'63 327 340 hp misfire - finding the ghost!

[Mel H.]

OK. I’m pretty stubborn about solving problems on my own, but admit I am stumped and now looking for help on finding the ghost in my '63.

Background: ’63 327/340hp 4 sp, original engine, rebuilt by previous owner 2010, just before I purchased. Besides replacing most internals, builder installed a 30-30 cam, so low vacuum at idle.

Overall car is great, but engine has a random misfire/buck/jerk that I’ve been unable to find and correct. Misfire (that’s what it feels like) is noticeable at cruise especially between 10 – 40 mph. Engine also shakes randomly, like a misfire, at standing idle (about once every couple seconds). However, it does run strong under acceleration, without misfire.

Here are some of the things I’ve done/tried so far.
1) Installed new coil …091 from Corvette Central (tests 2.6 primary and 12.3 secondary). Old was MSD from prior Petronix system.
2) Reset dwell to 30*
3) Adjusted idle screws to best rpms
4) Reset timing multiple times. Now at 19* base, 20 centrifugal, and 13 vac. Total = 52* No pinging.
5) Installed new B28 Vac (due to low vacuum). Starts 4.5”Hg…all in 7.5 (Vacuum 9/10”Hg at idle (w/o Vac Ad) –14“Hg at 650-700 idle rpm w/vac hooked up).
6) Installed bushings on vacuum adv rod and on distributor centrifugal ‘football’ pin (thinking it was getting too much timing at cruise) Installed light weight springs so centrifugal adv is all in at 2500 rpms.
7) Local Corvette shop replaced points and condensor. Had Petronix system. He replaced with standard points & condenser.
8) Pulled distributor and inspected shaft for alignment/wear. It was perfect. End play about .025 (high, but I think within typical range).
9) Sprayed carb cleaner around outside of intake, carb, and hose connections looking for vacuum leaks… no change
10) Checked and retightened all intake manifold and carburetor bolts
11) Pulled and double checked PCV valve function (AC 590). Working OK
12) Checked for electrical grounding in complete darkness. Even checked from under the car/engine. No grounding/arcing detected.
13) Battery is fully charged and alternator is charging within normal range.
14) Replaced plug wires and ensured correct positioning/arrangement… though spark plug heat shields (“J” shields) and ‘boomerrang shields’ are missing.
15) Checked four spark plugs (R43s) at random. All clean and appear new.

The random shake/misfire/bucking/jerking continues and I’m kinda stumped.

Should I try changing all spark plugs? Would they work OK under 'load', and not when coasting/idle?

Do valves just need adjustment? Has ~1,000 mi since rebuild, so time. Do hear clicking but doesn’t seem unusually loud/noisy to me. I use 15w-40 Rotella oil.

Or is it possible these are simply natural symptoms of the 30-30 cam engines? Never had one before (do love the sound of that 30-30!!)

So, I need a 'ghost buster' to help find this gremlin. Appreciate any ideas or suggestions.

Apologies for the length. Thanks in advance
Mel

[Adam S.]

Re: '63 327 340 hp misfire - finding the ghost!

sounds like a stuck lifter

[Stuart F.]

Re: '63 327 340 hp misfire - finding the ghost!

What carburetor are you using? Sounds like a severe lean surge is possible.

Stu Fox

[David H.]

Re: '63 327 340 hp misfire - finding the ghost!

I have the Comp Cams Nostalgia 30-30 which is ground with a 4 deg. advance built in and reduced valve lash to .012 and fuel injection on a 65. You did not mention your rear gear ratio, mine is 4:11 which helps at the speeds you are talking about. Jerry Bramblet has a good article on (ramjets that run) and he recommends autolite 295 plugs. I used them to tune the fuel meter just after I rebuilt it and they just would not foul like the AC,s do; black smoke and all!. and if you run AC,s you really need a hotter number like 45 or 6. I put my AC,s back in for a judging meet and it ran worse. never misfired but stumbled on acceleration, if I had a carburetor I think it would have backfired, as the fuel unit is not suseptable to sneezing . actually hard to notice unless you have both types of plugs to compare. On fuel cars the tendency is to blame the "unit" for these problems but the service manual warns to always check the things on your list first. I have regular points and coil as well. if you had a lifter or valve problem it would be more persistent. could still be your spark plug wires too.

[Mel H.]

Re: '63 327 340 hp misfire - finding the ghost!

Thanks guys. Could be a valve (or two) I suppose, but as David noted wouldn't it be there on acceleration, too?? Course, strange things happen. Is there a good additive worth trying? STP? Other?

Already replaced plug wires without improvement so dont think they're the culprit. Might have a good idea on the plugs, though. Again, strange things happen. Have a set of 45s I can try. Don't see any black smoke and plugs dont appear fouled, but lots of stories about fouled plugs on these cars. Worth a try.

Stu.... It has a Carter AFB 3461s (AM2). It's the second 3461s I've tried.... no change in misfire.

Thanks for your ideas....keep 'em coming!! That ghost is gonna get exposed sooner or later!!

[Timothy B.]

Re: '63 327 340 hp misfire - finding the ghost!

What carburetor are you using? Sounds like a severe lean surge is possible.

Stu Fox

I agree with Stu, what carburetor are you using and would like to add if you have 19* initial timing with 15 additional degrees vacuum advance so total idle timing is in the range of 34* that's too much. Have you tried the engine at 12* initial timing along with the vacuum advance.

If you have the 3461 Carter there are two calibrated vacuum leaks, one is the PCV and the other is the hot air choke, just keep that in mind.

After warm up, run the engine at approx 2000-2200 rpm and close the choke blade to see if the engine speeds up. That tells you it's too lean but you need to have the timing correct before messing with the carburetor.. Also, what type of spark plug wires are installed and have you checked ohm reading. Lighting lean mixtures requires a good secondary system so that reproduction coil comes into play, be careful with reproduction parts think about a NAPA IC-12 coil (double check that #)

Your vacuum readings don't sound like a 30-30 camshaft, I don't think a 30-30 will idle that low. What you report sounds more like a L-79 camshaft but that's OK.

[Duke W.]

Re: '63 327 340 hp misfire - finding the ghost!

Your idle vacuum readings don't make any sense. With the vacuum advance connected, total idle timing should be in the range of 30-34 degrees and idling at 900 should produce about 10" Hg manifold vacuum. Lower idle speeds will generate even less vacuum and idle instability, which is why 900 is usually the lowest acceptable idle speed with the 30-30 cam.

Your engine configuration works best with 24 centrifugal all in by 2500, 14-16 initial, and the B28 VAC. Too much low speed advance can cause bucking/jerking.

The breaker plate ground wire will eventually fail and may cause an intermittent miss before it fails completely. NAPA has repair kit.

Either your idle vacuum readings are incorrect or you have something other than a 30-30 cam. Use AC heat range 5 or equivalent in another brand for all normal road use applications; 3 is way too cold.

Google my name along with Hinckley valve Corvette San Diego and download the San Diego presentation and the 9/08 version of the valve adjustment paper.

Duke

[Stuart F.]

Re: '63 327 340 hp misfire - finding the ghost!

Exchanging one 3461S for another may not expose an inherent lean condition of the standard primary cluster for your application. On the ignition score; I have been running a Pertronix II unit with their "flamethrower" coil (full 12 volt input) for many years, and I have had a set of AC44's in my 63 L-76 engine for over 10 years and it will hit redline with no problem anytime - even after a period of "stop and go" traffic driving. It may stumble a bit, but will clean out quickly on the road. Fortunately, my engine has never been apart or messed with by any plumber since new. Over the years, if something didn't work right I fixed it - like my dislike for plug fouling when I had points, or my timing got all out of whack due to a tipping vacuum advance plate (I replaced it with a "Dyna-Flyte" ball bearing plate). Then, Duke put me on to the B28 vacuum advance and I now have a sweet running machine at idle, low speed or WOT.

On the AFB 3461s, I will admit the one I have continues to have a lean surge condition in all gears and all speeds that I have yet to sort out. I will probably put it back together again during the cool season after I attack it with my numbered drills and see if I can get it corrected. In the mean time, I love running my slightly modified AFB 3721SB which performs very well.

Stu Fox

[John H.]

Re: '63 327 340 hp misfire - finding the ghost!

I have the Comp Cams Nostalgia 30-30 which is ground with a 4 deg. advance built in and reduced valve lash to .012 and fuel injection on a 65.

David -

What are the lash specs from Comp for that cam? The .012" you noted is less than half of the specified lash for the factory "30-30" cam.

[David H.]

Re: '63 327 340 hp misfire - finding the ghost!

That .012 is the newer standard for solid cams unless it's a serious race roller which are about .020 to .024. The reduced lash is put back into the cam as added valve lift and slight power increase. I like the 4 deg. built in advance as these high duration figures we have do not help you leave a red light from idle. My original cam is worn on two lobes about .030 and .067 so I put it aside.
I also have a friend who got 3 of those carbs in a row from one of our famous venders and they did not even want them back! I still have one. I had to turn down the tips of his main jet needles in my little lathe to fix his problem which was as you are describing. I removed about .004" from each one. You could do this in a drill press with a dial caliper and sand paper as they are brass. Let me know if you need a carb. It will be cheap for you!

[Bob H.]

Re: '63 327 340 hp misfire - finding the ghost!

Duke

Can it be a leaking intake gasket? Seems I had that problem on my 340 a few years ago. Mine was leaking between 6 and 8.

[Mel H.]

Re: '63 327 340 hp misfire - finding the ghost!

Your idle vacuum readings don't make any sense. With the vacuum advance connected, total idle timing should be in the range of 30-34 degrees and idling at 900 should produce about 10" Hg manifold vacuum. Lower idle speeds will generate even less vacuum and idle instability, which is why 900 is usually the lowest acceptable idle speed with the 30-30 cam.

Your engine configuration works best with 24 centrifugal all in by 2500, 14-16 initial, and the B28 VAC. Too much low speed advance can cause bucking/jerking.

The breaker plate ground wire will eventually fail and may cause an intermittent miss before it fails completely. NAPA has repair kit.

Either your idle vacuum readings are incorrect or you have something other than a 30-30 cam. Use AC heat range 5 or equivalent in another brand for all normal road use applications; 3 is way too cold.

Google my name along with Hinckley valve Corvette San Diego and download the San Diego presentation and the 9/08 version of the valve adjustment paper.

Duke

OK. Not had engine apart so could be something other than 30-30. The engine shop/builder told me thats what he installed (not seller). Still, who knows.

Mine will idle decent at 700 rpms.. yes its smoother at 900...even better at 1100... but ok at 700, and will even run at 500 but dies occasionally at that level.

The total timing is within your range at 32* (w/vac connected).... 19 base + 13 from vac adv = 32 at idle, right? When I rev to 2500, its all in at 52, so I'm getting about 20 from centrifugal, right? This was 22 before I installed the distibutor bushing thinking I was getting too much advance at cruise, causing jerk.

But, let me clarify something. When I do the timing and unhook and plug the vac line, engine rpms drop down from 700 to about 500/600 level (bounces between the two) and is barely running (I do get about 10"Hg at this point). Do I set the base timing there.... or rev back to 700rpms and set it there?

Why do I ask? The advance appears to rise as I go back to 700... suggesting the cent is coming in too soon, right? I'm thiking there should be no change in advance from 500-700 rpms. Right now it has two black springs (light weight) installed so I could get it all in by 2500 (was more like 3500), but these may be too light. Agree? Regardless I've tried several combinations of springs and still had the misfire.

Will try a ground wire kit. Wire looks ok, but I'm sure its old. And will get some R45 or R46 plugs. Is there such a thing as too hot of plug (R46)?

[Gene M.]

Re: '63 327 340 hp misfire - finding the ghost!

My 65 250 horse with WCFB has .004" oversize primary jets no other carburetor changes. That was a long time ago recommendation from Tom Toal who was a carburetor tech at Rochester products that was versed in competitor carbs. Heads are "cleaned up".

I fixed my 65 lean surge by removing the carbon core wires and replacing with Packard 440. Also replaced the rotor with a longer tip version and installed a distributor cap with copper contacts. Installed old style Delco points not the Mexico junk. Runs real strong and no surge.

[Stuart F.]

Re: '63 327 340 hp misfire - finding the ghost!

David;

Are you referring to the primary metering rods? If so, what are you removing off the ends and why? We used to needle tip rods on WCFB's for racing, but it sounds like you are reducing the tip diameter. If so, why not just buy a set with smaller performance steps? Then too, his AFB may need some metering rod calibration spring changes due to his low vacuum. The rods may be rattling as they are hunting. It is conceivible that he might be better off with Edelbrock carb sized to fit his requirements. Wrecking a valuable 3461S carb is not the way to go to solve his problem. They are worth 3 times what you would pay for a new Edelbrock.

Stu Fox

[Timothy B.]

Re: '63 327 340 hp misfire - finding the ghost!

Mel,

I would set the base (initial) timing at the lowest RPM level the engine will run. Try the engine with 12* initial to see if that helps the surge, if you have the time plot the timing curve at different RPM's as it sounds fast which may be fine but it's good to know. You could also power time the engine at 36* by marking the damper, removing the centrifugal springs and speed the engine to approx 1500-2000 RPM as the advance weights will be spread out fully without the springs holding them. Don't worry about where the initial timing falls but check it for reference then re-install the springs and hook the V/A and go for a ride to see if that helped some.

After warm up try the choke blade test to see if the engine is lean, at 2000-2200 RPM the carburetor is still providing the A/F mixture through the idle circuit, that circuit involves the curb idle discharge ports and the transfer slot. After you set the idle RPM and adjust the emulsion screws, how many turns out are the emulsion screws and can you kill the engine by turning the screws to their seat.