Join Date: Aug 2010
Location: Arlington, Texas
Today I got started on giving it a full tuneup, even purchased a vacuum gauge. I pulled all of the plugs to inspect them, they all showed signs of normal combustion, tan coloring on the electrode. While I was at it, I went ahead and re-gapped them to .055". Previously they were .045". My thought is the high powered MSD box and blaster coil should be able to handle this gap. If not, that sort of steers my in the direction of faulty MSD hardware.
I double checked the firing order and the location of the wires, both on the distributor and on the plugs. As another measure, I checked the resistance of all the plug wires all of which fell within 2-3 kohms.
Re-installed plugs and wires and checked the timing with my light. It showed 8* BTDC I upped it to 12*. I've read that total timing should be 34*-36*. The stop bushing on my distributor is set to 21*, so I have a total of 33*. My real question is though, at what RPM should total timing be reached? I changed out the springs today to get the total timing to come in by ~3000 RPM I believe.
Got the vacuum gauge out to see how much vacuum I was pulling at idle and noticed that on two of the ports on the carb, the little rubber vacuum caps had dry rotted and were leaking. I replaced those and it smoothed the car out some. After addressing that issue I got onto getting the vacuum gauge hooked up. Once attached, I was able to get about 16 in Hg at about 600-700 RPM. A couple of questions on that though...
1. What should the idle speed be set to? I have a manual transmission car.
2. How steady should this mechanical vacuum gauge read? It was fluctuating maybe +/- 1 in Hg at a relatively low frequency. Is that normal?
With all that said, I didn't notice much if any backfiring through the exhaust. It did it once or twice when I started it up after letting it idle for probably 10-15 mins but after that I did not notice anything.
I also added some new gas and treated what I had left in there with some sea foam.
One thing I think I'm hearing (most noticeably at the exhaust tips) is an occasional...miss perhaps? I'm not sure how to describe it, sort a pause in the normal rhythmic pulse of the exhaust. As I describe it now it sounds as though I might have a cylinder misfiring on a semi-infrequent basis. Maybe this goes back to the increased gap? Although, I think this was actually present all along; I'm now just looking at it closer.
I probably should have gone ahead and checked for spark at each plug while I had them out, oh well. I'll do that next time I work on it. At least it can tell me whether I can rule out the ignition system or not.
I also should have performed a compression test while I was out there. I'll chalk that up to next week as well.
Will also check for vacuum leaks at all the external engine connections, carb and around the intake.