won't idle below 1000rpm after rod and jet change

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67cuda360

67cuda360

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just swapped intakes (torker 340 to a Edelbrock Air Gap) and I am trying to calibrate the carb (edelbrock 1806 Thunder series AVS).

I richened up the carb a bit because I thought it might have been running a little on the lean side, now it won't idle below 1000 rpm (at highest vacuum reading of 20").

The idle set screw is all the way out and it idles smoothest with the idle mixture screws turned out to about 3.5 full turns. My gut says this is too much

Is this a sign of being too rich?

I also noticed that when the idle set screw is fully turned out, the throttle arm doesn't hit the metal stop, is this correct?

Specs:
1974 360
solid lifter cam (specs unknown) 20" vacuum at idle
1806 Thunder series AVS
Air Gap intake
18 degrees initial - 36 total, all in by 2500rpm
 
Sounds like something else is holding the idle up. Like The throttle cable? Or a Choke Cam. Those are the 2 problems I had 2 problems with my Eddy 1406.
 
make sure the throttle is not hanging on the fast idle cam....or the fast idle cam screw is adjusted correctly...

the fast idle cam and screw is where the engine idles while on the choke...
 
What do the plugs look like? The best way to check mixture(without a gas analyzer) is to read the plugs. Any vacuum leaks? A lot of factors can cause it not to want to idle. It doesn't necessarily mean it needs to be richened up. Also check the linkage & cable. Disconnect the cable & see if the idle can be adjusted lower.
 
You....have....a....vacuum....leak

Check the both throttle bores are seating tight, and then look for carb/ manifold leaks.
 
Linkage is not held up by the throttle cable or the high-idle cam, I took the carb off and it looks like the throttle blades are fully closed so that should be as it was meant to be, even with the carb off the car and nothing attached to the levers, the throttle arm still doesn't hit the stop, I triple checked, nothing is obstructing it LOL.

In regards to a vacuum leak, I doubt I have one since my manifold vacuum shows a steady 20" of vacuum at idle with no fluctuations what so ever.

With the previous (stock) carb setup the car idled at 750-800 rpm, the idle mixture screws were set at 2 full turns and the car had the same 20" of manifold vacuum, could a rich running carb result in a higher idle...?

I'll post a pic of my spark plug in a sec.
 
a rich carb is not going to idle faster...just going to water your eyes and foul the plugs...
 
70aarcuda said:
a rich carb is not going to idle faster...just going to water your eyes and foul the plugs...
Click to expand...

I understand but wouldn't it idle faster if the idle mixture screws were turned out more like in my situation to get the highest vacuum reading? It is just that I ran out of adjustment for the idle set screw, to bring the idle down to 750-800 rpm
 
NO. A properly setup carb, the idle mixtures will "peak" at vacuum AND RPM with the mixture the "engine likes." More lean, RPM and vacuum falls off, as does too rich.

Before we had "smog carbs" with leaner idle circuits, many carbs could be richened up so much with the idle screws, that the engine would die.

I still say...............You have a vacuum leak

And from the looks of that plug, it is NOT running rich
 
I'll guess vacuum leak as well without much else to go on.

Check the low hanging linkage for interference with your intake.
 
I checked and nothing is interfering anywhere :) I had the carb off the engine and checked everything, it seems that the throttle arm is as far back as it will go, the throttle blades are closed.

If I had a vacuum leak, wouldn't that mean I should see a fluctuation in the vacuum gauge reading?

any thoughts on the spark plug image?
 
67cuda360 said:
If I had a vacuum leak, wouldn't that mean I should see a fluctuation in the vacuum gauge reading?
Click to expand...

No, in fact the early AFBs that had the great big idle speed screw in the middle essentially WAS a controllable vacuum leak!!! You moved the screw, which let in more air, adjusted the mixture screws, and "walked" back and forth until you got what you wanted

Like this'n

p3161709.jpg
 

Attachments

  • AFB.jpg
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If the old carb would idle at 750-800, then this carb should also idle in the same range.

I'm still guessing vacuum leak somewhere.
 
Maybe looking too close to the carb? Check the other end of your vacuum lines also. Hose split, tee cracked, bad advance canister, etc? Or maybe brake booster/line if you have power brakes?
 
Thanks guys,
I guess I was wrong, it is possible to have a vacuum leak while having steady manifold vacuum :). After checking with a spray bottle it seems I have a vacuum leak on the passenger side of the intake manifold, I'll have to pin point it a bit better, but it seems like I'll be pulling the intake tonight LOL.
 
Check carefully before you yank the intake. I'd be looking at the CARB long before the intake

(Many V8 intake leaks are going to suck oil out of the valley, causing fouled plugs, smoke, etc)
 
Was a check made to ensure that your intake manifold gaskets were thick enough before installing them.

If you do need to remove the intake, I'd put the intake back on dry move it to one side and measure the remaining gap. If the gap is in the .060-.090 range, a standard .060 gasket will usually seal it up. If you start getting over .100, add .050-.060 to the number and divide by 2 to get a gasket thick enough to provide a good crush. ex. gap is .120, add .060 = .180 /2 = .090. Look for a .090 thick gasket in that case.

I've BTDT with a too thin gasket and it leaked badly.
 
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