1939 v12 Stumbles

[jord]

While going down the road the car stumbles at around 30mph, checked for spark and all was ok. Checked all the plugs and they were all showing signs of too much fuel (rich). all black. Cleaned up everything. Does the vacuum advance have any effect? Also, now my idle adjustment does nothing to the engine. Carb kit was installed a couple of years ago.

Starts good.

electrical seems ok

What am I missing?

 

[edinmass]

Fuel pressure too high, diary carb, ignition advance not working, vacuum leak, KV’s issue, primary issue? The list is endless. First you need to actually diagnose the problem as mechanical, electrical, or fuel. 

[Ray500]

Everything from the fuel tank to the run components of the V12 are suspect!  Distributor and fuel issues are paramount in these problematic areas!    Don't overlook the fuel pump, it can intermittently loose pressure.  Carb is a big suspect too.  Best to redo the distributor parts, carb and fuel components till you resolve the issues!   If you can't adjust the air/fuel balance on the carb that would be a good place to investigate  There are places that the carb can be sent for rebuilding, just watch the size of the jets they install.  Some dump too much fuel into the engine, others sorta starve the engine for fuel.  Check the vacuum from the intake going to the distributor at different RPM's.  Mostly the windshield wipers and the distributor only use the vacuum from the engine.  But it has to be there!   Should be at least 17 inches of vacuum at idle, depending on the condition of the V12.  

[19tom40]

The black plugs and idle mixture screws having no effect usually means that the power valve in the carburetor is leaking.

 

 

[jord]

Thanks Ray and Tom, I am getting Jerry to rebuild my carb and ordering new terminal plates and condensers. While this is being done, I will check my fuel lines, filter and compression.  Ken checked the distributer and timed it as well, so I will only have the coil to check. Coil appears fine as all plugs have good blue spark. It was disappointing as I had a slot for upholstery next week.

[jord]

Still cannot get over 2.80 volts at the coil, Coil has been rebuilt by skip. I hooked up new resisters and still the same. I bypassed everything and went straight to the battery still nothing improves. Ordered new resistors from Chris and will try again, any thoughts. Also new condensers from Jerry

Paul

Thanks

 

Edited June 6, 2023 by jord (see edit history)

[19tom40]

If you have a good blue spark at idle, I would not worry about the voltage going to the coils, yet. The low voltage is probably not your problem. The low voltage could be coming from the higher resistance of the ignition resisters when they are hot.

 

Did you replace the spark plugs? I find that the Champion H-10 made today are of poor quality and use the MotorCraft  or Autolite. RockAuto has both brands.

 

Are you now able to adjust the idle mixture? Are your plug sooty again.?

 

I would look down the throat of the carb while the engine is idling to see if you can see any fuel dribbling in. There should be no fuel visible in the throat at idle. All fuel should be delivered through the idle port below the throttle pales. If all of the above are OK, then you will have to give a better description of the problem.

[jord]

Thanks Tom

 

I have not tried to start the car because of the low voltage. Do not have time to play with it now but will try to start it soon, will let you know. New Autolite plugs. Skip was saying the new resistors are sometimes poorly made.