new ignition....new problems
 

I have a '74 911 2.7 liter with CIS......

I just had my dead permatune cd box replaced with an MSD6a and added the petronics ignitor. It now hesitates when I accelerate from a stop and "knocks" and sputters at low idle (about 900). When accelerating at higher gears it seems fine.

I figured since it was sitting for about 8 months the gas was bad so I added fuel injector cleaner and a stablizer. I still had about 3/4 of a tank full of gas and didn't have a siphon.

It seemed to help a little but still ran rough. So I checked the spark plugs and they showed signs of being too hot. I replaced them with the same type (NGK brand) and regapped per MSD recommendations (about 1.25mm)........still runs rough,knocks and hesitates.

I then reduced the plug gap to .9mm and topped off the tank with 93 octane. This seemed to help a little more so I drove it for about 8 minutes or so and after a few good rev's it started to get worse. The exhaust now sounds like a badly tuned Mac truck. I checked under the car and noticed that the manafold port below the no. 1 plug had no bolts and you could see the glow of the pulsing spark(at night). I never noticed this before but could I have blown this loose by reving the engine if it didn't have any bolts? I think this has magnified the rough sputtering and knocking of the engine.

Could I have a valve adjustment issue? What does that sound like and does it go away at a higher rpm like this seems to do?

I know I have mentioned a few issues but I don't know if they are related. Any suggestions or advice would be appreciated. I am very much a novice at this so bare with me.

Thanks in advance,
Dave

Be sure the valves are checked/adjusted.



Doyle

I will be taking/towing it back to my mechanic who installed the cd box and have him check it. I have been paranoid about the valves. Are they typically sensitive and need to be adjusted often?

Dave

Doyle,
By the way, thanks for the quick response!

How sensitive are the valves and how often should they be adjusted?

thx
Dave

what heat range of plugs did you put back in. i use the BPR7's in my 2.7. signs of being too hot could also be from too lean or too much advance. advance shows up if you shut it down at WOT.
fix the exhaust then go from there.
check the mixture and vacuum leaks if it still runs bad, also timing and is the advance working.

For starters, If you have bad gas, it's too late for stabilizer. Once it goes bad, stabilizer will not bring it back to good. I hope you also added dry gas to absorb the moisture out of the fuel, if not, do that, after eight months of condensation accumulation you'll have water in the gas. This will cause the sysmptoms you are describing. If you have to run the old gas, throw in some octane booster.

Valves don't need to be adjusted every ten minutes, once a year or so would do for most of us. Look at the manual or Haynes for the official word.

Thanks for the replies...

I installed NGK BP7ES plugs and gapped them at .9mm+-.

Since it appears that the exhaust manafold/port pulled away from the engine I will address this. I also hear more backpressure "popping" when I down shift.
I am assuming this happened due to the increased exhaust noise. correct? The exhaust noise progressively got louder as I drove. Which I am contributing to the gasket/seal progressively pulled away creating the gap that I think I'm seeing.

Can you normally see the glow of the spark when looking under the engine where the manafold port is attached?

I'll have my valves checked since I have never done that in the 5 to 6 years I've owned the car.:eek:

MSDs often burn out the resistor in the rotor. might want to pop the cap and see. should be obvious if it's burnt. looks like a little white grub emerging from the epoxy.

plug wires. the MSD will find the weak link

what is a good plug wire?