Engine miss (67 427/400)

[Larry S.]

Please help out an old guy who used to be a fair mechanic but haven't used a timing light, dwell meter, etc. in years. My 67 427/400 has an engine 'skip' when driving under a steady accelerator. By this I mean if I'm going a steady, say, 45 mph I notice the tachometer suddenly dip a couple of hundred rpms, as if the engine had a hiccup.

This happens every 10-15 seconds. It fires right up, idles a little rough at the beginning, then smooths out. Acceleration is very good, although I haven't opened it up to full throttle lately to see if there's any breakdown there. I'm kind of afraid to with this engine miss, hiccup, or cutting-out problem.

Where do I start? And then where? Thanks.

[Jamie F.]

Re: Engine miss (67 427/400)

Wow Larry, that's a tough one to nail down, could be so many things...
Has the car been driven recently? Water or contaminates in the fuel could cause that as they pass through the carb.
Does it get worse under a heavy load, WOT?
Most probable is electrical. A poor connection somewhere, or a worn out component.
Try moving around your coil leads, dist cap and wires while its idling and see if you can cause some mayhem.
Jiggle your ignition switch too.
It's a way to start.
After that it's dwell, plugs and points to check...
Good luck!

[Larry S.]

Re: Engine miss (67 427/400)

Thanks, Jamie. Yes, the car was down for 2 months while it was being shipped to me, but it was shipped dry of gas. I put in 10 gals. of fresh gas, and it started right up. I guess I'll look for loose electrical components and if I find nothing then see what happens under acceleration (close to home!). Plugs, points, and condenser were just replaced by the previous owner, but who knows. Plug wires appear to be very new and stock. Now if I can just find that dwell meter and timing light....

[James J.]

Re: Engine miss (67 427/400)

How was the gas tank, clean, not so clean. May a piece of something in the dry tank got knocked loose and ended up somewhere in the pick-up, fuel line, filter. Just a guess. Good luck

[Larry S.]

Re: Engine miss (67 427/400)

Gas tank was amazingly clean and dry, James. Of course, I couldn't see inside the fuel lines, but if I don't find anything electrical, I'll flush the fuel system.

[Mark K.]

Re: Engine miss (67 427/400)

Does your 400HP engine have TI?
Does it happen more when the engine heats up?
It could be an aged magnetic pick up coil.
Or it could be the coil itself.
If you warmed the car up in the garage, would it have the same "stutter"?

[Tim S.]

Re: Engine miss (67 427/400)

Larry,

One of the simple things to do would remove the shielding. Furthermore, I would suggest a set a parts store wires. My Father has had a 400hp car since the early 70's and I would not be honest if I did not admit to fighting with it from time to time. The car always ran better when we stayed away from the braided wires. The quality of reproduction wires leaves a little to be desired in my opinion.

Checking the dwell will be a good idea as well. It is my experience that 400/435 cars are better to time by ear and vacuum. They can be a little finiky. How do the plugs look? Could you be experiecing a lean miss? If so, I believe it would be more consistent than what you are reporting.

Lastly, there are some VERY intelligent people on this site. You will probably get some questions/advice on timing curves. By the sounds of it, timing curves may be more than you want to fool with. Not knowing what has been done to your distributor prior to you owning it may prove to leave you puzzled. You sure wouldn't be the first person to struggle with a tri power so don't get discouraged.

I'm sure if you are not up to the task of seeing this through, someone here can give you a solid recommendation to a shop or individual near you.

Best Regards,
Tim

[Nick L.]

Re: Engine miss (67 427/400)

On the issue of wires, it's my experience with the 67 427-400 I have now that the repro braided wire plug boots are very, very tight on the current AC plugs (45XLS). It takes a lot more force than I'd expect to actuallly engage the clip inside the boot on the plug itself. I'd carefully remove them and grease the boots with dielectric grease and make sure they are fully seated on the plugs. It sounds obvious, but this has foiled me once before.

If you have an old school garage near by that has a Sun Machine or Bear tune-up machine (and a mechanic who knows how to use it properly), I'd start there and baseline the condition of the carbs and ignition system.

[Ken A.]

Re: Engine miss (67 427/400)

[quote=Larry Spencer (47114);423117]Please help out an old guy who used to be a fair mechanic but haven't used a timing light, dwell meter, etc. in years. My 67 427/400 has an engine 'skip' when driving under a steady accelerator. By this I mean if I'm going a steady, say, 45 mph I notice the tachometer suddenly dip a couple of hundred rpms, as if the engine had a hiccup.

This happens every 10-15 seconds. It fires right up, idles a little rough at the beginning, then smooths out. Acceleration is very good, although I haven't opened it up to full throttle lately to see if there's any breakdown there. I'm kind of afraid to with this engine miss, hiccup, or cutting-out problem.

Where do I start? And then where? Thanks.[/quote
Are you POSITIVE the engine is misfiring? You could have a worn out tach or a worn out tach cable or both.

[Larry S.]

Re: Engine miss (67 427/400)

Does your 400HP engine have TI?
Does it happen more when the engine heats up?
It could be an aged magnetic pick up coil.
Or it could be the coil itself.
If you warmed the car up in the garage, would it have the same "stutter"?

Mark, sorry ro be so long in getting back to you. It does not have TI. It happens more when the engine heats up. I do not notice any hiccup in the garage. Any futher ideas?

[Larry S.]

Re: Engine miss (67 427/400)

[quote=Ken Anderson (10232);423263]

Please help out an old guy who used to be a fair mechanic but haven't used a timing light, dwell meter, etc. in years. My 67 427/400 has an engine 'skip' when driving under a steady accelerator. By this I mean if I'm going a steady, say, 45 mph I notice the tachometer suddenly dip a couple of hundred rpms, as if the engine had a hiccup.

This happens every 10-15 seconds. It fires right up, idles a little rough at the beginning, then smooths out. Acceleration is very good, although I haven't opened it up to full throttle lately to see if there's any breakdown there. I'm kind of afraid to with this engine miss, hiccup, or cutting-out problem.

Where do I start? And then where? Thanks.[/quote
Are you POSITIVE the engine is misfiring? You could have a worn out tach or a worn out tach cable or both.

Ken, the engine is misfiring. I felt the hiccup first and then confirmed what I felt by looking at the tach. I do wish that these cars had a modern tach though, one that doesn't bump around as much.

[Larry S.]

Re: Engine miss (67 427/400)

Larry,

One of the simple things to do would remove the shielding. Furthermore, I would suggest a set a parts store wires. My Father has had a 400hp car since the early 70's and I would not be honest if I did not admit to fighting with it from time to time. The car always ran better when we stayed away from the braided wires. The quality of reproduction wires leaves a little to be desired in my opinion.

Checking the dwell will be a good idea as well. It is my experience that 400/435 cars are better to time by ear and vacuum. They can be a little finiky. How do the plugs look? Could you be experiecing a lean miss? If so, I believe it would be more consistent than what you are reporting.

Lastly, there are some VERY intelligent people on this site. You will probably get some questions/advice on timing curves. By the sounds of it, timing curves may be more than you want to fool with. Not knowing what has been done to your distributor prior to you owning it may prove to leave you puzzled. You sure wouldn't be the first person to struggle with a tri power so don't get discouraged.

I'm sure if you are not up to the task of seeing this through, someone here can give you a solid recommendation to a shop or individual near you.

Best Regards,
Tim

Thank you, Tim. You're right; it's always a shot in the dark about what previous owners may have done to the distributor (or any other part for that matter). I'm going to go through the basics this weekend (my garage is 100+ degrees when I get home) to check out everything I know to check. I did not know 3-2's were that finicky!

[Larry S.]

Re: Engine miss (67 427/400)

On the issue of wires, it's my experience with the 67 427-400 I have now that the repro braided wire plug boots are very, very tight on the current AC plugs (45XLS). It takes a lot more force than I'd expect to actuallly engage the clip inside the boot on the plug itself. I'd carefully remove them and grease the boots with dielectric grease and make sure they are fully seated on the plugs. It sounds obvious, but this has foiled me once before.

If you have an old school garage near by that has a Sun Machine or Bear tune-up machine (and a mechanic who knows how to use it properly), I'd start there and baseline the condition of the carbs and ignition system.

Nick, I know just the guy for that; he's nicknamed "Peanut", and he has such a garage. He's also 'old school' in another way: he's honest. I have a feeling I'll be seeing him soon. Thanks!

[James H.]

Re: Engine miss (67 427/400)

Larry,
this is a long shot.. but my 67 400 had a similar condition. Once your car warms up, disconent your choke linkage and open it up.. that will tell you if your choke is in need of adjustment.
Before I disconnected mine I had major missing at acceloration.. tried everything, then DC'ed the choke and it runs great..
Good luck,
Jim