Timing problems at low speeds/RPM

[Drew Gregg]

I was on my way to Moda Miami back on Feb 27 for the car to be displayed on the golf course. A week earlier,the car was on the road course at Homestead Race Track. The car ran perfectly even with the A/C on. The car ran great for the 2700 mile tour on the CCCA visit to the BMW factory and the Blue Ridge Parkway and Hilton Head back in Oct., November, 2025.
Then, 1.5 miles from my house on Feb 27,everything shut down. The fuse in circuit #7 (10 amps with the Holy Grail fusebox) blew several times attempting to get the car back to my garage. I had several circuits rewired and all was running again.
But the 123 dizzy advance curve was completely wrong and no where near the previous setting that had the car running great.
The timing was making the car run like it was retarded even when the advance curve was set at the previous curve.
New plugs and new ignition wires still show plug #6 was not firing completely.
Compression is 180 PSI in all cylinders.
Today we installed a stock distibutor and set the timing so the idle was smooth.
The engine is still not running smoothly at low RPM /speeds. Once the engine is over 2500 RPM it seems to be running well. Driving at 50 MPH seems normal,but the advance curve in the stock dizzy means there's no acceleration compared to the 123 distributor advance curve settings.
The voltage to all 6 wires is the same. But # 6 plug shows the fuel is not being burned completely.
The next will be a leak down test.
But it's hard to believe all of this has happened since the electrical failure on Feb 27.
Has anyone had a similar problem at low speeds?

 

[boonies]

Hey Drew. If you have changed the spark plug and wires (and distributor) and all the other cylinders are working as expected it is unlikely that it is still an electrical problem, but I would check the plug to make sure that it did not come with a factory defect. Easy enough with a volt-ohm meter to check to make sure the insulator is not damaged and grounding.

Then I start to think about your set-up. You are running triple Webers and I wonder if there is something in the right side idle jet of the carb closest to the firewall. You essentially have one barrel per cylinder which allows you to focus there fairly easily. Also easy enough to hold your hand over the air horn to see if that clears the issue without pulling the jet (assuming that is even the problem).

It would certainly be a crazy coincidence, but not unheard of that you picked up a speck of dirt during a fill-up.

 

[Drew Gregg]

Hey Drew. If you have changed the spark plug and wires (and distributor) and all the other cylinders are working as expected it is unlikely that it is still an electrical problem, but I would check the plug to make sure that it did not come with a factory defect. Easy enough with a volt-ohm meter to check to make sure the insulator is not damaged and grounding.

Then I start to think about your set-up. You are running triple Webers and I wonder if there is something in the right side idle jet of the carb closest to the firewall. You essentially have one barrel per cylinder which allows you to focus there fairly easily. Also easy enough to hold your hand over the air horn to see if that clears the issue without pulling the jet (assuming that is even the problem).

It would certainly be a crazy coincidence, but not unheard of that you picked up a speck of dirt during a fill-up.

Lance--Good ideas. The # 6 new plug was exchanged for #2 new plug. No change after another test run,so all of the new NGK plugs are good and the same ones as have been in the engine for 20K miles. I also tapped the #3 Weber in case the float was hung up. Now I'll try checking the idle jet. Note the main and idle jets and float levels were sorted before the CCCA tour. They were all running great.

 

[sfdon]

Check that the nose of your cam hasn’t gotten loose and started rotating

 

[Drew Gregg]

The latest--A leakdown test was performed on cylinder #6 and the valves are tight. All 6 new plug wires have the same voltage. The idle, main and accelerator pump jets were inspected and no debris was found. The top screens were cleaned on all 3 carbs. The 123 dizzy was set up with the correct advance curve. Pic shows the curve.
The engine still stumbles from idle to 2500 RPM. We need to sync the carbs again before bench testing the #3 carb. But I'm driving to events this weekend and the car is entered into a Concours next Sunday in Delray Beach. The engine runs fine at highway speeds.