I installed a milder cam and am in the process of retuning my carb. Previous cam was a MP 509 hyd and I installed a Lunati 60303 hyd. With the new cam I can't get the car to idle under 1000rpm and that is with closing down the butterflies past baseline settings. If I screw the IMS screws in to get the idle down and the AFR cleaner they are 3/4 turn out and I get an off idle stumble. I am working with a mighty demon 825 by the way.

I had previously drilled a .091" hole in each of the primary throttle blades to get the carb to idle right with the 509 cam. Could these holes now be my problem?

Don't know about the holes you drilled, but just a couple of things to consider:

* Keep playing with the IMS. Anything to get it to idle.

* Higher vacuum with a milder cam could be causing a slight delay in power valve opening. Try a higher # power valve.

* Perhaps slightly bigger accelerator pump squirters would help the off-idle bog.

* A bit more initial timing to help the idle?

I have 12-13"hg vac at idle now compared to 6-7" with the old cam. I have a 6.5 pv installed now with a 9.5 and 10.5 on the way. My timing is 25 I initial and 36 total.

I notice hat when I adjust the primary iss it has little effect on the idle speed but when I make a small adjustment to the secondary iss it has a much more dramatic effect on the idle speed. That is what has me thinking the drilled primary blades are my problem. I have replacement primary throttle plates but can't get he darn screws out to replace them. What's the secret to getting those screws out? Looks like he factory mashes the tip on them so they won't back out and drop in engine.

take a little peice of black electric tape and put over two of the holes and see how it idles. if that works then you can replace two of the throttle blades...worked for me

Probably too much initial timing now. Take some out and your idle speed will go down.

Take a small file to the screw ends where they were bradded over. It helps if you wire the throttle open and then put the throttle plate in a vice with some wood or soft jaws.

If they peened the stock brass screws over try rotating them both ways a little at a time until they come out That is if you don't want to grind the ends over so there not peened If there steel screws be very careful

The off idle stumble is caused by the too much transition. Take the carb. off and turn it over and set the transition, long slots, to have about .020 clearance between the butter flys and it. The holes will not hurt a thing holley put them in a lot of their carbs. Be sure to re set idle by turning front and rear adjustments the same- this is very important. After adjustment, take the carb back off and re check the slots and they should be the same. If not re adjust.

My transitions were set at .020" (small square on the primary) and barely showing on the secondary. I think the stumble may have had more to do with the IMS screws being in too far (only 3/4 turn out)?

Anyway... I decided to install new primary throttle plates without the holes. Was able to file the ends off the screws and get them to back out tonight. Waiting for some new screws to come so will have to wait to see if it has any effect on the carb tuning or not.

I had thought about backing off the initial timing a bit but then thought guys run with distributors locked out without any trouble. How can this be? Are they just large long duration cams that need this?