427 down on power

[patrickt]

Originally Posted by FatBoy

Would that be enough to cause my low power symptoms?

The only way to tell is to take it for a ride. Did you chat with the SA folks? Did they break the engine in on a dyno or did you fire it up for the very first time?

[Rick Parker]

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?

NO FUEL IN BOWLS

ABSOLUTELY!

[FatBoy]

Originally Posted by patrickt

The only way to tell is to take it for a ride. Did you chat with the SA folks? Did they break the engine in on a dyno or did you fire it up for the very first time?

I did speak to SA and they ran the engine up to break in the cam, but only on a stand, not a dyno so it wasn't under load and therefore wouldn't open the secondaries. They did say that they would fix any problems if I found any. They've been really good on that front, I had a problem with the gear lever being in the wrong position and they couldn't have been more helpful.

Paul

[Excaliber]

Seems to me the rule of thumb is 10% variance in cylinder pressure is acceptable.

[jhv48]

I bet it's a timing issue.

Check your initial setting first.

Then check to see if you are getting full advance at WOT.

[FatBoy]

Originally Posted by jhv48

I bet it's a timing issue.

Check your initial setting first.

Then check to see if you are getting full advance at WOT.

I've checked the timing and the advance and both are as they should be.
Resetting the float levels hasn't fixed it either.
I'm running out of things to check. I've just changed the spring in the vacuum secondaries for a lighter one, but I don't really expect that to make big difference.

Paul

[Ron61]

Paul,

Does the engine pull well up to 3,000 and then just flatten out and start to miss, or is it sluggish getting up to 3,000 under load? Also when you are just running it under no load. does it act the same way? That # 3 plug really looks as if it isn't firing at all and if they just ran the engine to break in the cam and not under any load, then it must have came from them the way it is unless you have added or changed something. I believe in an earlier post someone asked you if you had checked the valve springs as some engine builders use a light set to do the break in run with and then put the heavy ones in for the dyno and testing.

Ron

[FatBoy]

Hi Ron,
It isn't right all the way from tickover, but it really runs out above 3,000rpm.
Paul

[jhv48]

Is the sound the same from both of your exhaust pipes?

Or is one more muffled than the other?

[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

[JBCOBRA]

This may seem too simple, but I had a gas cap that would not vent properly, so I put it on a Bridgeport and cut a slot from the inside to the outside edge of the cap so it could breath really easily and that fixed it.
Hope that works
JB

[Rick Parker]

Are you using the pre-made (from MSD) dual wire cable (violet/green & orange/black)with the plastic connector ends on it? Or did you rewire the MSD box to the distributor? If you did the later you may have the distributor out of phase. Check those 2 wires very carefully. The violet stripeed wire in the cable does NOT connect to the Violet striped wire from the distributor.

[CHANMADD]

What cam and lifters are you using?

[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.

[TButtrick]

I'd be focusing on #3 plug. Try swapping #2 and #3 wires and take it for spin. Now see if #2 is fouled as #3 was. If not, you might try checking exhaust and intake lift per cam specs on #3. Take a REALLY close look at the rockers and valve springs on #3. Broken springs/bent valves/worn lobes can still give a positive compression check (at this stage) as your problem manifests iself at higher RPMs. Even with a completely broken valve spring, you can still have a positive compression check. A leak-down test on #3 might reveal a problem.

Your problem is most likely isolated to #3 and behind the dizzy (but not excluding the cap/rotor) BUT I've had a nightmare of problems with a 6AL. MSD quality does not parallel their marketing. The voltage source to your MSD has to be clean and at full potential. You can easily check with a DVM to see if there is a voltage drop across the source. Hook up one lead to the originating source to the 6AL and the other at the input to the 6AL. There should be no voltage drop across the source (zero resistance). I tossed the 6AL and stuck with good ol' Petronix after the box disintegrated. BTW, there IS a way to bypass the MSD 6AL. Do a search. It's out there.

[Excaliber]

A lot of the suggestions here, good though they be, are really about 'tuning' issues. If the engine is as sluggish as you suggest at 3000 rpm and higher, it's a serious problem. Even a catastrophic problem. Basic timing, a carb in the ball park and a reasonably functioning MSD should provide more than enough power to easily rev to 5000 and THEN perhaps loose power, fall off, needs adjustment or whatever. But 3000? Nope, you have a serious issue. Like camshaft to crankshaft timing, something basic and fundamental is wrong.