both lines will be insulated and run as far away from the heat sources as possible. More to come.
Greg Surfas

 

Greg,

Good logic on the larger fuel line in order to not starve the engine for gas. I do have a question: where is your Holley "Blue" pump located? As you know it is best to have an electric pump in the rear as close to the tank as possible. That way the entire column of fuel in the line is under pressure and better able to overcome the inertia of acceleration - and hold off vapor lock.

Caddylackn,

Your point about the fuel moving more slowly due to the larger diameter line is worth noting. That reality will be especially critical in my Caddy powered Studebaker due to the 5/8 inch (dash #10) size of the line. The good news is that the Holley pressure regulator does have a return port which will feed either a 1/2 inch or 5/8 inch return line to the tank.

Best,

bro. d

 

Bro, D
Tank is sumped with pump just at rear and below tank level.
Greg Surfas

 

Greg,

Nice setup!

First thing that came to mind was the accumulated cost of all the AN fittings and parts. They don't come cheap, do they.

Russell filter, ball-valve safety wired, everything done nice and tidy. Hope mine will be as nice when put on the car. Right now there is a sack full of fittings, a Holley Dominator 12-1800-2 pump, the appropriate pressure regulator, pre and post filters but so far it all looks like this: $$$$$$$.

Thanks for sharing that picture as it helps to see what things look like when done right.

Best,

bro. d

 

Good thread. I’m about to change my ROBBMC regulator over to bypass mode and send a -6an line back to the tank.........just to keep fuel moving.

 

bro. d
Thanks
Over the years I have done many, many projects on the cheap with the "that's good enough" theme playing. In retirement this is one of my long term projects and I am enjoying doing it right to the best of my ability. FWIW I have been told "there ain't no pockets in that shroud". Every time I have drained the tank or cleaned the rear filter or pulled the pump down to check it I am glad It went together this way.
Greg Surfas

 

Bro. Greg,

LOL!!

I do believe you are right about there not being pockets in the shroud. That gives a whole new meaning to "Use it (as in 'spend' it) or lose it."

bro. d

 

Okay,
Things have cooled off and had a chance to re-route the fuel lines and install a by-bass regulator. First try out ran okay. Since I am tired of flat bedding it home, I'll try a few more short runs before I consider the problem resolved
I consider the problem resolved, but I think this is it.
Greg Surfas

 

You talk about "gun shy", I just got back from putting another 10 miles of break in on the car. Made it with out any problems, but everytime the thing "burbled" (probably because the motor does not like going slow) my first thoughts were "another flat bed ride home".
Only 400 more miles of break in to go.
Greg Surfas

 

Speed up man! Give that motor what it wants.

 

Greg,

Seriously, you had me laughing out loud with that reaction to your latest "test drive."
However, I cannot not fault you one bit, having been there myself with other builds. In that light consider your honeymoon of years ago, wondering what to, and what not to do, and viewing that in light of today, following years of marriage.

That said, make sure you have the cell phone charged and with you … just in case … marriage or car!!

Best,

bro. d

 

I hear you. I dread sitting in traffic in any car after a bunch of motor or drivetrain work. I always am in fear being the guy in the intersection with a stalled car when the light turns green with 20 cars behind honking and yelling.

A triple A membership with towing is like $100/year and a good battery and a tool box in the trunk will install a little confidence to get you out on the highway or out of town.

You need to get out on some side roads and put on your old rear tires for proper break in procedure. Is the 400 mile break in mark for the rings?

Are those electric exhaust cutouts I see? If so I want to see a video sound clip with them open after you hit the 400 mile mark.