440 rich at idle and off idle stumble

[GPULLER]

I have a '66 that I am trying to get running right.  It has a terrible stumble off idle and is rich at idle.  Just got the car out of storage for the year, haven't had a real chance to mess with it too much.
Last summer I played with accelerator pump cams, that didn't seem to help.  Changed the squirters to the largest I had (cant remember what size right now).  The idle screws do nothing when adjusted.  Drilled 1/8" holes in primary blades.  Had the carb apart, all air bleeds are clean. It seems to idle and run better with the secondaries opened a bit. 
It is a 440 with a Mopar Performance .484 cam, Torquer II manifold, 750 mech secondary double pumper Holley with 50cc pumps, older Mopar Performance electronic ignition.
Drove the car to work today, quickly checked the vacuum by pulling the hose off the vac advance.  With the advance unhooked, idling (1000rpm) in park, it was pulling 10", in gear 8".  Going to tee the vac advance and check the vacuum with the advance hooked up.  Does that sound like the right amount of vacuum for the cam I'm running?  Figured if it was low I would pull the intake and reseal it, but 10" didn't seem low to me, maybe I'm wrong.  After I check the vacuum with the advance hooked up, gonna check out the power valve.  Not sure of the size of power valve or do I remember the jet sizes, its been a year since I changed them, think primaries are 76's or 78's.
I plan on ordering a cam kit for the accelerator pumps and more squirters.  At what size do you need the hollow screw, 40 or 41?
Lots of things I need to check, want to know if my vacuum sounds right, and if I'm heading in the right direction.
Any other suggestions would be appreciated!

Thanks!
Reed

[AnCieNt1]

Sounds to me like you might have a blown powervalve if it wont adjust when you turn the idle screws.. Also its just my opinion but with the cam you have now i really don't see it needing that much squirter  did you check the tip in when you set up you pump cam? it should pump fuel with any throttle movement. also you usually dont need to drill the throttle blades with a cam that small..

[GPULLER]

Power valve was new last year, but who knows.  We have a bunch here at work I'll take a look and see if I can find a 45, since my vac is only 8" in gear.  The accelerator pump squirts but not a huge amount at first.  Seems like it should be a stronger stream at first.
I didn't think that the throttle plates should have been drilled but it was worth a try.

Thanks for the reply!

[mikepmcs]

IDrove the car to work today, quickly checked the vacuum by pulling the hose off the vac advance.  With the advance unhooked, idling (1000rpm) in park, it was pulling 10", in gear 8".  Going to tee the vac advance and check the vacuum with the advance hooked up.  Does that sound like the right amount of vacuum for the cam I'm running?  Figured if it was low I would pull the intake and reseal it, but 10" didn't seem low to me, maybe I'm wrong.  After I check the vacuum with the advance hooked up, gonna check out the power valve.  Not sure of the size of power valve or do I remember the jet sizes, its been a year since I changed them, think primaries are 76's or 78's.
I plan on ordering a cam kit for the accelerator pumps and more squirters.  At what size do you need the hollow screw, 40 or 41?
Lots of things I need to check, want to know if my vacuum sounds right, and if I'm heading in the right direction.
Any other suggestions would be appreciated!

Thanks!
Reed

Your vac is correct, actually I couldn't even get to 10". That is a vac robbing cam. Mine was swapped for a k56 engle as per Ron's(firefighter's) suggestion. That fixed the vac issue.  I'm sure he will jump in with some sound advice pretty soon.  So the short of it is your cam is the reason your vacuum sucks(or doesn't in this case)
I'm running rich as well, so I'll piggy back off your thread for some info.   That's right, the beast is now running.

[GPULLER]

Did some wrenching over noon.  Power valve is good.  Numbers on the valve were a "0" "K" "5".  All other valves we had at the shop are the same. Checked it with an vac pump and closes at 5".  Vacuum is still 10" and 8" with vac advance hooked up.  The primary jets are 76's.

mikepmcs
You were running the same cam and had the similar vac readings?  Well, I don't think I'll be changing cams anytime soon...unless I get a stroker kit.  and if that happens I'll be back asking more questions!

[firefighter3931]

Reed,

The power valve has nothing to do with a rich idle....unless it is stuck open because it is sized incorrectly. Yours sounds fine from what you described. 

Where have you set the timing ? That cam will want at least 18* of base timing to operate properly and you should have 36-38* total in by 2600-3000 rpm.

The idle mixture screws are unresponsive for one of two reasons :

(1) you are not idleing on the idle circuit....you're on the main circuit. This happens because too much of the transfer slot is exposed. The butterfly mod (drilling holes) works well with big cams and single plane intake manifolds that produce a weak vacuum signal at the booster.

(2) An often overlooked problem, especially with carbs that have been sitting for awhile is clogged IAB's (Idle Air Bleeds). If the bleeds are clogged or partially blocked this will make the idle circuit inoperable or barely functional...idle mixture will be pig rich.  Get some gumout carb cleaner and clean out the idle and main air bleeds....drench it good. 

I wouldn't touch the carb as far as jetting until you do this stuff first....then see where you stand. You might have to adjust the jetting somewhat but focus on dialing in the ignition curve and straighten out the idle circuit and bleeds first. 



Ron

[mikepmcs]

mikepmcs
You were running the same cam and had the similar vac readings?  Well, I don't think I'll be changing cams anytime soon...unless I get a stroker kit. 

YES, same cam.  I put a electric vac pump on the car.  Hated that by the way, noisy, and vibrated the car. Opinions vary, but when I can hear and feel a vac pump over a mopar big block, something has to change.

[GPULLER]

Ron

Be honest, I'm unsure of the timing.  Need to check that.  Up until last summer the advance was unhooked.  It seems to not want to idle down with it hooked up. 

Sounds like I need to get into the air bleeds and them clean.  If the secondaries are plugged, will that still have an effect on the IAC?



Thanks!
Reed

[firefighter3931]

Ron

Be honest, I'm unsure of the timing.  Need to check that.  Up until last summer the advance was unhooked.  It seems to not want to idle down with it hooked up. 

Sounds like I need to get into the air bleeds and them clean.  If the secondaries are plugged, will that still have an effect on the IAC?



Thanks!
Reed

Reed, leave the vac advance blocked and tune w/o it. The vac cannisters are designed for engines that make 15+ inches of vacuum so there's no use trying to tune it. 

Does your Holley have the 4 corner idle provision ? If so, clean both the primary and secondary IAB's and adjust mixture on all 4 corners with a vacuum guage.


Ron

[GPULLER]

I will leave the advance unhooked.

No 4 corner idle.

Leaving for the weekend, will try some things and let you know on Tuesday. 

Thanks for all your help Ron. 

[maxwellwedge]

It sounds like you are taking your vacuum readings off the distributor vacuum. If you are the numbers are meaningless if you are looking for your engine vacuum numbers. Take a reading from a pure vacuum source - like off the intake.

[GPULLER]

Set the initial timing at 18*, and 32 at 3000rpm.  Flushed out the IAC's with a can of carb cleaner.  Was idling all on the secondaries, the idle speed screw was backed all the way out.  Closed the secondaries and opened the primaries.  Idle screws still don't have much effect.  Motor will kill with them turned all the way in, but after a turn there is no change in vac or idle quality.
Still idles fat, has stumble.  Bought ready to throw the carb in the shit can and get a different one.

maxwellwedge
When I took the vac readings I was pulling off the carb base plate which would be full intake vacuum.

[firefighter3931]

Set the initial timing at 18*, and 32 at 3000rpm.  Flushed out the IAC's with a can of carb cleaner.  Was idling all on the secondaries, the idle speed screw was backed all the way out.  Closed the secondaries and opened the primaries.  Idle screws still don't have much effect.  Motor will kill with them turned all the way in, but after a turn there is no change in vac or idle quality.
Still idles fat, has stumble.  Bought ready to throw the carb in the shit can and get a different one.

maxwellwedge
When I took the vac readings I was pulling off the carb base plate which would be full intake vacuum.

Ok, the timing sounds fine....no worries there. How does the spark quality look ? Pull a wire and ground it....you should be seeing a blue/white spark. If it's dull orange the ignition system is weak. That's not all of the problem but it could be contributing.

From the description of your primary idle adjustments it sounds like there is some issues with the metering block. I would pull it apart, soak it overnight and blow out the passages with compressed air....then reassemble. When you open up the idle mixture screws it should respond and lean out. The fact that it doesn't once you'ra past a turn indicates that there is restriction somewhere in that metering block.



Ron

[GPULLER]

Ron

Ordered a rebuild kit and a gallon pail of carb cleaner.  Gonna tear it apart and let it soak for a day or so.
After driving it more, at about 1200-1500 rpm or so, feels like its running out of fuel once its above 2000 it runs fine.  Driving in town at 30mph is about impossible with constantly feathering the throttle.
Didn't get too much time to work on the car.  The fuel pump went out in my Dakota yesterday so the Charger is my daily driver until I get the pickup fixed.

Thanks again!

[GPULLER]

I am happy to report that all signs of rich idle and stumble are now GONE.
My brother was nice enough to loan me the carb off his '70 Bee for the trip to "Mopars in the Park" last weekend.  Car ran great, but brother wanted his carb back...go figure.
Yesterday I finally got to cleaning my carb.  Got a genuine Holley kit, got 2 30cc accelerator pump diaphragms in the kit but only 1 50cc.  Luckily I had just put a new 50cc in the secondary last summer so I had to re use that one.
Weather here yesterday was pretty crappy so I didn't drive too much, just a few blasts down the driveway and back, runs the best it has in a long time.  If I only would have done this last year!

Thanks for everyone's help!

Reed

[Hemidog]

 

[firefighter3931]

Good work Reed ! 

Guess that carb was pretty mucked up inside huh ? 



Ron