Not sparking every rotation
 

I have an issue trying to start and keep running my 3W 80 with rcexl ignition unit.

If i manage to get it running it runs fine at top end and will tick over for a short while but then die.

Upon investigation I've found that it sparks on some revolutions but not others.

I've tried different ign units and different plugs and no difference. Also the pick up is brand new

Any thoughts welcome

How are you testing? Turning by hand? If so, newer versions of the Rcexl ignition won’t fire dependably when the prop is turned slowly. How is the plug cap? If the insulation is brown or black or if the cap has ever contacted anything, it could be bad and should be replaced. Caps are the most common failure on ignitions.

With the plug out (no compression) it should be possible to spin the engine with an electric starter or a cordless drill. Check if it misses sparks under that condition, because as Truckracer says, leisurely flipping by hand, you will or won't get a spark depending on how quick the flip is. If you flip by hand as if you are starting (vigorously), you should get a spark every single time.

must admit that i'm only spinning it over by hand so maybe that the issue. Its just that when running and ticking over and suddenly dies, its like it doesn't spark for a rotation.

maybe i need to check the timing again and fuel feed

Cheers

Sparking through the cap insulation can cause that. But then a number of other problems can also cause that. What does the silicone insulator inside the cap look like?

Thoughts, yea start here:
when was this engine made?
single or twin?
what ignition was it supplied with?
what prop do you have on it?
The reason for most of these questions is the old ignitions for 3W's were not driven by hall effect sensors. All our arms got tired one day trying to start a 3W that had been changed over the winter by the new owner. He just screwed the hall effect sensor in the holes for the old sensor. I put the prop at TDC to quick eyeball the timing and boy was it off. I unscrewed the sensor ziptied it in about the right place and the motor ran great. So sensor brackets are now available for older engine conversions (just if that is the case).
Other reasons I will think about for awhile.

I would try to readjust the low end needle and check rpm with a tack. Maybe your just trying to run it at to low of rpm?

Just wondering if there is progress or update on this?