Fuel hose connecting float bowl and nozzle

[jonathanrussell]

I thought I would share a problem I had that I have never seen before. 

My 72 240z with 3 screw carbs was running perfectly. With the floats really well adjusted using the 10mm method, the carbs with SM needles run great at about 2.5-2.75 turns down on the mixture screw. With Colortune, idle is a touch rich while 3k rpm is nice and blue.

I had been fiddling around with and testing out a lot of little things including fuel pump, some heat shielding around the carb float bowls, fuel pressure gauge, fuel pressure regulator, etc.

Suddenly when out on a drive I noticed that the engine was running out of oomph at 4500 rpm. I went on with my other projects but kept trying to figure out what was going on with this symptom. It got worse though and I started noticing it at all rpms. Just felt like fuel starvation. I felt really good about ignition because I had recently changed to Petronix elect ignition and coil and had tested successfully after. Was getting good spark. Finally, I decided to pull the air cleaner and look at carb adjustment. When I did this, I noticed that the front carb fuel hose from float body to nozzle was crimped some. It wasn't closed shut but was visibly crimped into a kind of drastic angle. I thought...no way that is the problem. But, I had an extra new ZTherapy hose and swapped. Started up and runs perfect. 

So, the crimped hose was enough to starve the front carb bowl. How did it happen? I am guessing that sometime when I removed the air cleaner backing plate I reinstalled and crimped the hose somehow. Hard to say. Will probably never know.

Just thought I would share in case someone else is struggling with similar symptoms and by some chance this solves the problem.

 

[moritz55]

Many thanks for sharing!  Great info to always check these fuel bowl/nozzle hoses when I pull the Airfilter backer plate. 

I am very much like you as I often fiddle to assure the engine components are always working to spec so I can head off a problem before it fails completely.  Started to have bucking/jerking when accelerating or going up hills, a loss of power problem.  This occurred after installing ZTherapy SU's and tuned them with Colortune also.  Thought it was my SU's and needed to tune/tweak them.  Finally after it finally stalled completely and would fire sporadically but not run I figured electrical problem misfiring?  Got it back to my garage I thought to check the rear fuel bowl for the heck of it since it was easy... and sure enough it was almost completely empty. Front fuel bowl was topped off pretty close to normal.  Replaced the mechanical pump and then added an electric pump for insurance..  my 4BBL Holley was more forgiving when the mechanical pump was marginal ... my SUs were not!

Thanks again for sharing....     

Edited June 5, 2019 by moritz55