Rough idle

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Followed your instructions, it runs a lot better now. Timing at 14*, idle mixture screws 2 1/2 turns out. idles at 750 and drops to 600 when in gear. Better but still idles rough. Pulling spark plugs this week and checking them.
 
Idles rough is normal for some cams.
Some cams want some idle-air bypass.
What were your cam specs again?
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But I agree to check the plugs, you may have killed them.

150rpm drop going into gear is still too much. You may have a tight TC; what does your TC stall at.
But more than likely your fueling is still off. After you get it a lil closer, you will be able to take some more timing out, and then it will get better.
Try this; introduce some dry air underneath the throttle blades and see if it smooths out. But be careful, if the rpm goes up, you will have to bring it down with timing retard else the test is not valid.
To do this, I use the PCV circuit; cuz I mean it's right there and in the right place,lol. What I do is install a variable orifice brass fishtank air bubbler adjuster in addition to the PCV, like Tee it in, and then fire it up. Then I give it air bit by bit, and subtract timing, and or throttle-opening, as I work it out; Always being careful not to create a tip-in hesitation.
You don't need the valve. You can Tee in a length of hose and drill holes in it. Or Tee in a multiple-nipple vacuum tap, and work with the openings it has. It doesn't matter how you get the extra air in there, but if you find that it works!, then you will have to figure out how to give the carb, that amount of air. But one thing I do not recommend is to introduce dry air into the secondaries; They must close up tight but not stick.
Good luck.
 
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DARTLARRY said:
Followed your instructions, it runs a lot better now. Timing at 14*, idle mixture screws 2 1/2 turns out. idles at 750 and drops to 600 when in gear. Better but still idles rough. Pulling spark plugs this week and checking them.
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if you're pulling plugs anyway, try a leak down test while you're at it.
 
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204/204/110+4 @.050 270/270 HFT
Oh yeah that will idle "rough"
It has 50* of overlap, and in at the spec of 106, the Ica is 61.5
It's kinduv a poser cam sounding a lil bigger than a 340 cam, but the power comes in a lil sooner, but not as much, so that's all good
But that 50* of overlap is not made for log-manifolds.
When the exhaust piles up in the logs, it will seek the path of least resistance, So at the end of the exhaust stroke , the exhaust valve will still be open for another 21.5 degrees and the piston is just starting down on the intake stroke, so there is a good chance that some of that exhaust is gonna back up into the intake at idle, and it's going the wrong way!
Or if the log gets pressurized, it can/will puke exhaust into another cylinder with an open exhaust valve.
Furthermore, after the piston hits bottom on the intake stroke, it will be another 61.5 degrees before the intake valve reaches it's specified advertised closing point, but the actual on the seat and not-leaking point ,could be more than 10 * later; So, the piston,at idle, is gonna be pushing some of that just inducted F/A charge back up into the intake.
Between those two events, your intake is gonna be full of crap going in all the wrong directions for it to idle smooth. That cam really needs headers to straighten out the idle airflow. Or, it's gonna want to idle at a higher rpm than usual, to reduce the amount of time for all this to happen.
All that to say that 750idle rpm may be as good as it gets, and whatever it's got for smoothness, may also be as good as it gets.
I think 14* of idle-timing is about as low as you wanna go with that 270* cam.
Before you do anything more on the carb; check your hot start. If it goes click-vroom and starts right up when you twist the key, without touching the gas , then I would leave it alone.
But if it cranks a bit before firing up or you have to give it pedal, then;
I would try 12*, and reset the mixture screws to 2.25T, and open the throttles a tad more, then see what happens; but I think you are pretty close. Make sure the wet fuel level is right on, and stable.
 
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That Edelbrock cam will do anything but idle "rough".
 
DARTLARRY said:
It starts right up, barely hear it turn over. It drives out fine, just idles rough.
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The specs on that cam are 420/420 204/204 ground on a 110. If it has much bump at all even when cold, I'd be surprised. If the engine is running what you describe as rough and I feel sure reading all your posts you know what "rough" is, I don't believe the camshaft is the fault. Have you put a vacuum gauge on the engine?
 
Yes, pulls 12 to 15 inches at idle. Maybe Im getting old, and used to the way newer cars run.
 
DARTLARRY said:
Yes, pulls 12 to 15 inches at idle. Maybe Im getting old, and used to the way newer cars run.
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What's the approximate compression ratio? You said .030 over with stock heads. Are they stock replacement pistons? If so, that means 8.5:1 max, so you can pull in probably up to 20* initial timing or more. Try that and see if it cleans up anymore. Of course, you'll need to limit your total timing to about 36* and all in by about 2500.
 
Stock pistons 8.5:1 compression if I'm lucky, heads are mildly ported, with 2.05 valves. I had it timing set around 20* before, but it was too much. I may bump it up to 16* to 18* initial and see if that helps. I did add a distributor with vacuum advance as well.
 
Finally got back at it today, set initial to 20*, total at 35*, all in at 3000 rpm. Drives out, and pulls very strong, still a little rough idle. I brought it back home and did compression check, all cylinders are at 125psi, except #1, it is at 110psi. I brought that cylinder up to top dead center, and filled it with 40 psi of compressed air. Air was leaking into the crankcase, I could hear it when I pulled the oil cap. Bad rings on that cylinder? I may pull, and replace it over the winter, it was plagued with low oil pressure(I believe due to cam bearings) anyway.
 
DARTLARRY said:
cylinders are at 125psi, except #1, it is at 110psi. I brought that cylinder up to top dead center, and filled it with 40 psi of compressed air. Air was leaking into the crankcase, I could hear it when I pulled the oil cap. Bad rings on that cylinder?
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It's interesting that one cylinder is 15 psi below the others, and it may indeed be weaker.
But have you tried the same 40 psi air test on one of the other cylinders? Rings are never a 100% perfect seal because they have end gaps, so I'd expect to hear some hissing air, even if a small amount.
 
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