MSD Blaster 2 installed onto '72 240z. Idling become unstable.

[tamo3]

Hi, I just got '72 240z with rounded SU carb.

Since cold start takes time, I also got new MSD Blaster 2 coil 8203.

After installed this coil, idling get unstable. I'm new to 240z and still studying SU carb setting.

Before, the factory original coil, it takes time to start up engine, but idling was stable.

Do I need to upgrade distributor also? or can I just adjust SU carb setting to make idling stable?

Thanks for your help in advance!

[Zed Head]

Did you get the MSD ballast resistor that comes with it and install it also? Looks like the MSD resistor is 0.8 ohms, the stock one looks to be 1.1 to 1.5 ohms. You might have too much resistance on the primary side.

Instructions are here -

http://www.msdignition.com/Products/Coils/Stock_Replacement/8203_-_Blaster_2_Coil_w/Ballast___Hardware.aspx

[steve91tt]

The new coil should not have hurt the stability of your idle and you should not need a different distributor. We need more information to diagnose the problem.

1. Condition of plugs, wires, cap, rottor, distributor

2. Is your car stock or has anything been added or deleted?

3. Have you done anything to check the tune on the carbs? Float levels, vacuum leaks etc.

4. Other than being hard to start when cold was the car runnning well through the rev band before the addition of the coil?

5. Did you change anything else when you swapped the coils? Could the plug wires have gotten switched?

With a little more information the folks on this forum should be able to help.

Good luck.

[steve91tt]

You posted at the same time I did Zed Head. I didn't think of the ballast resistor.

[Zed Head]

I just assumed the simplest installation, a straight coil swap, and noticed the resistance when I browsed the instructions.

Odds are good though, as you noted, that "a few more things while I'm changing the coil" were done. Who can resist...

[tamo3]

Wow! Thanks for the quick reply Zed Head, steve91tt!!

1. Condition of plugs, wires, cap, rottor, distributor

Before swapping coil, it everything was functional. All of them looks OK, but not sure. Especially I'm not sure how to diagnostic distributor condition.

2. Is your car stock or has anything been added or deleted?

My 240z is original no add, no subtract, no modification.

3. Have you done anything to check the tune on the carbs? Float levels, vacuum leaks etc.

No, not yet. Still studying how to now.

4. Other than being hard to start when cold was the car runnning well through the rev band before the addition of the coil?

Before swapping coil, once engine is running the idling was stable. After swapping coil, when I step on the gas pedal, it will misfire when RPM goes beyond 1500.

5. Did you change anything else when you swapped the coils? Could the plug wires have gotten switched?

When I installed MSD Blaster 2 coil, I also install 0.8 ohm ballast resistor that comes with 8203 package as Zed Head mentioned.

Thanks!

[Willoughby Z]

...noticed the resistance when I browsed the instructions.

Odds are good though, as you noted, that "a few more things while I'm changing the coil" were done. Who can resist...

Nice pun, Zed.

It's a long read but...

http://www.classiczcars.com/forums/showthread.php?37900-Electronic-ignition-Revisited-after-I-gave-up!&highlight=msd+blaster+coil

Edited January 31, 2012 by Willoughby Z
link added

[steve91tt]

Wow! Thanks for the quick reply Zed Head, steve91tt!!

1. Condition of plugs, wires, cap, rottor, distributor

Before swapping coil, it everything was functional. All of them looks OK, but not sure. Especially I'm not sure how to diagnostic distributor condition.

2. Is your car stock or has anything been added or deleted?

My 240z is original no add, no subtract, no modification.

3. Have you done anything to check the tune on the carbs? Float levels, vacuum leaks etc.

No, not yet. Still studying how to now.

4. Other than being hard to start when cold was the car runnning well through the rev band before the addition of the coil?

Before swapping coil, once engine is running the idling was stable. After swapping coil, when I step on the gas pedal, it will misfire when RPM goes beyond 1500.

5. Did you change anything else when you swapped the coils? Could the plug wires have gotten switched?

When I installed MSD Blaster 2 coil, I also install 0.8 ohm ballast resistor that comes with 8203 package as Zed Head mentioned.

Thanks!

Have you checked that the plug wires are hooked up in the right order? Mine will do what you describe if I get a wire in the wrong place. You might also put a timing light on each plug wire one at a time to check that you get a good even pulse from each cylinder. If you find one or more cylinders have an irratic rhythm then you might look at the rottor/cap/points/distributor.

[ConchZ]

By any chance did you open up the gap on your spark plugs when you upgraded the coil? My PO installed an unknown pretty chrome coil, and a Crane Fireball 700 ignition module. Some websites suggest opening up the plug gap with an aftermarket coil, so I tried it. Made the idle rough, and created random misses under load.

[tamo3]

After put it back to original coil and resistance, the symptom was same. It takes time to start up engine and I need to jump start with hooking up battery with other car.

Once engine get warmed up, I swap back to MSD Blaster 2 coil with resistance.

Now it works!!

The problem was just cold air temperature. I guess I need to study more about how to setup SU carb in order to quickly start up engine.

By the way, distributor to spark plug ins connected to 1-5-3-6-2-4 in counter clock order.

Thanks!