Shaky idle -help!

[V12T]

Here is a link to a video of my engine. 512 sixpack shaky idle

512 stroker, 10.3 compression, stealth heads, ultralight crank, sixpack, modest street/strip Comp hydraulic lifter cam, headers (unknown brand), standard Mopar electronic ignition. 727 trans.
Engine sounds like it is missing and shakes at idle. Starts OK with a few pumps. Pulled plugs – good colour. Fairly new coil, HT leads, ballast resistor and electronic box. Compression tested to around 190-200 for all cylinders. Running in the dark – no visible sparks. (shorting). Exhaust seems normal.
Checked header tube temps with infrared sensor. All getting hot so all cylinders firing.
Engine mounts seem good (jacked engine up, no separation)
Fuel delivery (pump) seems good.
Checked float levels on carbs. Tuned as per instructions. Cannot adjust front carb – seized adjusters – new base plate ordered. Idle (rough) around 800 – will not go lower. Throttle plates not binding. Thermostatic choke working normally.
Done a vacuum smoke test and can’t find any leaks. Vacuum a bit shaky around 16-17. Has brake booster.
Flex plate secure.
Timing around 16 degrees rising to around 36 when revved.
Engine runs perfectly at high revs on test run but sometimes stalls when stopping.

I think the problem lies with the sixpack, not ignition, but I am out of ideas. Anybody help?

 

[Xcudame]

On the six pack, all the idle is done on the center carb. The outboard carbs are your secondaries and shouldn't be doing anything at idle unless one of them is dripping gasoline into the intake. There are much better six pack guys than me that will chime in.

Where did you get your standard electronic ignition? I ask, because most are pretty crappy these days!

 

[V12T]

On the six pack, all the idle is done on the center carb. The outboard carbs are your secondaries and shouldn't be doing anything at idle unless one of them is dripping gasoline into the intake. There are much better six pack guys than me that will chime in.

Where did you get your standard electronic ignition? I ask, because most are pretty crappy these days!

Pretty sure outboards aren't dripping but will check again. Got the elec ign module here in UK. Black with gold heatsink. Could be that I suppose. Found a test online so will try that tomorrow.

 

[Xcudame]

These electronic ignitions are good! Mancini backs up their stuff!

Mancini Racing Orange Ignition Control Unit

 

[Chryco Psycho]

Idle screws are on all 6 bbls, front & rear are in the base , front two you say are siezed up .so that is part of the problem .

what is the idle vacuum in gear & power valve rating .
often the air bleeds are a problem & inserting a small wire into the outer idle bleeds really helps as you cannot change the & they are rated for a factory cam

 

[Xcudame]

I would say Chryco Psycho is a great Six Pack expert!!

 

[V12T]

Thanks for suggestions. Not worked on car today but will respond when I have.

 

[Righty Tighty]

I'm watching this thread since I'm interested to know the outcome, but I might also add that @halifaxhop supplies genuine Mopar ECUs if you do decide to swap yours out. He's in the US, however, so I'm not sure how practical/cost effective that would be with you being in the UK.

Good luck and keep us posted.

 

[V12T]

I'm watching this thread since I'm interested to know the outcome, but I might also add that @halifaxhop supplies genuine Mopar ECUs if you do decide to swap yours out. He's in the US, however, so I'm not sure how practical/cost effective that would be with you being in the UK.

Good luck and keep us posted.

Fortunately I have cousins in Ca and Or so get parts sent to them. I'm there July.

 

[V12T]

Idle screws are on all 6 bbls, front & rear are in the base , front two you say are siezed up .so that is part of the problem .

what is the idle vacuum in gear & power valve rating .
often the air bleeds are a problem & inserting a small wire into the outer idle bleeds really helps as you cannot change the & they are rated for a factory cam

Found a small fuel drip from centre carb RH primary booster. New float needle O ring and re-adjusted float level. Thought this would be the solution but no. Idle vacuum 16 in park, 13 in drive. Sorry to sound stupid but do you mean clean the idle bleeds with a wire or literally put wires in to effectively reduce the jet size.

 

[V12T]

Pretty sure outboards aren't dripping but will check again. Got the elec ign module here in UK. Black with gold heatsink. Could be that I suppose. Found a test online so will try that tomorrow.

Pretty sure outboards aren't dripping but will check again. Got the elec ign module here in UK. Black with gold heatsink. Could be that I suppose. Found a test online so will try that tomorrow.

ECU seems to test OK, BUT I only have 10.8v on feed wires.Earths all OK. Must be losing voltage in the wiring? 5.2Volts at the coil. Ran a temporary feed direct from battery. 6volts at the coil. Made no difference.

 

[Xcudame]

When he gets back online, PM (personal message) Chryco Phsyco. He is talking about putting wires into the air bleeds so it will run a little richer for a bigger cam.

 

[V12T]

ECU seems to test OK, BUT I only have 10.8v on feed wires.Earths all OK. Must be losing voltage in the wiring? 5.2Volts at the coil. Ran a temporary feed direct from battery. 6volts at the coil. Made no difference.

Also confirmed ballast resistor is OK.

 

[Chryco Psycho]

Yes restrict the air bleed with a small wire

 

[halifaxhop]

Is your timing jumping around? Use a non dial back timing light to check it.

 

[V12T]

Is your timing jumping around? Use a non dial back timing light to check it.

Timing is steady using a simple old fashioned timing light on No.1.

 

[Challenger RTA]

Just a question. At what RPM does it smooth out if at all?

 

[Old Mopar]

OP all six paks require a baseline set up, it appears that has not been done.
without the correct baseline set up all efforts are for naught

Float levels, timing, timing curve, idle screw setting, mixture screw settings center and outboards, thermostat [195], coolant mix, cross over blocked, spark plugs and wires, negative grounds, good ignition system, electrical system at 13.8v engine running, underhood temps not hot after heat soak etc etc etc.

 

[V12T]

Just a question. At what RPM does it smooth out if at all?

Hard to be clear about this. Stationary it seems to pretty much clear after about 2000 but still a even slight wobble up higher. On the road, under load it is not noticeable. What are you thinking?

 

[Challenger RTA]

There only a few thing it could be. I'm just bouncing somethings back. This might get a little long and drawn out but I'm drawing on my personal experience and others.You are working on narrowing it down. What is mentioned above is very good. I always look at the mechanical first. Mostly it can be seen or checked and if it's bad your done. A few things to consider that I'm sure you did or will. Compression and or leak down test. This is a place of concern. Floating of vale train. Is it a sticking valve bad guide or seat or a weak spring. Cam more than likely ok, Lifter?

Then there is the vacuum portion of that. Gasket intake,carbs gaskets x 3, head gasket. Distributor vacuum, vacuum advance and hoses. Seen this happen. A shipmate had 70 454. It would acted up time to time. At different RPMs it would act up. Stumble miss hesitate. Changed the points and condenser the same parts it had , basic tune up. After going through it for a day or two. found it. It was the wrong condenser both times. As the vacuum advanced and retard it was it was hitting the inside of distributor. Vacuum advance working? This may not be you problem just sharing it to be considered.
Then on to the air and fuel. you seem to be on top of that. There are experienced ones here. Myself I would consider the source. Meaning the fuel tank in good shape no rust. No pinched lines,fuel pump presser ok. What size line do you have? I have seen crazy things happen. I would purge the fuel system. Fuel filter? Something might be obstructing as pressure changes. Something floating around there. AS far as the 6 pak That is a different critter. It's goes from almost nothing to balls to the wall!
As mentioned a base line is a necessity. Right now I would discount that until you make sure the mechanical and others are correct. There are some very well versed members here to help with that.
Transmission problem not even going to go there but a possibility. Toque converter problems you never know. Keep it mind. Is there a check vale in the cooler line?
I see that you have worked on diagnosing the issue. This might help trigger something or someone with a solution.
Next for my area of mistakes. I know you covered that. The electrical. I'll be back.