MajBach
Chief Petty Officer
- Joined
- Jun 21, 2003
- Messages
- 564
Hi, everyone. Need some pro help with this one:
1999 Honda 90hp with 700 hrs and very well taken care of but probably only 100 hours of the 700 are from the past decade.
Issue: Outboard bogs down under hard acceleration - a common problem I have now read. Cause still eludes me.
I noticed this first trip out this year. None of the symptoms except for the odd spitting are noticeable when I have it hooked up to the muffs in the driveay. The motor seems to accelerate fine when I advance the throttle slowly but if I advance to WOT at any point during acceleration, there is an instantaneous change in sound and power, as if it lost one cylinder. There is also a shutter/vibration. The effect is most pronounced when I do this from idle. If I advance it slowly (or even if I let it just ‘go’ when I give it WOT) it eventually revs up and smooths out. However, I’m down quite a bit in top end – 31 knots when I used to be able to squeeze out 40. I tried toying with the mixture screws. Factory is 2 ¼ turns out and I tried every point between on one turn out to 3 ½ turns out. I may be imagining it but when set to rich it seems a tiny bit smoother and more responsive.
While I had the hood off to adjust the carbs, I noticed a new sound when the bogging down occurred – almost identical in sound to what you would hear from a grounded spark plug arcing. That got me to thinking that it may be an electrical problem and not fuel. The spark arcing sound only was noticeable (but fairly distinct) while under hard accel and of course I was at the wheel all the time so couldn’t pinpoint it. But, I also noticed that the sound was faintly there when it had maxed out top end– over the sound of the engine. The hood must muffled this. Even when I advanced the throttle slowly to get to wide open without bogging down, the noise appeared as it was approaching full out. The sound was instantaneous when I tried to hard accelerate too. Btw, I can’t say for certain what the rpm was topping out as as the tach started acting funny too this year. But it’s the same prop Ive used for awhile and it used to top out at 5400-5600 rpm. It sounded like it was not quite reaching that rpm but not enough to drop it down 9 knots. However, I was in salt water for the first time too so maybe increased drag?
Okay so there is a bit of a background leading up to this issue that I didn’t want to state up front for fear of influencing your first diagnosis: I rebuilt the carbs this spring.
Yup, last year I learned the hard way what happens when you store an outboard and forget to drain the bowls. When I launched for the first time, it couldn’t hold idle then I quickly noticed she was spewing gas from two carbs – needles were stuck. So, I replaced every bit of brass on each carb and new gaskets and O-rings on everything. Only thing I didn’t screw with were the needles and float adjustment. I was meticulous not to alter anything here and the needles were in new condition.
After rebuilding the carbs, she DID NOT run very well in the test tank. Initially only on three cylinders. In the process of determining which cyclinder, a different one dropped. Turned out I had a lot of water in my gas. This was gas I added to an empty tank from a jerry can that had about 1/3 water in it. Naturally, I got all of it out of the tank before going any further. I ran a bit of methyl hydrate in it after filling it completely up and siphoning all but a ¼ tank to ensure I got all the tainted gas out. Motor ran well in the driveway but the problems appeared first time in the water.
The only other symptom that persists that wasn’t there before (or nearly as bad) is the odd sputtering. Seems to occur at anything above fast idle and below say 2500 rpm but, it’s not very bad, just nagging – a constant reminder that all is not perfect in the world.
I also never sync the carbs after the rebuild – don’t have the adapter fittings. But, the motor runs smoothly at idle so I’m not inclined to believe there’s an issue there.
So aside from the book I just made you read, what are your thoughts? Can this be a resistor cap on one of the spark plug leads (had that problem on a motorcycle many years ago). I looked for signs or arcing or any type of tell-tale signs the wires for the plugs start – nada. Plugs themselves are probably two years old but less than 25 hours. Or, is this a fuel problem? I am still at a loss to understand how the power drops instantly - even while it is running smoothly - the moment I advance the throttle to much. If this is something that has to do with the air/gas mixture being thrown out of wack when the butterflies are opened too far, can a carb jet cause this? How would I narrow down which carb is the culprit?
Thanks a heap for taking the time
R
1999 Honda 90hp with 700 hrs and very well taken care of but probably only 100 hours of the 700 are from the past decade.
Issue: Outboard bogs down under hard acceleration - a common problem I have now read. Cause still eludes me.
I noticed this first trip out this year. None of the symptoms except for the odd spitting are noticeable when I have it hooked up to the muffs in the driveay. The motor seems to accelerate fine when I advance the throttle slowly but if I advance to WOT at any point during acceleration, there is an instantaneous change in sound and power, as if it lost one cylinder. There is also a shutter/vibration. The effect is most pronounced when I do this from idle. If I advance it slowly (or even if I let it just ‘go’ when I give it WOT) it eventually revs up and smooths out. However, I’m down quite a bit in top end – 31 knots when I used to be able to squeeze out 40. I tried toying with the mixture screws. Factory is 2 ¼ turns out and I tried every point between on one turn out to 3 ½ turns out. I may be imagining it but when set to rich it seems a tiny bit smoother and more responsive.
While I had the hood off to adjust the carbs, I noticed a new sound when the bogging down occurred – almost identical in sound to what you would hear from a grounded spark plug arcing. That got me to thinking that it may be an electrical problem and not fuel. The spark arcing sound only was noticeable (but fairly distinct) while under hard accel and of course I was at the wheel all the time so couldn’t pinpoint it. But, I also noticed that the sound was faintly there when it had maxed out top end– over the sound of the engine. The hood must muffled this. Even when I advanced the throttle slowly to get to wide open without bogging down, the noise appeared as it was approaching full out. The sound was instantaneous when I tried to hard accelerate too. Btw, I can’t say for certain what the rpm was topping out as as the tach started acting funny too this year. But it’s the same prop Ive used for awhile and it used to top out at 5400-5600 rpm. It sounded like it was not quite reaching that rpm but not enough to drop it down 9 knots. However, I was in salt water for the first time too so maybe increased drag?
Okay so there is a bit of a background leading up to this issue that I didn’t want to state up front for fear of influencing your first diagnosis: I rebuilt the carbs this spring.
Yup, last year I learned the hard way what happens when you store an outboard and forget to drain the bowls. When I launched for the first time, it couldn’t hold idle then I quickly noticed she was spewing gas from two carbs – needles were stuck. So, I replaced every bit of brass on each carb and new gaskets and O-rings on everything. Only thing I didn’t screw with were the needles and float adjustment. I was meticulous not to alter anything here and the needles were in new condition.
After rebuilding the carbs, she DID NOT run very well in the test tank. Initially only on three cylinders. In the process of determining which cyclinder, a different one dropped. Turned out I had a lot of water in my gas. This was gas I added to an empty tank from a jerry can that had about 1/3 water in it. Naturally, I got all of it out of the tank before going any further. I ran a bit of methyl hydrate in it after filling it completely up and siphoning all but a ¼ tank to ensure I got all the tainted gas out. Motor ran well in the driveway but the problems appeared first time in the water.
The only other symptom that persists that wasn’t there before (or nearly as bad) is the odd sputtering. Seems to occur at anything above fast idle and below say 2500 rpm but, it’s not very bad, just nagging – a constant reminder that all is not perfect in the world.
I also never sync the carbs after the rebuild – don’t have the adapter fittings. But, the motor runs smoothly at idle so I’m not inclined to believe there’s an issue there.
So aside from the book I just made you read, what are your thoughts? Can this be a resistor cap on one of the spark plug leads (had that problem on a motorcycle many years ago). I looked for signs or arcing or any type of tell-tale signs the wires for the plugs start – nada. Plugs themselves are probably two years old but less than 25 hours. Or, is this a fuel problem? I am still at a loss to understand how the power drops instantly - even while it is running smoothly - the moment I advance the throttle to much. If this is something that has to do with the air/gas mixture being thrown out of wack when the butterflies are opened too far, can a carb jet cause this? How would I narrow down which carb is the culprit?
Thanks a heap for taking the time
R
