Msd 4270 total loss issue

[Yz250fpilot]

I’ve got the older 4270 total loss installed on my Yamaha. While out riding last weekend, I bailed and the ski cut off due to the lanyard yanking off. When I got back on, it started right away, but immediately started to seem like it was only firing on one cylinder...then died within about 3 seconds. It turned over fine, but I could not get it to start back up. I switched out the plugs, and it still would not run. It is still getting fuel to the cylinders, but while turning the motor over with the plugs out and grounded, I only got a single spark with cranking it intermittently for a couple minutes in total. I tried a different coil (generic) that is new and never used and I still got no spark. I also cleaned and checked all my hot and ground connections. They are good.

I pulled the whole setup out of the engine bay so I could see the light on the brain, and it seems good. I also pulled off my flywheel cover anticipating possibly having to remove the flywheel because of a pickup problem. I applied power to the unit and the led lights up. I plugged my lanyard in, and the light goes out. I spun the flywheel/crank by hand and the led lights up when the magnet on the flywheel is over the trigger pickup.

Does anyone have any thoughts about what I might have going on here.

Also, another question, is it possible to move the flywheel back and forth by hand fast enough to get a spark when the magnet is going back and forth over the trigger pickup. I tried it, but still got no spark.

 

[Yz250fpilot]

The battery has been performing well. It is only about a month old and has about 3 hours of run time on it. It is fully charged.

 

[Yz250fpilot]

I have a ground wire attached to my coil base. I cleaned it also.

 

[Jr.]

Bad trigger. I ran that system for years. Happens on a regular basis.
I have triggers in stock and can get one out today if you don't have a spare?

Ski Ya, Paul

 

[Sasquachcrap]

Bad trigger. I ran that system for years. Happens on a regular basis.
I have triggers in stock and can get one out today if you don't have a spare?

Ski Ya, Paul

Paul, could it be a bad trigger? He did say when turning it over by hand the light on the brain comes on and off. And it to the original post I believe your brain is bad. You do not have to turn the flywheel over at any speed to initiate a spark. You should be able to Rotate the flywheel by hand and if the light comes on the plug should spark. You can mimic this byJumping to pick up wires on and off and seeing if you have fire.

 

[Jr.]

its a bad trigger. they act very weird when they go bad like this. will act normal when they have a long dwell time, as in rotating by hand.
keep in mind, this is an analog brain, not the digital.

P

 

[Yz250fpilot]

its a bad trigger. they act very weird when they go bad like this. will act normal when they have a long dwell time, as in rotating by hand.
keep in mind, this is an analog brain, not the digital.

P

I guess I'll cut the trigger wires and short 'em. That will be a definitive test on the trigger.

 

[Yz250fpilot]

Shorted the wires. The result is the same. The light comes on, there is a small click in the brain, and no spark is produced.

 

[Yz250fpilot]

And the winner of today’s trivia is.....


chupacabracrap!


I got another brain and wired it in.....shorted the wires... we have sparkage!

Thanks to everyone who chimed in on this topic. I need to go get some watertight connectors now and get this new (to me) brain wired in.

 

[Jr.]

Not s fast! Again, my experience! Change the trigger! They can and will fry the brain!
This is how most triggers short out, ( see pic below) If you changed the brain, but left the trigger?
My guess is you will loose another brain in a fairly short time span!

 

[Work&Play]

I just wanted to chime in on this conversation because it was very helpful. I have been chasing issues with my superjet 760 with an old analog 4270 total loss.
About a month a go I had a great ride with it, put it away, took it out the next day and it wouldn't start? After wiggling all the connections the best I could do was to have it backfire and still not start. I ended up pulling the carbs and rebuilding them, setting the pop off pressure, re-timing it, numerous times, then slowly rotating the flywheel and watching the re light come on as the magnets went over the flywheel as it was supposed to do. Sometimes it would come close to starting but it would run like crap, missing and backfiring. I finally got a new pickup, re-timed it, put it back together and low and behold it started! I took it out on the lake, adjusted the carb high and low settings and so far it is perfect!
The old pickup looks fine, no broken wires, no nicks in the wires from the flywheel, it looks just fine but IT IS NOT FINE! Thanks for all of you who added input to this thread, I know it is old, but for those of us still using the old analog MSD, this thread is an awesome resource! If your having timing issues, CHANGE YOUR PICKUP!

 

[Jr.]

I just wanted to chime in on this conversation because it was very helpful. I have been chasing issues with my superjet 760 with an old analog 4270 total loss.
About a month a go I had a great ride with it, put it away, took it out the next day and it wouldn't start? After wiggling all the connections the best I could do was to have it backfire and still not start. I ended up pulling the carbs and rebuilding them, setting the pop off pressure, re-timing it, numerous times, then slowly rotating the flywheel and watching the re light come on as the magnets went over the flywheel as it was supposed to do. Sometimes it would come close to starting but it would run like crap, missing and backfiring. I finally got a new pickup, re-timed it, put it back together and low and behold it started! I took it out on the lake, adjusted the carb high and low settings and so far it is perfect!
The old pickup looks fine, no broken wires, no nicks in the wires from the flywheel, it looks just fine but IT IS NOT FINE! Thanks for all of you who added input to this thread, I know it is old, but for those of us still using the old analog MSD, this thread is an awesome resource! If your having timing issues, CHANGE YOUR PICKUP!

to add more to this, i have been working to understand the MSD triggers for work im doing on a new system. I ran oscilloscope on the triggers as system was running. On the newer prodigital systems, the triggers actually show short circuiting within the trigger itself. I believe this leads to triggers failing, but more importantly, the reason the prodigital brains fail. Not an issue on the older analog brains.
just replace the trigger and enjoy the ride. Btw, If your interested in spare 4270 brains ? I have several I would sell at a very good price.