427 down on power

[Ron61]

I don't think this would really prove much, but if you disconnect both exhaust pipes and just run it through the headers, (VERY LOUD ) does that make any difference? I think you are going to wind up having to do that anyway as that # 3 plug and the symptoms you describe sound as if the engine may have to come out. My 69 Cobra with the 428SCJ that is bored .065 over and blueprinted doesn't even run well until it is over 3500 RPM. The peak power is at 6300. And I had a smaller cam put in to lower that.

Ron

[FatBoy]

Just a thought, I've run the coil leads (orange and black) alongside the distributor leads (green and purple). Could they be causing a problem with each other ?

Paul

[patrickt]

Originally Posted by FatBoy

Just a thought, I've run the coil leads (orange and black) alongside the distributor leads (green and purple). Could they be causing a problem with each other ?

ERA runs them down both sides of the engine to reduce feedback. So, before you pull the engine go ahead and separate them -- what have you got to lose? You've checked and disassembled your carb, checked the linkage, checked the timing and advance, checked the valve lash, checked the integrity of the fuel, checked the spark... and your car stil won't rev much over three grand.

There's still a possibility of exhaust obstruction, a bad MSD box, or something else that I can't even guess at. One last cheap test is to go out and buy a pyrometer and shoot it at your exhaust headers and see if there is a noticable temperature difference on them. Then, before I pulled the engine, I would put a new MSD box in and a new carb on. You do have the positive and negative feeds to the MSD box coming directly off the battery, right? Not the little "ignition on" feed, but the red and black power feeds. That's really important.

[FatBoy]

The black is bolted to part of the chassis i.e. earth,and the red is attached straight to the protected side of the main power fuse (Kirkhams have a main fuse behind the dash'.) Which is exactly how KMS say it should be done, so I can't imagine that is a problem.

Paul

[patrickt]

Originally Posted by FatBoy

...Which is exactly how KMS say it should be done, so I can't imagine that is a problem.

Nor can I. And I guess there's nothing unusual about the sidepipes -- you didn't buy them off a guy that was loitering around a street corner in an old London Fog trench coat, right? Hmm, thinking completely out of the box, will it rev to five or six thousand with no load on the engine?

[Chaplin]

Paul-
Check your carb tuning, I bet that your jetting is way off. But first, start with making sure the carb has the correct powervalve in it and then go from there. I would bet that the carb has the stock 6.5 powervalve in it, which probably is not right. The powervalve should be 2 numbers below your measured vacuum reading at idle. For example, if your vacuum was 8.5"/hg at idle, you would use a 6.5 powervalve. However, I would bet that your engine has less than 8.5" of vacuum at idle, which means that if your car has the stock 6.5 powervalve in it, the powervalve is dumping fuel from idle all the way on up, which would explain some of your sooty plugs and may also be why it doesn't want to rev when you get to the higher rpm, i.e., the engine was already supplying max fuel via the powervalve from idle and has no more to give when you get in the upper rpm range. I would also consider getting rid of the vacuum secondary carb and putting on a carb with mechanical secondaries. I used to be a big proponent of vacuum secondary carbs, but when I changed to mechanical secondaries on the cobra it was like night and day.

After you make sure you have the right pv in the carb, see if you can get your hands on an exhaust gas analyzer or a chassis dyno and measure the air/fuel ratios.