2.0 911S plug fouling problem

blau911 · 12:57 AM

Guys,
Last year I had my 1967 2.0 911 Normale engine rebuilt to exact 911S spec using original factory 2.0 911S P&C's, heads and cams. I had my Weber IDA 40's rebuilt using 55 idle jets and 135 main jets (did not change the emulsion tubes from F26 to F3 though) and switched to 37/40 intake manifolds. Also, running a correct 67 2.0S Bosch distributor.
The engine has appr. 3,500 miles on it currently and since day one has seemed to run a little rich. I had the valves adjusted back in the states after 1k miles and shipped the car over to Europe where I currently am living.
After driving it around most of the summer, last week I took it to a shop in Zurich to have them check out the why the engine was running rich. They adjusted the carb's checked the distributor, points etc and nothing seemed really wrong. However, they noticed that all of the spark plugs were fouled. They switched out all of my plugs for a hotter set of Bosch plugs (not sure which ones). Car ran pretty well for a day or two. However, in less than a week and after driving the car less than 30 miles, I noticed a serious loss of power and brought the car back into the shop who did the work. They were concerned that the engine had lost serious compression and did leakdown and compression tests. The good news is that my compression was very healthy and very even across the board, even better my leakdown results showed virtually 0% leakage on 5 cylinders and 2% on the 6th. Needless to say, I was very relieved.
Now they are unsure why the plugs are fouling and suggest now that I go with an expensive set of factory plugs which cost almost $40 a piece. I have seen on other threads and messgae boards that numerous guys with early 2.0 911S's are using NGK B7ES plugs which cost only $3.50 a piece. Another plug suggestion was the Bosch W3DPO. I am planning to switch out the plugs again and see what happens. However, I am wondering what else could cause such spark plug fouling - and in less than 30 miles? Anyone have any ideas or suggestions on what else may be wrong? I hate paying mechanics who are charging me over $100 per hour and are essentially shooting in the dark.
Since I used the same coil which may be pretty old as it came off of my original 2.0 normale engine, maybe it could be the coil? How about the CDI box, or even the Webers (I am not sure what difference the F26 emulsion tube versus the F3 would make)?
Looking for some good advice from someone who may have been here already.........

jluetjen · jluetjen's Garage

What sort of ignition system are you running? If you are running a bone stock original ignition system -- that may be your problem. 911's had an awful reputation for plug fouling until Porsche started to install the Bosche CDI ignition system. The engines with the 2.0S pistons were the worst because the highly domed pistons significantly interfered with the combustion chamber shape. Bosch CDI ignition systems are often available on eBay and other places, and I believe some on the BBS have even started to repair them the Bosch systems. Alternatively you can switch to a Crane or MSD ignition system which you can buy brand new almost anywhere. Personally I have an MSD ignition system in my car (a 2.0E which has 2.0S pistons in it) after the original Bosch system, and the MSD system definitely cleared up the engine's running below 3000 RPM. Other people have had good experiences with the Crane system.

Either way I would definitely replace the points in the distributor with one of the many pointless systems. It may not resolve the fouling issue, but you'll never have to set the points again. If you do a search on this BBS for "Crane", "MSD" or "pointless" or some combination of those you should be able to find a whole lot of information about people's experiences with different systems and how they are different or the same.

brokke · 12-07-2004, 02:31 AM

Plug fouling with the 2.0S engine was already in the early days a problem, thats why they switched to CDI ignition. My 2.4S engine with a stoch CDI ignition is running NGK BP8ES plugs. The plugs look fine and I never noticed any serious plug fouling. I also used some time ago WR4DPO plugs. I did not noticed any difference with the NGK plugs.

Peter
911 2.4S

Grady Clay · 12-07-2004, 08:57 AM

I agree with John, get a high power DCI and use inexpensive NGK plugs, BP8ES in warm weather and BP7ES in cold weather. Hot weather and a DE at Nurburgring I would use fresh B9ES.

I think one reason for the change in running/fowling is the change in weather. In cool/cold weather you need to make much more effort to get the engine hot every time you drive and then do some “sporting driving.”

Make sure there isn’t something else in the ignition system causing a problem. Could be cap, rotor, wires, plug connectors – damp conditions affect these also.

If sometime in the future (hopefully a long time) when you have the heads off, your engine would benefit greatly from twin plugs. You might take that in consideration if you decide to get a new current single plug ignition – is it up-gradable to twin ignition?

Off your topic; another thing I would be very concerned about driving an early 911 year-round in Germany is the dreaded RUST! Don’t have your nice 911 disappear into a pile of iron-oxide powder.

Best,
Grady

blau911 · 12-07-2004, 11:03 AM

Guys,
Thanks for the repsonses so far.
As rgerads CDI units, the car is running with an older Bosch CDI unit. I see that Pelican offers the "Crane/Allison XR720 Fireball System" which their online catalog states is applicable to 911 (1965-69). I assume that iuncludes the 67 911S. Seems cheap at only $131. Would this be good enough to replace my old unit? I was told by a mechanic last year when discussing replacing my current (older Bosch) CDI unit that it wasn't necessary to replace it as long as it was still working. He said that either the CDI works or doesn't. Any truth to this?
Pelican is not selling any MSD units. Are the MSD units more expensive and should I get one of these instead of the Crane set-up?
Grady, I will take your advice on the NGK plugs and go with the colder weather BP7ES plugs for now. As for the rotor, plug connectors and wires, they are all new and replaced during the rebuild. The mechanic has checked these and says that he does not believe they are the problem.

jluetjen · jluetjen's Garage

Check out the MSD Web Site and then check "Automotive Dealers". It looks like they have a few in Europe.

Grady Clay · 12-07-2004, 11:54 AM

Guys,

Feel free to correct me if I’m in error.

The original Kettering (ballast resistor, points, capacitor, coil) ignition was great for everything until there was a plug fowling issue. The ’69 CDI had exceedingly fast spark rise-time which tended to overcome mild plug fowling. The disadvantage was the spark was so short that normal light throttle running was compromised. This is where the aftermarket (at the time) CDIs came into their own. They combined the fast rise-time of a CDI with the long duration “fat” spark similar to a Kettering system. The later Porsche (Bosch) systems seem to embrace that.

Today there are high power aftermarket ignition systems that combine the best of both worlds – exceedingly fast rise time and fat (long duration) high energy spark. I think this is a good solution. The only down-side is the relatively rapid erosion of the sparkplug terminals. With inexpensive plugs, that isn’t an issue.

When you have your 911 engine “dialed in” and very consistent, that is where the more expensive Platinum plugs become an advantage. I think the reasons are; smaller electrodes which allow more mixture in close proximity to the spark, higher temp electrodes which allow high energy sparks without degradation, there is the issue of the catalytic effect of Platinum, and more.

Pelicans, please critique me on this.

Best,
Grady

rick2 · 12-07-2004, 12:53 PM

Hey Garth,
I use the XR750 on the 73S. John Jr. tilted his head and didn't know how to adjust. I don't have a fouling problem, and are running 150 jets (sea level.) There is a major problem, the ignition breaks up after 5000 rpm.
Just after coming up on cam.
My 2 cents.
Rick
P.S. What do I owe you for the plates?

kucharskimb · 12-07-2004, 02:03 PM

blau911

this might help a little
Weber Air Correction Screws

best of luck
matt

cstreit · cstreit's Garage

Quote:

Originally posted by Grady Clay
I agree with John, get a high power DCI and use inexpensive NGK plugs, BP8ES in warm weather and BP7ES in cold weather. Hot weather and a DE at Nurburgring I would use fresh B9ES.
Grady

I'll second that. THese are the plugs I use (not much track time on the 'ring though) and have had good luck when I previously had fouling issues.

campbellcj · 12-07-2004, 08:38 PM

Can't really add any value to the above, but I'll third the NGK recommendation...BP7ES and a Bosch CDI in my 2.2S -spec w/o any issues thus far.

blau911 · 12-08-2004, 03:36 AM

Guys,
I looked at my engine and it is running with a Permatune CDI unit which has a 6 prong set-up and what looks like an older faded looking light blue colored Bosch coil from the engines earlier days as a 67 911 normale motor. My mechanic advises me that whatever CDI unit I end up buying, it should be compatible with the coil. I was thinking of going with the MSD Ignition Control Box 6A (I have a rev limiter on the distributor already so I don't need the advanced version with the rev limiter). Can I use this with my current Bosch coil or would I need to buy a new coil? If so, which one? Also, another Pelicanite sent me a PM offering me a used Crane Fireball unit.
Whatever I buy, I need to make sure that I can install the unit without having to take a course on CDI rewiring and retrofit.
Thanks for all the advice so far...

jluetjen · jluetjen's Garage

Quote:

Whatever I buy, I need to make sure that I can install the unit without having to take a course on CDI rewiring and retrofit.

Here's most of what you'll need to know already posted on the Pelican BBS.

Rot 911 · 12-08-2004, 05:20 AM

I don't think you have a Permatune problem with the symptoms you describe. Those things tend to either work or not work. I would first double check to make sure you are not running the carbs too rich before I started diving into the ignition, although I would make sure I had good points, condensor, rotor, cap, wires and coil.

blau911 · 12-08-2004, 08:39 AM

Can anyone advise if there is a specific coil that I should be running with a Permatune CDI box? Assuming my Permatune CD box is okay, can anyone suggest a coil that works best with the Permatune cd box. If so, plse provide manufacturer and model.

Rot 911 · 12-08-2004, 08:53 AM

Quote:

Originally posted by blau911
Can anyone advise if there is a specific coil that I should be running with a Permatune CDI box? Assuming my Permatune CD box is okay, can anyone suggest a coil that works best with the Permatune cd box. If so, plse provide manufacturer and model.

A Bosch blue coil will work just fine with the Permatune CDI

john walker's workshop · 12-08-2004, 09:16 AM

denso irridium plugs usually work where others foul. get an equivelent to the BP7ES. not cheap either, but worth it if they don't foul. check the idle jets with a jet gauge to be sure they are what they're supposed to be. the number on them stays the same regardless of what drill was run thru them. you might try a slightly smaller main jet. factory was 125. 130 maybe, would clean it up enough to stop the fouling. float levels are correct right?

Rot 911 · 12-08-2004, 09:20 AM

Quote:

Originally posted by john walker's workshop
denso irridium plugs usually work where others foul. get an equivelent to the BP7ES. not cheap either, but worth it if they don't foul. check the idle jets with a jet gauge to be sure they are what they're supposed to be. the number on them stays the same regardless of what drill was run thru them. you might try a slightly smaller main jet. factory was 125. 130 maybe, would clean it up enough to stop the fouling. float levels are correct right?

Hot damn, JW confirms what I suggested in my post above! That's right I'm bad, uh huh! Uh Huh! Oh yeah!

blau911 · 12-10-2004, 03:20 AM

Guys,
Installed the NGK BP7ES two days ago, and so far no fouling.
I will be back in the states in a few weeks for Christmas and will be bringing my Weberes with me to have them re-examined and rejetted.
Curious to know if someone here could suggest a good book for the mechanically inclined novice for rebuilding and tuning Webers? I would like to get actively involved in it this time around so I can eventually do it myself. Why let mechanics have all the fun....

Rot 911 · 12-10-2004, 05:24 AM

Quote:

Originally posted by blau911
Curious to know if someone here could suggest a good book for the mechanically inclined novice for rebuilding and tuning Webers? I would like to get actively involved in it this time around so I can eventually do it myself. Why let mechanics have all the fun....

Here's a good one, can get it used at Amazon.com: