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302 High RPM Miss

6

65fast

Member
I am trying to get my 302 straightened out with some issues I am having with a fresh motor.

302
AFR 185's
9:1
Edelbrock 600
Autolite Plugs Gapped @ .040
ED Curtis Spec'd Cam & Springs.
Duraspark Ignition - All new reman parts.
Pertronix Coil
MSD Cut to Fit Wires.

The engine is having a miss which worsens as the RPM's increase. It is not very noticeable under 5000, but once RPMS climb, the misses become more apparent.

I have played with jets in the carb as I originally thought was a lean condition on the secondaries. I went from a 101 to 107 and the problem did not change. I have checked for the miss free revving the engine and it still exists while the car is not under load.

I am thinking my problem lies somewhere in my ignition system. I still have my resistor wire, but have jumped a power wire directly to the battery and the miss was still there. I am starting to wonder if my crimps on my plug wires are suspect.

Any ideas? Anyone every have issues like this with the Duraspark?
 
Is it a random miss or can it be traced to one plug/wire....? Random would be fuel or ign., one certain plug would be ign. or maybe valve.

Does it stop missing if you choke down the carb while running? That might eliminate rich or lean issues.
 
Perhaps a toasted Duraspark box? Lots of auto parts shops have module testers that can tell you if there's a problem with the box.
 
Did you bolt on a set of assembled AFR heads? I have heard a lot of bad things about their valve train pieces. If your problem is only happening at high RPM I would think this could be a probable area of concern. Maybe the springs are not up to it at that level.
 
"Horseplay" said:
Did you bolt on a set of assembled AFR heads? I have heard a lot of bad things about their valve train pieces. If your problem is only happening at high RPM I would think this could be a probable area of concern. Maybe the springs are not up to it at that level.
Click to expand...

You mean some kind of valve floating ??
Don't you have then some backfire in the carb ??
 
Using a timing light, you can move to each plug wire and see if the spark is steady. Bring it up to the lowest rpm it starts to miss and do this....I will eliminate the spark issue or pin it down...
 
"AzPete" said:
Using a timing light, you can move to each plug wire and see if the spark is steady. Bring it up to the lowest rpm it starts to miss and do this....I will eliminate the spark issue or pin it down...
Click to expand...

I'll second that. You could also measure the resistance of the wires. Since they were cut to fit I'd suspect an inadequate crimp somewhere.

Robert
 
Sounds good, thanks for the suggestions.

I take it the wire with the problematic crimp would have a lower resistance than all the other wires?
 
I'm probably confused here but are you having the same issue at normal operating rpm or only at the higher levels? A problem with a plug wire is not going to be so hyper sensitive to rpm range to the point it only happens say north of 5K unless somehow resistance or actual contact changes at elevated speed. At least in my experience. You can certainly check the wires as if this is the issue it would be quite obvious.

If this issue does only really happen when the engine is really turning does the power also seem to flatten out?
 
Are you still climbing the advance curve beyond 5k?

Sounds like what my cleveland did when I was running a duraspark without recurving it.
 
I really does only happen the most above 5k. I will have the occasional miss cruising a 3k on the highway, but if you mat the pedal and try to spin it up to 6,000+ it misses so much it just falls on its face. So, yes you could say it looses power.

Sluggo, I have not spun the motor past 3500 yet with a timing light on it. I think I might try that this weekend and see what happens. What plates were in your DS and what did you change them to?
 
"65fast" said:
I really does only happen the most above 5k. I will have the occasional miss cruising a 3k on the highway, but if you mat the pedal and try to spin it up to 6,000+ it misses so much it just falls on its face. So, yes you could say it looses power.

Sluggo, I have not spun the motor past 3500 yet with a timing light on it. I think I might try that this weekend and see what happens. What plates were in your DS and what did you change them to?
Click to expand...

Don't know. I sent it out and had it recurved. It was out of a 460 so it had an insane curve. It was recurved to 25 total all in by 3000 rpm with the initial set at 8-10 degrees.
 
I put a MSD box on the car today and problem solved! Car pulls great.

Probably should have done the from the get go.
 
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