Stumped...need fresh ideas!!!

[car62]

car(mustang with 2300)misses when coming off corner,doesnt clean up til it come back to an idle...sometimes 1 lap til the miss starts,sometimes 4 laps,sometimes 10 laps...lately it has been 1-2 laps.

here is a long list of what has been changed to try and cure the issue:

radiator
fan
complete cylinder head x3
head gasket
bottom end x3
intake manifold
carburetor
new fuel line
fuel fittings on cell
new fuel cell
new electric fuel pump (Holley red and blue)
all new wiring,new cables
new switches and push button
unhook tach completely
unhooked all gauge lights
starter
solenoid
battery
alternator(new,and unhooked/unwired)
distributor
module
coil
plugs and plug wires
checked cam(2A) and ignition(36A) timing

now for the strange part....

when we pulled the carb off to change the head a couple months ago,under the carb in the intake it was black under the carb,like it has been really hot..so we changed intake as well(carbed not EFI)

took complete head off another engine(no issues with this head)and put it on our bottom end...been fighting same issues last several weeks..pulled carb off yesterday,intake is black again under carb.

anyone got any ideas???

the sound it makes when it "misses" is like it dropped a cylinder or 2...sometimes if the throttle is played with,it will go away for 1/2 a lap.

[racerman]

Are you getting your fuel at the track? I've had problems with that before, so I tried getting it out of a fresh barrel a couple weeks and my problem was fixed. Usually though there is more people with bad running cars.

[car62]

no,fuel is bought down the road from a pump,alot of other racers get their fuel there as well as 2 of our other cars and nobody is having problems.

[racerman]

Maybe a ground to the engine has corroded? The black under the carb sounds like reversion from the misfire. That's odd, as much as you've changed.

[jatchis]

Have you checked the header/exhaust to make sure you don't have something clogging up one of the primaries? The black under the carb could be exhaust being pushed out when the intake valve opens if it's not evacuating a cylinder properly.

What do the plugs look like?

[return to dirt]

i think you need an efi intake. it sounds like a posible exhaust problem like others have suggested. did you do anything to it before it started acting up?

olin

[car62]

actually...we had a bung welded in the exhaust pipe about 6-8inches past collector for our crankcase vent system...we run the 1998 ranger cast iron manifold...well for 1 reason or the other,we capped the bung and quit using it for the crankcase vent system...also there was a crack about 1/4" parallel to the weld on the pipe...so i welded that up.

hmmm...maybe i better pull it all apart and look at it...see if something is plugged up.

[dirty white boy]

sounds like a stopped up catalytic converter....know theres not one but thats how it would act,...even turn inside of carb black if ran long nuff

[Headhunter]

Are you sure the cam timing is correct? If you change the head. carb. and everything else and put the cam in with the same location nothing will change. If the cam is opening the intake too soon you will blacken the intake. Is this a solid lift head or hydraulic? Lash too tight?

The plugs will tell the story, do they all look the same? What color are they? If they are all black then it may be a fuel or exhaust problem. If only one is black then look at the exhaust port.

[car62]

yes the cam timing is correct...advancing or retarding it does not change the miss...all 4 of the plugs are exhaust colored.

the head is a hydraulic head.

[Foghorn]

When you had the carb off could you see black coming up the intake runners? If so was it one cylinder or all four? If it is all four then I would look at your exhaust system. Do you run a muffler? Also you mentioned doing some welding on the exhaust system. Maybe you have a large piece of slag hanging in the pipe that is getting hot enough to ignite some unburned fuel coming down the pipe and the flame is coming back up the pipe. I know that might be a stretch but with your combination of jets and timing it is possible.

[car62]

yes it is in all 4 runners..and the spark plugs are white in color with exhaust soot on them that wipes right off.
yes there is a muffler,we are going to change out the entire exhaust system today.
stupid thing runs great in the shop,and free revs fine,but total different beast on the track.

[Headhunter]

Have you tried to close up the gap on the plugs to see if that helps?
What fuel are you running? If it is a higher octane than you need it may not be fully burned when the intake opens.
Hotter spark plug?
When you changed heads did you use the same cam? Maybe it was ground wrong.
Have you cleaned all the engine and cable grounds?
Maybe pumping up the HLA's?
Ignition timing marks off?
Bad wire or connector on the positive side of the ignition?
Bad switches.
Electric fan?

Just tossing out a few ideas...

[84Dave]

As has been stated here, the black in the intake manifold could very well be reversion. If so, the reversion will/can 'crap up' the induction mixture and cause misfires. Again, as stated here, carefully check your entire exhaust system. Is the muffler relatively new? Is it collapsed on the inside? Weld a short piece of small tubing into the exhaust pipe, put a pressure gauge on it, and check for excessive back-pressure @ WOT? -Dave-

[car62]

ok,pulled the entire exhaust system off the car today and replaced with complete system off another car that was new last year...when the exhaust came off problem car,all 4 exhaust ports are a very light gray in color...almost white.

[Headhunter]

I'm wondering if your not a little to lean and getting some detonation......

[car62]

exhaust wasnt the fix,running Dorton 350 with 75 and 76 jets...bumped up to 79 and 80...didnt change anything except made engine load up in pits....totally stumped!!!

[drtlvr]

I use like 62's in my Parker 350. 4.5 power valve. Have you tried jetting down? What about the coil breaking down?

[84Dave]

Time for a wide-band O2 sensor in the tailpipe to see what the AFR is doing? -Dave-

[Dan32]

we run 68 jets 70 are as big as we have ever had ur choking the engine jet it back !!!