Vapor Lock – 351 Cleveland in #ProjectSportsRoof

Vapor lock.   What is it, why does it happen and how to tackle and solve the problem.   We are going to do it together!

My 1973 Mustang with the newly re-constructed engine has gladly stepped up and volunteered  to be our test subject. (Sarcasm or dismay?  You decide!)

Where to start?  Let’s go from the discovery of the problem to the possible causes to the possible solutions.

Took the gray beast out for another shake down run. I ran down the to local auto parts store, about a 3 mile drive and it was a spirited drive.  I was searching for a bolt for the passenger side seat, some how misplaced the original when I was putting the new floor  panels and carpet in.  I was in the store for 8 minute top – they aren’t as friendly as they use to be.  Use to be you would show up and chat up everyone and discuss what you were working on.  These days you are lucky to find someone that knows what a bolt is.  (Sorry but that’s almost true!!)   As of this writing we are still in COVID19 lock down…(don’t judge me….I really needed that bolt!!!) and they were even less friendly.  Sorry…I digressed. (O.K., if I was really sorry I’d go back and remove this, so lets just consider it “color” and not digression).

After 8 minutes (most of that as the clerk silently pawed through some bolts in the back), I returned to the Mustang and turned the key.  It started hard – 4-5 tries.   On the drive back it kept feeling like she wasn’t getting gas. Temporarily losing a bit of power.   Got home lifted the hood and I could hear the gurgling in the carb.

Here are some specs on the 1972 351 Cleveland that is in my 1973 body:

351C V2

The block is bored out .o4o make it 4.040″

Crank machined .020 under.

Topped with a Edelbrock Performer intake and 1413 800 CFM 4bbl Carb.

Just replaced the cam with Comp Cam FC 268H-10 grind.

                                    — Gross Valve Lifit .494 Intake and .494 Exhaust

                                    — Duration .006 tappet lift  268 for both Intake and Exhaust

                                    — Valve Timing @.006

                                                             —Intake   Opent 28.0 and BTDC  Closed 60.0  ABDC

                                                             — Exhaust  opent 28.0  and BBDC  Closed 20.0   ATDC

Installed Specs

@106.0  Intake center line

Duration @ .050                       Intake 219                        Exhaust 219

Lobe lift                                       Intake .2860 and the same for Exhaust

Lobe separation                          110.0

 

What is vapor lock?  

Vapor lock causes a car to stop running when the fuel in the system overheats. It is most likely to happen when driving on hot days and in stop-and-go traffic. (It was only in the upper 80’s that day) Constant acceleration and deceleration makes your engine work harder, causing it to run hotter. (I was doing a bunch of accelerating – da!) Excess heat causes the fuel to vaporize. This keeps the fuel from reaching the engine.

Many carbureted engines have fuel pumps located near or next to the engine. (Yup!)  The pump’s closeness to the engine, as with some T-types, causes the fuel in the line to become very hot. When heated, fuel turns to a vapor, like water turns to steam when boiled. This process is hastened by the vacuum created in the line as the fuel is sucked into the engine.

When the fuel turns to vapor, the fuel pump can no longer move it through the system. As a result, the fuel doesn’t get to the combustion chambers; the car runs roughly; or it dies. Meanwhile, the car will not restart or will continue to have problems if it does.

So, the main cause is over heated fuel and I’m guess hearing it boiling in the carb is clearly not a positive thing.  Other cause could be:

— portions of the fuel line are to close to the engine or exhaust causing the over heating.

— to large of a carb leaving extra gas sitting in the bowls, being heated.

So, first I want check the positions of the lines.   Check out the video.

 

 

 

There is only the one area that could be the problem and that is from the fuel pump to the carb.  I pick up some Vapor Block
Fuel Line Split Sleeve by DEI.  So I’m gong to wrap that area.  We’ll see what happens, so check back

 

 

 

Thanks for check in!

Tim

#ProjectSportsRoof