6600 rpm breaking up

[image4you2see]

Well I have been fighting this for a couple of years now and have no other parts to toss at it or tweaks I can read to try and change stuff. Just finally trying to get others thoughts in case I am missing something.

Car~
1993 Mustang Origonal 4cyl car
Engine~
347 9.61
Quickfuel 750 carb (Did it with a Holley 650)
Ported Vic Jr intake (never changed it)
AFR 185 heads stock out of the box (springs have been changed to two different cams)
Magnafuel fuel system -10 to pump -8 to regulator (2) -8 to carb ( Had a lesser fuel system on it last year)
1" HVC spacer or 2" hvc spacer
K&N filter on or off with an open K&N top
1 7/8 Accufab long tubes to 3" collector to 3" x-pipe and Magnaflow mufflers (had smaller headers on it until last year with flowmasters)
N-91 cam (had a comp cam before)
Smith brothers 5/16 push rods (had comp cams with the older cam)
Stock brand new FORD oem lifters (with the old cam had a set of modified stock oem lifters from Joe Sherman racing)
Spring pressure right now is 172 on the seat 427 open @ 600 lift (had lesser with Comp cam then we upped them for the comp cam no change)
Instal heights range from 1.84 - 1.845
MSD 7530 (Had a 6al)
MSD hvc coil (Had a Blaster)
Ranged from NGK bkr5e and 6 gaped any were from 50 to 25
Two different converters
Taylor 409 wires (I don't think I ever changed them since build)
92/93 octane gas

Msd goes directly to the battery, car has all welding wire powers and grounds with multiple grounds even the heads grounded.

Two years ago the wide band showed no change and neither did the fuel pressure so that had me stumped. I changed cams and when it did it it showed the fuel pressure drop and the car go lean. So I finally put a good fuel system on it but it didn't change it and the wide band doesn't change when it does it. It does it in all three gears also..

The car runs great it has gone 10.66 to the 1100' mark and me having to drive it the rest of the way out. It has a 28" tall tire and a 4.56 gear in it, I understand I could change the gear and make a pass but if I can figure out this issue that shouldn't be happening this combo has a little more in it.

So a quick recap everything has been changed minus the intake manifold and the plug wires, who did the port work on the intake manifold is unknown but doesn't look crazy. I did fight a vacuum leak for ever on a port the had below the carb and had a gauge in it and I just plugged it. They also have a plug in the bottom of the manifold and one in each rear water port. It did it with two different cams and different spring rates and different lifters so I have kind of ruled out valve float?

Thanks for the time in advance an if I need to list something else please let me know.

[BigBlocksOnTop]

Check and make sure the gas cap is vented. Check the center electrode in the distributer cap...its carbon and the MSD's will burn them up if it is not the MSD carbon electrode.(I'm going to make mine from brass) Valve springs.

[image4you2see]

I forgot the distributor, it has a MSD and did it with two different ones as well as timing locked out and not locked out. Also did it at 36 degrees of timing down to 28. With the old can it went faster with 28 degrees. I have not got into making any passes with the new cam because of this same issue. Car has had a couple different caps and rotors and I did check fazing when this all started. It comes right in we're I read it was supposed to be.

Car has a ten gallon fuel cell went from a -6 vent to a -8 with the new fuel system. Will the cap being vented or not vented still a possible issue? I'll check it out still how ever.

[cnsperf]

Try a set of MSD wires. I have seen multiple problems with the taylor wires.

[image4you2see]

Will do an that has been on the back of my head as well but hard to swallow getting a set of expensive plug wires right off the batt.

I have switched between ngk an auto lite plugs. What heat range would you guys recommend with what gap?

A bad port job on the manifold would cause this would it?

[maxc]

Try a set of MSD wires. I have seen multiple problems with the taylor wires.

Me too!

[image4you2see]

Ok I messed with it some tonight after some changes. Still breaks up but it I around 6800 now. At WOT it is 13.2 then right when it starts to do it it goes to 15.x hard to tell because the fast wide band bounces around some.

I'm assuming a running issue in the carb how do you adjust it based off a high rpm stumble? I did actual cruise the car around in the street also since it was none out and noticed it was 14.6ish while holding the pedal at one speed an then give it a little gas it went to 12.5 or so if you say was climbing a long incline type situation when giving it a tad more gas.

[image4you2see]

Think im going to pull a little bit of timing out of it since it is at 36 an go to 32. I was also going to try a 7 plug.

[raceman14]

172# on stock hyd lifters seems pretty high. I am not a Ford guy but my Outlaw GM crate stuff will turn 8200 with 135-145# on the seat, hollow stem valves stock but still way less pressure.

Also I think you are off some on the plugs. I try to run an 8 range NGK with no more than .035" gap. That wide gap stuff will mess you up and cause skipping. I would set timing about 32* and see what happens.

What plug are you running now and what gap? Is it a washer style plug or a bevel style plug and how long are the threads and how much porcelean can you see sticking out of the plug and how much goes down into the plug???

I might have missed it but what is your fuel pressure? I don't run more than 5-7 on anything up to 850HP+.

[headshop57]

Is that a 302 ford engine?..... too much weight not enough torque,
26" tires 5.86 rear gears,???.... Maybe. Get a 351W engine, same tires same gears and spin it about 7800RPM at finish line, three speed trans with a transbrake, shift at 5600 RPM , CO2 shifter , first to second... very quick(1.2sec.) second to third before 60' mark, launch at 6000RPM and hold on.
Trim weight down about 2500 lbs with you in it, and the front wheels will come off the ground at launch.

[image4you2see]

172# on stock hyd lifters seems pretty high. I am not a Ford guy but my Outlaw GM crate stuff will turn 8200 with 135-145# on the seat, hollow stem valves stock but still way less pressure.

Also I think you are off some on the plugs. I try to run an 8 range NGK with no more than .035" gap. That wide gap stuff will mess you up and cause skipping. I would set timing about 32* and see what happens.

What plug are you running now and what gap? Is it a washer style plug or a bevel style plug and how long are the threads and how much porcelean can you see sticking out of the plug and how much goes down into the plug???

I might have missed it but what is your fuel pressure? I don't run more than 5-7 on anything up to 850HP+.

I was getting ready to post asking about heat range thoughts. I have been using ngk 5 & 6 heat range and they do have the washer. Right now gap is at 25 but I normally always gap my plugs at 32.

I'll drop timing down again, the car with old cam actually went faster with 28 degrees timing.

I'm a little confused by the spark plug question.

Fuel pressure set at 6.5.

[Horndog]

Check and make sure the gas cap is vented. Check the center electrode in the distributer cap...its carbon and the MSD's will burn them up if it is not the MSD carbon electrode.(I'm going to make mine from brass) Valve springs.

X2 ... gotta be either fuel, spark/ign/electrical, or valve springs.

Do you have a hood-mounted fuel pressure gauge to watch ?

[Horndog]

Any updates?

[MadBill]

A sudden silence like this usually means the problem is solved, so the urgency is gone, thus no time for close-out remarks by the OP for us to learn from. My money was on insufficient spark, the clue being it going drastically lean as a result, not a cause, as a misfire leaves unburned oxygen in the exhaust, which then shows lean.