Spark Plug Condition

[bchene]

Hello,
I have a '74 SIII 109 with an 8:1 unleaded head, zenith carb and electronic ignition. I have been trying to figure out why the condition of my spark plugs are not consistant across all cylinders. Cylinders 1, 2, and 3 look like they are much to hot. Very white and glazed/shiny electrodes. Cylinder 4 looks perfect, gray with very minimal 'dusting'. No signs of oil or cracking on any of the plugs. Can anyone enlighten me on why the plugs show this difference in electrode condition? Given that it appears the first three plugs are 'hot' and the fourth 'normal', what would account for the difference? Given their condition I would expect all to be 'hot", or all 'normal'? What makes a plug run 'hot'?

Champion 12NY and disco-tech ignition. The head is a rebuilt from our hosts with less than 2500 miles on it (unleaded).

Thanks

[mechman]

Sounds like your mixture is too lean, but something is going on in #4 to make it run a bit richer (or your spark cooler) than the rest. I would take the hot burning cylinders as your norm and correct for that, then check #4 for issues. Readjust your valves, too, while you're at it, just to eliminate them from the mix. If they've been running hot then they need adjustment.

Mech

*Edit: Oh yeah, check your timing, too. Running hot could be a sign of the ignition being waaaay too far advanced.

[Jeff Aronson]

Mechman, your advice sounds dead on.

I would also suggest that you check the mixture level on the Zenith [too lean?] and the timing [too advanced?]. Usually that would affect all cylinders but something is wrong here. You don't want to let this go for a long time because you risk burning a valve.

This is a long shot but when you installed the head, are you certain that you put the head gasket on facing the right direction? If you have inadvertently covered some water jackets, some cylinders would run hot [thus the white plug tips] while one or another would run fine. I cite this because it happened to me when a mechanic made an error and installed the gasket upside down. I had a burned valve within a few thousands miles because of it. When I replaced the gasket and the head myself, I was careful that the word "petrol" faced the right direction.

Good luck and keep us informed.

Jeff

[gudjeon]

Try a set of Champion RN11YC4's. I run these with electronic ignition and burn a nice light brown.:thumb-up:

[Donnie]

Hello,
I have a '74 SIII 109 with an 8:1 unleaded head, zenith carb and electronic ignition. I have been trying to figure out why the condition of my spark plugs are not consistant across all cylinders. Cylinders 1, 2, and 3 look like they are much to hot. Very white and glazed/shiny electrodes. Cylinder 4 looks perfect, gray with very minimal 'dusting'. No signs of oil or cracking on any of the plugs. Can anyone enlighten me on why the plugs show this difference in electrode condition? Given that it appears the first three plugs are 'hot' and the fourth 'normal', what would account for the difference? Given their condition I would expect all to be 'hot", or all 'normal'? What makes a plug run 'hot'?

Champion 12NY and disco-tech ignition. The head is a rebuilt from our hosts with less than 2500 miles on it (unleaded).

Thanks
If your Mech has a Laser thermometer, run the truck till it is warm, a few miles down the road, shut off the engine & quickly check the plug temp...also scan the head for hot spots, while you are at it.. this will help you narrow down the problem.....most of which, good advice has already been given

[Donnie]

Sounds like your mixture is too lean, but something is going on in #4 to make it run a bit richer (or your spark cooler) than the rest. I would take the hot burning cylinders as your norm and correct for that, then check #4 for issues. Readjust your valves, too, while you're at it, just to eliminate them from the mix. If they've been running hot then they need adjustment.

Mech

*Edit: Oh yeah, check your timing, too. Running hot could be a sign of the ignition being waaaay too far advanced.
I forgot to ask: if U shut off the engine for a minute or so, just to run into the store for a Guiness, do you find it reluctant to turn over or start? Do U get any pinging on a hard pull?

[bchene]

Thanks for all the advice. I checked the timing this afternoon and it is set about 5 degrees BTDC. Used the beer and timing light routine. Does 5 degrees sound right?
I also started to tinker with the carb. Backed out the mixture till rough, turned back in till smooth idle and then set idle speed at throttle linkage. Seemed to end up about 1/2 turn out on the mixture screw.
Will adjust valves and change plugs in a day or two after I have run it a bit and checked the current plugs.
I am worried about the gasket being on wrong. I did it myself and there is every possibility I mucked it up. I hope I do not have to pull the head. If I can find a temp probe and all sample spots are consistant does that mean the gasket is right?
Also, the truck runs great, pulls hard, does not ping going up a hill or pulling a load. Always starts on the first turn of the key.

[mechman]

Well, 5 degrees is about right, though it can vary a few depending on engine condition. Given that yours starts right away, has good power and doesn't ping, I'd say you've got that nailed.

Usually the mixture screw would be turned out around 1 1/2 turns from seated (in fully but not tight). How old is your carb? The needle screw seat might be opened up too far for decent adjustment - especially if it's old and a DPO screwed the sucker in tight once. Also, if you have a Zenith-Zenith and not a Solex-Zenith (Solex bought Zenith and continued to make the carb from pattern), the new mixture screws that come with the rebuild kits won't work. They're for the newer Solex-built carbs. The threads on the older mixture screws are MUCH coarser than on the newer ones. You have to clean up your old mixture screw and reuse it on the old carbs, or else you'll ruin the carb body.

Check for vacuum leaks around your carb and manifold. That would throw your mixture off! I use carb cleaner with the wand attached - if the engine stumbles when you spray, you've found a leak.

Was your engine ever rebuilt in the past? If so, the block deck may have been milled down 0.020" or so, effectively making your 8:1 motor into a higher compression beastie than you intended. Did you measure the deck height before installing the new head? Do you notice a difference in performance or temps if you run premium gas?

I'm guessing that #4 may have a tiny bit of oil getting into it, perhaps during cold starts. Often this is from a leaky valve stem seal - oh so common, that, especially if the head is getting hot. That could explain the little bit of color (NOT light brown I noted) on that plug.

I've been out of the Rover shop for a few years, I don't remember which plugs by code specifically you should use, but I'd suggest trying a cooler plug than what you have (if you can). I'd try Disco 4.0 spec plugs, they're made for the hotter spark of an electronic ignition.

Adjust those valves! If they're out, your vacuum will be off and you won't get a proper setup on your carb.

And Jeff is absolutely correct about the gasket-upside-down issue. I won't tell you how I know... I did catch it before it left the shop, but not before the job was done. :(

Mech

[JayGoss]

I forgot to ask: if U shut off the engine for a minute or so, just to run into the store for a Guiness, do you find it reluctant to turn over or start? Do U get any pinging on a hard pull?

Donnie- I have this issue (turns over but reluctant starting after it has been running and hot. No pinging that I can tell)- is this a sign of too much advance?

ps: bchene- sorry to hijack your thread- this just struck upon some issues I've been having. Hope you don't mind.

[s3landy]

I wouldn't worry about the head gasket. If it was upside down you would know it because it won't fit properly.

Mike

[Jeff Aronson]

I wish that were always the case. Mine went on upside down all too well :).

However, it's the least likely scenario and the one you can't control easily. Hard starting can be a sign of advanced timing and/or wrong timing, or points gapped incorrectly or pitted points. Check them, as well as the condition of the rotor tip and top. Remember to time the car after you've completed all points adjustments. Oops - just realized you're running an electronic distributor.

Also, if you have a vacuum leak of any sort [carb body to manifold, manifold to block] you'll run a lean mixture depspite your efforts at carb adjustment. It would make the engine run hot inside, too. Have you sprayed carb cleaner around the carb body and intake manifold to head, and seen if the rpm level changes?

Does your distributor brand have a recommended timing advance? Why not try O BTC instead of 5 degrees?

Good luck and happy New Year!

Jeff

[mechman]

I wish that were always the case. Mine went on upside down all too well :).

Jeff


Yup, happened to me, too, on a Mil-spec 2.25. I had to swap the short block because the old one had cracked at the rear main bearing carrier and would piss oil when it got warm. I had the truck all ready for delivery, sounded great and had POWER, but ran hot on the test drive. It was one of the few times the boss had good, relevant advice in regards to actual repairs.

I'm still leaning toward either a vacuum leak or the timing being too advanced. As JayGoss said, the proper idle setting may be TDC for your setup. If you have access to one, get hold of a timing light with an advance adjustment knob. Set it for the total max advance (I forget the number, but it's probably 15-20 degrees or so), then rev the engine to 2500 or so and see if your timing marks still line up. That's the best way to know if it's advancing too far at speed.

Mech

[Donnie]

Donnie- I have this issue (turns over but reluctant starting after it has been running and hot. No pinging that I can tell)- is this a sign of too much advance?

ps: bchene- sorry to hijack your thread- this just struck upon some issues I've been having. Hope you don't mind.
If your timing is too far advanced, it will "grunt" for lack of a better description, when you try to start it hot..It will sound as if your battery is going bad. A plug that is fouled or collecting a build up of contamination from the fuel that U R using, will act as a glow plug, if this happens within a few seconds. If your engine cranks smoothly, without any of the forementioned, then there are a lot of other factors that we would need to know to correctly GUESS..HTH, D