Weak Spark

[Paul in Edmonton]

I brought my tractor home to work on it in the garage, since I don't have a shop at the cabin. It's snowing right now, so I need to get it up and running ASAP, so it'll be ready to plow. (Unfortunately, it's hard to put in more than an hour or so each evening.) But all that aside, I've got a few questions...

I ordered a bunch of parts from Just 8Ns (since this site won't ship to Canada). These included spark wires, coil, cap, rotor, points, condenser, and gaskets.

I don't want to replace everything, but instead I want to understand what the problem is. I ordered the parts so I'd have them (since the lead time on buying them is over a week).

I started with the spark plug wires, since they were in lousy condition. I also replaced the wire providing voltage to the coil, since it was also damaged. Beyond that, I haven't replaced anything yet. I will definitely replace all the distributor gaskets before I finish.

The points look to be in good shape. I replaced them in the summer of '11, so they're not old. I recall that when I replaced them the old ones were visibly bad. That wasn't the case this time.

I've done all the continuity checks that Bruce has suggested in multiple posts.

I cranked it over last night, with an in-line spark tester attached, and I was getting spark on all plugs, but not a strong spark. (I plan on checking with a 1/4" gapped plug for comparison.) Note that I'm not providing it with any gas, so there's no question about it starting right now.

As an aside, I have other issues--the system will only turn over a few times before the battery gives up. I suspect a bad battery, but I will also be cleaning all the electrical contacts between the battery and the starter. I also plan on replacing the #4 cables with #1 cables, but my local store didn't have #1's in stock in appropriate lengths. I'll work on this problem separately, and ask back if I can't resolve it. But for now--is this enough to cause a weak spark? I guess I should check voltage at the coil while I'm actually turning it over.

So, back to my main question. If I'm getting spark, but it's not strong, what are the possible causes, and how would I diagnose them, without just replacing everything at once? (That might fix the problem, but I wouldn't learn anything!)

What should I be looking for, given the above, to suggest that the rotor, cap, coil, points, and/or condenser might need to be replaced (or not--I don't mind putting them on the shelf for next time)?

Thanks,

-Paul
 

[souNdguy]

the bad battery may be the bulk of the issues. if it only turns over a bit before dieing.. that means voltage to the coil is very low.

address that first to prevent tail chasing..
 

[Bruce (VA)]

6v or 12v, front or side distributor?

" I have other issues--the system will only turn over a few times before the battery gives up"

No, that is not an 'other issue'.

That is THE issue.

Weak battery = weak spark, as soundguy said.

You're on the right track to replace the cables & clean the grounds. While you are doing that, charge the battery. Then check it w/ a hydrometer (tip # 49)

But remember, while a hydrometer will tell you if you have a bad battery, it will not tell you if you have a good battery. Only a load test will do that.

You can do a 'shade tree' load test by checking voltage drop on a fully charged battery. Less than 5v means it's bad.

It's usually easier to pull it out & let the parts store check it w/ the correct load tester.
50 Tips

 

[Paul in Edmonton]

Thanks, Bruce and souNdguy.

I guess I have a course of action for now.

It's an 8N, front-mount 6V. I know I should have posted that before--sorry.

-Paul
 

[Paul in Edmonton]

New battery is installed. Also put in the new cap, rotor, and gaskets. (And as I said before, new spark wires and wire to the coil.) The new coil I bought will stay on the shelf for now.

Now there's strong spark on all four plugs.

Thanks for your help--I hadn't realized just how much the weak battery would affect the spark.

Now I just need to get some gas in it. Maybe later this evening or tomorrow we'll see if it will start...

(But I need to replace a rad hose that just started leaking first... There's never just one thing, is there?)

-Paul