Timing or Carb Issue? Or both? Neither?

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Righty Tighty

Righty Tighty

Blame it on the dog
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I'm having a tough time getting my car to idle smoothly (or at all), especially on a cold start. I just rebuilt the 318 LA in my 71 Scamp, and it's just getting broken in. Edelbrock 1406 650 cfm carb with electric choke, Performer intake, headers, Proform electronic distributor with orange ECU. The carb is brand new, along with the distributor and ECU.

I set the initial timing at 8* BDTC, but the idle wouldn't come below 2000 in park without retarding it to about 0*. I set the initial timing with the vacuum advance disconnected and plugged on the carb side. It WILL idle eventually around 900, but that's after at least 10-15 minutes of warm up. Even then, it's sounds pretty choppy.

When I shift into reverse or drive, it will die unless it's been driven for quite some time and is very sufficiently warmed up, or if I double foot the pedals and give some gas to prevent the engine from dying.

This morning when I dropped it off at the alignment shop, I idled past a gentleman in the parking lot who had some comments that caught my ear. Yes, I know I have a leak at one of the headers, but he said he noticed a fuel smell. That made me realize that my exhaust does indeed smell very rich. This is peculiar, because I had the idle screws set all the way to lean in order to keep the idle down.

One thought that I had while I was driving home from the alignment shop was that maybe my choke isn't opening? I think that would explain the high idle, rich smelling exhaust, long warmup time, and rough running, especially at idle after warmup. Does my theory make sense? I can't check it until later today when it's back from the shop. I've read here that 10* initial timing and 32-36 total is recommended, but 10 initial just wouldn't cut the mustard. I've also read here about transfer slots, but since my carb is new, I wouldn't think I'd need to start there when troubleshooting?

When I get the car back today, I'm going to test the choke circuit and watch to make sure it opens during warmup.
 
Sounds to me like a big *** vacuum leak. Set the timing and leave it alone. If this is a mild stockish cam it should idle fine at 8-10btc

But suspect your timing marks are wrong. You know how to use a piston stop?

Also suspect the magnetic pickup wires need to be reversed. Google "rotor phasing."

Do you have another distributor, one that you KNOW was working?
 
Funny you mention a vacuum leak. Was talking to a friend yesterday and that's what he said. I can hear much more air flow from somewhere when the engine is running, and at first I thought something was wrong. Then I simply dismissed it as being from the bigger carb and bigger intake. My cam is .455/.475, 220 @ .050, 112*.

I've never used a piston stop, but I've seen some videos. Looks pretty easy. I found TDC by bumping the engine with the #1 plug out, and felt the air pushing on my thumb. Then I manually cranked it until the marks lined up. The dampener is stock, as well as the timing cover, and I could only get the dampener on one way.


I looked up rotor phasing and also read a little about the polarity regarding the magnetic pickups. A line that caught my attention related to reversing the polarity: "You will notice that the timing changes significantly and may appear very erratic." When my car is idling, it's somewhat erratic. I'm not really hearing any misses, but it's not a smooth gallop and the RPM fluctuates by a few hundred.

Unfortunately, I tossed my old distributor. (I know, I haven't yet learned to keep old parts...)
 
To check if it's running too rich or too lean, try closing the choke flap a bit or partially cover the air horn with your hand to see if it helps or hurts. If you suspect it's too lean, you can also dribble a little gasoline into the carb to see if it smooths out the idle. I use an old oil bottle with a pin hole in the top to use as a gas primer can and dribble tester.
 
Righty Tighty said:
My cam is .455/.475, 220 @ .050, 112*.
Click to expand...
I can make that cam idle at 550 in gear.
To get into the ballpark;
Make sure the Choke is off-line
Make sure the secondaries are closed all the way, but not sticking.
Make sure the primaries are actually physically able to close.
Fix all vacuum leaks.
Pop the covers off the metering rods and make sure they are not bent, not jammed, and go down all the way.
Make sure the Base gasket is correct for the carb and intake.
Make sure you got the firing order right. Separate the 5 and 7 wires by a good inch. If they have to cross eachother, shoot for 90*.
Leave the timing lite in the toolbox.

Ok, ready; Start here;with the engine running,lol
Just pull on the Distributor and advance the timing, then reduce the idle speed, then advance the timing, then reduce the idle speed, repeat until the idle speed comes down to 700.
>If it won't go down there; or does but is not, in your opinion, smooth enough, then; it could be;
A) your Pick-up polarity may be reversed see note 2, or
B) your rotor may be out of phase, see note 3, or
C) we need some carb prep,see note 1,
Do A and/or B first; then go back to "OK,ready"above
> if it's working, then we're on the right track. Tell us what you found.
But if you have to go to C) and it still runs like crap, Time for a compression test.



note 1,carb prep
Yank the carb off, drain it. Flip it upside down. With the primaries on the curb-idle screw,eyeball the transfer slot exposure, under the primary throttles. It should be about square for that cam, to maybe a lil taller than wide. If it isn't, then make it so. Flip it rightside up. Adjust the mixture screws to 2.5 turns out from lightly seated. Pressure test the float valves to 7 psi. Remove the metering rods, then Pop the top and verify the float valve setting. Remove the primary squirter nozzle and verify the check valve/check-ball is in there. Put it all back together, metering rods last, and re-install it.
Fire it up and try again. When you crank it up, make a mental note of how hard the starter had to work. With your carb now set, DO NOT ADJUST THE curb-idle screw. From now on, you will adjust the idle speed with Idle-timing and or bypass air.

note 2, pick-up polarity
Put your timing light on it and see what the timing mark is doing. For best results the RPM should be below 1000.With a new chain, the mark should remain steady, and no drop-outs from the light. With the light still strobing, rev it it up slowly, just a couple of hundred rpm. The mark should move slowly in lock-step with the rpm. If your mark dances around wildly, or the engine craps out with rising rpm, or the timing light starts missing strobes or double strobes;
your magnetic pick-up is wired in reverse polarity. Pick a convenient spot between the D and the Ecu, and fix it. Then back to "Ok ready" above

note 3a, rotor-phasing
At this point you should first prove your TDC mark on the balancer, see note 4.
3b
After the TDC is verified; put your crank to TDC #1 cylinder on the compression stroke. Then CCW back it up to about 15* advanced.Now lets go to the D. Pop the cap. Check the alignment between the bar in the center of the pole-piece and the nearest vane. They should be near to perfectly lined up. If they are not, then make them so. Next, make sure the rotor is properly seated. Then take your Sharpie, and make a mark on the outside of the D, so you will be able to read it with the cap on, make a mark,adjacent to the center of the rotor tip. If there is already a mark close by, erase it. or make a different kind of mark.
Next, properly reinstall the cap, and check that the index mark you made is more or less, within a rotor-tips width, directly under a tower,any tower.
If it is, then that will be the tower that directs spark to #1 cylinder.
But if it is more than about a rotor-tips width from directly under; then pop the cap, then the rotor. Down in the reluctor, you will see two "slots" machined into the reluctor. Above the slots are arrows indicating CW and CCW rotation. On the distributor drive shaft you will find a rollpin installed into one of those slots. You want it to be in the slot marked CW, for CW rotation like the SBM is. If yours is not there, pry the reluctor up off the driveshaft. If the rollpin stays with the driveshaft,then just turn the reluctor to the CW slot, and reinstall it. But if the rollpin comes with the reluctor, pop it outta there, push the reluctor down on the correct CW index and re-install the rollpin last.and go to "Ok, ready"

note 4, TDC mark
To prove your TDC mark on the balancer you will need a piston-stop. And #1 sparkplug will have to come out. What you need to do is get #1 piston to TDC-compression Don't look at the balancer mark. Look at the piston. Well you can't but you can tell when it gets close by the puff of air that comes out of the hole. Ok get that done. Next, now look at the balancer. If the mark is close to TDC, put it right on the zero-advance mark. Take your new piston stop, and back off the stopper all the way until it retracts into the hole,then screw it into #1 cylinder. Snug it down. Next, by hand, screw in the center-pin/stopper until it touches the piston (stops turning), then back up the crank,CCW, to about 10 to 15 degreesBTC, and screw the stopper down to it,and set the locknut. Next; back up the crank CCW, a few degrees and then forward CW and gently crash into the stopper. Ok, now, adjacent to the zero advance mark on the timing cover, with a Sharpie, as accurately as you can, make a mark on the Damper.
Next; CCW back up the crank almost a full turn, and gently crash into the stopper again. And, again, make a sharpie mark on the Damper, adjacent to the zero-advance mark.
Now, half way between those two Sharpie marks is TDC. and you balancer mark should be right there! If it is, great. lets use it. But if it is off by a few degrees, you will need to make a new TDC index line on the Damper and then erase the other marks you made. Pull out the TDC tool and reinstall the plug and wire.
Ok now we have a verified TDC mark, go back to note 3b
 
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turn the idle up 'til you can walk to the front and it doesn't stall. with the air filter off spray wd40 or similar around all the gaskets, vacuum lines, carb etc. if the idle picks up at any time there's your vacuum leak. that would be my first check from your symptoms.
neil.
 
On my way to pick it up from the alignment shop. Over the phone they said they found and fixed two vacuum leaks. More to come...
 
So hey everyone, wanna know how stupid I am??

Picked it up from the alignment shop and asked where the vacuum leaks were. One was at one of the vacuum ports on the intake that I didn’t need, and temporarily blocked with duct tape. The other was the rear port in the carb for the brake booster. I FORGOT TO PLUG IT. It was completely open. Now the sound of rushing air is gone, and the engine idles wonderfully.

I posted recently asking where I should go for an alignment, and I’m glad I went to a Mom & Pop shop. I mentioned a tuning issue, and while all I was there for was an alignment, they quickly checked and found the leaks.

Boy am I a bonehead. It’s a good thing I have others around me to prevent me from doing more harm.
 
I’m so glad it was simple. I had a feeling I was going to end up chasing my tail trying to get it to run smoothly. Had Pops over this morning to double check the initial and total timing, made a couple fine adjustments and now she purrs like a kitten. Ended up a touch over 10* initial and 34* total @ 3000. Idles nice at about 750.

I thought I might’ve heard some lifter ticking, but couldn’t tell due to the exhaust leaks at the heads, confirmed today that it was just the exhaust making the noise. Now to take care of those damn exhaust leaks....
 
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