Johnson 9.9 HELP!!!!!!!!!

[Absolutbost]

I have a johnson 9.9 sailmaster with electric start that I converted to a short shaft for a 14' jon boat. This engine runs and all but at full throttle it will only push the 14' duracraft about 10 MPH!!! Does that sound right???? or what could be the problem?? Thank you for your help.

SCB

 

[fireman57]

Re: Johnson 9.9 HELP!!!!!!!!!

I'm not familiar with duracraft but if it is a fiberglass boat I think that you are probably doing pretty well. You might try trimming it in or out until you find the best setup.

 

[LORDY611]

Re: Johnson 9.9 HELP!!!!!!!!!

Not sure about your boat, but I have a 14' aluminum Sea Nymph (gamefisher) with a 9.9 and it flies! I used to pull the kids skiing when they were about 10 years old. With me and my tackle box I would estimate the speed at close to 20 mph.

 

[mcallan]

Re: Johnson 9.9 HELP!!!!!!!!!

Just a Question, but what do you have on it for a prop?? I had a guy once with a 15hp fourstroke evinrude, and he couldn't get the boat to plane hardly at all. I checked his prop and found that he had a sailboat prop on it. Put a 9 by 10 on it and the boat flew compared to what it did before. Mike

 

[ratracer]

Re: Johnson 9.9 HELP!!!!!!!!!

mcallan has the right idea on what to check first, the sailmaster as shipped was intended for use as auxilliary power for displacement hulls, not a planing hull. Besides checking that you have the correct prop - from memory the standard prop for a planing hull is somewhere around a 9 1/2" pitch, your prop might be a 7" - confirm that the motor trim is set at the proper angle.

What is the weight of your boat?

To give a baseline to compare against, my standard 9.9 pushes my 12' semi-vee at 22+MPH measured by GPS with a combined weight of boat/motor/fuel/misc gear/me is somewhere around 450 lbs.

 

[Absolutbost]

Re: Johnson 9.9 HELP!!!!!!!!!

Thanks guys, I have a new prop that i put on a couple months ago that is a 9.5x11. If its not the prop any other ideas? Someone told me it could be the spark plugs, and to try running SeaFoam through it with new plugs.........any thoughts on that. I appreciate your help!

 

[ezeke]

Re: Johnson 9.9 HELP!!!!!!!!!

OMC/BRP has a 10 X 9, 4 Blade prop that will probably get you in the race with ratracer. Part number is 176266.

Check with a BRP/OMC Evinrude/Johnson dealer.

 

[Solittle]

Re: Johnson 9.9 HELP!!!!!!!!!

A tip for this forum - There is no need to post the same problem twice. It gets confusing enough as it is.

 

[Absolutbost]

Re: Johnson 9.9 HELP!!!!!!!!!

I'm sorry, not trying to cause any problems, just so much information out there and i'm new so i kinda got excited.

 

[rwise]

Re: Johnson 9.9 HELP!!!!!!!!!

Thanks guys, I have a new prop that i put on a couple months ago that is a 9.5x11. If its not the prop any other ideas? Someone told me it could be the spark plugs, and to try running SeaFoam through it with new plugs.........any thoughts on that. I appreciate your help!

wait on the plugs until after the seafoam has ran through! Some have said that plugs had to be changed after they ran any de-carbon stuff

 

[Absolutbost]

Re: Johnson 9.9 HELP!!!!!!!!!

I have a johnson 9.9 sailmaster with electric start that I converted to a short shaft for a 14' jon boat. This engine runs and all but at full throttle it will only push the 14' duracraft about 10 MPH!!! Does that sound right???? or what could be the problem?? Thank you for your help.

Would a Hydrofoil help this problem?????

 

[OBJ]

Re: Johnson 9.9 HELP!!!!!!!!!

Let me add a couple things.

Start with engine setup on the boat. Look at the anti-cav plate, that's the plate right over the prop, and see if it's below the keel of the boat. If so, raise the engine till the plate is at least even with the keel of the boat, ideally an inch above the keel.

Check the rpms at WOT. If your not getting at least 5500rpms, drop the prop pitch. Most 9.9's can turn 6K rpm with no sweat. You may need to go to a 9 1/4 X 8 or even a 10 X 7 to get the revs up. Once the rpms are up, you can adjust the engines tilt angle for best on plane running.

Here's a rule of thumb for rpms vs. prop pitch......for every degree of pitch dropped or given, figure 150 to 200 rpms gained or lost.

 

[Absolutbost]

Re: Johnson 9.9 HELP!!!!!!!!!

Let me add a couple things.

Start with engine setup on the boat. Look at the anti-cav plate, that's the plate right over the prop, and see if it's below the keel of the boat. If so, raise the engine till the plate is at least even with the keel of the boat, ideally an inch above the keel.

Check the rpms at WOT. If your not getting at least 5500rpms, drop the prop pitch. Most 9.9's can turn 6K rpm with no sweat. You may need to go to a 9 1/4 X 8 or even a 10 X 7 to get the revs up. Once the rpms are up, you can adjust the engines tilt angle for best on plane running.

Here's a rule of thumb for rpms vs. prop pitch......for every degree of pitch dropped or given, figure 150 to 200 rpms gained or lost.

How can I check how many RPM's its running??

 

[OBJ]

Re: Johnson 9.9 HELP!!!!!!!!!

There are several tachs that you can use. Some timing guns have a tach function. Or, find a friend that may have a Tiny Tach. If your engine is a remote control, the control box may have a plug to connect a tach up to....most OMC/Bomby controls do.

Point is, you really need to know what the revs are to prop the engine out correctly

 

[Absolutbost]

Re: Johnson 9.9 HELP!!!!!!!!!

Hey guys,
I put on the spark plugs that you said to, and ran sea foam through the engine, and it got up to 15 mph with just me in the 14' jon boat. I dont get, these guys are saying their 9.9s are pushing their 14's 20mph, what should i do next? should i try a hydro-foil, like the doel-fin? Thanks for your help. Stanton

 

[Absolutbost]

Re: Johnson 9.9 HELP!!!!!!!!!

the boat will only go 14-15 with the new plugs you said to get and running sea foam through it. it helped but is there anything else i can do. Would some type of hydro foil help me get more out of it? Thanks