We just got a used sunl 90 that was not running for free. After checking it out and findind a bad safety switch in the brake handle it will now crank over but it is not getting any spark. I searched through the forums here for some help and started checking the cdi with my volt meter.

The kill switch pin on the cdi is open

The timing trigger is around .3 volts when cranking

but where the problem might be is the ac ignition power pin is only getting 30 volts while cranking. everything I have read on this site says it should be getting around 80 volts.

What do I need to check or replace now?

Thanks for any help

 

30 volts sounds very low to me, but I would think that this would cause a weak spark and not a "no spark" problem.

Just to be sure, did you measure the AC power to the CDI with the CDI disconnected? All bets are off if the CDI was hooked up while this was measured.

Is this a picture your CDI?



Measure the voltage on the "kill switch" pin with the CDI hooked up and the engine cranking. This is a complicated waveform with both DC and AC components. Do measure it on both the AC and DC scales and report back.

Measure the resistance through the ignition coil pin on the CDI wiring harness to engine ground. What is it? What it the resistance of the spark plug connection to engine ground?

I actually took one of these 5 pin CDI's and carved off the epoxy and traced out the internals a while back. I did the same thing with one of the 150cc/250cc style CDI's with the 2 pin and 4 pin connectors. The wiring connections and components between the two were so nearly identical (other than the connectors) they were obvious copies of one another. One of these days I will post the schematic(s). I still have to convert it to jpeg format and upload it to photobucket. Anyway I see nothing in the schematic that would prevent the CDI from firing with only 30 VAC coming in.

 

yes I was checking these with the CDI unhooked. I will go out right now and get the other measurements for you.

 

Resistance from ignition coil pin to engine ground is .7 to .9

Kill switch voltage while cranking is AC = .9 to 1.1v DC = .45 to .55

The spark plug connection to engine ground I couldn't get my meter to register anything.... would that mean my coil is bad?

 

I also tried disconnecting the kill switch wire from the cdi to check and see if I had spark then and still have nothing. Pretty sure that it is not the kill switch causing my problem

 

With 30 VAC from the stator you should be getting like 50 volts DC on the kill switch pin. The values you measured are way wrong. You won't get spark with that. Your stator output is low in my experience, but it should still make a spark. The kill switch pin voltages will not.

I'm betting 95% that your CDI is bad. Your symptoms match a shorted C1 or Q1 in the following schematic:



This schematic is generated from a 5 pin CDI that I chiseled off the epoxy and traced out the circuitry just because I was curious. I bought it on eBay for around $12.

The secondary winding on the coil should have resistance, but it is usually quite high. Mine reads 8K ohms (8000 ohms). Are you sure you were on a high enough scale? The resistance is in the spark plug wire path and not the resistance of the secondary wire itself.

 

just ordered a new CDI and will definately let you know what happens when I get it

Thank you for all your help

 

you said that the stator is low....should I go ahead and replace that too or just wait and see what happens with the new CDI.

 

I would wait on the stator. It may work just fine at 30 volts AC. Stators are more expensive and harder to change. I'd go with the easy stuff first.

 

new CDI but same readings.

at this point my son is thinking his 4 wheeler is never gonna work...