Problem starting (but have spark, gas, air)
 

Over the last several months, starting my 912 has become more difficult. The engine was rebuilt two years ago, and essentially have continued restoring it -- so it's not like I have put 50 miles on the car since engine rebuild.

At any rate, the spark is very strong and bright since it is generated by a Jacobs Omni Magnum. I have a Pertronix breakerless ignition (points). Also, FYI, I have new Weber IDF 44's, new Bosch blue coil, and there is plenty of gas squirting down the carb throats before trying to start. The fuses are all good. I also timed the engine the last time it was running (2 weeks ago).

Given the above, I am puzzled at why the engine does not start quickly. The spark is very intense, plenty of gas (and sometimes starting fluid), but it seems that only rarely does a cylinder fire.

I pulled the plugs and they basically had a little carbon build up on them, so I cleaned them with a wire brush and re-installed.

What part or electrical device is usually at fault when poor starting becomes an issue. Any suggestions?

thanks, lep

Lep:
I'd double check the initial (idle) timing. Are you sure you have strong spark at the plugs? If not, check the plug wires/dist cap and the plastic connectors that go onto the plugs. Also, the air passages on IDFs can get clogged. Longshots would be vacuum leaks, engine grounding strap & maybe valve adjustment.
Once started, does the engine run and idle well when warmed-up? While the engine is cranking, does it gain speed or is it "fighting" itself and just continuing to crank slowly? Does it spit back fuel or backfire? Once warm, will the car re-start easily or is it still difficult?
Bill.

The idle seems fine when it runs after start and also when hot. I am replacing the dist. cap and ignition wires today, so we'll see what that does. I'll also adjust the valves.

I looked at the schematic for the Weber 44 IDF, and there were the following that could be set:

1. Air bypass screw and jam nut

2. Idle mixture screw (which I adjust for a smooth idle)

3. vacuum ports (set screw)

4. vacuum advance port

5. Idle jets (near the top, above the mixtures screws).

I know the default settings for the idle mixture screws is 1.5 turns out, but I don't know the default settings for the others. I do have several air flow synchs that I could use for the idle air settings, so if you wanted to suggest what to do with the idle jets near the top, and/or the air bypass or vacuum set screws that would be helpful. (also, which can be removed to see if they are clogged with gum -- maybe the idle jet screws?).

The engine ground strap is secure, but I have read that the copper leads can build up resistance, so I am checking with an electrical engineer I know ( who is a battery/ignition expert on motorcycles/vettes/airplanes he owns ) to find out if resistance buildup on ground leads is real or is a minor issue or hoax.

Last, during cranking when starting, speed does not pick up with an increasing number of cyclinders firing, it just cranks continually. On some occasions, some of the cylinders will fire and it seems like something was exatcly right with the fuel air mixture. Re-start after running a long time is no problem.

Last, however, I think I need a new starter since I have never replaced it for 26 years (my how time flies). Nevertheless, the current starter seems to work without a problem.

Any suggestions on the above will be greatly appreciated.

lep

Problem solved - engine started
 

I adjusted the valves, pulled the spark plugs, wire brushed them and gapped them to 0.022-0.024 inches (one book calls for for 0.024, another 0.024-0.028), and I wanted to try a little smaller gap.

Started right up, but I did initially re-set the 4 carb idle mixture screws so they were all turned out 1.5 turns before starting. During run-time, I timed it at idle at adjusted the carbs. The spark plug wires are Beru's, and they are about a year old so no problem.

Thanks for the help.