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Distributor fix for V6

M

Mod_Squad!

Bronze Level Sponsor
A while back there was talk about limiting the advance on the distributor on the 2.8 V6. Did anyone ever come up with a solution for that? I'm on my 3rd carb and 2nd or 3rd distributor. I've had the car up on a dyno numerous times. I'm about 99% positive that the problem lies in the distributor over-advancing under full throttle conditions. If I nurse it through the 2800 to 4000 rpm range it's OK but if I punch it, it craps out. I think that the distributor is over-advancing at that point. I've changed power valves, rejetted, changed carbs, distributors, cussed etc. I'm still out driving the car though :).
I have yet to find an old distribbutor that isn't a rebuilt etc. I seriously considered going to a points type distributor and then putting in a Pertronix unit and see if that did the trick.
Any suggestions gladly accepted.
Thanks,
Bryan
 
R

RootesRacer

Donation Time
Going with a pertronics isnt going to fix your advance issue.

The pertronics would be a good replacement for points, but is inferior to the stock duraspark ignition.

What you need to to is to map the RPM timing advance with a light.

To do this, disconnect your vacuum advance hose, and measure the idle timing, and then measure are 500 RPM intervals.

IIRC idle should be 8 to 10 BTDC and should increase more or less linearly to about 28 to 30 degrees BTDC at 3200 RPM or so.

If it does not, your distributor mech advance is sticking or worn out.

After doing that, see what impact the vac advance has on timing and drivability.

Late 2.8 dizzys have a dual/differential diaphragm vac advance, which can do funny things if its not plumbed right. If you have 2 vac ports, then you might want to just run mechanical adv only.
 
B

Bill Blue

Platinum Level Sponsor
Bryon, I have trouble seeing this as a distributor problem. The distributor should have maxed out the advance by 3400 (or so) rpm. When you punch it, advance should decrease because of the vacuum decrease. If you did have to much spark advance, I'd think you would have pre-ignition issues.

Try retarding the spark 5-10 degrees. If the problem is spark timing, the problem should either go away on move to another rpm band. Note: This is a trouble shooting move, not a timing recommendation.

Have you tried another spark box? That sounds like a more likely candidate, but don't ask me why the problem would be restricted to a certain rpm range.

Bill

P.S.
It suddenly hit me that it could be spark breakdown. I'm thinking this is probably the rpm range with the greatest demand on the ignition system. Anyway, my thought about the sparkbox still stands, but add coil to the list.
 
V

V6 JOSE

Donation Time
Hi Bryan,

Your problem is with the two little holes that are behind the power valve. I had the very same trouble when I put the Holley four barrel on my first Alpine. You need to drill these two holes out to about .035/.040 to start with. If it still hesitates a bit, go up another .010 at a time.

The problem is that your power valve opens properly, but the two little holes don't pass enough gas to feed the extra throttle opening, so it leans out, and the engine falls on it's face. When you drill these out, you will notice a big improvement.

Jose :)
 
M

mikel

Donation Time
Bryan,

I was on the same path you are following. I am a total shade tree guy and by no means a pro. So here goes.
The problem sounds like what my car was doing, a real puzzle, enough to drive you crazy. And spend a bunch of crazy money fixing what I thought I fixed by replacement.
I went through 3 distributors before I started reading about them.

Upon inspection I found all 3 rebuilt distributors were modified by someone before the rebuild. I kept the cores to take apart.
Not to dispair you can make corrective adjustments with the distributor in the car after you first remove the distributor and do a basic inspection.

Rootes Racer has the info on advance written clearly so keep it in mind.

The first inspection of the distributor is made out of the car and is important and simple.
Hold the distributor casing and make sure there is no upward/downward play in the shaft. Also inspect the gear on the bottom of the shaft.
If the shaft moves up or down once you hit higher RPMs the shaft will move and change your timing settings. I found this to be the case in one of the rebuilts I used. Crazy stuff. I replaced this distributor as I found no way to adjust the play. I didn't trust adding shims.

After you do your inspection place the Distributor back in the car and set the initial timing. I have a Delta Cam and it requires the basic 12 degrees. Anything less than 12 on my car and it is hard to start.

As Rootes Racer noted plug the vacuum and set the inital timing than you can start checking your advance (with the vacuum plugged) with a timing light and a tach note the advance in a note book with each increase in RPM,s. It should max out at 28 to 30. But it may go higher if someone bent the weight stops inside the distributor.

If you took notes in your book and see the advance coming on too early. There are spring tabs which are bendable to adjust the spring tension.

Jose can comment on the engine and factory settings for timing and smog control. I will bet the advance was preset by the factory for reduced smog and not for performance.

After you are comfortable with the spring and weight stops you can adjust the vacuum canister on the distributor. It is adjustable with an allen wrench. The wrench fits in the vacuum tube. First mark a starting point on the side of the canister and count the number of turns one way or the other in your note book and write down the results. There is a spring and diaphram in the canister. The allen wrench adjusts the tension on the spring.

My guess is that your distributor is advancing too far and too early.

Hope this helps.
Mike
 
M

Mod_Squad!

Bronze Level Sponsor
Thanks to all for the advice. I'll print it all out and give it a shot. Jose, I did do the Powervalve mod like you recommended but I might not have done it to this newer carb. I'm positive I did it on the last one and it did help. A while back I built a modified distributor cap (2 actually) One of the caps has a big hole in the top so I can see down inside and look at what's going on. The other cap is notched about 3/8" or so from the stock location and it is the cap I've had to use from the beginning. I took tha car to a mechanic last year out of sheer frustration. On his analyzer, once we got it up around 4,000 rpm's or so, it would crap out and the instrument he was using showed that it was losing spark (trying to arc back to another plug). Like I said, at this point I really feel like it's over advancing.
Anyhow, thanks again to all for the advice. Looks like I'm going to rip into it this weekend and see if I can get her dialed in properly. I sure can't make it worse than it is :).
Thanks Again,
Bryan
:)
 
M

Mod_Squad!

Bronze Level Sponsor
Hi Bill,
That's exactly what I thought at first but I was assured by the mechanic that it wasn't the case. We pulled my distributor and removed the star wheel to make sure the guts were operating properly. He reassembled it and put it back in and the problem remained. I have pulled it numerous times and placed it back in, one tooth forward or one tooth back and in either of those scenarios it was way out of the ballpark. I'm going to keep looking for an original, untouched distributor and then proceed with all of the recommendations. I'll pull that powervalve and double-check that I've done the Jose fix on it as well.
Thanks again to all for all the tips,
Bryan
:)
 
B

Bill Blue

Platinum Level Sponsor
Bryon, how much plug gap are you running? Sounds like the spark is taking the easiest path, even though it is not the right one. Guys running turbo 2.3's have this problem at high boost, have to back the gap back to 30 thou or so.

Bill
 
husky drvr

husky drvr

Platinum Level Sponsor
Bill Blue said:
Bryon, how much plug gap are you running? Sounds like the spark is taking the easiest path, even though it is not the right one. Guys running turbo 2.3's have this problem at high boost, have to back the gap back to 30 thou or so.

Bill
Click to expand...

This is a problem that could also be aggravated by excessive resistance in one or more of the plug wires.

Just a thought,
 
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