Mercury 9.9 2 stroke 3 blade vs 4 blade

[williev31]

Hi I'm new to the site and have a question regarding prop selection for my merc 9.9. I recently purchased a Tracker Grizzly 1448 all weld. I put a 1993 mercury 9.9 2 stroke on it for now, saving for a 15hp 4 stroke. I took it out today and was very disappointed in its performance. I could barely get up to 8mph according to my humming bird FF. The motor would hardly hit 3/4 rpm. If it even got close to plane the prop would instantly ventilate. The ventilation plate is a good inch below the transom, and I tried all 3 trim positions. I have a brand new solas amita 9.25" 9" pitch 3 blade prop. I'm thinking a drop in pitch is needed, and a 4 blade prop help. I am debating between a 3 blade 8" pitch and a 4 blade 7" pitch. Im not expecting greatness here, I just want to get up on plane and the gas engine to be faster than the minn kota. What does every one think, and other suggestions are welcome.

 

[jestor68]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

The Tracker in question has a 16" transom height, so I must assume(?) that you have a 20" motor, if you're below the bottom with the AV plate.

I'm at a lose to see why you should be getting all this ventilation with a Solas prop set that low.

According to the prop selector, that is the correct pitch prop.

A 4 blade might help, the same pitch if you're getting proper rpm.

I don't suppose you know the rpm. A Tiny Tach would be needed to know the rpm.

You might try moving the motor off center an inch to see if the center keel is causing the issue.

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

I think I may have figured out the ventilation problem. The motor was run by the previous owner without the thrust washer. It wore the back of the gear case off by about a 1/4" so there is an exsessive amount of exhaust leaking there. I don't have a tach but will be looking for one soon. I can tell the motor isn't reaching rpm though. In the test tank it will wind right up, but pushing the boat it bogs at anything beyond 3/4 throttle and never catches up, unless its ventilates. Im going to try building the back of the gear case back up with the tig welder this morning and see if it helps slow the ventilation.

 

[MH Hawker]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

Unless you take the UL apart the heat will kill the seals.

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

I took the gear case apart and got it built back up. Took it to the water and the ventilation is completely gone. The boat still struggles to get up on plane and looses a lot of speed in corners. I couldn't find a tach localy so had to order. Guess I will have to wait to find out if a prop change will help.

 

[Sea Rider]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

If that's the newer 9.9 Merc rebadged Tohatsu 2 strokes version could pass it to a 15 HP for candy cost, will need a pic to check that. Which size is that boat ? What's the max HP transom rated ? Seems not ideal for 9.9 HP engine.....

Happy Boating

 

[steelespike]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

The 9.9 should pop on plane and run about 20 with a light load.
8mph sounds like it may be on one cylinder.
Many people don't realize they are on one cylinder but for the lack of power.

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

Here is a pic of the set up. Not the ideal motor for the boat I know, but a new motor ist in the cards for this year. Hoping to make this one work for the season. Did a gps run today with the ventilation problem fixed. It will do 15-16mph wide open throttle. Still wating for a tach to check RPM. If an upgrade to 15hp is possible id love to know about it. The boat is a 14' mod v so it should plane pretty easy, but it is rated for a 25hp so I know I can go up quite a bit in motor. If I could get it up on plane quicker and get a little closer to 20mph id be happy for now. Once I have an RPM I will let you guys Know.

Thanks
Will

 

[steelespike]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

If your running with the motor at that angle hole shot should be good but top end slow.
Adjust the trim out one notch.will slow hole shot but I think top end would be better.
What is the boat dry weight?Is it bare bones or with a floor live well etc.?
You may need to move some weight forward.

 

[steelespike]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

If your running with the motor at that angle hole shot should be good but top end slow.
Adjust the trim out one notch.will slow hole shot but I think top end would be better.
What is the boat dry weight?Is it bare bones or with a floor live well etc.?
You may need to move some weight forward.
Is the link n sync set right?Throttle opening all the way.
Is your speed lightly loaded?

It's hard to evaluate the motor if its loaded down.
An induction tach would help evaluate your results.

 

[Sea Rider]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

Float sib alone, from outside trim engine for decal to be paralell or engine at 90? with respect to water level, if you go boating that way with weight well deck distributed, lighty loaded though and healthy 9.9 engine combo should perform well. For top performance will need to install an induction good quality TT or Hardline tach, check achieved max rpm at wot. Probably will need a engine transom height optimization for best water performance under all water conditions. Trial and error is key...

Happy Boating

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

I have tried all trim postions, the #2 or middle hole seems to work best. Acording to tracker the boat is 437# dry, My motor is 73# and I have a 6 gallon fuel tank plus trolling motor, small deep cycle battery, and 2 10# anchors. The speed test was done with whats listed and just me in the boat. The boat seems to float pretty level or if anything its nose heavy with the trolling motor and battery. Im headed over too a friends to do a compression test today, and im still waiting for the tach to get here. I will report back as soon as I have more numbers.

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

well problem found, top cylinder 25psi bottom cylinder 26 psi. Guess no need for the tach. Found solution to my problem though 2009 mercury 15hp fourstroke $1500 on craigs list, bought and paid for, picking it up tomorrow. Thanks for all of the help guys, ill be sure to report back with new speed test after install.

 

[anzomcik]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

25psi on each cylinder and that motor will not run, let alone push you 8mph.Did you crank the motor more than one cycle to get that reading?

I hope your new 15hp will achieve what you hope for.

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

I had my neighbor who runs his own auto shop do it. He came over and we started the motor in the barrel and let it warm up. We pulled both plugs and held the throttle wide open. He had the snap-on guage that holds the pressure and I pulled it several pulls per cylinder, and we couldn't get over 26 psi no matter how much I pulled. He had never done an outboard so if there is a step we missed please let me know. I will probably set the 9.9 aside and re-ring it before I sell it.

 

[steelespike]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

I'd like to see the tester checked on a known good motor your new to you 15 perhaps.

 

[anzomcik]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

I'd like to see the tester checked on a known good motor your new to you 15 perhaps.

+1 I have had 4 cylinder outboard barely run with three cylinders at 100psi and one at 40psi. No way your cylinders are at 25psi and it still runs.

Let me ask this how easily does your 9.9 motor start? I know you have a different motor right now but I keep asking this because if you are going to pay someone to ring a motor that doesn't need ringed seems silly to me, you may have been over propped.

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

got out of work early tonight so I decided to give it another try, without neighbor here, swearing by his snap-on gauge. I tested the gauge with my compressor. With my hose output set at 150psi I still couldn't get the tester over 25psi. I swapped out the gauge head with the one off my compressor. After the motor tested 90psi on top and half way between 90 and 95 so call it 93 on bottom. Manual calls for 100-110. Still week but not as bad. The motor seems a little easy to pull over and can take a few pulls to start if cold. The dealer wont have the other motor prepped until next Wednesday now, so if the tach comes in this week I will still do a test run with it. I do want to make sure im not passing on a headache to the next guy. I may keep it for running the shallower rivers around here too.

 

[Sea Rider]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

Have you ordered a induction tach only or a hour/tach model. The latter could be installed tied/bolted around powerhead surrounding, will have spot on tracked run hours, excellent for preventive maintenances as oil/filter, gear box oil, spark plugs changes, boating hours, etc.

Happy Boating

 

[williev31]

Re: Mercury 9.9 2 stroke 3 blade vs 4 blade

Its the hour/tach, it came in today, if the weather works with me hopefully I will get to try it this week end.