one cylinder (sometimes)Merc 20 HP

[ksurratt]

Howdy, I have a Merc 20 HP 1988 with Manual Start. About 4 years ago it started getting spark to only the top cylinder. I have traded the plug wires and found them both to be good. I checked all the connectors mounted on the side of the switch box. It only does this intermittently. It started doing this when it was idling. I would smack the "switch box" (term from the Merc Service Manual) and it would run on both just fine for several months and then it would do it again. Now it has started to drop the spark at full throttle. It might be out for 1 min or 1 hour, then it will kick back in and run great. Now when it runs on one cylinder I usually let it idle while I'm fishing and pretty soon it kicks in the other cylinder. I took the switch box off the mount and held it in my hand while it was running on one cylinder. I smacked it with a srcewdriver and the spark started again and ran fine. Do I just bite the bullet and buy a new switch box? Are there any outlets for a used one? Thanks for your help and time.

 

[12Footer]

Re: one cylinder (sometimes)Merc 20 HP

No, don't buy a new one until you have removed the old one. When you take it out, look at all the connectors real good, and pay particular attention to the mounting bolt holes. If you ANY of that white corrosion, clean everything up with emery cloth and a dremmel drill with a baby wire brush attachment (they work great for this).<br />All the single connectors can be "re-stressed" with a small nail or pin to make them tight.<br />Re-mount it,and see how it does. If it still acts-up,it must be internal,and in need of a replacement.<br />I hope it's only corrosion.

 

[ol''joe]

Re: one cylinder (sometimes)Merc 20 HP

If you do need a new switch box try the local auto parts store before you go to a merc dealer. I bought a box for my inline 6 for $100 less than the dealers price.