Points Distributor Dwell
 

Hi,

My points distributor which was last used was nicely set at 28 dwell when running but perhaps got moved around , I'm kinda surpised.

I got my engine started and set base timing to 16 Initial which was a headache, i just never assumed perhaps the dwell gap changed that much.

When I hooked up my dwell meter it was at 5 Degrees for V8, surprised it even started, lots of misfires. Condition of points is near new

As I moved it towards the standard 28-32, needle moved in right direction but would go as far as 10-12 and the engine just stalled. Do you need to move up idle up to say 1500 to overcome it as you adjust dwell which is that far off? I don't think my meter is broken?

Curious if you think it's better I just set the gap using a feeler gauge with battery disconnected to 30 thousandth of an inch and try to re-fire it? Then check?

Leads are green to positive coil and black to ground. Switch in right direction.

Only other way I can think is slowly move dwell more open screw. idle 1300 rpm then re-adjust timing in increments , dwell then timing, slowly getting it to move the needle over farther.

Just learning, thanks again.

Dwell meter positive goes to coil negative

That'll help a lot.

Ok thanks! I'll re-do the test!

If you have to use the feeler gauges... Set the gap at .019" and don't forget to lube the cam.

Clay

Rule of thumb for dwell changes
 

Remember that for every degree of dwell change, your timing changes TWO degrees at the crankshaft. When the dwell increases, the timing RETARDS.

Since you moved it from 5* to around 12*, you retarded the timing about 14*. That's why it stalled.

Dwell should be set at 30* or point gap set at at .019". With new points, set to .019" and then do the final adjustment via dwell meter.

Best way to adjust points is via the dwell when the vehicle is running. We've always used 28* for new points and then readjusted them to 30* once the rubbing block has 'broken in' after a few hundred miles.

Try this procedure:

Bump your initial timing up to around 30* and tighten the distributor clamp.

If the engine is still idling below 1500-1700 RPMs, Give your idle speed screw about 1/4-1/2 turn in - increase the idle 400-500 RPMs.

Adjust the dwell to the 30* you're looking for. Your timing will back down to around 10* but it should still run.

Then re-adjust the timing to the 16* you have now and adjust the idle speed to whatever speed you prefer. You may have to adjust timing and idle speed a few times back and forth to get where you want to be.

Then re-check the dwell in a month or two, after the engine has been run some and the rubbing block on the points has polished itself to the distributor's points cam.

Good luck!

Thanks Joe Garage, I'll hook up the damn thing right and see where I'm at, thanks for teaching me more about it!

I don't think that's right. One degree of dwell change = one degree of timing change.

There's a two-to-one ratio of crank degrees to distributor degrees...but one degree of dwell change = 1/2 degree points close sooner, plus 1/2 degree points open later = one degree of dwell change. 1/2 degree points open later (which it the thing that causes timing change) = one degree of timing change.


Agreed. Points open later, which retards timing.

That's correct. It IS a one to one correlation.
 

Forgot about the fact that 1/2 of the change would be in front and 1/2 behind.

Thanks for correcting me. :)

Be aware the rubbing blocks on the point sets being sold at chain part stores today are very soft and will wear quickly. NOS GM in the foil packs,Accel/NAPA(same thing-different package) are still currently good.
It’s getting harder to find common tune up parts that aren’t throw aways.

I was taught hook to distributor side of coil back in my teens. I remembered that forgot alot of other things.

I fired it up , then moved it a small amount to 31-32 dwell, then after warming up to temp i adjusted distributor timing to get max vacuum, about 14-16 , then backed it down a bit . It measured 20 initial. I then attacked the idle mixture screws(2) for best vacuum. Gained 1-2 inch of vacuum. checked 02 sensor, and it was 11.5 or so. I leaned it out to about 13.2 at idle. So time for a test drive to feel raw power of points action.

WITH or WITHOUT the vacuum advance connected?

WHERE is the vacuum advance connected--manifold; or ported vacuum?

Adjusting the timing at idle for "max vacuum" is almost certainly going to be WAY TOO FAR advanced. 20 degrees of initial timing (assuming no vacuum advance) is in the range of starter-motor kickback problems, and shattered starter housings. In addition, depending on how much centrifugal advance the distributor allows, you could be way over-advanced at high speed.

Be careful!

Lean-dropping the idle mixture screws a little bit does wonders for tailpipe emissions while not affecting idle quality very much. See how it runs, but you have--maybe--gone too far lean. I lean-drop based on a vacuum gauge not an O2 sensor; I lose 1/4--1/2 inch of vacuum from best idle for the two screws combined.

Not a bit better than HEI "action"; potentially worse at higher RPM as the coil fails to saturate at a lower rpm with points than with HEI.

Hi Schurkey,

Thanks again for helping out ,always enjoy your posts. I've ran with 18 initial for quite some time over the years. I have an imi starter and it's never kicked back or been an issue, always started for me.. really enjoyed that starter over the big one!

My off idle advance doesn't come on till about 1200 rpm and I'm under it at about 950 in idle and 750-850 in drive. My mechanical advance from factory was limited to 18, I did a blip to 3000 and set gun to 36, it hit the zero line . so I'm bang on 18+18 = 36.

Vac advance is currently not hooked up. When it was , it was crane limit adjusted to 6-10 degrees , to ported. so i think , that this is what I would consider quite optimized distributor?

You're saying if I have a HEI, that has the adapter to run the old points coil and not HEI coil in cap, that it would work a bit better than this points? If so I'd switch for sure on your recommendation. I just had to go back to stock since the crane xr-i fiasco screwed me Royally .

[Elvis Voice] Thankyew, thankyew verra much! [/Elvis Voice]

OK. I have an IMI on my boat. (454 Chevy)

Idle speeds seem high. Consider adding vacuum advance, and reducing the idle speed.

Are you SURE the advance is "all in" at only 3K rpm? Wouldn't be unusual for factory advance to need higher rpm to fully extend.

In most cases, an engine used primarily at part-throttle should have vacuum advance. Improved throttle response, improved fuel economy, reduced plug fouling. Potential for lower heat rejection to coolant. Too many benefits to overlook.

The amount of vacuum advance, and the amount of vacuum needed to activate it are both part of the tuning process. Manifold vs. ported = use whichever works best--but that's generally (not always) manifold vacuum.

Every vehicle I own either came with electronic ignition or got converted to electronic ignition, starting when I was in trade school in the Dark Ages. I have no use for points until we're attacked with an EMP device.

Using an EXTERNAL coil on an HEI has some benefits, but I would not use a POINTS coil with an HEI.

There's a jillion stand-alone HEI coils in the Treasure Yard, mounted to '87--'99 TBI and Vortec trucks. There are other stand-alone HEI coils on various other vehicles going back to '75 (generally inline 6 or 4-poppers.) And there's plenty of expensive aftermarket stand-alone "HEI" coils, often OEM-style coils mounted in stupid heat-sink brackets as if that did any good. The last oil-filled "canister" coils I bought were Crane Cams (bought out by Comp Cams for their FAST line) low primary resistance PS50 (black) or PS60 (Nickle plated.) At that time, and at least up to May 2019, they were claimed to be "Made in USA".
https://www.summitracing.com/parts/fst-730-0050

"Points" coils have primary resistance of 1.4--3 ohms. HEI coils have primary resistance of about half-an-ohm. They flow more current, they charge (saturate) faster, and they produce more spark power. The HEI module is fully capable of handling the half-ohm primary resistance, there's no reason to cripple it with a 1.5-ohm coil.

One of my vehicles has a large-diameter HEI with an external coil, all hot-roddy. I have other vehicles with the large-diameter HEI using the stock in-cap coil, but with a low-resistance button between coil and rotor. For street use, that's all the ignition coil that I think is needed. Simple, easy, effective, inexpensive.
https://www.summitracing.com/parts/fst-730-8412
(FAST says this low-resistance button works only with "their" ignition coils. Not true. But if you like, MSD sells a comparable part for half again as much money: https://www.summitracing.com/parts/msd-8412 )

ALWAYS set dwell first before timing. IF you do timing first, then dwell, you're going to have to go back and reset the timing.

Both of my Motors Manuals from 1970 and 1972 list the dwell range on every Pontiac V8 to be between 28-32 degrees. I've always set mine down the middle at 30 and "fahget about it".

Hi Schurkey,

For sure i want the ported back and running but i switched from single plane to performer rpm and as such i have lean bog. Just went from 31 squirter to 42 and that definitely went in right direction . You can see the 02 react differently and not just fly off into "----" land above 19. , it hits about 16 now and when i stab the throttle it just falls on its face even at 1/4 pedal stab - fast. amazing the difference just switching intakes does.

Trying to work that out and then you bet I'd try and run ported again, will try manifold in hopes idle could be dropped down too. manifold just never worked with old intake.

Once I get the bog done, guess go up to 47 and hope for the best? or maybe just get a 50 cc pump shot ?
actually this vid seems to offer an opinion

i for sure would like to but a hei coil that sits in cap and then remove the old points coil. i think that would be a good upgrade. i have two hei chips so could always carry one in glove box.

i do have a nice crane hi-6 OLD SCHOOOL gold capacitive discharge box i was thinking of triggering with another points distributor I have. wonder what would be better, I believe it has rev limiter which is nice.

Do the points distributor with HI-6. They are a nice unit. I set up my brothers sbc with one and a iron distributor, yanked the HEI out of there he was having problems with.

I have found that at NAPA anyway, the quality of Marine application points is much better than for automobiles.

Speaking of dwell meters…havent played with points since 1979 ….and my old dwell meter has disappeared. What are you guys using for dwell meters now a days….and what and where’s a good one to be had.. thanks for any info