tryin to break in new engine, ruff idle

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screeminDemon

screeminDemon

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I shut it off after 5 min at 2100 rpm because I didn't like how it kept missing every 5 seconds and it would drop 2-300 rpm, sounding almost like muffled backfire.

I checked the gap on the magnetic pickup of my new distributor and it was .009 to .010. I converted to electronic ignition with the new motor.

1976 LA 360
punched 30 over, stock pistons and rings
fairly big summit cam, probly too big
edelbrock torker340 intake, holley 600 carb, rebuilt when?
stock 360 heads rebuilt w/ new stainless valves and double springs for big cam
headers
elec ignition w/ orange box

What do you think the top one or two likely culprits might be?

Thanks for your suggestions
 
I ran it for a few more minutes today after messing with the timing, spark plugs and tried setting the distributor reluctor gap to .007 - .008.
It still ran rough, missing or not hittin on all 8, saw sparks and even a couple small flames come out of carb at startup attempt.

Doesn't sound like a carb issue does it?

PS - the cam is summit 1798 and it has advertise duration of 284 degrees. supposed to have a 480 lift with 1.5 rockers but I'm using stock rockers that are not true 1.5.
 
If you have flames during startup your cam or ignition is out of time. Have you put on a vacuum gauge? Are you 180 out on the dist? Recheck ignition timing - dist shaft slot should be facing forward and aft @ #1 tdc. Did you swap #5 & 7 plug wires by accident? It's a common mistake. Check your plug condition and find the dead cylinder. Check cam timing.
 
If you primed your engine by removing the intermediate shaft, it's real easy to get it off one tooth when you replace it. It will still run and you can get it pretty smooth, but it will back fire and you'll know something is just not right.

Big screw driver and a telescoping pocket type magnet make it easy.

Since then I've marked it with a center punch, so I have more to remember than just a slot, and I put a paint mark inside the engine to line up with it, and I take a picture, just in case something comes up and it takes longer than I thought.
Cause I don't want to do that again.

I had a new carburetor on mine, so I thought for a while that the carb. was the problem.
Just a thought.
 
Sounds like maybe the diizy is a tooth off.I wouldn't keep starting it for a few minutes you will wipe out your cam.
 
Thanks for putting wind back in my sails once again, you mopar folks are awesome!
I bet thats exactly what it is: dizzy is a tooth off. I don't know why I never thought of that, its behaving like that is exactly what the problem is.

Will let you know later today
 
mopar distributor do not have tooths to be off.....the distributor shaft sits inside the intermediate shaft....

pictures from the service manual shows the slot on the intermediate shaft pointing to the front intake bolt on the driver side for proper installation...

but it does not matter where it points...as long as went #1 cylinder is at TDC the distributor point is at #1 TDC....and rotor cap is pointing at #1 on the cap...

if you feel better with the slot installed as the service manual shows..take a large screw driver and move the intermediate shaft Clock wise and walk the shaft around then drop it in to line up...but it does not matter...

chevies get a tooth off...mopars do not...

besides you would be looking at a constant miss ....not a intermediate miss...
 
I kinda had a similar prob years ago...except a loud pop every so often....although I didnt have the electronic conversion I had put in an accell supercoil and distributor....well I didnt put a ballast resistor between coil and distributor...it was getting to much power and causing it to cross fire....dont know if it helps but just a guess...but it does sound like a timing issue
 
Well, after re-checking TDC, I pulled out the dizzy drive gear and re-istalled it "one tooth off" but it didn't make any difference, still idles pretty rough. I think AARCuda is right - it doesn't matter with mopar about 1 tooth off, so long as you point at #1 plug on dizzy when at TDC.

Also checked to make sure all my plug wires were going to correct cylders.

Cam timing? I lined up the dots on the gears when I assembled the engine as the book said. How could I have gone wrong there?

I gotta walk away for awhile... Any other suggestions are appreciated. Thanks again for all your help folks!

PS - I have a new ballast resister installed.
 
I believe I've eliminated timing as the issue. Maybe its amount of spark. I used my multimeter to check some voltages in my newly installed elec ignition with key on: 13v @ bat. 11v @ ballast, 7v @ coil.

Does anybody know the correct voltages? shouldnt coil get 12v?
 
Factory; 12v at crank, about 7 at run. does the acell pump work? Has the carb been gone over? What is initial and total timing? More specs on the cam, degreed in at?
 
Have you checked float levels?? if one or both are too high, it could be flooding, and that will cause a hiccup at fast idle, as you described, and will likely die at idle.. just a thought.. if you have a full face shield,, look down the carb while it's running, to see if fuel is dripping down the throats, any dripping will be your hiccup... WARNING.. that hiccup is a backfire, and will burn your eye-brows off, without the face shield..

Definition of experience,.... the ability to recognize when you're about to make a mistake.................... AGAIN...
 
Thanks aarcuda, I agree !
If I remember right, the reason I changed the position of the dist. slot was, because when I went to time it, I found that I was limited to how far I could turn the dist. , because my vacuum advance would hit my sending unit, and I needed more.
Sorry about that. This was a while back.
 
70 DUSTER CRATE said:
Thanks aarcuda, I agree !
If I remember right, the reason I changed the position of the dist. slot was, because when I went to time it, I found that I was limited to how far I could turn the dist. , because my vacuum advance would hit my sending unit, and I needed more.
Sorry about that. This was a while back.
Click to expand...

that is usually the only problem with where the slot is lined up with...the vacum cannister hits something ..

have you checked your plugs....make sure they are gapped correctly...

it is going to take a processes of elmination to figure it..
 
Ok if you have had the intermediate shaft out it may be off.Yes what aar said but the gear can still be off position and if its off alittle everything will not line up right.If #1 cyclinder is at TDC and the rotor is pointing at #1 on the cap you are good to go.My brother had the same issue on his TA Challenger when I helped him break in the motor.He had intermediate shaft off position which allowed it to point close to #1.I pulled the shaft repositioned it and put it back in, and then it was dead on #1.

I don't know maybe I just have been messing with Big Blocks too many years.LOL Jim
 
Ya I checked the plugs, have em gapped at .035 - .037 and they look pretty clean.

Thanks for the voltgage specs, it looks like I'm Ok there.

I don't have any more indepth info on the cam or the timing, just know I've played around with the timing alot already.

But ya, I agree, its a process of elimination. I suppose it could always be the carb, a couple of you mentioned. I know its been rebuilt but I don't know how long ago. float levels? But wouldnt I see black smoke comin out the exhaust if it was too rich?
 
Also make sure you have not burned any plug wires.What do you know about the carb?I noticed you put rebuilt when?
 
The exhaust doesn't have to be pushing out black smoke, if the carb is just dripping, due to incorrect float level, or plugged air bleed, will cause symptoms you describe.. more likely carb drip than reluctor gap, or timing out a tooth,, and if dizzy was out 180 degrees, it wouldn't run at all...JMO

sorry,.. just re-read symptoms, and carb wouldn't cause flame outta carb at start-up,, but still think the carb is dripping at fast idle, and prob slow idle too, causing your miss every few seconds.. again JMO
 
Since you have multi-meter OHM every spark plug wire and they should be close to each other...disconnect at cap and at plug and ohm test each one,of course plugging them each in while going to the next...
Start with number one and you can double check your firing order.

You can get hiccups and back fires with a lean condition as well...
Vacuum leaks..
Did you set your 2 air/fuel mixture screws.
They are on each side of the metering block behind your front fuel bowl.
I turn them in till they seat lightly and back them out 1 1/4 turn each.
You can fine tune it after breaking in your cam!!!!
You need to break in that cam before anything else.
Try to do all your diagnose without continually starting it.
Here is a Holley link to your Holley.
I am guessing it is a Holley 0-1850 universal 600cfm
List number is on air horn on front of carb.

http://www.holley.com/data/Products/Technical/199R7948-5rev2.pdf


TXDart
 
screeminDemon said:
I shut it off after 5 min at 2100 rpm because I didn't like how it kept missing every 5 seconds and it would drop 2-300 rpm, sounding almost like muffled backfire.
Click to expand...
It does sound like it is loading up...On that link it tells you how to adust the floats also.
Are the plug wires new and What kind?
TXDart
 
Its either timing or the cam is already wiped out. I mean for flames to come out of the carb.

A bad plug wire should not cause it, unless you got 2 bad wires and the spark is jumping across the wires.

Don't think too rich or lean from the carb would cause flames either.

What is your timing set at, like total timing? Have you turned the dist while the motor was running and listen to the engine rpms increase and decrease as you advance and retard the timing?

I like advancing the dist--with vacuum advance disconnect--and hearing the rpm's pick up, once it seems to not be increasing in rpm's stop advancing the timing and back it off a touch. That should give it around 35 degrees total timing.

If the timing is right on 35 give or take a few and the motor is still acting up, I would run a compression test on all 8 cylinders. They all should be close to the same psi, if not pop the valve cover off and see if the rockers are moving the same distance down opening.

You did tighten the rocker shafts correct, I had rocker shaft bolts snap but that was at high rpm's. The shaft will bend if the end bolts break--still I had no flames, just miss
 
I only saw sparks and a flame the first couple times I tried starting it. And I may have had the timing off at that time. After that I began messing with the timing, taking it to the point of hard starting/worse performance when too far advanced and the other way until it was running crappy too far retarded. It ran rough the whole way through.

Today when I started it up it ran fairly smooth at first, and I was feelin pretty good, then got steadily worse when it heated up. I shut it off after 10 minutes because it was missing and coughing too often.

I drained the oil and there was not a spec of oil in it so I think the cam is still ok.

My wires: new accel yellow 8mm. I will ohm check them as suggested. My card is holley 600, 8160 model I think.
 
Compression test is a good idea too. I looked at the rockers today and the only concern I had was #1 exhaust seemed too loose. I figured it may be a compressed lifter that will fill when the engine runs.

My second concern: the elec choke slowly opens the main carb intake flap fully after a few minutes running. This may sound like a dumb question, but could that be causing a too lean condition, if its fully open?
 
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