1977 GS750 Has anyone ever seen a Dyna S fail? ???

[Andersonspartsplus]

I have a 1977 GS750. 4 into 1 and pod filters. I am experiencing intermittent ignition failure. Cold and Hot. Low RPM and High RPM. It has a Dyna S and the green 3 ohm coils. I replaced the coils last year when 1 of the originals failed. I put almost 4,000 miles on it after that. When the problem first started I removed the carbs and found them still very very clean. I then put a stock coil on both sides and the problem still happens. I checked the output of the charging system and battery voltage, both are good. I traced the 12v power wires to the coils and the trigger wires all seem to be good. All thats left is the Dyna S ignition.

When riding the bike at various speeds and various stages of warm up and running temp it will suddenly drop 2 cylinders. I continued riding it and sometimes it will come back around and run on all four sometimes it happens quickly sometimes it lasts for several miles.

I also tried running it on prime petcock postion to rule out lack of fuel from failing petcock diaphragm. Tried even plugging the vacuum line and running it on prime that way....no dice. Problem still happens on prime.

Has anyone had or herd of a Dyna S failing? Failing intermittently?

Any help or advice would be greatly appreciated.

Thank you

Jim

[Andersonspartsplus]

I also made sure the gas cap was venting properly! It is. No difference with cap on or off.

[azr]

I've had both a dyna S ignition fail (just one of the pickups) and I had one of my dyna green coils fail. Dyna is a great company and rebated me on both products (the ignition was years old but the coil was only a few years old). If you go to their website they give step by step instructions for testing the pickups and the coils. Your problem sounds like either a wiring issue, something is loose and intermittently making contact or one of your pickups is failing. Is the problem consistently with the same two cylinders?

[Coady]

Spark plug worn/gap?? Though this would be more evident at idle. Or a dodgy connection to one of the coils? Or dyna as you suspect.

[chef1366]

Yes I have and a 2000.
Call Raymond at Dynatek and say big Bill from Bako sent you.

[Andersonspartsplus]

Thanks for the info so far guys.

I have swapped and gapped spark plugs twice.

It will idle all day long ( or until I think it is getting to hot ) no problem.

The problem only shows up while riding. Riding it cold or hot makes no difference it just happens. Just cruising low RPM's or Balls out it just seems to crop up.

I have swapped both coils with known good coils and the problem still persists.
The biggest problem is that since it wont do it in the garage I am having trouble diagnosing it.

My latest plan is to use a noid light in the spark plug wire. When she falls on her face if the noid is flashing i will move it to another plug wire and so on. I have had a coil fail and this feels very similar except that even when hot it will straighten out and then for no reason and no certain amount of time or miles it drops a duece.

Does any of this make sense?

Has anyone had similar symptoms when their DYNA S failed. On and off kinda thing?

[bwringer]

I saw a Dyna ignition fail when it got hot.

After chasing an intermittent failure for a while, we left the ignition cover off and rode 20+ miles on a cool day with no problems.

Popped the cover back on, and one pickup stopped working within a mile. We repeated the experiment a few times to make sure.

I believe Dyna sent the owner a new one without too much fuss and all was well.

It happens.

[kdo58]

mine failed went back to points, I dont like being stranded on the side of the road.

[chef1366]

If you call dynatek and have a multimeter they will tell you an easy way to test both coils.

[Andersonspartsplus]

Ok guys,
I used a noid light in line with the plug wire on number 1 cylinder. Went out for a ride and when it dropped 2 cylinders the noid light quit flashing. Back to the shop, switched plug wires and coil leads to fire 1 and 4 off of the other coil. Rode it for about 10 blocks and it dropped 2 cylinders again and the noid light was not flashing. I have checked all the connections very carefully. I believe I have narrowed it down to a faulty Dyna S.

This thread is not a shot at Dyna in any way. I have used several Dyna set ups and all worked great.

This is a 1977 GS750B. The Dyna S was installed on the bike when I got it. I have no idea how old it is although it looks brand new. I have seen ignition modules fail on cars that were only a couple of years old.

I still think Dyna is a great company especially with tech support. I will be replacing this Dyna S with another Dyna S that has a 1 year warranty.

An inline spark plug noid light is a great addition to any tool box. They are only a few dollars and let you see exactly whats happening with the spark.

Thanks to everyone!