miss in 340 hp '62

[William F.]

Recently my stock '62 340 327 has developed miss that I so far haven't been able to find its cause,. Seems ok in 1st and 2nd to reasonably high rpm, but under full throttle in 3rd, starts to miss badly around 3-4000rpm will miss some even when I throttle back, sometimes bogs down and will barely go 40 mph. Seems to clear a bit if I push in clutch, rev, then back in gear. Some, but not all the time runs ok for long period of steady 60mph cruise, but not if you accelerate. Not points-changed with same miss, not plugs, changed with AC R45s, same results. Don't think it's carb. Could it be a bad coil? It's a made in Mexico 097, no cracks visible. I could substitute a known good one from another car. Bad "Packard TV Suppression plug wires? Notice can wiggle the 2 pieces of metal that lead into each end of ballast-normal?
Where do I go from here? Help!
Thanks in advance

[Timothy B.]

Re: miss in 340 hp '62

Bill,

That's going to be a process of elimination. It could very well be a coil or spark plug wires, is a made in Mexico 097 a reproduction coil? How old are the wires? Swap in another coil and try to eliminate that then go from there.

You don't think there is any dirt in the carburetor do you?

[William F.]

Re: miss in 340 hp '62

Gas in glass Fuel bowl with filter looks fine. Can see pump shot and gas coming out AFB boosters when you open throttle and look in carb. Would favor ignition but I'm asking. What's max resistance of any plug wire to be good? Refresh my memory, please.

[Richard M.]

Re: miss in 340 hp '62

William, Your plugs wires(suppression type) should read between 10k to 20k ohms based on length. IIRC, about 500 ohms per inch, so the longer wires will read higher.

I recently had one on a BB go bad on me. Intermittent to 100k ohms when I wiggled the distributor end contact. So when you test them with a ohmmeter, use alligator clips and give the ends a twist and wiggle to check for intermittent terminal connections.

Rich

[Domenic T.]

Re: miss in 340 hp '62

William,
The plugs (45S) sound a bit hot for a 340HP. Also sounds like it may be running out of fuel under load in the higher gears.

[Mark E.]

Re: miss in 340 hp '62

High load at moderate to high RPM is a good stress test for ignition perf and fuel delivery. I would check the ignition first. I've had almost new plugs miss under these conditions.

Also, original design suppression cables may be good for show but they're very delicate. The core is a woven material impregnated with carbon which breaks down with movement, vibration, heat and age. Their resistance goes up virtually every time they're handled. If they're not the problem now, there's a good chance they will be as they age. Save them for shows and get a good set of spiral core cables for driving.

[Ken A.]

Re: miss in 340 hp '62

The new wire that Packard makes uses Kevlar for the core and resistance is 250 ohms/FOOT!

[William F.]

Re: miss in 340 hp '62

Let me review: Was missing with the old R43S plugs as well as the freshly installed R45s ones. Plugs not the problem.
Are these new Packard wires available in7mm diameter and correct lengths and with straight distributor ends to fit my 327? Who makes best set of small block wires from a functional aspect (as long as they are 7mm diameter and have straight distributor ends)? Which spiral core sets will work?
Can just one bad wire cause this significant "miss", almost a shutdown? By the way the old #5 plug had significant amount of black fouling; others probably ok- various amounts of tan/ brown deposits.
Thanks

[Joe R.]

Re: miss in 340 hp '62

Can just one bad wire cause this significant "miss", almost a shutdown? By the way the old #5 plug had significant amount of black fouling; others probably ok- various amounts of tan/ brown deposits.
Thanks

William,

Yes, one bad wire is enough to cause the engine to run pretty rough. It sure sounds like your #5 plug wire is bad.

Joe

[Richard M.]

Re: miss in 340 hp '62

William,

Yes, one bad wire is enough to cause the engine to run pretty rough. It sure sounds like your #5 plug wire is bad.

Joe

William, I agree with Joe. 1 bad plug or wire could cause this issue.

Do you have the spark plug heat shields installed? The #5 wire is directly behind the center of the exhaust manifold and is susceptible to heat failure, especially if the plug shield is missing. Same for the #6/8 plugs. That exact problem happened to me many years ago. i didn't have a plug shield on #5/7 and it melted the #5 plug wire boot causing a miss and a fouled plug.

Rich

[William F.]

Re: miss in 340 hp '62

No plug shields.
I searched many threads in the archieves about best functional, correct length, straight distributor end of wires for my '62. Many recommended the Delco 508N set but seems to be question as to whether they are still available. Any spiral core wires of correct length in 7mm diameter size-understand Pertronix set has at least one wire that's too long. Taylor? Please give current recommendations with above criteria- for driving, not for judging. Don't guess distributor ends have to be straight, could live with 90* ones if lengths correct, etc. (Going to check wire resistances this morning, just getting mu ducks in a row in case wires are the problem.)
Thanks

[Richard M.]

Re: miss in 340 hp '62

William, Every small block engine of the era used the spark plug heat shields. If you run without them, and have radio shields installed, it's even worse on the wires.

In case of any confusion over terminology, these are what I'm speaking of.....



These are the wires I use exclusively on small blocks.....

http://www.zip-corvette.com/57-74-283-327-350-spark-plug-wires.html

Rich

[William F.]

Re: miss in 340 hp '62

Just got through checking everything electrical I can: Plug wire resistance in wire to where old plug was fouled reads good-20K; swapped a coil known to be good; V's to resistor same as batt; output to coil from resistor slightly less than battV. Same bad miss when doing a pull in 3rd at about 3500-4000; almost dies for a while when I back off then so so at cruise. Sometimes starts missing just at steady cruise, also. Believe it's fuel starvation rather than electrical but is strange that problem occurs whe car warms up, not so much still operating temp is reached. I have a paper filter in the glass filter bowl; metal ring on fluted paper filter is on downside.Is this correct? I do see a small fleck of filter paper in bottom of bowl-maybe stopping up flow into carb?? Also, No fuel comes up into upper part of glass housing above the metal ring-is this the way it's supposed to work? Anything to check inside AFB carb? Other suggestions? Very frustrating!
Thanks

[Timothy B.]

Re: miss in 340 hp '62

Bill,

Other than dirt or a low float I can't think of anything else easy to look for in the carburetor.

So when the engine is cold the problem is not there? With the choke partially closed does the engine rev up in third gear? If the problem is fuel related, (engine going lean) it's possible the carburetor could have debris in the venturi clusters but there is only one way to find out. These clusters contain the idle feed restriction, both high and low speed air bleeds. Also, the main jets are located in the float bowl floor and maybe they injested something restricting the flow.

[William F.]

Re: miss in 340 hp '62

Tim et al,
If I remove the carb top, guess I can see fuel bowls and jets, right? How can I blow something through venturi clusters and related passages without further disassembly? Looking into carb while running and gunning engine, I can see good pump shots and at least some fuel coming out of primary venturis but looks liquid rather than atomized-mean anything? Another thing, Looking at clear fuel filter bowl, gas never gets above about 1/4 way up in bowl-normal or not? Your question about choke, Choke set lean and only closes about 1/4, maybe 1/2 way even when starting