Help GSX250 1981 Only one spark - Ignition Coil?

Hi all. It's my first post but I'm sure won't be my last as have a GSX250 bobber project on the go.

Long story short, the bike wiring was a total mess. Twisted wires together then covered with tape running all through it. I've decided to strip it out and rewire it properly but before I do I want to get it ticking over so I took out old electrics and wired in a basic running circuit.

After pressing the start button the starter motor kicks in but engine doesnt fire up. I took the spark out and tested them only to find I'm only getting a good spark on the RH plug. Checked the LH plug but no spark. Stuck the working RH spark plug into the LH HT leads but no spark. This makes me think it's a bad coil? The resistance of the primary winding is fine on both coils but the resistance of the secondary winding for both coils is around 17k ohms when the manual says 23-25k.

I would love to know any thoughts or further tests I can do to resolve the spark problem. Any help would be greatly appreciated!

 

Great link! Thanks. I'll give that a go

 

Awesome, will check them out!

I can't do any checks until Friday but I did check before and know that both coils are getting power. One thing I did notice was when I checked the volts through the spark plug caps, one had a constant 12v-ish reading (the one that doesn't spark) and then press the start button it actually drops in volts whereas the working side has a very small/if any reading and then when I press the start button the volts jump way up, as I would have expected. Thoughts?

I appreciate the input so far!

 

Will swap coils over and see what that does. Will post update once I have tried that.

 

Okay so first go back at the bike today. Swapped the coils over and boom, the coil that worked now doesn't and the one that didn't work now does, which means the coils work so it's the wiring further back (thanks for that suggestion!). After a little testing with a multimeter I've ended up back at the Ignition Control Unit, and more specifically the B/Y wire that feeds into it from the coil. Weirdly I'm getting a 4.94v reading from the B/Y coming out the Ignition Control Unit whereas the White wire (the other one that feeds into the other coil and works) is coming back as 0v - I assume that being what it should be unless I hit the start button.

Am I dealing with a faulty Ignition Control Unit or does the issue go back to the signal generator? Any checks I can do?

Thanks again so far!

 

Thanks ruckusman. Just to clarify you're thinking is the issue lies with the the main ignition transistor? Are those replaceable/repairable?

 

Unfortunately, my unit is epoxy backed so it will be a hard time getting into it. There is a youtube video detailing how to get into one by using heat to work it off but looks quite messy! I'll see if it's feasible first, else I'll be looking at trying to source a second-hand unit I think.

I noticed on the thread you shared that @Brendengra mentioned that both the 32900-44410 & 32900-47020 units are possibly compatible with the gsx250 - is there any way of confirming this please? My current unit is labeled as 32900-47026 with a 1984 date so obviously isn't the original unit for my bike but means units around that year seem to be compatible, I have attached a photo.

As always, thanks for the help so far everyone

 

I had a go at the Ignitor box but it was caked in Epoxy and a nightmare to try and get apart (without breaking it). I've checked out Carmos unit as well as trying to source a second-hand unit but coming up pretty pricey, which is when I came across a company called Boyer Bransden. They sell digital ignition systems for GSX250s as well as a bunch of other bikes for a decent price (£139) with a 5 year guarantee (http://www.boyerbransden.com/microdigitalmicropower.html). It actually just arrived so will fit today and let you know how it goes. Anyone else had any experience with these?

 

Ahh, they've been around a while then. Good to know!

Fitted it today and sparks on both plugs, happy days!! Just gotta refit carb I cleaned yesterday and fingers crossed the thing fires up. I'll then need to set the ignition timing properly, will give this forum a search for any threads on the subject - however, I do have the workshop manual.

Appreciate all the help up until now guys

 

Update: Put everything back together but still not getting the bike to start.

I'm getting strong spark on both new plugs, the carbs have been cleaned, the timing has been set. I turned the engine over with a little easy start into air intake bit still nothing which means it's not necessarily a carb issue. The battery was fully charged. Have ordered a compression kit to test the cylinders as it's the only thing I can think left to check.

Looking for any other suggestions? Bit of a head scratcher to be honest.. I was pretty confident it'd fire up.