OLD husqvarna rancher 50 not starting - seems to have spark, compression, fuel, timing?

[jff]

Hi all,

I inherited and OLD husqvarna rancher 50 and I can't get it to start. been working on saws my whole life and this one has me stumped, I can't even get it to fire. Has spark (outside of the chamber, at least) and I've tried the old plug and two brand new plugs. Has fuel, I can see the atomized fuel when I have the plug out, AND the plug comes out wet, AND I've even tried dumping some fuel right into the chamber. Seems to have compression... First pull (throttle closed) hits about 105, within 3 pulls I'm over 150. Timing seems good, flywheel is locked into place and the hall sensor gets passed just before TDC, which I assume is close enough that I should expect it to at least pop a little?

But I get nothing. No popping even with fuel right in the chamber. I'm totally stumped—any recommendations?

Thank you

 

[ammoaddict]

Hmm. Have you tried unhooking the kill switch wire just to see if it will fire that way?

 

[jff]

Hmm. Have you tried unhooking the kill switch wire just to see if it will fire that way?

I have not but I just tried and no dice. I get good spark with the kill switch attached properly, assuming it's set to run

 

[ammoaddict]

Hopefully one of the experts can help you. I'm just an amateur. If I happen to think of something else I will let you know.

 

[Pioneer]

Sometimes you can get a spark outside the engine, but not under compression. Check both ends of the coil wire, they can come loose. Then check the wire resistance, it should be next to nothing. If it all looks good, suspect the coil, I've had bad coils drive me nuts when they mimic the saw never wanting to stay in tune. The usual giveaway is when the coil heat soaks, fails, and then restarts again when cold.
In your case it might be throwing the timing out if its bad. I've had a Ducati coil go bad on me on a 257, which interchanges on the 50-55.

 

[Vintage Engine Repairs]

You’ve crossed off compression as being an issue as well as fuel supply.

That leaves a few things to check / are currently unanswered.

1). Spark strength (including magnet strength)
2). Spark timing (failing coils can do strange things)
3). Fuel quantity (and ratio to air & leaks)
4). Fuel quality
5). Skirt condition / ability to seal the ports

Work through each one and you’ll find your issues

Edit:

For future reference, get an inline tester for spark rather than testing at atmospheric pressure. The cost of one (very affordable) will be cheaper than time wasted chasing your tail.

 

[jff]

You’ve crossed off compression as being an issue as well as fuel supply.

That leaves a few things to check / are currently unanswered.

1). Spark strength (including magnet strength)
2). Spark timing (failing coils can do strange things)
3). Fuel quantity (and ratio to air & leaks)
4). Fuel quality
5). Skirt condition / ability to seal the ports

Work through each one and you’ll find your issues

Edit:

For future reference, get an inline tester for spark rather than testing at atmospheric pressure. The cost of one (very affordable) will be cheaper than time wasted chasing your tail.

Thanks. A few questions:

1) I think the timing should be okay, I thought these saws have a key that prevents the timing from going out. Plus, just visually, it looks like the magnet runs over the sensor just before TDC, which should be at least close enough to get it to pop, right? Like it may not run well but it should at least fire, I think. Or am I way off?

2) I think fuel quality is fine, I bought brand new premixed fuel. I'm also not super concerned about fuel quantity right now as I'm just trying to get it to pop by putting fuel right into the chamber.

So I guess that leaves skirt condition and port sealing, and spark strength?

I had assumed that if my compression was reasonable, I'm probably sealing the ports good enough to get it to pop, is that right? Same thing with skirt condition?

So I guess the most likely culprit is coil. I'll figure out what year this saw is from and try to replace the coil and report back. In the meantime, I'm happy to buy an inline spark tester, but do those tell me if I have spark under compression or just whether or not power is getting down to the plug? Like, if power is getting down to the plug but there's not actually a spark, will an inline tester still fire or will it only fire if there's spark?

Thanks!!

 

[Vintage Engine Repairs]

Thanks. A few questions:

1) I think the timing should be okay, I thought these saws have a key that prevents the timing from going out. Plus, just visually, it looks like the magnet runs over the sensor just before TDC, which should be at least close enough to get it to pop, right? Like it may not run well but it should at least fire, I think. Or am I way off?

2) I think fuel quality is fine, I bought brand new premixed fuel. I'm also not super concerned about fuel quantity right now as I'm just trying to get it to pop by putting fuel right into the chamber.

So I guess that leaves skirt condition and port sealing, and spark strength?

I had assumed that if my compression was reasonable, I'm probably sealing the ports good enough to get it to pop, is that right? Same thing with skirt condition?

So I guess the most likely culprit is coil. I'll figure out what year this saw is from and try to replace the coil and report back. In the meantime, I'm happy to buy an inline spark tester, but do those tell me if I have spark under compression or just whether or not power is getting down to the plug? Like, if power is getting down to the plug but there's not actually a spark, will an inline tester still fire or will it only fire if there's spark?

Thanks!!

Hey,

As modern coils have electronic componentry of which one of the roles is to set spark timing (often variable in the newer coils), it can literally just fail internally and thus your timing could be way out of whack.

Can I make a suggestion. Instead of just buying another coil, buy a timing light, one that takes d cell batteries and learn to time the engine. I have a video on it and not only may it not be the coil, thus you have wasted your money, but it will be very useful for future diagnosis.

I have this one, but I doubt you’ll get that make where you are, but I bet you’ll get the exact model under a different brand name. Grab a cheapie on Amazon if you can.

This is where you start to become a competent mechanic rather than a parts swapper who throws money in the trash over and over.

Just a suggestion.




Edit:

Sorry I forgot the last part to your question. Yes an in-line spark tester tests ignition under engine compression.

A cheap one will be perfectly fine. You want a gap of about 6mm to call the coil good.

I really regret spending the money on my Oppama one, its junk. This one will be fine:

 

[Old2stroke]

The timing light is the best tester as you can actually see it in bright light and the inductive pickup only gives a trigger to the light if sufficient energy has passed through the HT lead to produce a spark and it does the testing under actual running conditions without introducing a different/extra spark gap. Every electronic module has a minimum RPM that must be met before a spark is produced and a common failure mode is for this RPM to increase beyond starting speed and this can be checked with a timing light. If there is a question about spark timing, it can be easily checked with a timing light, can't be done with an in line tester. Location of the coil relative to the FW magnets at TDC is a rough check but not conclusive, 5 deg BTDC relative to 2 deg ATDC can be the difference between run and not run. A timing light won't test for spark strength but a good test is to gap a plug to 0.080" and if the ignition will fire it in open air, it probably will in the engine. Sometimes when a coil is failing with just weak spark, gapping a plug to 0.010" will get the engine to fire.

 

[Vintage Engine Repairs]

The timing light is the best tester as you can actually see it in bright light and the inductive pickup only gives a trigger to the light if sufficient energy has passed through the HT lead to produce a spark and it does the testing under actual running conditions without introducing a different/extra spark gap. Every electronic module has a minimum RPM that must be met before a spark is produced and a common failure mode is for this RPM to increase beyond starting speed and this can be checked with a timing light. If there is a question about spark timing, it can be easily checked with a timing light, can't be done with an in line tester. Location of the coil relative to the FW magnets at TDC is a rough check but not conclusive, 5 deg BTDC relative to 2 deg ATDC can be the difference between run and not run.

I think you are misunderstanding why I recommended the spark tester.


The spark tester is to test strength of spark under compression, the timing light recommendation was for confirming the ignition advance.

They’re not interchangeable and one won’t replace the other.

 

[jff]

Hey,

As modern coils have electronic componentry of which one of the roles is to set spark timing (often variable in the newer coils), it can literally just fail internally and thus your timing could be way out of whack.

Can I make a suggestion. Instead of just buying another coil, buy a timing light, one that takes d cell batteries and learn to time the engine. I have a video on it and not only may it not be the coil, thus you have wasted your money, but it will be very useful for future diagnosis.

I have this one, but I doubt you’ll get that make where you are, but I bet you’ll get the exact model under a different brand name. Grab a cheapie on Amazon if you can.

This is where you start to become a competent mechanic rather than a parts swapper who throws money in the trash over and over.

Just a suggestion.

Just bought a spark tester. I have a timing light but it's not a D battery kind, it's the 12v kind. I have used it on 2 strokes before with a battery, any particular reason I can't use it on a chainsaw? thanks

 

[Vintage Engine Repairs]

Just bought a spark tester. I have a timing light but it's not a D battery kind, it's the 12v kind. I have used it on 2 strokes before with a battery, any particular reason I can't use it on a chainsaw? thanks

Perfect, that will be just fine! Here is a video: just use a paper printed degree wheel taped on the flywheel. No need for this one I have.

 

[cookies]

are you pulling it over fast enough? with the plug out its pretty easy to hit 250 rpm using the recoil.

 

[aokpops]

About the exact same saw with the same trouble. Have both a 50 special and 51 Husqvarna The 50 would not start blue spark 125 compression bottle feed it nothing. Put a new piston in nothing check flywheel key. Took the coil out the 51 and put in the 50 started right up. I learned. To run resister spark plugs no resister will knock the coil out of time. Had this happen a few times even with 4 cycle engines .

 

[Vintage Engine Repairs]

About the exact same saw with the same trouble. Have both a 50 special and 51 Husqvarna The 50 would not start blue spark 125 compression bottle feed it nothing. Put a new piston in nothing check flywheel key. Took the coil out the 51 and put in the 50 started right up. I learned. To run resister spark plugs no resister will knock the coil out of time. Had this happen a few times even with 4 cycle engines .

You may want to consider a small engine compression tester, 125 is either very very low or it’s not a suitable tester.

 

[Old2stroke]

I think you are misunderstanding why I recommended the spark tester.


The spark tester is to test strength of spark under compression, the timing light recommendation was for confirming the ignition advance.

They’re not interchangeable and one won’t replace the other.

It's always nice to have both testers, however some people are strangely reluctant to spend money on diagnostic tools so the only point I was trying to make is, if you are only going to buy one, the timing light is a more versatile tool and, as I pointed out in my edited post, a reasonable tester for spark strength is just a re-gapped plug.

 

[Vintage Engine Repairs]

It's always nice to have both testers, however some people are strangely reluctant to spend money on diagnostic tools so the only point I was trying to make is, if you are only going to buy one, the timing light is a more versatile tool and, as I pointed out in my edited post, a reasonable tester for spark strength is just a re-gapped plug.

A re-gapped plug still doesn’t test under compression. Either way, OP, best of luck, it’s a fun challenge - keep us updated.

Edit: you mentioned 2mm gap in atmospheric, that’s still too little, you need about 6mm.

 

[Old2stroke]

A re-gapped plug still doesn’t test under compression. Either way, OP, best of luck, it’s a fun challenge - keep us updated.

Edit: you mentioned 2mm gap in atmospheric, that’s still too little, you need about 6mm.

Unfortunately, can't gap a plug to 6mm, even with the side electrode removed, the biggest gap you can get is about 3mm. However, in over 50 years of chainsaw repairing I have never found a saw that will fire a plug in air that is gapped to 0.080" and not fire it under compression (stock engines). You have found that some of the in-line testers are junk and I also have a few of them, so prefer the simplicity of a gapped plug. If I recall some of my early work on ignition systems, it would take about 60kv to arc a gap of 6mm and that might be pushing the limits of what chainsaw ignitions can do and not a necessary test as 20kv should be enough to work in a chainsaw.

 

[Tony Mayhew]

I have a pretty good system that works for starting chainsaws, And there will probably be someone sniveling about it! But it's a proven way to get one lit. I pull the plug and read what it's telling me if it's fuel fouled or is is very cold out i take a BernsOmatic propane torch with a brazing tip that pinpoints exactly where you want the tip of your flame to go and I hear up the plug just enough to dry it off and add a hundred degrees to the end of the sparkplug. I turn the kill switch to off and with choke open and throttle wide open and filter out of the saw i pull it over a couple of times flushing out the old stagnant air and fuel soaked nasty crap and get some fresh clean oxygen inside the cylinder! Because if there is one thing I can assure you, it's that a fire loves it some oxygen! I squirt little shot of Berryman carb & choke clean inside the sparkplug hole and get that hot sparkplug in and tighten it up, turn on the kill switch pull the choke all the way out and then just barely push it back in just enough to crack the choke plate open. Pin throttle open if your saw has one, and set the saw on the ground and do not drop start the damn thing or your sure to break the plastic starter paws off sooner or later and im betting on sooner! Your saw should have 38 to 41 inches of rope on your spool or you will pull it and when the pull starter comes to an abrupt stop your gonna break stuff! Foot in back handle, one hand on the handle bar and pull that bastard like you mean it! I never pull more than four or five at the most times! But I usually have fire in the pipes by the second pull. And don't forget to push the choke back in! I see this all the time on chainsaws and especially on power washers, men get so damn excited about getting it started that they forget all about turning the choke off

 

[jff]

hi all, just reporting back. Timing looks good, bought a new coil and getting a very strong spark outside of engine now but still not even a pop with gas right down in the chamber. I haven't gotten the spark tester yet but it's supposed to come today. I'm very confused. Only thing I can think of is maybe my compression isn't as good as I think it is? But it got up to 150+ with maybe 3-4 pulls, that seems good to me! First pull was over 100 and that's with the throttle off.

Anything else I should be checking until the spark tester gets here?

thanks