Warm up trouble after MSD install

[layzee]

Installed MSD in my 72 a couple of weeks ago, used 6A unit, blaster coil, gapped NGK plugs and Clewett wires. At first everything seems great, idle is much better, and hot starting is a snap.

From cold however, the car is a bit more reluctant to start. When it does it will idle fine without any additional throttle about about 1000-1200rpm, but pressing the gas makes the rpms dip like the car would stall. After 20 seconds of warmup or so this goes away and the car will rev fine.

The drive to the highway is about a mile from my house, that is all fine. Within a couple of miles at highway speed there is a definite misfire and bucking. Strangely, this seems also to be related to warmup as it also goes away within a couple of minutes. After that the car runs fine, seems to make great power throughout the rev range.

Any ideas? Thermostat on MFI perhaps?

[Steve@Rennsport]

The very first thing I'd do is check ignition components before touching the fuel injection.

Plug wires, plug connectors, coil wires, cap and rotor are just a few. Remember, MSD's make a LOT more current and any high resistances in the system will cause trouble.

Time for some detailed detective work,.....

[GaryR]

Aren't you supposed to use an MSD (or similar) Blaster Coil with the 6A or 6AL?

Edit: I'll read more carefully next time...

[jasonlee]

I think he has already installed a blaster coil.

[layzee]

I was running the Clewett wires before MSD install, they were fine, rotor arm and cap are both new-ish, no signs or wear at least. The coil is also new - MSD high vibration blaster coil.

As I said, the car runs better than ever when hot, particularly idle and pickup from low rpm. I mean I could live with it like this, but something's not right

[Steve@Rennsport]

Phil,

I'd agree,...something doesn't sound right to me, based on experience.

This requires a detailed, methodical approach to troubleshooting that assumes NOTHING. Just because something was OK several weeks (or months) ago, is no guarantee that its OK right now.

Remove and measure each plug lead's resistance

Measure the rotor's reistance as they are prone to burn with MSD's and wide plug gaps

Make certain that ALL plug wires are completed seated on the plugs and on the cap & coil.

Once you know that the ignition system is in absolutely perfect condition, then its time to look at the MFI pump and the cold start system.

[layzee]

Sound advice Steve, will do. Thanks.

[JFairman]

Did the idle speed rise a bit after installing the MSD?

Are you using the purple and green trigger wires?

If you are, and the idle speed is higher the polarity may be backwards.
If thats the case the MSD is triggering off the beginning or rise of the square wave trigger signal and 911 ignition should be triggering at the end or fall of the square wave.

The motor will still run with that backwards but the timing will be advanced around 15 degrees from it and ignition will be inconsistant at times.

[DUK]

Measure the rotor's resistance as they are prone to burn with MSD's and wide plug gaps
Quoting Steve here.

I've had this happen a couple of times. Just reduce the gap by .010 and make sure you use no grease on the rotor. And double check the trigger wires.

[cfries]

I thought with MSD ignitions, that the rotor is supposed to have no resistance as opposed to the stock 500Ohms which acts as a rev limiter. I could be mistaken

[jstobo]

I had a similar problem after installing a MSD in my 69. After trying several things I finally decided to regap the plugs. I had gapped them at .045 because of the MSD but I cut back to .030. Problem solved. No more misses during warm up. If you gapped your plugs according to the MSD instructions try setting them closer. Good Luck.

[graybrown]

I posted the following on a thread called "Clewett Wire Install" hoping I can save someone some of the problems I have encountered when using Clewett wires with an MDS Blaster coil:

I spoke with a guy at Clewett Engineering today. I bought an MDS box and High Vibration coil from Pelican, which didn't improve my gas mileage over 12 miles per gallon. I knew the coil to distributor wire was probably not properly seated in the MDS coil but didn't give it the attention it should have had. It has been nice here lately (Massachusetts) and the T needs to get some excercise and I finally decided to get really serious about this car. I replaced the center wire with the old one and now the car is what I have been waiting for (for eight years). The Clewett coil to dizzy wire is designed for "stock Porsche coils" and I have actually had the wire pop out and, obviously, the car died. No matter how hard and how much dielectric grease you put on the wire, it will not seat into the MDS coil. The Clewett guy says to squirt a couple drops of WD40 into the cap on one end of the wire and loosen the cap so it slides up the wire (it is firmly glued to the wire) then the wire end will seat. These are great wires with one small flaw if you marry them with the MDS system. I hope this will help someone.