MSD unit Best location

[Number1_dog]

I have a 1979 911sc with a short stroke 3.2, max Moritz P&C, 9.3 compression, 46 PMOs, 964 cam grind with a MSD ignition. See the location of the unit in the picture. Last year at this time on a hot day the unit stopped giving spark. I replaced the unit and all was well until an Autocross today. It was hot today and on my last run all hell broke loose, the engine was reving with out any input from the gas pedal. I let it cool down, it started but my tach was not working and I had an erratic idle. Gas pedal cable was ok and not binding, and the clutch cable seemed ok. I am thinking that the MSD unit over heated because it is tucked into the rear fuse panel cover. I think if I put it on the bulkhead next to my fuel regulator gage it will be in a cooler place. Richard at PMO recommends the MSD unit, any other alternatives?

[Number1_dog]

Location in f unit

[Number1_dog]

What no one has an opinion!!!!!

[Showdown]

That’s kind of the default location for just about everyone and it seems to be a fine one without widespread issues.

Maybe there’s something else going on with your unit?

[3literpwr]

Mine are installed back to back on the same side as yours and I think it's a good location. Now, for your issue.

1. MSD's only provide spark, not air or fuel...and engines don't rev without air or fuel.
2. They are designed for engine bay installation. (likely designed for 140C) like most automotive electronics.
3. Look at your throttle linkage and make sure they are setup proper and are lubricated...keep in mind how little throttle is required to rev the engine.
4. Would be good to verify your timing when warm.

All said, it's not impossible you have a failing unit, but I think you should look elsewhere before you jump to a overheating MSD.

[3literpwr]

Here is the engine bay of the car that won the East Africa Rally this year. It's running twin units that look an awful like the ones MSD makes for Summit. Regardless, this car is running in one of the harshest rally environments for hundreds of miles and grueling stage.

https://www.summitracing.com/parts/sum-850610?seid=srese1&gclid=Cj0KCQjwvqeUBhCBARIsAOdt45ZOTtCOFyoKWv9U6o-h5SVf8u6RNw2W8YFr4UITXRhyjdLYFups1poaAvYDEALw_wcB

[Number1_dog]

I have gone through two units in two years. The first unit was installed when I did my PMO conversion in April 2020, it failed in June 2021 and was replaced. Now in May 2022 I am having problems. The CD unit in your picture is further back on the left bulkhead than mine is. And it is tucked in can covered by the rear fuse panel.

[Number1_dog]

And my tach doesn’t work now

[Showdown]

It sounds like maybe there’s an electrical issue with your installation if you’re burning through these units which are remarkably stable.

Is your MSD’s power source fused?

Have you checked for shorts?

[AlKidd]

Im running a streetfire without issue.

[stownsen914]

It is interesting that the tach doesn’t work. Many possible reasons for that, but the MSD is one possibility.
How high is this self induced revving? Are we talking hundreds of RPM, or thousands? Ignition timing or faulty ignition could cause a bit variation in RPM, but I wouldn’t think it would be like really stepping on the gas.

[Number1_dog]

It also continues to run for a few seconds after I turned the ignition key off. I was told there was a lot of smoke I guess the carbs were loaded

[Number1_dog]

I had the car towed home on Saturday and pushed it back into the garage. Sunday I had family stuff to do. Just went out and checked alll MSD connections made sure the distributor was fixed checked the carb throttle cable and return springs and all was well. The car started immediately and the tach was working and it idled correctly. I took the rear fuse panel off so the MSD unit can get more air around it. I still believe the MSD unit may have overheated, but once cool it is now working.

Thank you all for your suggestions and recommendations

dog

[Showdown]

Could there be a vibration issue? Something coming loose after the car has been thrashing about? A ground wire that’s barely holding on?

[3literpwr]

The sticking issue comes from the carb to carb linkage and when hot. Can't be cold...if the motor is hanging on throttle, you need to push down on both linkages and see if it settles.

[GG Allin]

Anyone put theirs under the front seat? I have mine out now and want to address the messy wiring. I'm going to terminate everything unneeded and clean it up real good. Out of sight would be best.

[hootster2310]

Number_1 dog,
I have an 80 Targa, I also have my MSD located in exact spot as you. I installed it in 2011 and it worked flawlessly until last summer, it would start and run fine after sitting overnight for about 20 minutes than just die, let it cool for about 10-15 minutes and the cycle would repeat, it would die sooner if car was already warmer than starting from a total overnight cold start. Tony aka boyt911sc helped me isolate and narrow down the cause!! I called MSD, they gave me info to send it back to them which I did, they performed a full systems check / refurbished for like $35 and returned it. I covered shipping both ways, they also included a tech sheet of what they performed and the diagnosis of the failed and replaced components, in my case I believe it was some unstable capacitors if my memory serves me correctly, it corrected my problem!! I will say they definitely stand behind their product which is pretty awesome these days!!

[al lkosmal]

I use the MSD Streetfire with my EFI kits that are configured for CDI ignition. It is smaller and, with a custom mounting plate, can be mounted in the stock Bosch CDI location.......very reliable....not had any fail, that I am aware of.......however....coils will go intermittent on you....failing when hot and then working ok when they cool off......until finally, they fail for good.

regards,
al

[PeteKz]

What Al said. That is a common way coils fail.