Ignition problems!!! PLEASE HELP!!

[stuewerr]

Hi everyone, I am new to the site but I am really in desperate need of help! I purchased a non running Wacker BTS1035 cut off saw on FB marketplace, I know not a chainsaw but pretty damn close. When I got it home I realized there was only a weak/ intermittent spark. Bought a new coil, cleaned up the carb gave it a few pulls and boom started right up. Tuned the carb, shut it down and thought life was good...

The next day I went to use it, again started right up but as soon as I got to about half throttle it would shut off, like someone hit the kill switch. Gave it a few more tries, same thing... starts and idles perfect but as soon as it gets to about half throttle is dies. Figuring it was a fuel issue I pulled the carb apart and cleaned it again but no luck.
Figured it was time to check spark so I pulled out my $3 harbor freight spark tester and fired it up. Showed a strong spark at idle and low rpms but as soon as it got to half throttle the spark completely dies.
Assuming the coil could have been junk from the factory I started an exchange with Amazon, but when the new one came it was the same problem.

What makes my problems even worse and why I am pulling my hair out is that every 3-4 starts it runs great! Gets to full throttle, a couple misfires but runs strong until I shut it down and then we are back to a suicidal spark!

Any help would be very much appreciated, I’m just not sure what else could be the problem. I have no idea what would just kill a spark like that

 

[rupedoggy]

Is that Chinese built?

 

[stuewerr]

Is that Chinese built?

I think Wacker Neuson is a German company but my guess it it’s probably Chinese built like everything else these days

 

[buzz sawyer]

What is the gap between the coil and flywheel magnets? Could also be a wire shorting to ground when hot. I had that happen to a saw once.

 

[frank_]

i,ve had a similar problem where the kill wire was earthing out at set rpm because of vibration

 

[J D]

Yup, my money is on a kill wire that's been pinched & is earthing out... I'd still drop a new spark plugs in it tho (make sure it's the plug that's specified for the saw)

 

[stuewerr]

What is the gap between the coil and flywheel magnets? Could also be a wire shorting to ground when hot. I had that happen to a saw once.

Gap is on the smaller side because there is no adjustment on the coil. Calls for .012-.016 but it’s closer to .008. Could too small of a gap cause this? I have disconnected the entire kill switch thinking that’s the problem but still same issue

 

[buzz sawyer]

Gap is on the smaller side because there is no adjustment on the coil. Calls for .012-.016 but it’s closer to .008. Could too small of a gap cause this? I have disconnected the entire kill switch thinking that’s the problem but still same issue

I was concerned that the gap might be too wide. Aside from the second coil being bad, the only other thing I can think of is something in the H side of the carb floating around and blocking fuel. Also had that happen once. It was under one of the welch plugs.

 

[dando127]

It almost sounds like fuel to me. If you spray gas in in the catb at full throttle will it stay running? Open up the low jet a little more and try again.

 

[J D]

Is the HT lead part of the coil?
You need to establish for sure if there is spark or not when it dies & work forward from there.
Any tacho should work for that but it will still read ok if there's a short in the plug so definitely replace the plug if you haven't.

 

[stuewerr]

Is the HT lead part of the coil?
You need to establish for sure if there is spark or not when it dies & work forward from there.
Any tacho should work for that but it will still read ok if there's a short in the plug so definitely replace the plug if you haven't.

The spark plug lead did come with the coil, I have not checked to see if it is molded into it or if it could come off. Do you think the wire itself could cause issues?

Using my harbor freight spark tester I was able to conclude the spark disappeared when the engine shuts off. The lightbulb glows bright and steady until it gets to that half throttle and then cuts off completely.

I will be picking up some name brand plugs on my way home from work today. Maybe it’s just that simple?

 

[HarleyT]

Unplug the kill wire and try running it. See what happens.

 

[heimannm]

Refer to post #7...

 

[HarleyT]

Refer to post #7...

I suggest the kill wire, not the switch.

 

[HarleyT]

Sounds like a bare spot on the kill wire, so it should be disconnected at the coil to find out.

 

[Vintage Engine Repairs]

Are you sure it’s actually losing spark and not lean on the H side and dieing? Upload a video.
The spark tester you’re using can’t tell you the strength of the spark, only that it is or isn’t sparking. If a saw is lean and you pull the trigger and it dies, the spark will stop at the same time. I wonder if you’re approaching it from the wrong angle.

Spark is generated by the flywheel, if the flywheel stops because the engine is lean then the spark stops.

 

[dando127]

That's what I was thinking. I have an engine with a tillotson carb that was acting the same way. The ignition system was all good, but it would bog and die as soon as it went past 1/4 throttle. I started with a spray bottle of mix gas, and sprayed in the carb as I opened the throttle, and it kept running and revved higher. Thats when I realized it was a fuel issue. In that case I opened the low jet more and that fixed it.

 

[stuewerr]

Are you sure it’s actually losing spark and not lean on the H side and dieing? Upload a video.
The spark tester you’re using can’t tell you the strength of the spark, only that it is or isn’t sparking. If a saw is lean and you pull the trigger and it dies, the spark will stop at the same time. I wonder if you’re approaching it from the wrong angle.

Spark is generated by the flywheel, if the flywheel stops because the engine is lean then the spark stops.

Definitely losing spark, the light completely shuts off on the tester yet the engine is still spinning. If it was a gas problem I would still see spark until it comes to a complete stop, plus Iv tried spraying gas and starting fluid into it at its choke point to see if that gave me a different result but no dice. Not to mention when it does have its moments of running fine it goes from idle to the rev limiter without any hesitation.

 

[Vintage Engine Repairs]

Definitely losing spark, the light completely shuts off on the tester yet the engine is still spinning. If it was a gas problem I would still see spark until it comes to a complete stop, plus Iv tried spraying gas and starting fluid into it at its choke point to see if that gave me a different result but no dice. Not to mention when it does have its moments of running fine it goes from idle to the rev limiter without any hesitation.

Ah ok understood, good stuff. Have you tried checking the HT and ground leads with a multimeter to see if they are grounding?

 

[stuewerr]

Ah ok understood, good stuff. Have you tried checking the HT and ground leads with a multimeter to see if they are grounding?

Actually no I haven’t, that would probably be a good place to start just to rule it out. I also came across a thread about weak magnets in the flywheel. I checked mine and the don’t seem incredibly strong, wondering if maybe that could have something to do with a spark problem at high rpm