# Troy Bilt Super Tomahawk Chipper with 195432 B&S 8hp horizontal



## TryingToLearn (Jan 18, 2021)

Ran when I first acquired it but would stop and be difficult to restart. Found the start stop switch wasn't doing anything & had to pull the plug wire to stop it. Researched and checked for info with little luck. Started working again but ran rough & stalled then couldn't get it started. Replaced the carb after last session of not getting it to run. Learned how to check for spark with tester and wasn't getting any. Put in new plug with no joy. YouTube taught me to check the magneto and I found out why the stop switch wasn't working - it wasn't connected. It was also broken. Rebuilt the switch, re-insulated the ground wire and spark plug wire. Reset the magneto. Now came the fun. Checked the spark again and still nothing. Grounded one end of the tester to the engine and got a spark. Reconnected the wire to the spark plug with the tester still in between and got no spark. Retested with it grounded and no spark. So the long and short of it is why would I get a spark when the tester was grounded (indicating the magneto was working. no spark when the switch was off as it should be) but no spark when connected to the plug? Wiring is simple - ground wire from chassis to magneto and then to switch. No grounds in the loop. What else could I check?


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## paulr44 (Oct 14, 2008)

What spark tester are you using? What did you gap the coil to?


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## TryingToLearn (Jan 18, 2021)

paulr44 said:


> What spark tester are you using? What did you gap the coil to?


Thank you for the reply Paul. Tester is an in-line no name but I wouldn't understand what difference it would make. I did not put in my narrative that I had tested it on my car, lawn tractor and chainsaw with no issues. The fact that the only time it didn't light up was when it was connected to the chipper spark plug, by my logic (however faulty it may be) says it's not the tester. The coil was gapped to a business card which resulted in the tester lighting up when grounded. I also used the same grounding method between the tester and spark plug to ensure it was making contact with the plug. Are there other possibilities that I'm not seeing?


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## paulr44 (Oct 14, 2008)

It makes a big difference, if you're using an in-line LED tester and grounding the lead to the engine as you described. As for the gap, a business card is typically 0.010", which is fine for most engines.

A spark plug under compression requires a lot more voltage than one in free air. Once you understand that, the puzzle pieces are...
An in-line LED tester does not impose a load on the ignition coil, while a _adjustable-gap _or _large-fixed-gap_ type does. This load is required to stress test the coil under harsh plug-firing conditions.
However, using an inline-LED _on a spark plug that is in installed_ will at least provide a minimal test. LED testers are _excellent _to diagnose losing spark on multi-cylinder engines.
The tester I use most: KD Tools KDT2757 ((same type can be found for less $$) don't get the HEI one)
The tester I use for serious testing: Oppama PET-4000 (not cheap)
I have other test equipment ($$), but need not elaborate for the problem at hand.


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## TryingToLearn (Jan 18, 2021)

Wow, who knew? Thanks for you patience. Again, with my (apparently faulty) logic, the amount of voltage required in one instance shouldn't have anything to do with the amount of voltage required to light the in-line tester. If the coil is producing sufficient voltage to cause it to light when grounded to the chassis, wouldn't it be producing the same when connected to the spark plug thus lighting the tester even if it won't cause the plug fire? 
Then back to the issue, what else could be the issue?


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## paulr44 (Oct 14, 2008)

Think about it this way, for the LED to illuminate it needs a path to ground with a *fair *amount of system voltage, that's all. It's not a stress test of the coil. If the voltage (pressure) isn't sufficient to jump the plug gap, then it won't light. The plug gap UNDER COMPRESSION imposes a load that you don't have when simply grounding the LED to the block etc. This help?

Put the spark plug in and the LED in-line to the plug and pull over. If it produces a bright glow then the ignition is probably ok. If doesn't glow or is faint, then the system is weak.
If weak reading, your next step should be to *isolate *the coil from the kill circuit and *re-test*. An abraded kill wire that's shorting, even if it's not a bad short any short will affect it, and of course a bad kill switch will as well.

But as I said before, because of the type of tester LED's are, we use those primarily for loss of spark situations when running and/or hot, not cold-start. Or as an indication.
This is why I suggested you get a gap-type tester.

You had the blower housing off when you reset the magneto, so I'm assuming it has an external (of the flywheel) ignition coil. If so, the coil is probably weak. However, if ever a kill wire or coil primary wire goes to under the flywheel, then it has breaker-point ignition. Then you'd just need to tune it up, and check the coil for cracks.





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Conditions that affect the discharge voltage | Spark and Ignition | Basic Knowledge | SPARK PLUG | Automotive Service Parts and Accessories | DENSO Global Website


An explanation of the mechanism of producing a strong spark between terminals to cause combustion of the air-fuel mixture.




www.denso.com












High voltage spark and air compression


Honestly I do not think automotive techs would know the answer to this question so being said from a physics stand point about the relationship between the high voltage spark on a spark plug and compression in a engine. I have had experiances where there was spark on the plugs but the engine...




www.physicsforums.com












How to diagnose a weak ignition system


The following issues can present in different ways or operating states, but the most prevalent ignition problems include a cracked spark plug porcelain or weak ignition wire insulation.




www.agriculture.com












(Jim) Firing Voltage versus Compression - Farmall & International Harvester (IHC) Forum


Discussion topic in the forums at Yesterday's Tractors.



forums.yesterdaystractors.com




quote from last link:
NOTE Compression pressure - required voltage increases in direct proportion to cylinder pressure or as the air density increases.


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## TryingToLearn (Jan 18, 2021)

As I said, I appreciate your patience. I believe I understand your explanation and next day above freezing I'll check out the links provided and the spark plug wire which I needed to reinsulate. This would fit in with the abraded wire situation. Will also recheck the ground wires and try this with the rebuilt kill switch out of the circuit.


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## TryingToLearn (Jan 18, 2021)

3 weeks, 31" of snow and I'm back with good news. I read the articles you mentioned and understood some of them - thank you! I did pick up enough additional knowledge to realize that I had placed the coil on backwards after taking it off to clean and re-insulate the spark plug cable. Read more and realized the cable needed to be replaced so simply bought a new replacement coil. Installed it correctly and finally got it running consistently making me realize I probably didn't have to replace the carb in the first place. 
Next issue is how to determine for the carb adjustments when I'm at the recommend 1750 RPM at idle. Open to any and all suggestions!

Thanks


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## paulr44 (Oct 14, 2008)

The idle mixture screw is the upper one on the side, at the top of the carb., the high speed mixture screw is on the bottom sitting at an angle.
For that model, typical mixture screw adjustments (fine tuning always required), 3/4 to 1 turn for idle, 1-1/2 to 1-3/4 for high speed.
Idle doesn't need to be as high as 1750, if you want to turn it down. You don't want the clutch engaged or banging away at idle.


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## TryingToLearn (Jan 18, 2021)

paulr44 said:


> Idle doesn't need to be as high as 1750, if you want to turn it down. You don't want the clutch engaged or banging away at idle.


I guess my question should have been - how do I determine what the RPM actually is?


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## paulr44 (Oct 14, 2008)

Amazon.com: Searon Small Engine Tachometer Hour Meter inductive Tachometer for Outboard Engine Chain Saws Tractors Lawnmowers Motorcycles Marine Engines RC Toys PWC ATV : Automotive


Buy Searon Small Engine Tachometer Hour Meter inductive Tachometer for Outboard Engine Chain Saws Tractors Lawnmowers Motorcycles Marine Engines RC Toys PWC ATV: Tachometers - Amazon.com ✓ FREE DELIVERY possible on eligible purchases



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There are much better ones on the market, but they come at a price.


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## TryingToLearn (Jan 18, 2021)

Thank you Paul. I guess this beats how many times the light in the spark plug tester blinks in a minute!


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