Carter WCD carburetor and ignition settings on an 8-cyl flathead (1949)

[Sebastian S.]

I am currently working on the carburetor and ignition settings for better acceleration and smooth idle.

Ignition system:
- Pertronix 1183N6 "Ignitor" Ignition Module for Delco, early 8 Cyl with 6v Negative Ground

Distributor:

• Original Delco distributor
• Everything has been thoroughly cleaned and greased / oiled

Fuel supply:

• HARDI fuel pump type 1776 with fuel delivery capacity of 50-60l/h at 0,20-0,28 bar, 6V / 3A
• Fuel pump safety controller PN 12003 by Revolution Electronics, with 3-sec priming and auto-off in case of missing ignition signals (=motor off)

With factory settings according to service manual

- Static advance timing of 6° before UDC --> that means, that you have to add 6° to all measurements in order to get the full advance reading before UDC!

RPM	Total advance in ° (tolerance +0°/-4°)​	Measured total advance in °​	Vacuum advance + total advance in °​
500​	2	0	0
800​	4	2	7,5
1000​	5,75	4	15
1200​	7	5,5	21
1500​	8,75	7	27
1600​	10
2000​	12,5
2400​	15
2800​	16
3200​	18
3600​	21,5
4000​	25
4200​	27

The idle speed screw is limited to reach 1500 RPM max. Currently, I don't have a solution how to run the engine faster + measure at the same time. Any suggestions here?



According to the data and my measurements:

• It looks like mechanical advance works fine up to 1500 RPM.
• Vacuum advance kicks in at about 680-700 RPM and looks good too.

1st. testdrive with 6° static advance (0° according to service manual) and 585 RPM idle:

• Starts up fine.
• Engine idles ok, but every 3-5 seconds, there is a putt sound and the engine block shivers a little. Misfire?
• RPM meter shows some slow rolling between 472-485.
• Above 40 mph the engine does hesitate under load - max speed without hesitation is about 50 mph.

Conclusion:
Idle mixture seems not to be perfect + engine is too retarded at higher RPMs. Idle mixture maybe too rich?

Adjustments afterwards:

• Adjusted distributor to 4° static advance timing (6°+4° = 10° UDC) --> when turning distributor counter clockwise to achieve new setting, RPM increased by 15-20 RPM in idle.
• Adjusted both idle mixture screws until engine ran as fast as possible (leaner mixture!)

2nd. testdrive with 10° static advance and 550 RPM idle:

• Starts up fine.
• Engine idles good, stable at 550 RPM (+- 3 RPM).
• On high RPMs, engine does hesitate slightly under load. Max speed without hesitation is about 65-70 mph.

Conclusion:
Idle mixture seems to be good for the static advance timing. Engine shows some hesitation at higher RPM under load – still 2-4° too retarded?




Adjustments afterwards:
Nothing so far.


...to be continued.

 

[melsg5]

what is UDC? I know BTDC Before Top Dead Center and ATDC After Top Dead Center
later Pontiacs typically can use as much as 36 degrees total mechanical advance. You would set the timing at idle to 12 degrees and the mechanical advance in the distributor would add another 24 degrees to achieve the 36 total. In addition to that the vacuum advance can throw in about another 10 degrees for a total of 42 degrees when just cruising at a stead engine speed. Depending on compression ratio this type of timing curve might require 93 octane gasoline, using the US average system of RON and MON.

 

[Sebastian S.]

Hi melsg5



I also know Top Dead Center, but early Pontiac manuals just call the top piston position UDC = Upper Dead Center.

Regarding your static timing, I agree that it should be somewhat higher and 12° sounds good for me. The manual just say "turn distributor until borderline detonation appears" but unfortunately, I don't know how this might sound and I don't want to put too much stress on the engine.

Max. vacuum advance is up to 11° / automatic advance up to 25° according to handbook --> like you calculated. Thanks for that! It's a relief to have another opinion here.

The engine is listed with 106 hp and should have 7.5:1 compression. Gasoline is not a problem here, minimum octane here is 95. But...who are these guys RON and MON you mentioned?


---> I will try 12° next time.


I know, there is some more work to do:

• Check piston compression
• Check UDC / TDC position to match with harmonic balancer marks
• Check function of vacuum advance with a gauge and a syringe (still waiting for those to be delivered)
• Clean and rebuild carb (next winter!)

 

[Sebastian S.]

Depending on compression ratio this type of timing curve might require 93 octane gasoline

Hm...maybe 7.5:1 compression isn't high enough to allow any borderline detonation with 95 octane fuel? Could that be?

Wait...what is the max. "safe" advance including vacuum and total? I could measure max. advance and set the distributor accordingly...than check static advance degree to find the maximum advance. Would that make sense?

______________________________

 

[melsg5]

RON is research octane number and MON is motor octane number. RON is the higher number and in the US the average of the two is posted on gasoline pumps ron+mon/2. Your 7.5 compression is extremely low by modern standards so your 95 I believe is the RON number, here is a link where they discuss Swiss octane ratings Fuel octane - English Forum Switzerland . In your case I would probably not go higher than 10 and listen with the windows closed for a rattling sound from the engine when under heavy load such as going up one of those wondrous mountain paths where the edge drops down for thousands of feet, If your maximum vacuum advance is 11 it should be fine.

 

[Sebastian S.]

Hey guys

Bad news...my fuel pump is defective. It works for about 5 minutes after a cold start, then stops pumping. Yesterday, I ordered two low-pressure fuel pumps to set them in parallel – that should improve flow and should keep the motor running in case one fails again.

I will keep you updated....stay tuned.

BTW: Missing fuel might have been a reason why the engine hesitated at higher rpms.

 

[melsg5]

The wonders of older vehicles.