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Yet another timing problem!


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8:43 AM
Apr 11, 2023
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Motor is a 383, believed to be a ‘69, in my ’66 Coronet.

- Jegs distributor, looks like a clone of the MP one with a magnetic pickup and vac advance. Default light blue springs and I haven’t touched the vac advance.
- Unknown “Purple” cam, but probably the MP 268/284 (they seem to have bought everything from Jegs and that’s the only “purple” cam they have)
- Edelbrock TM3 single plane intake
- Edelbrock 600CFM carb


Car starts and runs, very rich idle, but pulls OK and mixture seems to clean up off idle, no clouds of smoke etc. Static timing looks to be 30-40*. I can’t check with my dial-back light due to spark scatter, but my old timing light shows the timing is stable and advances as expected both mechanical and vacuum (which is disconnected for setting timing of course).

So far I have checked:

- Balancer TDC is correct, checked many times with a stop and a whistle tool
- Reluctor pickup connections are not switched/swapped
- Distributor is 180* out, but plug wires moved to compensate. Rotor/wire #1/reluctor trigger line up as expected
- Carb is rebuilt and thoroughly cleaned, transfer slots set square And idle screws around 1.5 turns out
- Installed a variable idle air bleed to see if that can weaken the idle mixture, it does need a little air and then it idles ok at 800 RPM and revs fine up to 3K, and the idle screws work. I haven’t tested further as I’m worried about the total timing by that point.
- Plugs are pretty black, it’s only really idled and started on choke so I’m not sure that tells me much.

So - what have I missed? I haven’t checked cam timing... Could that cam and the single plane intake just need a lot of advance and/or fuel?

Was the cam degreed? What is your fuel pressure?
About 5PSI, it’s not throwing extra fuel in, I can see the check valve stopping fuel. It’s a stock (and new) type mechanical pump. Also float levels are fine, checked a few times!
About 5PSI, it’s not throwing extra fuel in, I can see the check valve stopping fuel. It’s a stock (and new) type mechanical pump. Also float levels are fine, checked a few times!
Was the cam degreed?
How do you know it's rich with the timing bouncing 30-40? That isn't going to cut it. You are putting the cart in front of the horse. The first thing you need is a acurate way to set the timing. It probably needs between 15-20 degrees intial. With factory heads 36-38 total with the vacuum disconnected. Then look at the mixture. Why do you think it's rich at idle? You have no smoke, no O2 sensor data, and it idles well with the screws 1 1/2 turns out. What is the rich issue?
Timing should be all in at ~3000 rpm. On a 383 - 451, I shoot for 38*-40* and let the idle timing fall in where it may. That carb is too small anyway, I'd go 625cfm or a 750 if the engine is healthy with any kind of cam in it. I'd dump the TM3 and use a DP4B (if you can find one at a reasonable price).

Chuck (snook)
I have no idea if the cam was degreed, I bought it as a badly running project. I’ve sorted out a lot of issues already, now down to this.

i think it’s rich at idle because the plugs are black and it stinks when idling. It seems to clean up as it’s revved. It does idle, yes, but it’s very antI social! There is some smoke, it smells like gas.

When I say “advanced by 30 to 40”, I should clarify that it’s not moving around, it’s stable, but without degree tape I can only estimate. It’s some way away from the timing marks anyway.

I've also checked for play in the timing chain, and it’s negligible.

I’m wondering now if the magnetic pickup wires are incorrectly connected. The colors match the Jegs and MSD manuals, but I have seen threads here where they’re built wrong.
Big-A, do you mean that 30+ at idle is ok?
You can swap the msd trigger wires to test. If it's a non digital box the timing will be retarded more when correctly connected. If it's a digital box the timing should be more advanced if the wiring is correct. You don't need a advance style timing light. Measure the circumferance of the balancer. Divide that number by 10. Take that answer and make a mark ahead of zero. that mark will be 36 degrees.
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I would NOT swap the p/up wires unless they are already reversed. Swapping the p/up wires advances the timing a LOT, but more worryingly it affects rotor phasing; wrong cyls may fire causing backfiring etc. The black p/up wire on the Chrys dist should connect to the Green wire on the MSD 6 box [ correct polarity ].

Spark plugs. Use a 5 heat range in NGK.
There is nothing wrong with the 600 AFB carb; in fact, it is an excellent choice for your combo given the mild cam. Cam sounds like it is a Magnum cam replica, which is out of breath on a 440 at about 5500 rpm.
The Tarantula intake on the other hand is a very poor choice. Pretty dead below about 3500 rpm.
The small primaries of the 600 AFB will help some with throttle response.
Idle will need to be richer with that intake because of the poor carb signal it provides.
Giving the engine about 25-30* of timing at idle will make a big improvement. [ See below ] You can see the effect by simply rotating the dist with the engine idling.
I suggest you try this & report back.

Thanks! I checked the wiring from the distr. to the 6AL and polarity is correct (unless the distributor is manufactured incorrectly). I will indeed mark the balancer to get a more accurate assessment of timing and report back.

interesting that 30* of initial is ok, then I guess I need to make sure total timing isn’t crazy!

I also read on another forum that running too lean at idle can also cause unburned fuel in the exhaust - and on another thread, that the gaskets on the idle venturis will go in upside down and cause the idle circuit to not work correctly. Will check the gaskets also and report back after Xmas since I’m not going to get car time!

thanks for all contributions!
Hi! Reporting back…

First, I made a mistake. It’s an Edelbrock 1407 which makes it 750CFM, manual choke.

It does have heat range 6 plugs already, I use Champion Copper. I used to use NGK in everything but think they’ve gone downhill.

I did some tweaking this morning and have some good progress I feel. I got my digital timing light working by powering from another battery off the car.

I opened the transfer slots a tiny bit (i.e. screwed in the idle screw 1/8 turn) which raised the idle, then retarded the timing from where it was. Readjusted the idle mixture screws and, since my timing is now hopefully good, moved back to ported vacuum advance.

It’s definitely cleaned up the idle somewhat, it starts a tiny bit easier (it was always OK though) and there are still no hesitations off idle.

Specs now are:
- 18* initial timing, idle is just a tad over 600rpm
- 42* mechanical advance, all in by 2800, plus the vac advance which I still need to measure.
- Idle screws are 1 1/4 turns out
- I also have an adjustable idle air bleed which is just cracked open, this is emulate the adjustable type PCV valve which I can’t use as there are no baffles in my valve covers. That’s a to-do…

How does that all sound?
42 degrees is playing with fire. Seen more than a few decks burned between 3/5 or 4/6. 38 degrees has always been my safe limit. However the 18 intial is fine. I'd limit the mechanicle advance to lower the overall number.
Champion J12 ? I don't know what a heat range 5 Champion plug is that you say you have in the engine.
My suggestion is to put a dual plane manifold on it and try a known carb. Rebuilding a carb( putting new gaskets and needle/seat, does noit guarantee the carb is good, only that the replacement parts are new. Carbs are more complicated than people think. You have so many variables with unknown cam specs, unknown internals, aftermarket parts...
. A dart board tuning session.
Start from the beginning. Recheck everything and assume nothing..Wire the cap correctly and so on.
I will certainly check the total timing. It’s a pain to adjust, but as I said I was working on the idle to start.

Leo, I’m not sure what you’re saying about the carb? It works fine, all passages clear, float height correct etc.

The plugs are equivalent to an NGK 5 heat range. I’ll get the number tomorrow when I’m back out on the car stuff.
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