isky mega cam

[torqueflite]

I have an Isky 270 mega cam in my 383 Charger ....not my choice of cam but it was already in the moter when I got it. The moter runs real rich at idle [ the fumes burn your eyes evan with the shed door open ] which I can't seem to fix , and it has an off idle flat spot also that Im trying to get rid of .
In saying that... once you get through the flat spot and up to crusing speed she goes real well .
The best idle vacuum I can get with a new Holley 670 is  10".
Cam spec's are 
Duration @.050   221  deg
Lobe centre       108   deg
Valve lift            .465"
I have degreed the cam to check it and it is installed straight up.
My question is ... If I advance the cam 4 deg do you think the idle vacuum could be  improved or would I not see a lot of difference.
cheers John.

[aifilaw]

my initial response is yes, you will get another couple degree's of vacuum... but based on the duration I'm not certain of that fact. It will definitely shift our power-band as a whole towards the low end a couple hundred RPM.
I don't have time to run the numbers on that and check in depth, but I'm bettering firefighter will probably know off the top of his head.

[max]

runs real rich at idle [ the fumes burn your eyes evan with the shed door open ]

the richness at idle as you discribed with a holley carb unsally means the power valve in the carb is blown or is too weak.

[deputycrawford]

    Also, with a cam that small, you should not have the richness of the engine. I would change the power valve. While you're at it, turn the idle screws all the way in and see if ther engine stalls. If the idle screws do nothing then you are not using your idle well in the carb. That would explain the off idle stumble on take off. Start with the power valve, then move to the stumble problem. Do some tuning research and you will fix it.

[firefighter3931]

My question is ... If I advance the cam 4 deg do you think the idle vacuum could be  improved or would I not see a lot of difference.
cheers John.

John, to answer your queston ; idle vacuum won't increase much if at all with a 4 degree centerline advance. The idle is a product of the cam profile and in this case the tight 108* lsa will create lots of overlap which makes for a "dirty" idle. A cam with a wider lobe seperation would be a better choice, inmo. That cam is not overly big....just a little tight on the lobe centers.

Carb tuning might help out. If it's running real rich then there could be power valve issues or it might be getting too much fuel at idle which is adjusted through the mixture screws and air bleeds. The avenger series carbs don't have adjustable air bleeds so tuning can be difficult. The correct power valve should be 2in smaller than the idle vacuum reading. Also, if the idle speed is set too high then the carb will be idleing on the main circuit instead of the idle circuit. This often happens when large overlap cam profiles are used with carbs that aren't designed for the application. The fuel curve and metering on the avenger series carbs are more suited to a milder type build.

Start with the idle mixture screws....keep turning them in until it leans out and see if the engine will stay running. The idel speed needs to be under 1000 rpm for it to be running on the idle circuit. You will probably have to swap out the power valve as well....something like a 6.5 PV would be in the ball park. What is the idle vacuum reading with the car in gear....that will be your PV reference point. 



Ron