Occasional, Weak Spark Harbor Freight Predator 212 Question

[PGB1]

Hello All!

Someone had my Wacker Plate Compactor and the original engine stopped working, so he bought a Harbor Freight Predator 212 engine. It sat for many years unused, then returned to me recently.
The Trouble: No Spark (Plus ants and larvae paced into the carburetor and who knows where else.)

I bought a replacement ignition coil and had no spark. I got another one and have a weak spark perhaps every dozen pulls only. (Using a spark tester without spark plug involved). The kill switch wire is disconnected to eliminate other causes, such as low oil sensor or On-Off switch. The flywheel and magnet, I removed the rust.

On this forum, I learned the gap is to be 0.010". When that failed to give good spark, I tried 0.012 and 0.016" (Things I read elsewhere.) I set the gap both at the flywheel and at the magnet (which is too short to be under both legs of the laminations at the same time.).

Coli Resistance Readings: Plug Wire to Laminations = 3.4 K-Ohm. Kill Wire to Laminations = 1.8 Ohm.

Can any of you think of why there is only a rare (and weak) spark?

Thanks For Sharing Your Knowledge!
Paul
PS: Not really related, but the original engine is Kohler K91 breaker point style with the coil under the flywheel (Some models it is a cylinder type outside). Also no spark. I haven't investigated.

 

[Mark H_NO]

What kind of spark tester? How dark is it where you're testing? I often need to find good shade to test spark, or I can't see it. The light bulb/LED tester is not a very good test, but it tends to show spark too often, which isn't your issue. Make sure you have a good ground for testing. What kind of plug, and where did you get it? Most here will say to get it at auto parts store to avoid clones. Where are you getting the coils?

 

[slomo]

New doesn't mean new. Let that percolate a bit.

Might take 15 new coils to make/get a good spark.

Yes open gap tester is a must. Many ways to do this. Simple 12v test light connected to a clean ground. Can vary the probe or pointed end, in and out of the plug boot. Looking for max gap the spark is thrown. Needs to be 1/4" or better. Most push mowers can barely hit the 1/4" gap mark with fresh coils.

Close the coil to magnet gap down to 0.006". Usually two sheets of paper. Get a caliper out and measure. Used to say a business card. Those can be over 0.015" thick or more. Not good for these weak azz coils.

 

[Auto Doc's]

Hello P.,

If you have the "flash bulb" type spark tester, throw it away, it's a junk gimmick some idiot put on the market years ago. You need an open-air adjustable gap type spark tester.

Question: Are the coil hold down screws plain steel, back oxide coated or gold anodized colored? I ask this because I have seen the wrong "gold" screws used and the coil would not ground properly when bolted down. Gold anodizing acts as an insulator and not a good ground conductor.

How did I learn about this?

From a 5500-Watt B&S Storm responder generator.

I spent a couple of hours (a few months ago) parts swapping and playing the part elimination game on an 8HP engine on this portable generator that I was having this same problem with.

Fortunately, I had two generators with identical engines so I could finally figure out what was happening. I swapped the coils and left the kill wire unplugged, then the flywheel. All that was left was the screws, and that was my problem.

I replaced those two hold down screws, and the engine has been starting and running great since then.

 

[PGB1]

What kind of spark tester? How dark is it where you're testing? I often need to find good shade to test spark, or I can't see it. The light bulb/LED tester is not a very good test, but it tends to show spark too often, which isn't your issue. Make sure you have a good ground for testing. What kind of plug, and where did you get it? Most here will say to get it at auto parts store to avoid clones. Where are you getting the coils?

I apologize for my gap in attendance to the thread. (Or to the engine) Troubles took me away.

Mark H, thanks for asking. The spark tester is shown below. As far as shade goes: Not much luck yet. I tried having someone hold a box to make shade with only seeing a weak spark. Hopefully I can check in the evening or a cloud day.

Simple 12v test light connected to a clean ground. Can vary the probe or pointed end, in and out of the plug boot. Looking for max gap the spark is thrown. Needs to be 1/4" or better.

That's an interesting method, slomo. Thank you for sharing it. So far, 0.006' is still weak spark, but as mentioned above- shade is lacking. I tried every thousandth between 0.006 and 0.010" one at a time.

Question: Are the coil hold down screws plain steel, back oxide coated or gold anodized colored?

They're plain, carbon steel. I made certain mating surfaces of laminations and block were clean and resistance is zero Ohms.

Even with the weakness of the spark, I expected at least one fire with starting fluid, but nope. (Plug is new and sparks when tested in another engine)

I'll go back to this engine very soon I hope! With luck, today.

Thanks All for the above suggestions.
Paul

 

[StarTech]

Here's something to test. How strong are the flywheel magnets? And make you don't install the coil upside down.

 

[Auto Doc's]

That is an interesting homemade spark tester you show in the picture. Have you been able to confirm that it works on a known good running engine?

 

[PGB1]

Here's something to test. How strong are the flywheel magnets? And make you don't install the coil upside down.

Thanks for the idea, Star Tec.. Unfortunately, I've no gauss meter, nor would I know how strong the one magnet should be. (Just one magnet)
I think the coil is upright. The old one had kill wire coming off the bottom & spark plug with the top. So, I copied.

 

[PGB1]

That is an interesting homemade spark tester you show in the picture. Have you been able to confirm that it works on a known good running engine?

Thanks Auto Doc. Good Point! Yup, I've used that tester often over the years. Before working on the current project, I checked it on my generator. (The wire to the spark plug is a scrap of 10,000 volt neon sign wire. I used it so the potential won't jump out of the insulation.)

Yesterday was rather dark outside & I tested again. Still the spark is weak and yellow. It is also intermittent- I may have to pull 6 - 10 times before any spark. This makes me ponder what StarTech wrote about the magnet. (Engine only has one)

Paul
PS:
For comparison, my generator (Honda GX 340) has a large, blue spark on every partial pull.

 

[slomo]

Yesterday was rather dark outside & I tested again. Still the spark is weak and yellow. It is also intermittent- I may have to pull 6 - 10 times before any spark.

Tells me the coil is near dead and needs replaced. Best time to check spark is at night. Push it outside the garage and watch for spark color and gap jumping distance. Yellow is faint. Blue or purple is what you want.