New 408 stroker runs rough at idle

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IDK if this is gonna help but I'll tell what I would try.
Before we start;This is an idle only post.
Mechanical;
> If you have a Solid Lifter cam, Lash the valves to the loose side of the spec.
Ignition;
>At idle you can drive that engine with tons of advance, Same at low roadspeed, as long as you do not feed it so much throttle as to drive it into detonation. So for this test, I'm gonna assume you won't floor it.I will not buy you a new engine
>for this test you must disable the V-can and plug the carb port.
Fuel
>You must ensure that the float level is adjusted right and is stable at all times.
Air
>at 5000 ft your atmospheric oxygen molecules are very far apart. That engine is gonna want a lotta lotta idle-air to get the oxygen it needs; and the fact that it doesn't respond well at idle, proves it.
>the black plugs are also proving the lack of air, and the metering-rod propensity to flood the carb.
Bypass air;
>Bypass air; All air into entering the engine has to be controlled by the combination of;
the primary throttle adjustment,
the Bypass from the PCV, and
the Bypass thru the holes you drilled, and
thru any other Bypass we might have to introduce. That engine wants air and lots of it.
>The reason we have to supply Bypass air from other sources, is so that the transfers don't flood the engine.As they currently seem to be doing.
Coolant;
>Ok now, this is very important, the coolant temperature has to remain stable. You MUST have a stat in it. I like-em hot. I shoot for a minimum coolant temp of 195. Whatever you are running, the important thing is that the temp is stable at idle; you cannot properly tune the idle if the temp is wandering around. So check it every couple of minutes. Do not run less than 185. Do not continue with this test, with an unstable water temperature.
Other:
>You must prove that the PCV circuit is working. I don't care if it works poorly or not, but the circuit has to work. With the engine running, pull the PCV hose off the carb port. The rpm MUST change.On a stock engine, they will usually stall. At 5000 ft, with primary throttle valves too far open, Ima guessing yours should rev up a lil.
>Install a vacuum gauge on the sparkport.
> bring your IR temp-gun
> hook your power brake hose to the correct port on the carb, or better is to the intake plenum, but not to one of the runners. For this test, pinch it off.
> move the car out of the building and bring your fire extinguisher. I also will not buy you a new garage, or a new car, if your stuff catches fire

Ok, with the stage set;I'm only gonna work on the idle in this post.This is an idle only post.
1) Pop the M-rod covers and pull the springs out. re-install the covers. This is gonna make her hard to start shortly, so you may have to splash a few ccs down the primaries later.
2) remove the carb. Put her on the curb-idle screw, and keep her there. Drain it. Flip her over and set the Transfer slot exposures to a lil taller than wide. Close the secondaries up tight but not sticking.
OK, set the mixture screws to 2.25 turns out from lightly seated.
Blow out the IABs with compressed air. I have to assume they are working,and I can't be there so it's up to you to make sure they are gonna work.
>You should have one of those thick paper insulator gaskets on the intake,and I like one paper gasket on each side of it. Make sure it covers all the sealing surfaces of both the intake AND the carb, and does not interfere with the closing of the throttles.
Re-install the carb and fill it with gas.
>After this;
DO NOT TOUCH THE CURB-IDLE SCREW
> While the carb is off and empty;
Blow out the PCV port to prove it's working. Blow out the PCV valve from the engine side. Blow out the hose.
>Other;
Check that your crankcase is NOT overfilled.Check that the rad is properly filled.

In a second we are gonna twist the key, but first; loosen the clamp on the distributor just enough so that you can tug some timing into it, then splash a few ccs of gas into the intake.

Are you ready? I said ARE YOU READY!
Ok hit the key
As soon as the engine runs, tug some timing into her so she will run at 850 OR more;
Do not even put a timing lite on her!
Let her come up to temp. Check it with the IR gun. Find the hottest spot, and let that spot be your test-target.
DO NOT TOUCH THE CURB-IDLE SCREW


With the engine now warmed up, and idling at 850 by the timing adjustment; Hop in, put your foot on the brake pedal, and put into gear, any gear. Measure the rpm drop.If it stalls yur in big trouble,lol. I mean, it's a stroker right, I thought they made tons of low-speed torque,lol.
Yur target is a 50 to 100 rpm drop no more.. This will be aggravated by a low-stall TC, so we gotta tune for that.
If you are already in the zone, badaboom lets move on. if not, see note1
Ok put her back into park.
Now, lets see where we are at. The engine should be idling really sweetly. Grab a shop-rag and stuff it into the secondaries. The idlespeed should not change much, nor the quality. If it changes more than 50 rpm,see note2.
Ok so lets see where the timing is; but first check the sparkport signal. There should not be any vacuum there; if there is see note 3. move the gauges to read manifold vacuum. What are you getting. I need an idea of what we are dealing with, since I have not seen your camspecs. Until then, I'll assume 9 inches minimum.
Ok so now read your idle-timing; and I'll assume you have proved your index mark is on the money. If you haven't see note 4. What have you got?
I'll guess mid to high 20s.
Low 20s is fine for idle, but hi 20s usually causes too much idle drop into gear. with a too-tight convertor.
Ok so with low 20s we'll leave it there for awhile.
Next, lets fix your idle fueling.
Pull the shoprag out of the secondaries.Observe the speed change and direction.
If the speed went down,see note5. If the speed went up, then the engine wants more air.or less fuel. so mess with the mixture screws and see what happens;
if it seems to run better with less fuel, then reduce the transfer fuel by backing out the curb-idle screw 1 turn, and diddle the mixture screws some more. If the idle speed drops below 800, pull in some more timing.
If it seems to run better with with more fuel, then do the opposite..TIMING will be your speed control.
Your idle fueling, and quality is set by the transfer fuel together with the mixture screws, and the mixture screws tell which way to go, by what the engine likes or doesn't. You will try to end up with about 2.5 turns on the mixture screws, with the transfers at a lil taller than wide. So keep track of what you are doing with the transfers.
If if, if the diddling does not produce the expected results, then, the system is out of adjustment range; and either the engine is not getting enough air, or too much. So take your shop rag and begin to cover the primary bores, from back to front. If the speed drops, she wants more bypass air. If the speed goes up, she wants less bypass air.
I'll assume she wants more bypass air.
So, your first go-to is the PCV. The 318PCV is not gonna cut it. You will need something off a radical low-vacuum engine, like IDK, I have never run a stroker, but Ima thinkin maybe a 383Magnum from the late 60s. Whatever you use it should be new, so the spring is fresh.
Here's the deal with the holes you are drilling in the throttles, which is the next go-to;
1) if you go too big, the idle speed will rise, and you will have to take out timing to reduce it; so if you are already in the high 20s for timing, then happily drill away.
2) if you go too big and end up at less than 14*, then you may begin to have problems at throttle tip-in, or stalling when going into gear.I hear other fellas recommending hi teens to low 20s, and IDK for a stroker.
3) I run 3/32 to 5/64 holes in my 750DP on my 230* cammed 367@14* idle-timing. I got up to 1/8 but that just increased my speed too high, and I had to reduce timing which led to other problems

4)if you drill too big, you can close them up, move over, and start again, see note 6..
5) the holes need to be chamferred on the topside only and burs removed on the underside.
6) after every size change; you will need to return all carb settings to the start point, and reset the idlespeed to 800/850 using timing. Then start over to determine if the engine liked the change.
7) if you reach a frustration level you just can't get past; pop the top and reduce your wet-fuel level in the bowl by 3/32...... and yes, start all over. 3/32 is a big jump and should immediately provide relief.

> When you are getting close;
the mixture screws will again work, and
the rpm drop into gear will come into the zone of 50 to 100 rpm,
and the timing will come down to less than 20*, and
when you pop the PCV hose off the carb, the rpm is most likely to want go down or stall, and
The engine will continue to run sweetly down at 750/700/650, maybe even 600, all by retarding the timing. My 367, not quite as radical maybe as yours, happily pulls itself on hard level flat pavement at 550rpm, at 5* idle-timing, with that 276/286/110 (.008 tappet), 549/571 lift Hughes cam. I don't drive it at 5, I just idle it down there when I need to drive 4 mph with a manual trans and 3.55s.
Ok so I'll fill in whatever notes you need, as you may need them
Happy HotRodding.

Edit1;
Just to reiterate, this is for idle-tuning only.
Your Power-timing may have to be revisited when yur done, and after you get that sorted, then the Vcan has to be sorted.
Later on you can learn to trade one timing for another, to better driveability .

Edit2
IDK why that colored part is, but I cannot make it black, so I made it dark brown,lol. Computer is happy.

notes here
Dam A/J
You are the man
Tune on Chief
 
I tell you what, idle that engine down to 550 and yur gonna see that estimated 9 inches plummet. Idle it up to 1200 and watch the numbers climb.
That is why others and I suggested a starting point of 850 rpm. Altitude plays it's role as does idle-timing.
When you hear a small cam idling like a top-fuel wannabe, you know that cam is either a poser or a guy tuned it to do that.
I remember when I had the 292/292/108 cam in my 367 at 11.3. After the cam break-in it idled all rumpidy-rump-like, too. But after a few hours it calmed right down. I could tell it was a big cam for a streeter, and if I had wanted what it had to offer, I would have kept it. But I owned the mistake almost right away, sold it, and pulled it, hyup in that order.lol .
I measured that cam as about 249@.050. I think I found it advertised a few years later, at 248@.050
I replaced it with a 223@.050, and reset the Scr to 10.7, and that made a real nice streeter. I'd still be running it today, if somebody would have told me they were gonna take the ZDDP outta the oil.Hyup, she dropped 3 lobes right after an oil change. That lil learning business cost me a G-note CAN$.
IIRC that 292DC idled at 9ish for vacuum.
So did the 223@.050 Hughes ....... but about 300rpm lower, and 8* less idle-timing,lol. I really liked that 223.
IDK what it would take for a streeter to idle at 5inches @ a typical 750rpm, and I'm never gonna build one either.

But I have sure tuned a lotta lotta motorcycles that idled down there, at 1000rpm even.
 
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I tell you what, idle that engine down to 550 and yur gonna see that estimated 9 inches plummet. Idle it up to 1200 and watch the numbers climb.
That is why others and I suggested a starting point of 850 rpm. Altitude plays it's role as does idle-timing.
When you hear a small cam idling like a top-fuel wannabe, you know that cam is either a poser or a guy tuned it to do that.
I remember when I had the 292/292/108 cam in my 367 at 11.3. After the cam break-in it idled all rumpidy-rump-like, too. But after a few hours it calmed right down. I could tell it was a big cam for a streeter, and if I had wanted what it had to offer, I would have kept it. But I owned the mistake almost right away, sold it, and pulled it, hyup in that order.lol .
I measured that cam as about 249@.050. I think I found it advertised a few years later, at 248@.050
I replaced it with a 223@.050, and reset the Scr to 10.7, and that made a real nice streeter. I'd still be running it today, if somebody would have told me they were gonna take the ZDDP outta the oil.Hyup, she dropped 3 lobes right after an oil change. That lil learning business cost me a G-note CAN$.
IIRC that 292DC idled at 9ish for vacuum.
So did the 223@.050 Hughes ....... but about 300rpm lower, and 8* less idle-timing,lol. I really liked that 223.
IDK what it would take for a streeter to idle at 5inches @ a typical 750rpm, and I'm never gonna build one either.

But I have sure tuned a lotta lotta motorcycles that idled down there, at 1000rpm even.

From memory mine was 320 adv and 256 @ 0.050 solid with 490 lift. After i stuck a 750 edelbrock on it i modified the boosters to function like a holley by drilling out the cross channel restrictor and blocking the secondary air bleed and it idled just like the holley did.

Heres a good thread on Vacuum @ Idle.

Newbie - idle vacuum vs duration

412 SBC cam 285/305 112 LSA 10.5" @ 1200 rpm. 2 * 4 barrels.
351 Cleveland 204/225 114 LSA 20" @ 800 rpm - 1*4 barrel
438 Cleveland 268/278 113 LSA 18" @ 800 rpm 1* 4 barrel.

And these are Duration figures @ 0.050
 
So it turns out the throttle plates weren’t centered properly in the bore causing them to have an excessive gap. Loosened the screws, and got the blades as flat as possible. Drilled the holes out to an eighth inch, and now at 600 rpms, the motor will die with both screws turned in. I did bump the initial timing up to 16 degrees, and installed the fattest advance stop bushing so it would be 34 total, and checked and it’s 34 right on the nose. It no longer seems to have the nasty hesitation when taking off, but one problem remains. The car runs rather hot, about 210 ish degrees even when going 60 mph on a flat road. But I’ll do another post for that.
 
Link the new thread for quick & EZ Access.
So it turns out the throttle plates weren’t centered properly in the bore causing them to have an excessive gap. Loosened the screws, and got the blades as flat as possible. Drilled the holes out to an eighth inch, and now at 600 rpms, the motor will die with both screws turned in. I did bump the initial timing up to 16 degrees, and installed the fattest advance stop bushing so it would be 34 total, and checked and it’s 34 right on the nose. It no longer seems to have the nasty hesitation when taking off, but one problem remains. The car runs rather hot, about 210 ish degrees even when going 60 mph on a flat road. But I’ll do another post for that.
 
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