testing coils under load

[chewyj]

My 1987 Mercury 70hp will not accelerate past 1/2 throttle. The problem occurs only under a load. My question is whether or not a coil pack could work at idle, but not work under a load? Right now, at idle, I can pull plug wires and get spark to jump 1/2 inch.

 

[sirlespat]

Re: testing coils under load

All I can tell you as the air presure increases so the dielectric strenght increases. it is harder to jump a spark in the compressed atmosphere of the cylinder.<br />When testing sparkplugs use an old plug grounded to the block. if you dont the spark voltage can become higher than normal and in very rare occaisions cause damage elsewhere. Better to look at the colour of the spark at the test plug.<br />Blue and fat = very good spark thin and yellow not so good