427 down on power

[Paul Gillespie]

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.

[FatBoy]

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

[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?

[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

[xlr8or]

It could if it was running out of fuel.

[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!

[Excaliber]

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

[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?

[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.

[JBCOBRA]

Hi Fatboy!
Did you get it running?????

[FatBoy]

I'm going to try to get it on a rolling road this week if at all possible.
Thanks for all the suggestions, I really do appreciate it.
I re-routed the distributor leads around the opposite side of the engine bay and away from the coil leads and there has been an improvement. However, I also changed the vacuum diaphram spring for a weaker one, so I don't know which change made the improvement
I suspect the #3 plug was red herring and may have been down to a misfire caused by the parallel running of the coil and dizzy leads. I've looked at it again and it now looks normal.
I'm still inclined to think it is a fuel issue as it also won't pick up cleanly.

Paul

[A98Coupe]

Hi Paul,
I have just recently imported a Kirkham 427 direct from the Kirkham bros, and I also have a Southern Automotive prepared 427 S/O. I have been following your threads on build progress with interest and would like to know if you've sorted your misfire problem yet? Just in case I get a similar problem when I get to that stage.
Also, I'm trying to source some Auburn friction modifier for the diff., but can't find anyone in the UK who sells it...........what have you used?

Stuart

[FatBoy]

Hi Stuart,
You have a PM.

Paul

[FatBoy]

I've just fitted the new double pumper carb that Bill at SA sent me and I'm very pleased to report that it most certainly seems to have fixed whatever the problem was.
I took it out for a short run and it's a totally different animal and also sounds different, much cleaner and more even.
I'm going to Le Mans in July, so I now need to get some test miles on it before the trip.
It's going to be a great weekend.
Thanks for all you help and advice.
Paul

[Chaplin]

Glad it to say it- told you so Nothing like an easy fix to make you feel better.

[Johan]

Bill Stands Behind His Work !

[FatBoy]

Originally Posted by Johan

Bill Stands Behind His Work !

SA have been very supportive and there has never been any question about them not seeing this through to a totally satisfactory conclusion.
The only delay has been caused by the distance involved.

I hope the sun shines this weekend.

Paul