How much overlap is in that cam? You could get it”better” but if there’s a lot of overlap it will never be clean

 

Here's a copy of the cam card.

 

I ran that cam in my 388 but it was 11.7:1 and ran on 110. Locked out timing at 36*.

Probably going to need more initial timing.

 

24 degrees of overlap. You can install Catalytic converters. Any way to lean the idle circuit on the carb.

 

68* overlap

 

maybe I'm thinking wrong but I was taught the engine runs "seeing" advertised numbers and .050 numbers are for easy comparison of profiles. I hope the cam guys chime in. pull the carb off and see how far up the transfer slot the throttle plates are at your best idle speed.how many turns out are your mixture screws? do they function correctly; can you get it to stall the engine going in? are you running a vacuum advance? it will help in lowering the throttle on the slots. just throwing things out there hope it helps.

 

Oldguy67 brings up some important tips for getting the idle mixture right. The relationship of the throttle plates to the transfer slot is important. When the motor is up to temperature, timing and idle speed set pull the carburetor off. The throttle plates should just be exposing the transfer forming what should look like a square. The picture is what you should see if you have the carb set right.

 

Try running your fuel pressure at 4.5psi and see what it smells like. I do that on all my Eddy carbs and most of them have a pretty clean idle after that.

 

Have you checked the step up springs under the plunger that holds the metering rods? If they are too stiff for the vacuum of the engine you will get a rich idle.

 

overlap is your problem u r not going to get rid of the smell

 

If he had a Holley or that style of carburetor it would be easier to fix. It can be done with a bigger overlap cam but the Eddy carbs are a pain to work with IMO.

 

Drill some 1/4" holes in the throttle blades?

 

Carb may be jetted too rich for that big an engine.

 

18* of initial not enough for that cam. More like 24-25*
Try that...
We run a 238/248@.050 and 254@.050 and they idle fairly clean,both have Holleys.

 

I forgot about the fuel pressure issue with these carbs, as was mentioned try to keep it around 5 psi. Also check the float setting, mine all needed an adjustment. Then get more initial timing.
My wagon 489 has this same carb, same compression, but a smaller cam. 22* initial is where mine is.

 

Thanks everyone for the feedback so far. I do have some step-up springs on the way. I'll try adding more initial advance and see how it responds and hopefully, I can reduce the throttle plate opening at idle. I did read a lot about drilling holes but that is my last resort. I'll try going down to 4.5 psi, right now I'm at 5.5. And in the end if overlap won't allow me to get rid of the rich idle smell I can just live with it. I'll make these changes and report back what happens.

 

The step up springs can be checked by loosening the screw on the cover and move the cover out of the way. The plunger should be sucked down the at idle, if its up or bouncing it will be rich.

 

You CAN get it cleaner at idle with more tuning.Get ignition right then move on to the carb, if you have to drill the plates start small and work your way up. Again as a last resort. Think you need more timing @idle for sure. Keep at it!

 

I just found this well written article: Ignition 101

This helps explain a lot. Now I'm looking forward to seeing how it responds to more initial advance.

 

You need way more timing advance at idle. That will allow you to close the throttle blades and maintain the correct idle rpm. It is not your fuel pressure, as you are at 5.5 now.
You need at least 25 at idle, preferably more.
What head casting number, and what plugs are you running now?
What distributor?

 

You need way more timing advance at idle. That will allow you to close the throttle blades and maintain the correct idle rpm. It is not your fuel pressure, as you are at 5.5 now.
You need at least 25 at idle, preferably more.
What head casting number, and what plugs are you running now?
What distributor?

Ngk plugs. I would need to pull one for the number. Heads are 3872702. Distributor is a davis unified ignition HEI street/strip.

 

are you running a fuel pressure regulator on the edelbrock carb? mine likes 5.5 lbs of fuel pressure to much pushes the needle off the seat on mine, most holleys can handle a lot more pressure. all the edelbrocks I have used have a bad idle until I started running a fuel pressure regulator , never a problem after that with the carbs.

 

Yes. Currently set to 5.5 with a bypass regulator. It's pretty steady.

 

Did you adjust it as lean as possible with mixture screws when hot idling without misfire ?

 

I set my initial with vacuum advance connected to full manifold. The engine idles great at 26 degrees, 800 rpm. Very easy to start when hot, no kick back. I checked the step up springs and they are held down at idle, no bouncing. Getting a steady 15 inches of vacuum at idle. I was able to close the throttle blades more at idle and not getting eye watering exhaust anymore.

Engines idles and revs awesome, however the total timing comes in at 3000 and is around 52 degrees. Is that too much? If that is too much what is a safe number if I need to limit mechanical advance?

I haven't driven it yet to check how it responds under load.

 

52* total + vacuum is close to factory. If you get some jerking you may need to reduce vacuum advance some.

 

If you are saying that you have 52 degrees at 3000, when the timing is full advanced, and vacuum advance connected, you might be ok there. Only way to know is to drive it.
You really need to know the idle timing, then how much at full advance, with vacuum advance disconnected. Then see how much the vacuum advance adds at idle, and at steady throttle at full advance (if there is a different amount added at idle than when revved up, that tells you the idle vacuum is too low to keep the cannister pulled in all the way).
You also MUST know how much timing at full advance with vacuum advance disconnected, as this is the amount you will see under full throttle/full load acceleration. And this is where too much advance can cause engine damage.