Been chasing a problem and looking for some help/ideas that I haven't thought of yet.

548" BBC, 1050 dominator on alcohol setup by Rupert, 15:1. 7psi of fuel pressure on a magna fuel return style regulator. NGK -9 plugs gapped at 0.020", 32° of timing (locked), MSD 7AL2, MSD billet distributor, MSD 2-step and a MSD Blaster SS coil.

The car starts and runs good. Launches good and has been deadly consistent but breaks up most notably after the gear shift. I can hear it and I can feel it.

To date I've changed to the -9 plugs from -8 and reduced the gap to 0.020" from 0.030" with no change. I went from a 185 to a 205 main jet all around with some improvement. Gone up and down with timing with no change.

I stage with 150 degrees of water temp and see about 20 degrees of rise after a run.

The jet change seemed to make the most improvement but I barely have any material left in the jet extensions in the rear bowl to go much bigger, not to mention I think it's more jet than I need already.

What am I missing?

Edit: after re-reading the manual and looks like I may just be running the wrong coil. Not sure how I missed that in the first place but I suspect the coil decision was made with my wallet rather than what's right. Looks like I need an 8201 coil so perhaps I'll start there unless there's something else obvious.

This message has been edited. Last edited by: CSRacing,

I had several 7AL-2 boxes do that. Both checked out good with MSD ignition tester. So MSD said there was nothing wrong with them. I would try a known good one.

I have another 7AL2 on a shelf that I can try, but I just edited my first post. I think I'm just using the wrong coil.

8251 is another option that I use rather than the expensive 8261.

20 degree temperature rise is too much, would indicate a lean condition.
Most guys I know with alky carbs stage at 160 and above.
Look for a 5-10 degree temperature rise.

is this 12 volts and are you useing k&r switch panel/relay board

a msd tester may be beneficial to locate the issue

On alcohol I always like to go into burnout box at 160* plus and stage at 180*If it is too cold it will not run clean down track.

I have a MSD ignition tester and I do not trust them very much. I had one box that would run a 5.09 nice and clean then next pass a 5.49 banging and popping. Ignition tester always said it was good, tested clean to max RPM 14,000 or what ever it is. Called MSD several times and they told me if tester says it is good then box is good and led me on wild goose chases. Changed box and it ran 5.04 over and over.

I have basically the same set up and had the same issue for a few weeks. New magnetic pickup in the distributor straightened right up.

A MSD Blaster SS Coil PN 8207 is perfectly acceptable with a 7al2. Review this chart

https://documents.holley.com/t...coil_compability.pdf

If engine will achieve the rpm shift point without missing, and then after the shift drops 500+ rpm and starts to miss and you can feel it, it makes one doubt it’s ignition imho. But here’s what else I think.

I think .020 plug gap is extreme and .030 a better choice even with methanol.

If you haven’t already, remove the distributor cap and leave the wires attached to include the coil wire. With a multimeter set to ohms, meter from the contacts inside the cap to the spark plug boot. All reading should be close to same with shorter wires slightly less in resistance than the longer ones.

Check to see that the carbon ball in the center that the rotor tang rides against is present.

Remove the rotor and turn it over and look at the bottom where the spring tang is riveted to the tang that makes contact with the distributor cylinder towers. Should not be discolored from heat. Some rotors use a screw that holds the two tangs together. Check tightness. When you place the cap back on the distributor you should feel it touch the spring tang the last 1/8” of cap engagement to distributor base.

Here's my last suggestion that I and others have seen fail and give ignition miss. If you use a toggle switch panel for the ignition ON, switch the ignition ON to a different switch output not being used. If all switches are used switch with one that is seldom used like tail lights. We’ve seen these switches fail and during the vibration of high rpm intermittently oscillate on/off/on rapidly. If you use a stand alone toggle switch for ignition ON, try replacing it.

Switching the ignition box with another known good one would be good to try also.

The Magnetic Pickup for All MSD Billet Distributors should meter between 500 - 700 ohms if using distributor trigger.

The 8276 Non-Magnetic Pick-up for MSD Flying Magnet Crank Trigger Kits should meter 70 - 90 ohms.

This message has been edited. Last edited by: markemark,

quote:

Originally posted by Curly1:
On alcohol I always like to go into burnout box at 160* plus and stage at 180*If it is too cold it will not run clean down track.

I have a MSD ignition tester and I do not trust them very much. I had one box that would run a 5.09 nice and clean then next pass a 5.49 banging and popping. Ignition tester always said it was good, tested clean to max RPM 14,000 or what ever it is. Called MSD several times and they told me if tester says it is good then box is good and led me on wild goose chases. Changed box and it ran 5.04 over and over.

That sounds like what happens when the red 7AL-3 boxes go bad. If you put a timing light on the car and bang on the box, you'll see the timing jump. Then you send the box to MSD, they tell you there is nothing wrong but they 'updated the board / relay' and then the box miraculously works fine again.

Changing a carb and ignition box is quick and easy to do and could help you narrow it down quickly. I would change them out and see if it eliminates the problem. If you do not have a spare I am sure someone would loan you one to test.
With the carb I always blow out all of the air bleeds real good until you can see and hear they they are open. You probably know that but any time carb acts stupid first thing I do.
Think there may be a better choice than that Blaster coil. You do not have to spend much money on coil if you do not want to. There is a Ford coil that has same specs as the MSD 8261 and available at any auto parts for cheap. (Less than $20) I use the MSD 8261 and have a few spares but I have one of those cheap Ford generic type coils to for in an emergency.
Quick, easy and cheap to try another coil so would try that to. Thing is you do not have to spend $325 for a new coil to find out if that is problem.
I use the Smileys Racing Ultra spark plug wires. They are the Moroso Ultra 40 spark plug wires even in Moroso box but they are around half price of the Moroso. Those plug wires have worked better than any others I have ran.

I hesitate to say this because I run alcohol. But they say some larger cubic inch Big Blocks work better on gas than alcohol due to cam design or what ever.
If trying the easy, obvious things do not fix it I would consider trying a known good gas carb.

On alcohol the problem may be as simple as too cold of water temperature. Mine will not run good at all under 160*

Thanks for the input so far guys.

To answer some of the questions/comments made so far:

The distributor, cap, rotor and coil are all brand new with maybe 20 passes on them. I will measure the resistance of the pickup but I'd be surprised if it's bad already. Same with the cap and rotor but I will do a visual inspection.

Switched power to the box comes through a relay panel that is also new.

My coolant temp was misstated. Looking back at info, I stage at 160-170 and see less than 10 degrees of rise by the time I look at the gauge on the return road.

I'll take the carb apart and make sure it's clean.

Plug gap was 0.030" until this past Sunday when a fellow racer recommended trying 0.020".

I get breakup before the shift as well but it's most notable after the shift.

I have an 8251 coil coming that I will try along with a spare 7AL2 as well. Will report back with whatever I find.

If you havnt messed with the carb (float adjustment mainly) since it came from Rupert, id say your wasting your time taking it apart. If you ignition is good, alky will go down the track clean lean or fat.

Sound electrical to me

Did it just develop this problem or has it always done it? Were there any changes just before it started?

quote:

Originally posted by Jonesz:
If you havnt messed with the carb (float adjustment mainly) since it came from Rupert, id say your wasting your time taking it apart. If you ignition is good, alky will go down the track clean lean or fat.

Sound electrical to me

Haven't touched anything on it aside from idle speed until this weekend with the main jet change.

quote:

Originally posted by CURTIS REED:
Did it just develop this problem or has it always done it? Were there any changes just before it started?

I feel like it's done it since I put the billet distributor and coil on the car, which hasn't been very long. I was running a crappy large cap HEI prior to that as it's what I had. I suppose I could reinstall that and try it as another troubleshoot step as well.

I have had a host of issues this season that have blurred everything. I have everything else sorted out so now I'm focused on this last bug.

quote:

Originally posted by CSRacing:

quote:

Originally posted by CURTIS REED:
Did it just develop this problem or has it always done it? Were there any changes just before it started?

I feel like it's done it since I put the billet distributor and coil on the car, which hasn't been very long. I was running a crappy large cap HEI prior to that as it's what I had. I suppose I could reinstall that and try it as another troubleshoot step as well.

I have had a host of issues this season that have blurred everything. I have everything else sorted out so now I'm focused on this last bug.

Try drilling a vent hole in the distributor cap. If it's a crank trigger, make sure your pickup gap is correct and your distributor is phased.

quote:

Originally posted by BD104X:

quote:

Originally posted by CSRacing:

quote:

Originally posted by CURTIS REED:
Did it just develop this problem or has it always done it? Were there any changes just before it started?

I feel like it's done it since I put the billet distributor and coil on the car, which hasn't been very long. I was running a crappy large cap HEI prior to that as it's what I had. I suppose I could reinstall that and try it as another troubleshoot step as well.

I have had a host of issues this season that have blurred everything. I have everything else sorted out so now I'm focused on this last bug.

Try drilling a vent hole in the distributor cap. If it's a crank trigger, make sure your pickup gap is correct and your distributor is phased.

Not a crank trigger.

quote:

Originally posted by CSRacing:

quote:

Originally posted by CURTIS REED:
Did it just develop this problem or has it always done it? Were there any changes just before it started?

I feel like it's done it since I put the billet distributor and coil on the car, which hasn't been very long. I was running a crappy large cap HEI prior to that as it's what I had. I suppose I could reinstall that and try it as another troubleshoot step as well.

I have had a host of issues this season that have blurred everything. I have everything else sorted out so now I'm focused on this last bug.

So years ago my car used to do that exact thing when I just ran off of the distributor/8201 coil. I first used it with weights in it, then locked out and it would do it. I changed to a crank trigger and never had a problem after. Mine was a little more pronounced than yours sounds but it was always there. Caused zero other problems aside from that though.

I don't know why some people can run only a distributor/coil set up and have no problems at all.