1985 LT250EF CDI Problem

[Snick]

Bought the project a few weeks ago with weak and intermittent spark. I could smack the CDI box with a screwdriver and it would work fine for a few days. Now, the smack trick is not working and machine is running awful with the weak spark and will most often not fire enough to turn the engine over through combustion (cranks very good). I ordered the GY6 CDI to see if I can get it going again as these CDI boxes are way too expensive even used. battery is fully charged and charging very good.

 

Wondering if anyone knows how the GY6 (6-pin AC) CDI would wire to this machine. Attached is the electrical diagram. My confusion is with the green and orange wires sharing the 2-pin connector and the Blk/Red wire that runs to the magneto solo. How would I get AC power to the CDI through pin 1 on the GY6 when the CDI has two wires to the pickup-myabe just try one (orange then green) at a time?

 

 

 

 

^PINOUT:

      5   6

      2   4

     1    3

Edited September 15, 2024 by Snick

[Mech]

The green and yellow are for the trigger coil, and the black/red is for charging the capacitor in the cdi.  If you are lucky the charge wire B/r, will go to what they call "magneto coil" and the two trigger wires ca go on "ignitor" pins. If not, you will have to provide some earths to pins and to one trigger wire.

You may have to swap the polarity in either or both those two sets of wires to get it to go right.

[Gwbarm]

Good project im curious as to the outcome. I have not had much luck at doing this.

[Snick]

Got fire, but timing was way off. Gotta figure something out given the CDI prices for these.

 

I believe this is what I had initially and had no fire, then swapped 6 and 1 and had fire for a minute with timing way off - $8 CDI might be dead:

Pin 6:  Tagged into AC on a yellow wire from magneto

Pin 2: coil

Pin 1: blk/red (Magneto)

Pin 4: ground

Pin3: Open (grounded to 3)

Pin5: kill switch

 

There are so many different wiring diagrams for the GY6 boxes. No idea what is correct, but at $8 it's not the end of the world.

Edited September 16, 2024 by Snick

[Snick]

Next CDI I will try O and G to the "igniter pins" which would be 1 and 3 and B/R to 6 maybe.

Edited September 16, 2024 by Snick

[Mech]

The trigger windings might need swapping around the other polarity to correct the ignition timing.

The cdi fires when it gets a signal from the trigger coil, and on older bikes(like this) it's common for the firing to be triggered by the AC voltage coming from the trigger coil rising to a certain point, then, as the revs and speed of the flywheel magnets get faster, that critical voltage needed to fire the cdi occurs earlier in the rotation, while the magnet is further from the trigger than it had fired at low revs. If the firing was too early, you might need to move the pickup coil further away from the flywheel, and/or, reverse the wires. It might be that the trigger coil is wound such that it sends the wire into a negative voltage leading up to the magnet, then a rising(positive) output after the magnet has been passed. Then you will get ignition timing that is retarded, and that gets more retarded as the revs rise.

Swap the trigger windings first, then if that doesn't get it firing at the right time, swap the capacitor charge wires about. Inside modern cdi there are integrated circuits that count the pulses of AC coming from the stator, and only fire after a certain number of AC waves and then a trigger signal.

To be sure whether the cdi is going to run the bike(and it probably will), then you need to try the wires in all four possible combinations of connection polarity.

[Gwbarm]

The problem i had is they would start and run and idle but would not keep up with the timing advance i figured it may be specific to different engines and gave up.

[Mech]

Old style cdi used the rising trigger voltage to trigger the coil and that then automatically advanced the timing because the trigger voltage is higher at higher revs. The higher voltage meant that it got to the trigger point voltage sooner in the AC wave. Those type cdi could have their timing and advance moved by positioning the trigger coil closer to the magnets.

Later designs use digital components to calculate the revs and advance the timing by a combination of digital and analogue means. These sorts take their initial timing from the point the rising voltage from the trigger stops rising and starts to go negative. Instead of triggering at a certain voltage on a rising wave like the earlier designs, they trigger as the voltage changes from positive to negative. That point never changes and the digital timing control allows a better advance curve.

I'm pretty surer that Snicks bike, and the replacement cdi, will be the earlier design.

[Snick]

Started with the GY6 and the ultimate "FLYPIG" (lol I am not kidding) Racing CDI for $10 to see what happens since they are so cheap. Sounds like Gwbarm has already been through these though. Oh well, I can validate GWbarm for only $20. Found some that are programmable for are $55 but from France.  Thanks for the replies.

 

Is the ignitor to the  Green and orange wire in my schematic and the Blk/Red to the magneto coil? Confusing as it seems the "ignitor" is actually "charging"/powering the CDI box and the magento (blk/red wire) actually sends the signal to fire the coil on pin 2.

 

I would really like to find a replacement solution to the 32900-24510 CDI given the ridiculous pricing.

Edited September 17, 2024 by Snick

[Mech]

Have you provided an extra earth when needed and tested the three wires(and an earth), in each of the four ways they can go onto the cdi ?

[Mech]

The O and G can go two ways onto the + and - ignitor pins, and the B/r and an earth could go onto the magneto pin in two different ways. It gives a total of four ways they could go.

Then it may be that the ignitor pins are meant to be connected to the B/r and earth wire, and the O and G are meant to be on the two ignitor pins. Then there would be another four possible combinations of ways they could go.

You need to try them in all eight combinations of ways...

[Snick]

OK, runs really bad with chinese cdi Gy6 that I thought and hope is dead. Having to hold throttle open a bit to get it to run. Will pull carb and clean just for good measure even though replaced with clean tank, new lines and fuel filter a week ago.

 

Will have a couple new CDI boxes in a few days so I can do more testing.

 

Wiring is blk/red to magneto coil pin 6 and green and orange to pins 1 and 3 on CDI where polarity (+ and -) does not matter.

Edited September 17, 2024 by Snick

[Snick]

Gwbarm, did you try an adjustable?

[Mech]

If you have a timing light check the timing. It could be too advanced or too retarded, but we might be able to get it right by swapping wires ..

[Snick]

Looks like timing is 10BTDC <1700RPM and 35BTDC>3800RPM

[Snick]

This looks promising with 2 programmable timing curves: https://transmic.fr/product/analog-ac-cdi-v28p/

[Snick]

One video I ran across showing the "racing" CDI has 25 degrees of timing at idle all the time. That should at least get a good idle and decent running machine based on the the timing stated in the manual.

[Mech]

No that won't give a good idle.

Edited September 17, 2024 by Mech

[Mech]

Racing engines don't idle, and they don't have centrifugal clutches,,

The timing is set by the trigger coil, and they can't know what the timing is going to be until they know what engine it's going on. I'd keep away from idiots that make claims like that,,

[Snick]

OK,  when this started I had 2 problems at the same time. Main power wire from battery (fused line) was damaged with an intermittent connection when turning handle bars, which I solved. Then, I thought CDI was the problem given the screwdriver smack fixed the CDI a couple times but the problem this time was the chineses carburetor. It was acting up at idle and run good at higher RPMs, so I pulled the carb and bowl...and the low-speed jet fell out! Ugh...and I almost pulled the bowl before I installed it.

 

$8 CDI works fine on this machine.

[Mech]

Ha..  Ok. Well done.

"Perseverance always wins, giving up never does.".

[Snick]

OK, I need to update after the warmed-up test ride. It runs good until about 3/4 throttle, but it really needs more timing after that. Idles OK. I guess one of these $8 CDIs can get you by, I just don't think the $8 CDI is the solution. Waiting to hear back from the guy from France to see if that might work at $54...I think/hope it will as it can be programmed for two timing points, which is what the manual shows for this machine. Will see what I can get from the adjustable Chinese CDIs.

Edited September 17, 2024 by Snick

[Mech]

The cdi will be fine. I doubt that the 3/4 and up problem is timing.

I'd try lifting or lowering the slide needle.

[Gwbarm]

What you describe in post#22 is exactly the problem i had and tried a couple of different ones with the same result. I didnt really try any further.

Harvey Spooner on U- Tube has videos showing how to make them out of GY6 CDi he installs everything in a box with D Batterys and calls it a portable CDI. Very interesting Videos.

[Gwbarm]

I missed your question, the ones i tried were not adjustable.

[Snick]

The guy from France got back to me and I am not sure I understand what he means. He posted this pic and asked "How much is the advance timing?" I told him the manual reports "timing is 10 BTDC when less than 1700RPM and 35 BTDC when greater than 3800RPM" and asked if the timing for the two points could be set to match that profile. Got a little language barrier here.

 

Edited September 18, 2024 by Snick

[Snick]

Looks like this Gy6 CDI is 22degrees at idle and 24ish thereafter using my HF light. I guess that is all we can expect for $8. At least the GY6 gets these back on the trails at a reasonable price.

Edited September 18, 2024 by Snick

[Gwbarm]

Good reasearch!

[Mech]

#27.. you could try increasing the air gap between the trigger coil and the flywheel.

[Gwbarm]

Thats a pretty fancy light for Harbour Freight, i dont have one with the advance degrees on it, i guess its time to upgrade, but i use it so rarely. 

Thanks for the tip Mech, i didnt know you could change the advance by increasing the air gap.