07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

[sstreed]

I have a 22' pontoon boat with a mercury 90 hp 4 stroke EFI. Currently I am running the stock 13 pitch propellor and can only run about 1/2 to 3/4 throttle running 5500 to 5700 rpm at 20 mph. If I go WOT the rpms shoot up to the high 6000's. Does anyone have any idea's what I should be running for a pitch? 16p or 17p? I heard that every pitch knocks 250 rpm's off. Supposedly that is the stock prop for that boat with 22" pontoons. The pontoon was upgraded with 27" toons supposedly that makes a huge difference on what pitch prop i run. I just do not want to keep buying props until I find the right one. Hopefully someone has run into this and can help! thanks so much!

 

[usskydvr]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

Generally every 2" of pitch increase will decrease RPM by 300-400 RPM. Are you sure your tach is correct? For a 22ft pontoon with a 90 hp 4 stroke a 13-14 pitch should be in the ballpark. Maybe your prop hub is bad, allowing slippage.

 

[180shabah]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

When the revs jump tothe high 6k range, I assume that there is no corresponding increase in speed. If so, your answer is not simply a pitch change.

Your prop is losing its bite in the water. This could be due to the engine being too high and being lifted out as speed increases. Or turbulence between the logs is aerating the water.

In the first case, lowering the engine will help, in the second, lowering may or may not help. More aggressive prop designs might help, but start with engine height.

 

[steelespike]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

Don't know what the gear ratio is but a 13 might be little small for a 90. BUT::
As suggested is there a speed increase as it over revs or does it seem more like ventilation(cavitation) Empty revs?

 

[sstreed]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

Thanks for the responses everyone... The boat willl increase speed as I throttle for example 5k rpms approx 14mph and at 6k rpm's 21 mph only but only can go 3/4 throttle before going over 6k rpms and engine goes into safe mode. Yes, the tachometer has been checked by Mercury dealer... They water tested the boat and said I need more pitch but unfortunately didn't have any props for me to try out! Thanks!!

 

[sstreed]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

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Thanks for the response...The boat willl increase speed as I throttle for example 5k rpms approx 14mph and at 6k rpm's 21 mph only but only can go 3/4 throttle before going over 6k rpms and engine goes into safe mode. Yes, the tachometer has been checked by Mercury dealer... They water tested the boat and said I need more pitch but unfortunately didn't have any props for me to try out! Thanks!!

 

[laser24]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

i have a 24 foot pontoon with same motor etc, and it came with a 15 pitch and i have exactly the opposite problem, depending on amount of people on the boat i cant completly tach it out.. even with just me i can barley get 5500 rpm .. i am going to drop to a 14 pitch.. i think in your case , shorter boat you should be running a 15 or 16 pitch.. i would try a 15 first

 

[wasilvers]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

maybe you guys should trade props?

 

[DennisTN]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

Interesting...I have the same motor on a 20 ft pontoon and the same problem. It never happened before but yesterday, after taking on 4 people, I hit the REV limit at about 3/4 throttle. I'm curious if you solved this problem with a new prop? I also notice I burn fuel at 5k/20 mph at a high rate.

 

[steelespike]

Re: 07 mercury 90 hp 4 stroke Efi Hitting Rev Limiter

You guys are going to get yelled at.These old threads are for reference only and you will do better if you open your own thread.
Welcome DTN this thread will likely be closed so you should start your own thread. Pontoons allways have a high slip number and there is allways a lot of turbulance
that can change with loading.Trim is nearly useless on a toon usually only allowing a few degrees of adjustment. If you move some of your passengers around you may solve your venting.
The added load may expose a part of the underside to the water causing turbulance
4 blade props usually help fight slip and venting.