There is another clue, is also runs on occasionally when it is turned off and then spits back through the carb.

Another suggestion of lean mixture ?

Paul

What is the water temp. of the engine after you drive it for a short time? The miss and other things are starting to sound more like maybe a timing or fuel issue.

Ron

1. They wouldnt have left some 'soft' valve springs in for the run in period would they?
2. Some wally hasnt stuck a 3k check chip in you MSD by chance?
3. Has your MSD been rewired for a waterproof plug & the wires crossed in error?

What you are describing is exactly what mine was doing. After swapping out every piece in the ignition system except the the ignition switch, I found that it was the voltage regulator. It was spiking and causing the MSD box to go crazy.

Disconnect your alternator and see if the mis disappears.

Drive it with out the air filter. See what happens.

Dwight

3000 is when most of our FEs are just starting to wake up -- and throw in the dieseling and you've got some real clues. How 'bout bad fuel? Water, alcohol, crap in the fuel? Put a timing gun on it and double check your timing at idle; anything between 10 and 15 BTDC will pass for now. But I don't think it's a timing issue, I'm betting on fuel (that means condition of the fuel, carb. adjustment, and linkage) or the spark.

If its missing above 3000, something is wrong, you are right to be concerned.

- Check your firing order closely
- Look under the cap for a burned rotor or rotor button in the cap
- Make sure you have the right MSD rev limiter in it if you run one
- If you run vac advance, disconnect it and try it, sometimes a partially broken wire on the module can intermittently break contact when vac advance pulls in
- Make sure all plug wires are separated so they cant cross fire
- Check for gross vacuum leaks
- Check all plug wire resistance
- Check valve train adjustment and/or bent pushrod

Fatboy,

Have you done this yet? Please do so if you haven't. They will be very helpful.

I would check through everything twice. Did you get an owner's manual with the engine?
Have you checked the power timing? Should be 36-38

have you check the fuel filter?

Hi,

I pulled the carb this morning and took the float bowls off. Everythinbg was very clean as you'd expect from a brand new carb with no signs of debris. I checked the diaphram for the vacuum secondaries, which again, was fine.
I've checked the distributor cap and that is OK with no signs of burning.
The advance is mechanical and that is nice and free with no sign of binding.
I have good fuel pressure (around 7psi) at the carb. I'm running a Holley electrical pump with a Carter mechanical pump, as recommended by KMS.
The MSD has a 6,000rpm limiter fitted.
The plug wires are Accel Hi-Temp Super Stock Spiral Wound with separators fitted.
I'm still inclined to think it is fuel starvation, but I don't know where the restriction is.
Here is a picture of the plugs. There is a pretty wide variation of colours with 5,7 & 8 looking almost unused and 3 looking pretty sooty.

http://www.clubcobra.com/photopost/d...m/DSC_0002.JPG

Thanks again for your input, it is appreciated.

One more point, I have a manul on rebuilding Big Block Fords and it recommends separating plug leads 7 & 8 to prevent induced firing. Do I need to take this into account with the plugs leads I have? The leads have been run adjacent to each other as suppled by SA, but they are in clips and don't actually touch.

Paul

3 doesnt look too good to me, may want to check that wire and plug, especially with an MSD. May even want to check compression on that hole

427 Stang is right about #3 looking bad. Looks as if it isn't getting any spark at all of a very weak one. As for the leads to #7 & #8, yes, separate them as much as possible. I use the good wire also and after dark with them just separated by the plastic spacer I have seen them cross over once in a while, so I put them two spaces apart. Remember the high ignition voltages are more prone to do this than a stock one was.

Ron

By any chance can you put your finger on the #3 header without burning your skin (or without burning it as bad as you do on the other header tubes...)?

I haven't run it today, I've been checking everything else.
I've pulled the rocker covers off to make sure the valves are opening and closing properly, which they are.
I think I'll give SA a call tomorrow to see what Bill says.

Thanks,
Paul

I have just had a similar problem manifest itself and I am about 99% sure its a cam lobe that has gone flat(SH**T) Check for a loose rocker as a telltale sign

I wouldn't worry to much about the 'run on' condition when you shut the engine off. Thats generally caused by one or two things.
1. Idle speed to high.
2. Octane rating of the fuel to low.

As the engine continues to push the pistons up and down AFTER you turn the key off (which is ignition only) the pistons continue to draw a fuel/air through the carb. Just enough for the compression stroke to 'self ignite'. A small piece of carbon glowing red hot perhaps, acting like a 'glow plug' ignites the mixture. Or it might simply be the 'heat of compression', like a diesel engine with no spark plugs. Higher octane fuel is harder to ignite so it takes a 'real' spark to set it off, thats why higher octane fuel works to eliminate 'run on' or 'dieseling' as some call it. By closing down the carb butteflies, and thus lowering the idle speed, it's more difficult for the pistons to pull in a fresh charge of fuel/air, thus starving the motor to death.

Run on can be a VERY serious problem, until you get that resolved use the clutch with the car in gear to stop the engine at the same time you turn off the key. Run on can cause a timing chain to jump, break pistons and wreck havoc in general if it's pronounced and allowed to continue. In some cases the engine will actually run BACKWARDS, very bad when this happens.

We can help
 

Is your fuel pressure gauge near the carb.? What size fuel line do you have from the tank to the carb.? Do you have an electric fuel pump? Where is it mounted? Below the tank or above the tank? Did you use silicone sealant in your gas tank, maybe to seal around your sending unit? Silicone and gas do not mix! Ask me how I know.
Dwight

Paul:

Is it a matter that the engine does not (1.) gain RPM quickly or (2.) Does it go "Flat" and "Nose over" when it reaches a certain RPM or (3.) Does it begin to miss, stumble and refuse to gain RPM.???

While it is running, drop a few drops of water on the individual pipes relatively close to the heads.
Do the drops all skittle and dance like they are on a "Hot" surface"???

Got to ask why that #3 plug looks so poor. I put a new motor on my Cobra this summer brand new plug wire was bad. I had pulled my plugs and had one that looked brand new. when I restarted I put the timing light on on the wire in question and found that is was not flashing steady light but was flashing some. I replace the wire and got a contast steady flash on the timing light issue was resolved. My cobra is running a 331 fuel injection with a 10PSI blower so in my case the plug was getting washed off injector under boost and the fuel was igniting in the pipe. With what you see in that picture #3 is not firing correctly so I would start looking a the cap, the wire, and the plug.

I've checked the compression on all cylinders and they are all between 140-150 psi. However, interestingly #1 - #4 are all lower than #5 - #8.
I've also checked the fuel level in teh carb and both float levels were low requiring a couple of full turns on the adjustment nut to get the fuel to the check window.
Would that be enough to cause my low power symptoms?
If that doesn't fix it, I've borrowed a new carb to try that.

Paul

It could if it was running out of fuel.