Backfire thru carburetor

[Russell Reay]

After curing the starter problem, the car started right up, and I went for a test drive. Within 1/2 mile It was clear that the engine had very little power, and responded poorly to the throttle. Deal with timing first--Used the timing pin, located dead-on TDC with flashlight in the spark plug hole, all plugs look good, 6.35 V at both coil contacts and at points, condenser tests good, dist. body is good (2 of them), rotors are good, rotor gaps are a little variable, but have been for a long time, set the dist. cam timing per NuRex tool instructions and Paul Shinn video---won't start. Installed two different Zenith carbs and one Tilly. Spark lever fully retarded, throttle lever down a couple clicks, Gav open ~1/4 turn, choke works as expected, gas valve open--won't start. All I can get is backfiring thru the carb. Mayday, mayday, mayday.

 

[Wick]

Check the wire from the starter to the terminal box. Sounds like no spark

 

[nkaminar]

Timing is off. It sounds like you have verified that the pin for timing is correct by looking at the piston with a flashlight. Set the engine to TDC on cylinder #1 with the pin. Move the timing lever all the way up. Loosen the cam just enough to turn it. Check the points gap to be 0.018 to 0.020 when fully open. Put the rotor on and rotate clockwise until the rotor is point to cylinder 1. Take the rotor off and turn the cam clockwise so that the points are just closing. Tighten the screw. Double check the timing by turning the cam counterclockwise to view the points opening. Go back and forth clockwise then clockwise to make sure that the timing is such that the points open at TDC. Check that the rotor is pointing to #1 when the pin is in the divot.

Do not use the NuRex tool. It can lead to a mistimed engine. You can use it as a wrench to move the cam, but that is it. Just make sure the points are just starting to open at TDC and the rotor is pointing to #1 plug.

Check that the high tension lead from the coil to the distributor cap is all the way into the coil and the cap.

 

[Y-Blockhead]

Do as nkaminar suggest. Your rotor should be in this position (see below) when your points are set at .020" and #1 cylinder is at TDC.

 

[Russell Reay]

You have confirmed my feeling that the problem is all in the timing. I think I misunderstand how to deal with backlash. In the attached pics the screw that secures the cam is tight, but with my fingers I can turn the cam--and I think the whole shaft-- about 30 degrees, but there is no spring tension in either direction. Pic no 2 shows the rotor position turned CW to the max. Pic no 3 shows it turned CCW to the max. I assume the arc between the two extremes is backlash. If this were any of the many engines I worked on in the 60s, the backlash would be small and spring-loaded. I would just loosen the bolt that holds the distributor in place, turn it until the points just open, and declare victory. Please continue my education.

 

[TMarsh]

I agree that the nurex tool is good for a tool, but I would use the instructions in the red book. I have the tool and had the same problem till I used the red book method.

 

[Y-Blockhead]

If you can turn the rotor that far it makes me think you have a Nu-Rex auto- advancer? The rotor should be in the position as in the picture in post #4 when turned all the way CW. Lever fully up. That will be 0° at TDC. Fully CCW is full advance ~30° BTDC.

 

[nkaminar]

Blockhead has a good point. Take the valve cover off to see what is going on. The "about 30 degrees" at the distributor cam is 60 degrees crankshaft rotation. Way too much for the stock setup.

 

[Russell Reay]

UPDATE: Removed valve cover to determine that I do not have an auto advance. Reset the timing per the red book--didn't seem like I did anything different than previously--it started right up, and runs as before. Maybe I will just drive it a while and quit fooling with it.

 

[Bob C]

I would look into why you have so much backlash. Most likely wear in the shaft coupling area and distributor drive gear.

 

[Russell Reay]

Took her on a 60 mile road trip today to get native strawberries and cremees (non-Vermonters call them soft-serve ice cream cones). The covered bridge is VT's longest and the site of my boyhood swimming hole. Thanks for all the suggestions that helped get her started and road-worthy.