How critical is operation near WOT for new 9.9 HP 2017 Pro-Kicker on a pontoon?

onepyramid

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Jun 20, 2014
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Here's the situation...our lake has a 9.9 HP limit and a 24' length limit. No huge wakes, no waves, nothing to overcome but 300 acres of flat water and some wind.

Here's the problem...just bought a brand new Lowe 22' pontoon from Cabela's. They have been supplying boats here for years. I specifically told them I wanted a prop that would allow the engine to spin up to normal operating range...a lower pitch unit. They, of course, ignored me and sent the boat with the stock from the factory 10" diameter, 8" pitch, four-blade prop.

Here's the results...engine at WOT will only turn 3100 rpm and it surges like crazy. (It is not just me...Cabela's has delivered five new Lowe pontoons this year, all with the same set-up and all with the same symptoms.)

Here's what they are proposing...To their credit, Cabela's is trying to fix the problem on all boats. They have done two boats already, with one obvious result of eliminating the surging of the engine at WOT. The fix was to exchange the four-blade prop with a three-blade, 10" diameter but with a 9" pitch. However, the maximum rpm now at WOT has dropped to 2400.


Back to my original question....Will restricting these engines to a life of never seeing anything above less than half of the engines maximum rpm cause problems later down the line?

Mercury says this engine has maximum rpm of 6,000. But the Pro-Kicker 9.9 has limited low pitch prop options...the smallest is a three-blade with 7" pitch. Mercury tech says either move back to the standard engine, or have the existing prop re-pitched. I am sure Cabela's will not like either option.

My experience from the past....used to have a two-stroke Mercury 9.9 that plugged the exhaust ports after about four years of operation. Local mechanic diagnosed it immediately as improper pitch prop....he cleaned up the engine, installed a lower pitch prop and the engine spun up and ran like a top for 20 years.

I am trying to avoid this same problem with the new engine, but do not know if similar running conditions for a four-stroke engine are as detrimental. I look forward to your guidance and thoughts.
 

Scott Danforth

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Your lugging the motor. It is important to the the RPM up to its RPM range
 

ahicks

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Geez, if your dealer refuses, or is too ignorant, to fix the issue, I say go for it yourself! Common sense says the engine should turn rated rpm. If it won't turn rated rpm as it comes from the dealer, do what you need to do to get it right. There's no shame in having your prop customized (re-pitched) by a good shop. I would ask that the diameter be kept as large as possible to allow the engine to develop maximum thrust. Don't let them cut the diameter down to raise rpms to the point you're looking for. The shop needs to actually re-pitch the blades!
 

Scott Danforth

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I would call the customer service line at Lowe
 

ondarvr

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Prop designed can vary a bit for some of the small motors, you want the highest thrust prop, it's the one with most blade area, and the larger diameter.

​The surging is most likely the prop ventilating as the power increases with the RPM's, lowering the motor can help, an extra long shaft motor would probably be better.

​Next is just have the prop reworked to a lower pitch so you get the RPMs up, this will increase performance across the board too.

​A better motor would be the Merc Bigfoot, it's designed to do this exact job.
 

onepyramid

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Thank you all....you have confirmed my thinking.

If this motor has a max rpm of 6,000, as stated by Mercury, should I expect it to normally operate in the 5000-5500 range at WOT on my boat....again, assuming proper pitch and size prop??
 

ahicks

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That's what I would do. Normally, I'd try to max out performance by running a prop that will let the engine run right at max rated rpm. Here, it's not like you're going to be pulling a tube or anything. I'd go for the 5-5500 range like you're thinking of to keep the engine noise down, fuel usage and engine life up.
 

onepyramid

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OK, this is different. I did not think of this before, but just put the engine in neutral, so I could rev it without load from the gear box and prop.

In neutral, with no load, the rpm will only max out at 3100.....same as when I am on the lake pushing the boat.

Maybe they put governors on these things at the factory? Any other explanation you guys can think of for this max rpm in neutral?
 

ondarvr

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There may be a rev limiter on the ignition that will keep you from destroying the motor in neutral, also, the throttle travel is limited in neutral, you can't get full travel out of the linkage to open the carbs completely.

​This may or may not be the issue will running it on the boat, if the linkage is out of adjustment it may not allow full travel of the throttle cable.
 

ahicks

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Your tach could be out to lunch as well. Many have different settings on the back that must be set correctly, to match your engine's requirements, before they read correctly. This one not set right would be my first guess.

Does it read some stupid low rpm on idle?

Oh, and free revving in neutral is a really bad plan.
 

onepyramid

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Yes, I know that is not a good idea...and was just trying to check this aspect.

At idle, it reads 600 rpm.
 

ahicks

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I'm not familiar with the specifics on your engine, but would expect something in the 800 -1000 rpm range on idle. So I suspect your tach is not working correctly, and most likely cause would be the tach isn't set up for your engine correctly. If this is a new(er) boat, I'd be speaking with the dealer. If that's going to be a pain in the butt (I HATE dealers!), maybe you could post the tach manufacturer and we can try to give you a hand. Actual setting of the tach is really easy, done on the back side. It's just coming up with the correct setting that may require some homework.More detail on the tach may yield an answer for you right away from somebody that's just had to set theirs. Dealers are notorious for being too incompetent or lazy to set them up correctly when they sell/install them....
 
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