What is the effect when dwell angle is too large?

[caproader]

Guys, I just hooked up my craftsman RPM/Dwell meter to my MFI 2.7 with Bosch distributer.

The book says that dwell angle should be 38 degrees plus or minus 3 degrees. My dwell meter says that my engine dwell is 45 degrees. Timing is right at the TDC called for in the 2.7 spec book and it advances (without the vac hose) very nicely to 35 degrees at 6000 rpm.

Anytime that I have started to play with adjusting the points gap, I spend the next three fiscal quarters chasing the adjustment. Too much, then too little, then even more too little, etc.

Before I tear out what little hair that I have left, what happens if I leave it at 45 degrees of dwell?

Burn a valve?
Bad gas mileage
Detonation/knock
Run on after engine shut down
premature spark plug wear
fouled plugs
A plethora of naked lady pictures on the internet

The engine seems to be running strong. I am inclined to humor it but would like to know if I am playing with fire.

Thanks,

John, member #322
sporto 73 S
73 MFI 2.7
90 hp neck snapping, heart pounding, adrenalin pumping 1969 912

[Flieger]

The dwell doesn't really matter on a CDI car since the capacitor charges so quickly that only a tiny dwell time is necessary. Just set the timing and let the dwell fall where it may.

[RSTarga]

I agree, the only thing to watch is that the points don't close up to much due to rubbing block wear. It'll start backfiring and stalling. I forget higher dwell=points wider or is it the reverse? I try and do this as little as possible and always forget. It's a good idea to have a spare set in the glove box for an emergency, I speak from experience. Make sure and have that special grease on the lobes.

[edmayo]

Higher dwell means the point gap is closer (they're closed longer) If you start with a closer gap then the mileage will be less before they close to the point (pun intended) that they don't open enough and the back firing and tach bounce you mentioned will start.

[caproader]

Thanks Ed. that would explain the occaisonal back fire. Now to reset the points

BTW, I found a spare distributer on the shelf, Bosch # 0 231 184 006. Not sure where it came from. Can I use this in my 2.7 MFI mobile? It would sure make things easier if I could set the points in the 006 while it is out of the car.

John

[edmayo]

I don't have that information here at home, I'll get it for you tomorrow. I always remove the distributor to set the points. By the way, I notice you've seemingly, purposely not mentioned the "sporto" What do I read into that?

[caproader]

Ed,
About the sporto: I decided that maybe my ex wife was right when she said that I needed "Professional Help". There is a great mechanic at the dealership here quietly toiling away in a far corner of the shop. I had it towed over on Monday, gave them my budget limit and told them to call me. I needed to decrease my frustration level and increase the working area in the garage so I can work on the 912.

About the Marelli points: For the time being I think that I will hang onto them until I run accross someone who needs them. Until then, they go back in the parts drawer. Let me know if you need them.

About the distributer: My Bosch interchange book ends at 1975. I could not find the 006 part number listed there. I am not sure where I picked up this distributer, but I think I remember that it might have had a 'MM' rebuild tag on it when I found it.

John

[caproader]

Ed,
And if I have a choice, is it better to have the point gap be a little on the 'too much gap" side or a little on the "too little gap" side?

John

[edmayo]

For a CD you can be a "little" on the too much side (less dwell) because of the rapid discharge of the CD, as opposed to the old Kettering ignition where you tried to squeak in as much dwell as you could and still have the points give reasonable mileage between settings. Setting with a feeler gauge should be .013" to .015"

I couldn't find that distributor number. Would the tag indicate "Motor Meister" rebuilt it ? Oh dear!!!

See!! if you had listened to her back then,,,,,,,,,,,,

[caproader]

Thanks Ed. .014 it is. Now for a timing question:
The spec book calls for 5 degrees after TDC for the T, E and S, but TDC for the 2.7. My engine is 2.7 MFI (started as a 2.4 Liter E) with a 911E distributor. Should I set my timing at TDC or 5 degrees after? Is the timing difference because of engine size, distributer advance curve, US crap gas, or ROW Runability?

Thanks

John

"If I knew when I was a virgin what I know now, things would be different. But you have to go through the unvirginating process to get the knowledge."