[jessgator1]

Hi all (newbie here).

1966 Mustang w/ 289, A/C, Auto Trans, Power Steering, Power Brakes.

Book says I need .034 inches in the spark plug gaps on the motor. I pulled the plugs on the passenger side and they are about .044 (Brand new Autolite plugs). I am considering "tapping" the gaps to get the .034 inches the book says, but with the power steering, A/C, Brakes, they are kind of a pain to get to. Will adjusting the .01 inches really make a difference?

Any chance the extra gap will affect how the car idles? I installed a Pertronix II and a Flamethrower coil and it bumped the timing up to about 22 degrees. The car still idled/ran great, but I didn't want to leave the timing there because the book says it should be 6 degrees. I've read on some posts that 8 degrees works better and I've got it sitting at 9 right now and it has affected the start/idle (makes it rough and quits sometimes in reverse).

Checked the vacuum and it's holding steady at 16".

I guess this is kind of a loaded thread here.

So, in summary, the car idles a little rougher with timing set at 9 degrees and I would like to get it back to where it was when I had points in the car. Is it worth adjusting spark plug gap from .044 to .034. Is that gap the more likely culprit as to why the car is idling a little low or is it more likely the fact that the vacuum is sitting at 16"?

thanks guys/gals.

 

[1966er]

I have mine gapped at .045 & using the Pertronix Ignitor II. Leave them be.......

 

[Nor Cal]

1966er's right. I don't think the plugs are the culprit. The book says .034 for the gap but that's using a stock points ingnition. If you have an electrical ignition like the Pertronix you're able to get away with a larger gap. So that's actually a good gap you've got there.

I also like mine set at 8 degrees BTDC so I don't think 9 degrees is your issue. I'm inclined to think it's a vacuum problem or something. I'll let someone with more experience in that area chime in though.

 

[RF Mustang]

The old 289's like timing set anywhere in the 8 - 12 degrees' BTDC. If you find novacuum leaks, advance your timing a little more but no more than 12 BTC.

Wear and tear and a lot of milage on a motor almost makes each one unique in how they run. It can require you to make certain adjustments "outside" the spec's to suit their desire to operate as they should.