CDI coil pack issues

[Sprocket86]

Could a defective CDI coil pack cause a lack of higher RPM's but other wise run fine at idle and slower RPM's?

Something is not quite right with my Lawn Boy Duraforce 2 cycle engine that I have adapted for use on my Sprocket mini bike.

The CDI coil pack high tension lead was pinched and I repaired it with heat shrink. I had no spark when I started this build and then one day I was spinning the engine by hand and all of a sudden I had spark. I have my suspicions here.

 

[ole4]

I had a defective CDI on a hs50 and it was tough to figure out. I at first thought it was a jetting issue. Would start and run fine then as engine warmed up start misfiring till it would not run right at all. Replaced it after eliminating everything else.

 

[FirePowerMinis]

Could a defective CDI coil pack cause a lack of higher RPM's but other wise run fine at idle and slower RPM's?

Something is not quite right with my Lawn Boy Duraforce 2 cycle engine that I have adapted for use on my Sprocket mini bike.

The CDI coil pack high tension lead was pinched and I repaired it with heat shrink. I had no spark when I started this build and then one day I was spinning the engine by hand and all of a sudden I had spark. I have my suspicions here.

I can't recall if the DF was included, but coil failure was a problem on the LB. Guys speak of baking them as a temp fix. Internal wire breakage, I think. DF, pretty sure, uses a 2-stage ignition, retarded for starting, advanced to run.

 

[metal man]

Ya its sounding like a bad coil ya got one to swap out and test ¿

 

[Sprocket86]

I had a defective CDI on a hs50 and it was tough to figure out. I at first thought it was a jetting issue. Would start and run fine then as engine warmed up start misfiring till it would not run right at all. Replaced it after eliminating everything else.

I'd like to replace my coil with a O.E.M one but I'm still not 100% this is the problem. I know these coil packs have issues and do go bad but it's mainly a no spark, no start issue. My engine just won't rev up lets say past 3k!!

 

[Sprocket86]

I can't recall if the DF was included, but coil failure was a problem on the LB. Guys speak of baking them as a temp fix. Internal wire breakage, I think. DF, pretty sure, uses a 2-stage ignition, retarded for starting, advanced to run.

I googled the issue and it appears that the DF engine had issues with ignition coils. I did read on the 2 stage ignition and I'm wondering if the 2nd stage is giving me problems. It almost seems like the engine hits a wall and just stops climbing in RPM'S. I'm beginning to wonder if the Comet Tav is somewhow holding the revs back. I even does this when I hold the back wheel off the ground and pin the throttle WOT!

So it's not a load issue. The engine also seems to run really rich at times. I also suspect the pop off pressure is set to low on the Tilly carb and that my crankcase pulse fitting to the carb is not needed or is providing to much fuel pressure. My fuel tank sits higher then the carb but the fuel line still has a spot that it runs higher then the carb so I figured I would need the pulse line for suction. Lawnboy Biker, where are you lol!

 

[Sprocket86]

Ya its sounding like a bad coil ya got one to swap out and test ¿

I'd like to try this but I have no spare coil to test. These coil packs are known to go bad. If mine has failed, it has done so in a uncommon fashion.

 

[bikebudy]

Not the same CDI pack but, yes I have had a CDI have good spark until the higher RPM range.

So it could be that. I tested by using a inline spark tester that lights up.

When at low RPM the light was bright, then after a certain point in RPM high range, it would fail and go to half bright.

I replaced the CDI and all was good.

 

[Sprocket86]

Not the same CDI pack but, yes I have had a CDI have good spark until the higher RPM range.

So it could be that. I tested by using a inline spark tester that lights up.

When at low RPM the light was bright, then after a certain point in RPM high range, it would fail and go to half bright.

I replaced the CDI and all was good.

Hey this sounds promising and thanks for the info. I'm pretty sure I have one of those inline spark plug testers. I'll try that out and report back.

 

[Sprocket86]

Sorry for the delay on my findings. So I think my test results are narrowing down my lack of performance issue. I installed the inline spark tester and ran the engine. The light in the tester is very dim but it's consistant throughout the RPM range.

If I remove the spark plug and place it on the cylinder head I do get a nice blue spark and you can hear it. I tried the spark tester on a electronic ignition equipped 3.5hp briggs flatty and the light was much brighter.

What do you guys think?

 

[Havasu Dave]

I think you have a weak CDI. Lack of, or weak spark under compression is indicative of this. That's what that in line tester checks for you.

It takes more voltage to fire the plug under compression than it does sitting on top of the block and grounded.

 

[ole4]

If it is a weak spark couldnt you close up the plug gap to .012 to .015 and see if it runs better? If it runs noticeably better then it proves you have a weak spark.

 

[Sprocket86]

I think you have a weak CDI. Lack of, or weak spark under compression is indicative of this. That's what that in line tester checks for you.

It takes more voltage to fire the plug under compression than it does sitting on top of the block and grounded.

Yes and this makes sense. I tried the inline tester with the plug installed, engine running and with it out of the head just grounded to the block. Both tests had the same brightness.

 

[Sprocket86]

If it is a weak spark couldnt you close up the plug gap to .012 to .015 and see if it runs better? If it runs noticeably better then it proves you have a weak spark.

I could try this and see what happens. Thanks for the tip.

 

[MB165]

lawnboy has a history of CD modules crapping out on the 2cycle engines........... have checked your exhaust ports and muffler for carbon buildup??

 

[Sprocket86]

lawnboy has a history of CD modules crapping out on the 2cycle engines........... have checked your exhaust ports and muffler for carbon buildup??

Hi there. I've read a lot about these failed coils and even my local small engine shop says it's a random thing. They believe the failure happens when you shut off the mower (aka, grounding the kill wire). I ended up buying a new coil yesterday and the new one looks quite different from the old one. Says "Made in Germany" so I think it's a quality piece.

Well my LB duraforce engine is a brand new short block and this is my current exhaust set up, it's also new. She's clean as a whistle lol.

 

[MB165]

yup your good on the plugged exhaust thought....I think there were two coils which would interchange and they look the same. I don't remember if its for the newer or old C/D models, something different internally. that German coil might be a prufrex?? never had any of that brand come back dead. or doa out of the box, hope there's no rev limiter in it. just curious, what carb are you running?

 

[Sprocket86]

yup your good on the plugged exhaust thought....I think there were two coils which would interchange and they look the same. I don't remember if its for the newer or old C/D models, something different internally. that German coil might be a prufrex?? never had any of that brand come back dead. or doa out of the box, hope there's no rev limiter in it. just curious, what carb are you running?

I'm running a Tillotson HL-239b diaphragm carb that's gravity fed. Yes I hope there is no built in rev limiter either! It could be. Has the letters P X S or something close to that.

 

[MB165]

how is it configured to get fuel into the metering chamber? where does the pump driver port go?
put it up on a stand and when it starts to level off on rpms, try and spray some carb cleaner in the intake and see if it speeds up.

 

[fillup]

had a new plug lately two stoke can ruin a plug fast try simple first fillup