Miss when trim is active

[allout]

Hi, I have a 85 merc 140 hp 4cyl.. The problem is when it gets hot @ higher speeds it misses and falls on it's face when I use the trim..There is a slight miss without the trim but not nearly as bad..New plugs, cap, rotor, points..Alos valve noise, sounds like spark det from bad gas but put a tank of 93 oct in it..boat did sit alot before I bought it..Thanks any help would be great..l feel it may be a coil...

 

[Don S]

Re: Miss when trim is active

The problem is when it gets hot @ higher speeds it misses

How hot is hot? If just normal engine temp, I would start by checking all the ground cables going to the battery. Sounds like they may be loose, corroded, or deteriorating cable ends.
Also check the alternator belt, is it tight? It runs the alternator and the circulation pump. You could have low voltage, and a slipping circ pump would cause it to overheat.
I would also do a compression test, and check timing and advance timing. Has it had a full tuneup lately?

 

[allout]

Re: Miss when trim is active

normal temp, not overheating. Alt belt is new and tight. Just tuned it up. Also never had a slow crank due to a low battery..battery is new also. Havent done a comp test or leak down test yet.