Carb tuning

[mustangman1974]

Ok today I was messing with my carb to try to get it tuned, and I noticed something I hadn't noticed before. Here is some background:

I check all the plugs a whitieh powder with a red tint( I think thats good)
I let the car warm up to about 190 degrees.
I connect vaccum guage, rpm guage, timing light, and AFR meter.
I tune it to the smooth idle of 810mv or 13.1-12.5 to one it bounced 60 mv.
Idle is at 1000 in park about 700 in drive.
Timing is at 10 degrees.

A/F meeter is in driverside of motor so I am actually on reading one side of the engine. When I pull the #5 plug wire I noticed the A/F ratio went to 17-18 to one. and it onle did it with that plug wire.

What would cause this?

 

[D.Hearne]

You cannot tune a carb at idle with an Air /fuel meter and expect it to be correctly tuned for all driving conditions. You're only setting the A/F ratio at idle. Set your timing, then set the idle speed to where you want it (1000 rpms is way too high in neutral) then adjust the idle mixture screws til you get the smoothest idle. Ditch the A/F meter, oyu're overly complicating the tuning process.

 

[mustangman1974]

Anything less then 700 rpm in drive the car stalls. To be honest I never had this new motor to run right since I put it in 3 years ago. Runs like a dog compared to the prior engine. Not having in-depth experience, and tunning finess I have to go the only route I know and that's techie.

I usually tune then go flogged it on the freeway. The A/F stays in the 13:1 range all the time and only richens up when I first floor it. I have settle with the fact the motor is goning to be a dog, it has the explorer cam, and not the cobra cam like ordered. To bad I found that out after the warrenty was up.

I messed with it today it was lean missfiring on the way home. I turned both needles 1/2 turncounter-clockwise and it seems to alievate the major drop when I unplug a wire. However it still misses in gear, but its so dam irradic I cannot pinpoint it.

 

[D.Hearne]

Well it's not the cam. There's nothing wrong with the Explorer cam and running a carb. I've got the same cam, 1.7 rockers, ported E7's, a Ford A321 intake, topped with a Holley 570 carb. It runs exactly like it's got EFI. Smooth as s--t from idle to 6000 rpms. You've either got a carb problem or something's not right with the ignition system. Not having experience with either of what you're running, I really can't tell you more. But it's not the cam, if that's the cam you really have. Might be, you've got the "base roller" cam in there, if it's a reman engine.

 

[68RCodeConv]

Look for a vacuum leak. Dial in some more initial timing - that will let you close the carb butterflies some more and get back on the idle circuits.

Unplug the vacuum advance when setting the timing.

 

[65ShelbyClone]

I will add that the the '93-95 Cobra and Explorer cams are both similar and milder grinds than the '87-95 5.0 HO cam.

 

[mustangman1974]

well I have installed the intake about 4 times thinking its a vaccum leak. It doen't suck oil, nor change in vaccum or idle with propane around the intake head area. Carb, unless all 3 carbs I have are jacked then its not that. The distributer seems to fire good. I can hold the spark plus wire about 2 in away from the cap and it still sparks. They only thing I have noticed is the dwell changes as the timing advances. I have never heard from Mallory whether the MBI has dwell compensation so that might be it. Otherwise I have not ideal. I tried tonight to give it more timing to make it 12 and 36 total and it pingged pretty bad so I backed it off to 11 that seems to be the most I can get with pump gas.

I know its gotta be something simple. Its just been soo long I am just brain fried on the tuining. My old setup ran great and I just maintained. That's easy.

 

[D.Hearne]

What octane fuel are you feeding it ? Mine pings on 87, not at all on 89 with the timing set at around 12-16* BTDC. Idles at 500 rpms in neutral (it's got a manual transmission)

 

[mustangman1974]

89 octane with lucas fuel additave. I have a c-4 automatic. I ordered another edlebrock base to see if the miles had worn out the throttle shaft of the 1406.Thats all thats left unless its something in the long block itself. Which is out of warrenty. grrr

 

[woodsnake]

D. Hearne, your set up idles at 500 rpm?? My junk idles at 950.....
How did you do that?

 

[D.Hearne]

D. Hearne, your set up idles at 500 rpm?? My junk idles at 950.....
How did you do that?

It just does. I'm only using the center carb at idle, the end carbs are fully closed. I think at lot of it has to do with the wide EFI type LSA of these cams. (Ford Alphabet's)