Distributor pickup phasing

Today I put medium springs in my distributor and set the FBO plate to 10 deg advance. Fired it up and set the initial to 24 degrees. Still has a Top Fueler idle but with 272@.050 I can't say that's a surprise.

Idle vac only about 5" and quite unsteady. I hooked up the can to a Mity-Vac and gave it a squeeze... the timing mark suddenly changed a huge amount and the engine died. Let off the vacuum and it caught again. What I think that's telling me is there's a phasing problem, but not with the rotor to cap (the vac advance moves the pickup plate, not the rotor). Only the centrifugal advance moves the rotor relative to the cap

Just to add to the fun, as the engine was coming to a stop the second time, I let the distributor pickup wires get caught in the alternator belt/pulley and it ripped them up.

But it's not all bad - looking at the mess, I realized that I'd connected the wires backward from the reluctor pickup... which is probably also causing my phasing problem!

Fuel pressure also 4.5 lbs, idle mixtures 1.5 turns out, secondaries cracked... lots of things still to tune. Oh well, enough for one day!

Yes the can moves the plate which does alter rotor to cap alignment when it fires (RP) and centrifugal advance does not. when you pump up the can it changes RP and also greatly increases the reluctor gap & if you are at .008" at rest then that is OK & either one out of whack or a combo of both can cause it to act up. fix the wiring/set the reluctor gap at .008" with a brass gauge or just get it close but not touching & it might be slightly closer at the bottom so eyeball it good. On RP You are at an advantage cuz have the pump at your disposal. turn housing till the magnet is dead even with a tooth & lock it down & make a mark on the metal dist housing outer top perimeter rim just below where the cap seats for where it is clocked (confirm that the springs are retracted all the way which they should be but the slots could be gummed up so twist the rotor back against rotation to confirm) then replace the cap & make another mark on the rim vertically inline with the cap terminal bulge next to the 1st one then remove the cap for easier viewing & see how far they are off then pump it up & see how far it shift away from an acceptable alignment. RP from the can shifts CW on a BB and CCW on a SB & it shifts .024" around the arc for every degree of vac adv (see the # on the bottom of the can arm). the cap terminal width is .214" and the rotor terminal width is .244" & you want them in close proximity & also there is the radial distance from rotor tip to cap terminal and when the combo of RP and radial distance becomes greater than what the available voltage can jump then it will misfire (+ the reluctor gap issue potential). if you need to change RP position or increase rotor tip dimention holler & I will give more info & 3 or 4 options for that.

been there, done that! you would think the car wouldn't start but it will. mine idled pretty well too, it wasn't until i went out on the road did the problem raise it's head. it og coarce didn't occur me because i had been working on something else so of course i was chasing my tail for awhile before i had an 'ah ha' moment!

Yes pick-up coil wires backwards will change the timing. I forgot how much but I think it was at least 12 degrees or maybe more. Ron

the pickup generates its AC voltage when the tooth JUST moves past being dead on with the magnet so a .069" change in distance before reaching that "position" (from switching polarity directions) would change crank timing 12 degrees (& change phasing)

Wires swapped, timing reset. New problem... with my big cam (272@.050) it won't idle properly with up to 24 degrees initial, unless the PCV hose is disconnected allowing more fresh air into the engine. Carb is set to .020 (square) transition slots on pri & sec, and 3/32 holes in the primary throttle blades).

In fact it likes full advance (34-36) at idle. But that will certainly cause a hot starting problem... I do have a dash-mounted retard unit that has 0-15 degree range. So I see three work-arounds:

1) Always remember to turn the dial to -15 degrees when hot starting;
2) Use super-light distributor springs so advance all-in by 1200 (idle);
3) Start cranking then turn on ignition.

I'm thinking about the super-light springs. I already have an FBO limiter plate. That way the cranking timing will be 18 degrees, but when it starts the timing will immediately come up to 34.
Thoughts?

I believe this is the point where you start drilling holes in the throttle blades.

R.

That's what I figured, so as I posted, I already drilled 3/32" (~.100) holes in both plates. Not nearly enough.

If it idles "right" with a foot of PVC hose hanging off the 3/8" baseplate port, that's going to require huge holes in the blades to let in that much air.

I wouldn't want locked out advance for the street. I'm wondering if we are missing something related to the AF ratio (which is what we are trying to figure out) OR if it needs a more race orientated carb to go along with that cam

What is the PCV hose plugged into when it is not "idling right"?

The PCV valve in the valve cover. It's brand new and functional.

What's interesting is if I just stick the open hose inside the valve cover hole, the engine also starts missing and slowing down. Yes, there's a breather on the other valve cover. Removing it didn't change anything.

I always thought that there would be mostly fresh air in there... doesn't look smoky or smell gassy. Could it be that the new rings aren't seated yet, since they haven't been under load?

Odd, I was thinking the PCV might be too small not allowing enough air flow, but then you did the hose trick in the cover and that ruled that out. Unless you are somehow kinking the hose or blocking flow someway? Maybe the hose if bad internally?

I changed the oil, now Brad Penn 10W-40 "With High Levels of Zinc and Phosphorus!" Says so right on the bottle

The break-in oil did smell a bit gassy but no obvious metal particles. Only a very small amount stuck to the magnetic oil pan plug. Don't have a filter cutting tool at the moment but I saved the filter.

With the timing set at 34 initial, the idle is acceptable at 1000-1100 rpm and 6-7" vacuum and the PCV connected. Wideband showing mostly 13.5:1 although it does wander some between 13 and 14.

It does fight the starter a bit after several minutes shut down, but dialing out some timing from the dash took care of that. Guess I will have to lock out the distributor...

Disconnecting the PCV hose at the valve now causes too fast an idle (1600 and 9" vac). I can control the idle speed with my thumb partially plugging the hose. Hard to drive that way though.

Perhaps R. Dogdays had the right idea - drill the throttle blade holes somewhat larger, maybe to 1/8"...

At some point (soon) I'm going to quit tearing my hair out and send it to Thumperdart!

Don't tell me you have vacuum advance hooked to manifold vacuum.

Questions:
1. Have you drilled all 4 throttle blades, or only the primaries?

2. Why are you trying to run a PCV valve on an engine like this? You really don't want that recurculated sh!t getting sucked back into your induction system...

3. Where is your vacuum advance connected (direct manifold vacuum or a carb port that only pulls vacuum at higher RPM, but not at idle)?

4. Stick car or automatic, and what stall if an auto?

Doesn't matter where I hook it, there's not enough vacuum at idle to activate the can! Right now I don't have it hooked to anything.



OK, in the order you asked:

1) only the primaries with 3/32" holes so far.

2) to get the "recurculated sh!t" ventilated out of the crankcase, I don't like sludge and acid formation... although I have considered just installing a second breather.

3) see above. Doesn't matter at 6-7" of idle vacuum.

4) stick.

What do you think?

My last combination with a 266 at .050 SFT cam worked with...
- 1200 RPM idle
- 25* initial
- 35* total
- full advance around 3000
- carb had all four plates drilled with ~ .110" holes
- no vacuum advance, although it would have probably been helpful at my 3500 highway cruise RPM

I have a loose converter, but a stick car is going to be more prone to low-RPM detonation under a load. Otherwise, your option of locking out the distributor and dialing back the timing when starting sounded reasonable.

Thanks for the data! Those are quite similar parameters to my initial try (1200, 24/34 in by 3000), except that I didn't have .110 holes in all four plates. With 3.91 gears and 295/50R15 tires, I will also be cruising at 3000+.

I have noticed that this cam idles smoothest at 1200 also, although it will tolerate 1000 but a fair bit lumpier.

Would you recommend the four smaller holes over two larger ones?
I'm thinking that if I screw up, I only have to repair or replace two blades

Start with 4 x . 093 or .100 and see if that gives you enough bypass air. Throttle blades are cheap and you can buy pre-drilled sets, too.

Oh, dump the PCV and run at least 2 breathers.

I'd be curious as to what the cranking compression is.

I can tell I've gotten older....... The 272deg cam and "street" duty no longer seem like a good idea to me, whereas 25 years ago I would have been up for trying it(maybe).

25 years ago I didn't get a chance to try it, so now I am

The cam is actually the old Mini-Express .654/278@.050, .024/.028 lash that I bought used and had Schneider Cams reground to restore the lobe taper (and also reface the mushroom lifters). It is now .652/272@.050, .016 lash.

Anyhow I know it won't make a lot of power below 3000, but from there to 7000, anyone who's run one has been very happy with it (and as originally advertised by Direct Connection, "comes very close to roller cam performance at about half the cost"). Back when the Big Roller was .750, 286.

Haven't checked the cranking compression, it is what it is... may measure someday once I get the rings broken in under load.

Right now I am having trouble choosing between:
1) locked timing at 34, current primary blade holes, or
2) 24 initial, 34 total, holes in all four blades as needed to idle.

Which would you do? Limited street, even more limited strip.
thanks.

I don't recall what your cr is, but I dont know if I believe the bottom of the good part of the power curve will start at 3000rpm.
Over 4000 more likely, especially if the cr is on the low side for that much duration.

As for the timing, I'd lock it out..... Get it all warmed up..... And see how high it can be before fighting the starter.
Then I'd modify the distributor so I could start at whatever point that is, and end up at wherever I wanted the total advance to be.
My guess is I'd end up with initial at 30-ish, 36-38 total. Since it's a stick I'd use the lightest springs and the advance would pretty much just be there as a starting aid.
If I thought I really needed vacuum advance, I'd have it limited way down to about 5deg, and require a fair amount if vacuum to operate, so the only time it would function would be at part throttle cruise.
I wouldn't be using a pcv valve.

I don't know what your carb is, but it really should be something with 4-corner idle, and I'd likely end up with holes in all blades.

After it's got a few hundred miles on it, you may want to pull the carb and look down the intake ports with a bore scope/camera.
It might make you question that cam decision.

Dyno sheet:
10:1 446, rpm intake, 22deg @.050 less than your cam.

OK, that's another vote for locked timing

I'm using a Jacobs "Boost-Master" (aka "Turbo-Timer") retard unit and rev limiter. It has two 0-15 degree retard knobs, originally intended to switch from one to the other with a pressure switch. In my application the second retard will be for nitrous and will be activated by throttle microswitch.

So I can dial out 15 degrees of timing at start; just have to remember to twirl the knob when hot. It starts fine when cold at 34.

Re: vac advance, with my 10.3:1 CR (iron heads, quench) I figure it will tolerate some advance at cruise. Idle vac is only 6-7" so definitely won't be activating the can at idle.

Carb is an old 2-corner 800 DP. I'm having discussions with Dom (Thumper) and he's going to make me a better carb. In the meantime I might as well play with this one. BTW he also favors locked timing with this cam and CR.

You and BradH are both recommending that I not run the PCV valve. Can you please tell me why? thanks.

I prefer not to contaminate my intake charge with oil vapors, or have oil residue building up in the intake runners or the backs of my intake valves.

IMO, the negatives outweigh the positives.
If you feel you "must" run one, I'd plumb an oil separator/catch can into the line.

The cranking compression test is more about getting more info to have a better idea about how much trouble it'll be getting any drivability issues sorted out.
The lower the cranking pressure, the harder it will be to make happy.

Thanks for the info. That dyno sheet is interesting... what does it look like below 3900? Did you start your pull at 3k or less?

There's still 492 ft-lb at the bottom of your sheet, that will move my A-body on the street without going to 7K on every shift

What do you mean about using a borescope? I assume there'll be soot from reversion?

This project really won't see much use, just a little "Saturday night special" driving and maybe an occasional trip to the strip. I figure the bottom end will be soft but the higher I spin it, the more power it'll make. At least someday when I get better heads. Besides, I can always change cams if I have to.

The pulls were started at 3500(498.2ft/lbs)so no idea what it would be like at 3000.
I wasnt the one actually running this particular motor....... I probably would have started at 3000 if I had been running it myself.
On these mild street motors I like to see the point where the bottom starts to really fall off, and it's obviously lower than 3500 on this one.

It takes way more than a big cam to make power to 7k on a bb mopar.
If the heads, intake, carb, headers won't support it, then it just noses over wherever the smallest "cork" starts to come into play.
Then you can have a situation when the cam is too big to make any bottom end power, and the rest of the build won't support high rpm power..... So you end up with a motor that's just kind of "flat" in the car.

I'm sure a few trips to the track will reveal where your combo sits.

Track is 90 miles away and I don't have a trailer (or a decent pickup that can tow it)... will have to depend on the butt-dyno for a while. Lots of straight lightly-traveled roads out this way.

Yes, I'm definitely aware that any chain is only as strong as the weakest link. My plan is to gradually upgrade pieces as money, time and interest permit, and I am on a budget. I do expect that the high end will be somewhat restricted even with a relative lack of low-end... for now. A decent set of heads is in the future when I have another $2500+ to sink into my toy. I am not looking for every last horsepower or tenth here, just something I can have fun with.

If I lose the PCV I can use the 3/8" baseplate port with an adjustable needle valve to get all the bypass air I need without drilling any more holes.

As we spoke, it's not an IDEAL combo w/that much duration, old style ported iron production heads,10.3 comp. and that carb so I'll get a stock looking DP dialed in w/adj. everything w/extra bleeds so you can tune all circuits if needed.............As far as timing, I like locked w/that much duration or super fast adv. but prefer locked and also am curious as to how much cranking comp. it has because it DOES matter and I now for the first time in years run a PCV valve w/a homemade oil seperator and I love it and only a few miles due to rain but intake/plugs are clean..........

Thanks for all your help, Dom. You're definitely teaching me more about carbs than I want to

Meanwhile I drilled a pair of 3/32" holes to the secondary throttle plates, about 1/4" in from the transfer slot/idle ports as instructed. Now it idles at 1100 (6" vacuum) or 1200 (smoother, 7" vac) with the transfer slots in the right place, the PCV system connected, AND the timing set at 24 initial! Sounds pretty nasty out back. Wideband dances a bit between 13.5 and 14 when fully warm. It does not want to idle consistently at 1000 or slower.

Opening the throttle to 2000+ (no load) makes 15" of vacuum which will certainly activate my advance can. Should I really limit it to only another 5 degrees?

I still need lighter springs in the distributor because it didn't sound like it was all in until well over 3000 (no helper available today to read the tach). Maybe reset the FBO disc from 10 to 12 deg while I'm in there (for 36 deg all-in if that's safe on pump swill).

Also I'm definitely going to install an oil separator in the PCV line. I agree that burning oil on purpose is generally a bad idea

Sounds like it's going in the right direction and I lock all my stuff out but that duration will be happier w/more lead at least most I've messed with...........