Bogging down at speed

[crookedmullet]

I've got a 1991 80hp 3 cyl. Merc that I just can't seem to get running right. I've replaced, all fuel connections, fuel filters, spark plugs, cleaned all carbs(completely taken apart), new diaphgrams in the fuel pump, and the compression in all 3 cylinders are great. At idle, the engine runs like a charm. At the beginning of the day, it will run at full speed for a mile or so and then bog down. The rest of the day, it will never get back on plane. I've checked the fuel and there's no water present. What can make my engine run better? <br />Any suggestions would be greatly appreciated!

 

[BF]

Re: Bogging down at speed

maybe an electrical problem or bad spark plug is causing spark to fail once it gets hot (?) have you checked the spark on all 3 cylinders once it starts acting up? When it runs bad is there one plug that looks oily? Is it overheating? (Water pump been serviced?) Is the fuel line OK (sometimes the bits in the primer bulb come loose and and intermittently block the flow). Is the vent on the gas tank clear?<br /><br />Those are a few ideas.<br />HTH,<br /><br />Brent

 

[crookedmullet]

Re: Bogging down at speed

I know it's not overheating, cause I am getting good flow. I haven't checked the plugs after it acts up. I will now though. I have a personal hate for primer bulbs. When I was rigging my boat, I had to purchase 3 bulbs all at separate occasions cause they were all restricting flow. Thanks for the suggestions, I'll will try them out.

 

[crookedmullet]

Re: Bogging down at speed

update:<br />After talking to a few people about my engine troubles, they suggested that the powerpack may need to be replaced. If that's the case, why would it run at speed for a short while, and then bog down? Any suggestions?

 

[red10]

Re: Bogging down at speed

it could possibly be a bad coil since it runs fine when cold then it heats up and resistance goes higher and less output

 

[mark.24zg]

Re: Bogging down at speed

CM,<br /><br />It sounds like your experiencing a similar prob as me. I to have checked my fuel lines, changed water & fuel pump, compression (good), spark (not after subsequent problem). People had even told me it could be the reed valves, but a mechanic explained that you notice poor idle and popping as pressure vents back through your carb etc..<br />Mine will be back on the water shortly and I'll keep you informed if I make any progress please do the same. E-mail add can be available <br /><br />Lata <br /><br />Mark

 

[Hank 911]

Re: Bogging down at speed

At the beginning of the day, it will run at full speed for a mile or so and then bog down. The rest of the day, it will never get back on plane. <br /><br />CM <br /> I went through that with my bass boat(glass). Same symptoms. It had a small chip on the bottom and was taking on water into the hull. Didn't get full but it sure affected the performance. Just a thought.

 

[randycc58]

Re: Bogging down at speed

power packs and coils both can heat up and break down after running for a while. If you suspect the power pack you can carefully remove it, having marked the wires, and take it to your marine dealer to test for you. We have people bring theirs in all the time for us to look at.

 

[crookedmullet]

Re: Bogging down at speed

I very much appreciate all the responses. I purchased a new stator kit and switch box and am going to install them both this weekend. I'll keep everyone posted.

 

[crookedmullet]

Re: Bogging down at speed

I'm finally back from traveling and have an update on the engine. I replaced the switchbox and stator and along withthe stator came the voltage regulator, whichI installed. I took the boat out this weekend, crossing my fingers that it would work fine. At idle it worked fine, it even ran at speed for a mile or so and then it just bogged down, I idled around for 20 minutes or so and then threw it up a come of notches and came right up on plane only to bog down again. It ran like that all day. I checked the primer bulb and it was hard the whole time. A mechanic told me that the engine would use the fuel in the filter until it ran low and that's why it's bogging, the fuel can't keep up with the engine consumption. Has anyone heard this before and might know a solution to the problem? I've also read related topics on this forum to were a spun hub solved all problems, is this possible with such a sporadic problem as I have?<br />Thanks

 

[ehenry]

Re: Bogging down at speed

When you say your engine is bogging you mean that the RPM's drop. Correct? If it were a spun hub your engine RPM's would rev WAAAY up when the hub turns loose.

 

[crookedmullet]

Re: Bogging down at speed

Yes, the RPMs do drop when the engine bogs down. I'm definitely not getting the spun hub effect, I wish I was though so I can make it an easy fix.

 

[ehenry]

Re: Bogging down at speed

If your bulb isn't collapsing when this happens that pretty much rules out the gas tank vent. You said about that when this happens that the buld is still hard....then I'd lean towards something electrical thats breaking down as it heats up.

 

[KCLOST]

Re: Bogging down at speed

I wish I would have read this post earlier....<br /><br />Once a switchbox fails, it normally doesn't come back... It sounds like you've already found that your old one was ok, as well as the stator....<br /><br />Anyway, here's what I'd do.... Get a remote tank 1 to 5 gallons in size... Also buy a new fuel line with primer bulb with the correct fittings.... Open up the vent on the tank and run the engine with that tank and the new line and see if the symptoms remain.... Let's rule out the tank, existing line, bulb, vent, tank filter etc....<br />Let us know...