2 dead cylinders

[bmstang]

I have a 1978 evinrude 235hp all cylinders change pitch when i disconnect the plug wires except 1 & 3. 5 back fires and spits at times all electrical ends check out great spark and tried swapping coil packs did not help. Motor only powers up to 1900. I figure it's the 2 cylinders and probably cylinder 5 but what could be the problem any help on this would be great thanks.

 

[Barnacle_Bill]

Re: 2 dead cylinders

Do a compression check.

 

[emdsapmgr]

Re: 2 dead cylinders

After your compression check, see if the dead cylinders are getting fuel. Are #1,#3 plugs wet or dry? An inductive timing light is good to show spark on each plugwire. It will show misses and nofires. Swap the two identical power packs and see if the ignition problem moves to the other head. If it does-replace the pack.