Irregular miss under load😫

AnthonyG

AnthonyG

Well-known member
'49 Engine, oversize valves, 3/4 cam Holley 94 electronic dist. no vacuum adv.
Started with engine irregular missing losing power under load above 2500 rpm. Been keeping up with several similar threads. Changed 12v coil, checked voltage out of ballast resistor - 3.5v. Engine smooth and runs great revving beyond 3000 rpm and at idle under no load. Starts immediately hot or cold. Plugs light brown? What am I missing?
 
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GM engine has under 2500 mile, what do you think would cause sticking valves? Can't ever hear at idle or revving up while sitting no load. If it were valves wouldn't it happen then as well as on the road. That's why I was leaning towards something electrical. Timing / distributor maybe? Ran fine for a couple thousand miles? No pinging and seems like plenty of power up to that breakup point?
 
As part of the elimination procedure I tore down the 94, which was rebuilt a couple of years ago & cleaned checked it & replaced Power valve. Tried another 94 with similar engine performance during process.
 
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Just to be clear, your 12 volts yes, 12 volt coil yes, 3.5 volts out of resistor? Is that what you said?
Martin.
 
Hi Martin, yes to all.
Ted, what ballast R. should I go for? Ho high is too high. From reading some threads on points or in my case electronic dist. too much can cause premature wear on both?
 
I had that sort of thing early on. have you tried chocking it while the power loss is happening? Mine perked up when I choked it and one of the experts here had me check for a vacuum leak, which I found between the carb and the manifold.

bill
 
AnthonyG said:
Hi Martin, yes to all.
Ted, what ballast R. should I go for? Ho high is too high. From reading some threads on points or in my case electronic dist. too much can cause premature wear on both?
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The electronic distributor specs should determine the coil and ballast resistance. I have a Pertronix that wants full voltage to a 1.5 ohm coil.
 
What system Malory or pertronix Check with the suppler ,the module can fail with the wrong set up,. 40Cpe is correct 1.5 volts for pertronix .Ted
 
Tony,
That 3.5 volts to a 12 volt coil is, as you can tell from above posts, is way to low.
The right resistor is what the manufacturer of that electronic ignition says. What make is it?
Martin.
 
Also while your checking what resistor they want, double check on what spec coil. Some of them like a standard points type coil, some want a specific electronic ignition type coil.
Martin.
 
scooder said:
Tony,
That 3.5 volts to a 12 volt coil is, as you can tell from above posts, is way to low.
The right resistor is what the manufacturer of that electronic ignition says. What make is it?
Martin.
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Looking at your profile pics the distributor is a mallory and you are using a ballast resistor. Can't tell what coil it is ???
Mallory makes two coils and its pretty common to see someone use the .6 ohm coil . This coil is too low of resistance!!! You need 1.5 ohm coil.
Also i would question the wiring , make sure you have battery voltage going to the module. They need at the very least 8-9 volts .
Install a 1.5 ohm coil and bypass the resistor for a test drive . Let us know what that does....:eek:
 
I know long time use without a resistor will cause premature wear, will a short test run without to see if the problem goes away hurt?
 
What is the stock resistor under the dash rated at on a '35 ford? I have mine jumped beings I was using the ballast resistor the engine builder supplied when I received my engine with the ignition installed already.
 
Re: Irregular miss under load��

Don't know what you are using for plug wires but Pertronix and possibly Mallory recommend suppression wire (with electronic ignition) such as spiro-wound to eliminate radio interference that causes problems like skipping.
 
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i had some skipping under load. voltage but lower than it should be at coil. it turned out my ezwire system coil fuse was corroded. eventually it wouldn't start at all. biggest help in diagnosis was running a wire directly from batter to coil, by-passing ignition circuit. started right up. indicating ignition prob.
 
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