1985 LT250EF CDI Problem

[Mech]

It only works on older style systems as described in #8 Gw. And it can change the base timing at the same time as the advance, but how much it changes the base(or advance) varies depending on how high the trigger voltage the cdi needs, and how many windings there are on the trigger winding.

[Snick]

Gun is great for checking ignition modules. Shocking how unreliable the GM ICMs are.

 

 

[Snick]

Got the adjustable purple CDI and did some more testing. It actually has a curve, which was a surprise. When adjusted fully counter-clockwise it has about 20 degrees at 1600 RPM and 54 degrees at 3800 RPM. I chose 3800 as that is what is reported in the LT 250 E (85-86) service manual. However, the curve just continues to the moon and can achieve 60+ degrees as the engine speed increases beyond 3800.

Edited September 20, 2024 by Snick

[Gwbarm]

Does it run well at that setting

[Mech]

What do the bearings sound like, and is it smoking yet ?

[Snick]

It has full revs with the purple adjustable CDI, unlike the $8 CDI (static 22 degrees) where the engine falls off about 3/4 throttle. Have two more coils in the mail to check timing curve on before I take out for test runs. I hesitate to say it runs well without test driving. Worried the advance is too much on the purple one, but I will just keep a eye on the jug temp.

 

I haven't noticed any bearing noises this far ( about 3 miles) and I don't see any smoke. 6000 mile machine.

[Mech]

Too much advance breaks compression rings and destroys big end bearings.. It doesn't have much effect on temperature.

Coils don't affect the timing.

You have about twice the advance your bike is meant to have at idle speed, and more than it's meant to have all through the range.

Manufacturers have worked out how much advance engines can stand, and what's best for them, and trying to better all the years and years of testing and accumulated knowledge isn't a good idea.

You should try to tune it close as you can to specs. The consequences will be dire if you don't.

 

[Gwbarm]

53 minutes ago, Mech said:

Too much advance breaks compression rings and destroys big end bearings.. It doesn't have much effect on temperature.

Coils don't affect the timing.

You have about twice the advance your bike is meant to have at idle speed, and more than it's meant to have all through the range.

Manufacturers have worked out how much advance engines can stand, and what's best for them, and trying to better all the years and years of testing and accumulated knowledge isn't a good idea.

You should try to tune it close as you can to specs. The consequences will be dire if you don't.

 

The very reason i decided to spend the money and get a new one.

[Mech]

Good idea, and what I'd do with any slightly newer bike.

The older ones though can often be got to run pretty well with some other bike's cdi. They all(even the later ones), run very similar timing and curve. If the capacitor gets enough charge, and the trigger coil produces adequate voltage, we can tweak things and get them to run close to specs.

[Mech]

My sons have spent countless hours at the dinner table discussing and debating what they were going to do next to get some bike running by a combination of slotting the mounting bolts so the trigger coil could be advanced and retarded, and then how much air gap it should need to get the right curve. It's a process I've been through probably a dozen times, and they have been through scores of times(not all as successfully as me though.. haha. I know when to quit).

[Snick]

Seems to have full power with the purple adjustable CDI set to the least aggressive timing (counter-clockwise). I think it is still too much timing, but this is way better than the 22degree static $8 CDI.

 

Still waiting on 2 CDIs and will update again when I get some timing info from them.

[Snick]

"New Racing C.D.I." (blue non-adjustable) is about 80 degrees at idle (1600RPM) with little to no change when increasing engine speed. I tried two of these as the timing was so ridiculous on the first one; they are both ridiculous.

[Mech]

Nothing runs at 80 degrees advance.

Check/test your light.

[Gwbarm]

What RPM is full power on your machine.

[Snick]

Last one I am testing is the TRC 9745. Idle (1600) has 23 degrees where 3800RPM has about 80 degrees.

 

Overall the purple 6 pin CDI is the best replacement option at about $13 to replace the Suzuki 32900-24510.

[Mech]

If an engine has 80 degrees of ignition advance... it doesn't run.

[hfrost112]

might need to try this