Spark Plug Diagnosis

Mon Jan 29, 2007 12:51 pm

I changed the plugs on my Cub this weekend. Been wanting to do this since I bought it in Nov. 2005. Not sure how long these have been in it, but I thought some of you Doctors of Cubology would be able to make some assessments of my Cub based on how they look.

I do get some blue smoke as those who saw it at CubFest DeGraff and CubFest N.E. 2006 can attest.

Mon Jan 29, 2007 1:24 pm

The plugs that I replaced (pictured) are Autolite #386.
The new plugs are Champion D21 (502).
I did set the gap to .023.

Mon Jan 29, 2007 1:59 pm

From the color of the plugs it looks like #2 is burning just right. The other 3 appear to be running a touch lean. All in all they look good. Just my opinion.

Mon Jan 29, 2007 4:21 pm

I agree with Donny #2 looks great, 1&4 ok, 3 little lean but good
all in all.

Mon Jan 29, 2007 4:38 pm

I have a DM degree (Doctor of Motors). I usually charge, cash only, for professional advice. In this case I will make an exception and take two laying hens.

Normal or normal worn. Kinda hard to tell from the photo angle and with out a closer look at the electrode and insulator. #3 could be too hot of a plug as well as #1 and #4. Other possibilities on #s 1,3 & 4 are lean fuel mixture and ignition timing. And the last possibility is that this engine does not have a lot of running time on this set of plugs.

So, when can I expect delivery of the hens?


Mon Jan 29, 2007 4:43 pm

Are the differences caused by build up of crud on the intake valves?

Eugene, funny you should mention laying hens. We just so happen to have 15 with plans on adding 6 this spring. Two years ago we had 25.

I have no idea when these plugs were put in, but I would guess that I've put around 50 hours on the Cub since I bought it.
(Actually I personally have put maybe 10 hours on, Erik (my oldest) about 10, Aron, about 20, and Emily about 10.)


Mon Jan 29, 2007 4:52 pm

I just noticed your list of tractors & I was wondering, is there something wrong with you that might be contageous or is it a mental condition? You see, I saw my first Cub in late December and I already have two. I still find myself looking at the "for sale" section, looking for another great deal and it makes me wonder. Is it just me or are people like you implanting some sort of internet based cyber mind scrambling code that is messing up the nurons in my brain......BUY ANOTHER CUB, BUY ANOTHER CUB, BUY ANOTHER CUB........... :lol: :lol: :lol:

You have quite an impressive list!!

Mon Jan 29, 2007 5:37 pm

Eugene: You jest about taking two hens instead of cash but I can remember when that was a commom medium of payment. I don't remember much of the late 1930's and early 40's but one thing I do recall is peddlers traveling from house to house making repairs on cookware or selling items. My parents bought a new woodburning cook stove and they traded live chickens as part of their payment. It had a reservoir for water mounted on one end of the stove so warm water was available whenever the stove was in use. A big improvement over the burned out unit which they had been using. Dan
Last edited by Dan England on Mon Jan 29, 2007 6:19 pm, edited 2 times in total.

Mon Jan 29, 2007 5:39 pm

I believe it's a disease. I "cut my teeth " on a cub, then was without one for probably 30 years. Scotty saw one at school and decided he liked them. He got a Needs work cub for Christmas 2 years ago. We restored that one and somehow are upto 5 cubs and 2 cadettes between us. Hope they don't find a cure. Ed

Mon Jan 29, 2007 6:23 pm

Are the differences caused by build up of crud on the intake valves?

Something up setting the air fuel mixture could be causing the white insulators. Could be manifold gasket, valve tappet gap, lean air fuel mixture, etc.. #1 cause is wrong heat range.

Suggest doing a complete tune up including valve tappets. I'd check the plugs again at the next tune up.


Spark Plug Analysis

Mon Jan 29, 2007 9:42 pm

Seems like 3 is running a bit hot, but no visible harm. Bet you get good mileage! Run 'em.

Tue Jan 30, 2007 11:59 am

If you are planning on replacing them I would drop to a little cooler plug. I guess those all look lean to me. I like to see them light tan. I spose on a low RPM 4-stroke engine a having them that light probably isnt a problem. If I saw those on my snowmobile engine I would be worried. My guess is either the gasket between the carb and manifold or the manifold gasket could be leaking. I run D21s in my cub becuase it burns some oil.

Tue Jan 30, 2007 1:48 pm

Does anyone else use an anti-seize on their plugs? I do, out of habit from working with aluminum heads, but is it desireable with cast iron heads?

Tue Jan 30, 2007 1:55 pm

FCUBMAN wrote:Does anyone else use an anti-seize on their plugs? I do, out of habit from working with aluminum heads, but is it desireable with cast iron heads?

It's desireable enough for me. It allows loosening the plugs with one tug on a 7/8" box end wrench and spinning them the rest of the way out with fingers.

Tue Jan 30, 2007 2:19 pm

I'm not sure that you would call it "anti-seize" but my dad taught my brother and I to put a couple of drops of oil on the threads before installing the plugs. Still do and have not had a problem removing a plug yet.
I do the same thing on the wheel lug nuts when I rotate tires and put the snows on and take them off. Never had one I could not get off.

Thanks for all the feed back on the condition of the plugs and what it means.