1994 4.3 Merc I/O Intermittant Engine Problem Under Load

[Yet2sail]

My 94 twin 4.3 engine Carver will run fine at first with no problems at full throttle. If we cruise for a while 10-15 min at 1200 rpm and then try to power up the starboard motor won't go above about 2000 to 2400 rpm. If I push it above that it will almost die until I back the throttle off and then I can get it up to low 2000's again. We smell gas when this is happening. If we stop for 10 15 minutes motors off, it will run fine again. I looked at the choke and it is wide open. It runs fine at the low 2000's but won't go above that. I can see the tach bouncing around when it is stumbling. I see it has electric fuel pumps. I don't know if its fuel or ignition. Because we get a strong fuel odor, I would think some kind of heat related ignition problem? I just don't know. Any ideas or suggestions? Thanks much. Terry.

 

[Bondo]

Re: 1994 4.3 Merc I/O Intermittant Engine Problem Under Load

My 94 twin 4.3 engine Carver will run fine at first with no problems at full throttle. If we cruise for a while 10-15 min at 1200 rpm and then try to power up the starboard motor won't go above about 2000 to 2400 rpm. If I push it above that it will almost die until I back the throttle off and then I can get it up to low 2000's again. We smell gas when this is happening. If we stop for 10 15 minutes motors off, it will run fine again. I looked at the choke and it is wide open. It runs fine at the low 2000's but won't go above that. I can see the tach bouncing around when it is stumbling. I see it has electric fuel pumps. I don't know if its fuel or ignition. Because we get a strong fuel odor, I would think some kind of heat related ignition problem? I just don't know. Any ideas or suggestions? Thanks much. Terry.

Ayuh,.... Welcome Aboard,... Disconnect the tach, 'n Try it...

If it runs right, Change out the tach...

 

[Yet2sail]

Re: 1994 4.3 Merc I/O Intermittant Engine Problem Under Load

I would have never thought of that. Funny thing is, it is duel helm so there are two tach's with these sync gauges to tell you when the motor rpm's are out of sync. I will try to disconnect the tach signal at the motor just to see at first and then go from there. Thanks a boat load for that suggestion. By the way this boat is new to me so just trying to working out the kinks. Of course it didn't do this on trial. Terry

 

[Bondo]

Re: 1994 4.3 Merc I/O Intermittant Engine Problem Under Load

I would have never thought of that. Funny thing is, it is duel helm so there are two tach's with these sync gauges to tell you when the motor rpm's are out of sync. I will try to disconnect the tach signal at the motor just to see at first and then go from there. Thanks a boat load for that suggestion. By the way this boat is new to me so just trying to working out the kinks. Of course it didn't do this on trial. Terry

Ayuh,.... Sounds Good,... Keep Us posted on yer progress,...

 

[Yet2sail]

Re: 1994 4.3 Merc I/O Intermittant Engine Problem Under Load

Ok, first thing is I took out plugs on one side to check. Looked a bit dirty and blacker then I would like. Then I checked fuel pump output 1&1/4 quart in 30 sec. which is good. I did this at home. Then I disconnected the tach signal wire off the coil. Went to the river and ran around for quite a while with no problem. Then the stbd engine started acting up where is wouldn't go above 2200 to 2500 rpm. I pushed it and kept stressing it until the engine died and it wouldn't restart. First time it did that. Checked if it has gas and it did. Went home and I haven't looked any more. Since the stbd engine has a new coil the previous owner was trying to fix this problem is my guess. Not sure how to debug the Merc ignition.

This is a 94 4.3 with 4 barrel carb. Don't know what version ignition this is or how to debug what is bad. But now I can look at it on muffs. I was going to search on here a little but if you have some pointers that'd be great.