Weak spark

[Daz1981]

Hi all,

I'm brand new here so go easy on me ;D

I have a 1990 XTZ750 and I cannot solve the issue of a weak spark. I've replaced the generator, the pick up coil, the ignition coil, the rectifier, the spark plugs and caps. The CDI unit has been repaired. However none of this has solved the issue.

If I take off the spark plug caps and short the HT lead to the frame I get a good spark, but when I refit the cap and plugs its back to a weak spark. ???

Can anyone help me with this issue? I'm at the point of tipping petrol on it and setting it alight.

Regards

Daz

 

[Koinz]

Any chance you have high resistance in the plugs. You can try non-resistor plugs for troubleshooting purposes. Make sure the gap is correct as well.
Make sure you have a good ground from the engine to the frame. Sounds like you replaced every other part that could be a problem.

You may have to light it up ???

If your trying to solve a non-start issue, compression could be a culprit as well.

 

[autoteach]

there is a resistor in the plug cap. there may be a chance that those are bad. Check and verify.

 

[Don in Lodi]

Good arc to chassis ground... how do you know you've got weak spark when hooked up? Are you grounding a naked plug so you can see the arc? '90, as mentioned, it's prolly a non resistor copper core that's meant to be in there. If it's just spinning over, there are two more sides to the triangle, fuel and air, and all the variations there of.
I think I see, are you unscrewing the cap from the cable to see the arc?