Spark Plug advice needed for 66/67 911

[lars1965]

These Bosch WR5dc + 15 have been running 7.000 km in my 911 from 1966 with stock kettering ignition gap 0.8 mm. The engine runs perfect at idle down to 5-600 rpm with no popping from the exhaust. No popping at acceleration , a slight hesitation at 4000-4500 rpm at constant speed in 4-5 gear,
pulls very strong when flooring the pedal with no popping or hesitation.

when going down the gear from 5 to 1 ( deceleration ) a slight popping from the exhaust.

when started cold , it pops slightly the first 3-4 min until it hold 800 rpm idle

what do you think of the looks of the spark plug ?


thanks

Lars

[trdking]

I can't tell you how many spark plugs that looked great turned out to be not so great. Freshen the plugs at regular intervals.
The popping is more likely poor timing, cam lash or poorly seated or burned exhaust valves IMO

[edmayo]

I hope you're not complaining

[Orval_F]

The best thing you could do is install a good CD ignition system. That, coupled with unleaded gasoline, extends the life of both engine and plugs.

[Jon B]

I can't tell you how many spark plugs that looked great turned out to be not so great.

In the old days, you could clean and check spark plugs in a test cabinet...





Jon B.
Vista, CA

[lars1965]

I hope you're not complaining

Hi Edmayo

please explain....? does these plugs looks ok to you , I fear that they look a bit lean , but I`m not sure with this bad unleaded gasoline we have today, and I dont want to go richer if not neaded

[edmayo]

Yes, I'm saying they look good, possibly a bit lean, but spark plugs don't color like they used to with leaded gas. You really need devices like a air/fuel ratio meter to determine mixture. Since you say it pulls very good I doubt you're too lean. Are you running all stock components and jetting?

[lars1965]

hi Ed, I dont know the jetting yet, I need soon to check when I put anti percolation gasket between carbs and manifold later this week, but as a base 2.0 911/05 engine with early 901 cams, I suppose main is 125 air is 180 and idle 55 and a F3 or F26 emmulision tube is correct?

would smaller gap , say 0.6 help on the high end hesitation at steady speed ?

[edmayo]

There can be many causes for your symptom, but lets try some easy things first, since the idle system is still contributing at 4,000 I would try a step up to 60 idle jets, and gap the plugs back to the book setting, which I think is .6 or .7 (trusting to memory here)

[lars1965]

Thanks Ed

Do you know a good source for weber idle-main- air jets? so I can get some different sizes to try with

Lars