80 hp cuts out at 3000rpm

[johnwilli]

divo,(7/16) I feel for you for I have a similar senario that I've been working on for 3 weeks. I have a 1972, 80 hp Mercury sn #3189988 which ran good. The original 33 year old trigger and switch block went dead and I had it replaced with after market CDI by a competent mechanic. After a dozen good outings the engine began to stumble and stalled and the bulb collasped. Placing it back into neutral the engine fired up and pumping the bulb helped. First thought-fuel! Read many articles on fuel systems and their affect in the forum. Rebuit the carbs and fuel pump, replaced fuel lines, bulb, tank vents, compression are all at 145psi and followed Clams Canino instruction for syn to the tee many,many times. New plugs and wires are all firing with same color and lots of spark. Engine fires up with little choking, idles fine and quiet at 4BTDC, max retart at 23BTDC with remote starter, carbs open properly. Stator is for charging only. Engine begins to hesitate staring at 1500rpm on up to 3000. Then it quits under load. Bulb is now hard. Could these old reeds be responsilbe or do I need to go to the trigger/switch block route. These performed fine setting up syn, but with no load. Loading is the only common element, but! Forum has great feedback.

 

[79 Silverline]

Re: 80 hp cuts out at 3000rpm

Did you ever stick a timing light on it? I'm having a very similar problem myself, and I notice that it's dropping spark when I get on the power. It idles pretty well, but refuses to run once you open the throttle past a certain point - completely reworked fuel system from the tank to the carbs. I suspect that the trigger (or maaaaaaybe my brand new CDI switchbox) is getting funky. I'm going to replace my switchbox and trigger (I sorta had an accident that cooked them, so I have no choice) and we'll see what happens. Good luck with it.

 

[johnwilli]

Re: 80 hp cuts out at 3000rpm

This evening in the darkness I ran the engine to check for sparking - nothing. Used my timing light on each spark plug and all were firing. My timing at idle is 4 degrees and steady and max out is 23 degrees and again stable. Both were measured under load. The engine was stumbling all the way to 23 degrees and finally died at 3500rpm. I am in the water tied to a dock. Can tis still be fuel starvation. Do the reeds affect fuel metering????????????

 

[79 Silverline]

Re: 80 hp cuts out at 3000rpm

Sure they were firing, but did you check really closely to see if it's missing? Hard to catch, but when I put the light on mine, there was a very subtle miss at idle, hard to tell until I throttled it up to the point where it starts cutting out - then you could see big gaps in the flashing light. If the timing light is showing perfect spark that's timed perfectly, you'd think that the ignition system is ok.<br /><br />As for the reeds, I read a post where Clams Canino said that reed problems show up as low RPM/idle problems. I know you said you rebuilt your carbs and replaced the whole 9 yards on the fuel system, but did you replace needles and seats? Mine were sticky and did all sorts of wierd stuff, including leaving me stuck in the middle of the water once.<br /><br />It's gotta be spark, fuel, or something with the motor.

 

[johnwilli]

Re: 80 hp cuts out at 3000rpm

All along it was the rectifier. The home page fop CDI Electronics has a downloadable manual and in the manual it states the voltage must be within 12 - 16. I've seen 20 volts on my meter so I pulled the darn thing and it didn't check out.<br />Thanks iboats for this forum.