Help with carb sync/disabling front carb engine quits

[Captain Obvious]

I was basing recommendations on the original claim that the float bowl levels were correct. If that's not the case, then of course all bets are off! 

I'm a big fan of the clear tube method of setting the bowl levels. I believe it to be more truthful and more reliable than the other methods (like the ten turn down method).

Forget all the other tuning stuff until you get the bowl levels (close to) right. If your rear bowl is near dry, then it would make perfect sense that your rear carb sounds like a jet engine compared to the front, and it still won't run on that carb alone.

Just to test other things, you could fill the rear bowl to the correct level and see how the piston lift test performs. The car should run maybe thirty seconds or so on the fuel in the bowls before they run so low the fuel can no longer be pulled in.

[David F]

Test fuel mixture settings with both carbs connected to fuel supply.  If the engine stumbles and slows when the rear carb piston is lifted, then it is lean.  A lean condition can be caused by low fuel level (bowl) or a vacuum leak.  Have you checked for large vacuum leaks at the throttle shafts?  Spray carb cleaner at the shaft bushings when the engine is running.  If the rpm goes up significantly, here could be the problem.  If the carb is sucking air in at the throttle shafts, it won't suck in much fuel from the nozzle.

[jalexquijano]

How do you measure this 1/16 inch below the nozzle? Digital caliper or else?

[Mark Maras]

 Just eyeball the 1/16". You'll have the fuel level closer than using the 9/16" grey area setting.

[882993md]

On 3/6/2018 at 9:43 AM, David F said:

Test fuel mixture settings with both carbs connected to fuel supply.  If the engine stumbles and slows when the rear carb piston is lifted, then it is lean.  A lean condition can be caused by low fuel level (bowl) or a vacuum leak.  Have you checked for large vacuum leaks at the throttle shafts?  Spray carb cleaner at the shaft bushings when the engine is running.  If the rpm goes up significantly, here could be the problem.  If the carb is sucking air in at the throttle shafts, it won't suck in much fuel from the nozzle.

Crazy busy last few days no time to work on the car until today.

I did spray carb cleaner on both throttle shaft bushing and no change in engine rpm.

Howard

Edited March 11, 2018 by 882993md

[882993md]

I used the clear tube on the rear carb to check the fuel height and it seems I'm actually a little high by 1.5-2mm (I didn't bother adjusting the float at this time).

I started the car with choke and the rear carb was backfiring until the car warmed up and I synced them using the (snail type) synchronizer.

At roughly 1,040 rpm both carbs were synced to the 12 mark. I tried to get the rpm down to 750 but then the carbs would go out of sync with the front at 5 and the rear at 11.

Lift the rear pin-slight decrease in idle to approximately 950rpm

Lift the front pin-immediate stall

Both jet adjusting nuts at 2.5 turns.

I checked plugs 2 and 5 and both were black. I cleaned them but forgot to check them again before calling it the day. I will check tomorrow.

Howard

Edited March 11, 2018 by 882993md