motor accelerates when i hit a wave

[seeplaker]

1977 70hp

Took the boat out for the first time this year. I notice the motor not reaching full rpm's. When I hit a wave the motor would come alive and reach full rpm's then the motor would start losing rpm's once I hit smooth water. I then repaced all 3 needles and clips. Still doing the same thing.

The motor starts and funs fine just not reaching full rpm's until I hit a wave. Any help or ideas to correct this would be great. Thanks.

 

[orbanp]

Re: motor accelerates when i hit a wave

Are the carbs clean? Any chance that when hit by a wave it dislodges some dirt in the carbs? Similarly, check the fuel pump for foreign matter.
Also, try pumping the priming bulb when the motor starts to loose power and see if it helps. If so, that might indicate problem with the fuel delivery.
You also might want look at your gas tank, some debris could clog the fuel pick up that gets dislodged by the impact of the waves.

Good luck, Peter

 

[Captain Caveman]

Re: motor accelerates when i hit a wave

I know that this sounds simple, but you're not talking about the prop coming out of the water when you hit a wave and over-revving are you?

 

[pn]

Re: motor accelerates when i hit a wave

i'm guessin, float adjustment.

 

[Cap'n Chaos]

Re: motor accelerates when i hit a wave

I had a speaker in my truck that would go silent if I hit the right bump. I'd be looking for a loose wire or connection....just my opinion.

 

[LongLine]

Re: motor accelerates when i hit a wave

Try triming your motor up a little. Sounds to me like it's plowing the water and struggling with the load on calm water. Just as Capt. C. implied. When you're going over waves, the boat is actually riding higher on the water i.e. less contact with the water, hence less friction load so less struggle for the motor and it speeds up. Mine gains about 3 mph when Trimmed up a little.

Tom B.
(LongLine)

 

[colding]

Re: motor accelerates when i hit a wave

I'm having a similar issue. Recently had the timing sensor replaced on my 05 90HP Johnson by an outboard mechanic. While he was testing after replacing the part, he went ahead and re-adjusted my carbs while it was running. Now, I cannot reach full RPM either. I use to reach 5200 RPM at about 45 MPH. Now I can only reach about 32MPH at 4200 RPM. And like the original poster, if I'm running in choppy water or hit some wake, it will temporarily get a surge to the full rpm but it immediately goes back down to 4200 rpm. It also struggles to reach that 4200 rpm. I used to just hit the throttle and it would take off like a rocket. Now, if I give it full throttle from the start, it bogs down and won't plane. I have to gradually increase the throttle as the speed increases. Takes about 30 seconds now to reach full rpm's.

Could it possibly be that he incorrectly adjusted the carbs? Or could it be a totally different issue?

 

[Javelin JD]

Re: motor accelerates when i hit a wave

If you haven't done so I'd take it back to that mechanic and have him go through it and try and correct the issue. We're supposed to take things to them to fix and foul up.

 

[colding]

Re: motor accelerates when i hit a wave

I only took it to him for the initial problem, the timing sensor. I'm assuming the adjustments he did while it was running was the idle speed adjustments and wouldn't have anything to do with the high speed issue I'm having. I'm going to order some carb rebuild kits and new high-speed orifices for the float bowls just in case. My only question is, could this be an ignition issue instead? Coil/CDI/Power Pack? I could take it back to him, he only charges me $65 per hour for diagnostics and he said he can almost always diagnose the issue within that hour. I'm pretty handy with a wrench, so I'm not afraid to do the repairs myself, I just don't want to replace parts that don't need to be replaced, especially if it's a power pack or regulator/rectifier, which are a couple hundred dollars each.