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Drilling Throttle Plates??

Posted By: 69sixpackbee

Drilling Throttle Plates?? - 06/09/08 09:39 PM

Since I put my 446 Six-pack back together I cannot get it to idle now. I put the 2355 pistons in it,(had 2266's in it before) "Stealth" heads and Cometic gaskets with a combo yielding 10.6:1 CR. This time I put 1.6 rockers on with the same "509" cam. It was idling fairly well before with the mixture screws out about 3-turns and the idle stop screw on the solenoid was just near the point that the butterflies were close to uncovering the idle transfer slots. Now, I am noticing gas dribbling out of the boosters in the center carb when trying to idle. The stop screw is screwed in considerably further now certainly uncovering the idle slots. The mixture screws do nothing now as you would expect having the stop screw way out. I kept the same "45" power valve in the carb but am thinking of drilling a 3/32" hole in each butterfly to try and bring the idle in again as a start. I really cannot get a decent vacuum reading yet since I cannot get a smooth idle but before I did the engine freshening up it idled in the neighborhood of 7". I have read drill on the same side of the transfer slots and I have read drill on the opposite side...who is right??

Am I going about this the right way or should I try something else.?? I definately do not have any vacuum leaks as I tried to locate any and none were found.

Thanx,
Bud
Posted By: HemiStan

Re: Drilling Throttle Plates?? - 06/09/08 11:52 PM

Have you recurved your distributor since the rebuild? I was about to drill holes in my plates but after getting some advice from a member on here and spending some time with the distributor, it runs like a new car!
Posted By: BobR

Re: Drilling Throttle Plates?? - 06/10/08 01:21 AM

My 416 small six pack has all 6 of the throttle plates drilled. It idles perfectly but there does seem to be a dissenting opinion on doing this. -Bob
Posted By: 69Cuda340S

Re: Drilling Throttle Plates?? - 06/10/08 01:27 AM

Some times you have to drill holes with high duration cams. But before you do try giving it more initial advance and that may allow you to turn down the throttle for proper transfer slot alignment.
Posted By: 69sixpackbee

Re: Drilling Throttle Plates?? - 06/10/08 03:02 AM

Quote:

Have you recurved your distributor since the rebuild?



Negative..same distributor advance. MSD billet with all in by 2500.




Quote:

Some times you have to drill holes with high duration cams. But before you do try giving it more initial advance and that may allow you to turn down the throttle for proper transfer slot alignment.



I have the same initial...16 BTDC. 20-more in by 2500RPM.

My original as-built, 446 had a CR of 9.8:1 with big valve & massaged "906"'s w/ 1.5:1 roller rockers and the TRW 2266 forgings. What has changed is the higher CR thanx to the TRW 2355's W/ Speed-Pro file fit rings, Cometic .027" thick gaskets and the polished, shaved and port matched Stealth aluminum heads.
I stepped up to 1.6 roller rockers which give me a theorhetical lift cam of .543" from my D.C. 509/292 cam. I am also running the same but brand new, Crane anti-pumpup lifters.
I guess drilling the blades is no biggie. I will probably start with 3/32" (.093") holes.
Posted By: dave571

Re: Drilling Throttle Plates?? - 06/10/08 03:57 AM

I think 20 or more initial with that 509, will give you better idle

My cam specs are similiar to a 509, and I run 24 intial.

Drilling the plates isn't a big deal. It's filling them back in that's a pita.
I've done it, but why not exhaust other options first.
Posted By: 68LAR

Re: Drilling Throttle Plates?? - 06/10/08 11:15 AM

Quote:

Now, I am noticing gas dribbling out of the boosters in the center carb

This is ususally caused by the float level being too high. Try lowering the float just for the heck of it. You will probably have to make some carb adjustments after doing this.
Posted By: Dart 340

Re: Drilling Throttle Plates?? - 06/10/08 01:03 PM

Quote:

Have you recurved your distributor since the rebuild? I was about to drill holes in my plates but after getting some advice from a member on here and spending some time with the distributor, it runs like a new car!



Can you expand on this a little more please.
Posted By: 69sixpackbee

Re: Drilling Throttle Plates?? - 06/10/08 03:11 PM

Quote:

This is ususally caused by the float level being too high. Try lowering the float just for the heck of it. You will probably have to make some carb adjustments after doing this.


I have the center carb just to the bottom of the sightglass (have clear plugs instead of screws) and the outboards are in the middle. I am running a Holley blue pump regulated to 6PSI as the inline gauge confirms.

Thanx!
Bud
Posted By: 69sixpackbee

Re: Drilling Throttle Plates?? - 06/10/08 03:18 PM

Dave,
I have gone as far as 30BTDC and though it did improve it still "dribbled".
I know the "509" is not that radical of a cam. In fact, it has been pretty "street friendly" at least for me. Tall gears and a high stall has also been a contributing factor Otherwise, I cannot see why it should be so bad to dial in the idle. I have read where folks have gotten 11-12" vacuum at idle with this cam but the best I ever got was 7".
Anyway, I am going to tinker a bit more and play aroud with some of these great suggestions from you guys.
I'll keep you posted.
Thanx!!
Posted By: RobX4406

Re: Drilling Throttle Plates?? - 06/10/08 03:39 PM

Quote:

Dave,
I have gone as far as 30BTDC and though it did improve it still "dribbled".
I know the "509" is not that radical of a cam. In fact, it has been pretty "street friendly" at least for me. Tall gears and a high stall has also been a contributing factor Otherwise, I cannot see why it should be so bad to dial in the idle. I have read where folks have gotten 11-12" vacuum at idle with this cam but the best I ever got was 7".
Anyway, I am going to tinker a bit more and play aroud with some of these great suggestions from you guys.
I'll keep you posted.
Thanx!!



Won't matter how far you advance the timing if you have fuel dribbling into the engine. You likely aren't getting the 10+" of vacuum because of the rich condition. Try lowering the float level as suggested to start. You should not have any fuel dribbling from the boosters at idle.
Posted By: Dart 340

Re: Drilling Throttle Plates?? - 06/10/08 03:47 PM

I cracked my secondaries ever so slightly to avoid drilling the plates. Seemed to work well also.
Posted By: 68LAR

Re: Drilling Throttle Plates?? - 06/10/08 04:05 PM

Quote:

Quote:
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This is ususally caused by the float level being too high. Try lowering the float just for the heck of it. You will probably have to make some carb adjustments after doing this.


--------------------------------------------------------------------------------


I have the center carb just to the bottom of the sightglass (have clear plugs instead of screws) and the outboards are in the middle. I am running a Holley blue pump regulated to 6PSI as the inline gauge confirms.





As I said, this is the usual case. I would still lower the outside carb float levels to the bottom of the site glass hole. The next thing I would do is check the power valve and power valve gasket. Make sure that the gasket is the right one for the valve. Make sure the power valve is the right size.
If you have the throttle blades to far open, exposing too much of the transfer slots, this will cause an increase in velocity through the boosters and syphon gas. Having the outside carbs float level higher may be causing an over rich condition making it necessary to open the center carb idle speed screw too far and creating the problem you are experiencing. I'm just thinking of different senerios that can cause what you are seeing. Fuel from the boosters comes from the main jets, or power valve. Both feed based on velocity passing through the boosters. With the throttle blades closed and little or no transfer slots exposed, there should be no gas dripping from the boosters. As you open the throttle blades, velocity increases and the gas should begin to syphon as you transfer to the cruise and power circuits.

Your distributor? Is it a stock unit? Are you running vacuum advance? Do you have it hooked to port or to manifold? If to ported vacuum, then try switching to manifold. This will advance the distributor at an idle and cruise, allowing the idle speed to be slowed down.
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