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Author Topic:   Yamaha 90 on classic Montauk

gakirby posted 01-11-2011 10:33 PM ET (US)
I have a 2001 Yamaha 90 on my 1989 classic Montauk. Overall I love this combination but throughout this past boating season my engine had been acting up. Reading other threads regarding this boat-and-motor combination has led me to believe that at around 3,800- to 4,000-RPM my [MONTAUK] should be reaching about 30-MPH. What I am experiencing however is that I get about 22- to 23-MPH at 3,600- to 3,700-RPM. I think I have two [concerns].
First, the boat came with the engine mounted on the lowest mounting hole, meaning that the cavitation plate is level with the bottom of the hull when the engine is trimmed level. I've learned through this site that raising it up a hole or two can improve performance by reducing drag. I talked to my mechanic about this and he made fun of me saying that he mounts them on the lowest hole as well because that is how the cavitation plate is supposed to line up. Who is right? How high up should the engine be if it should be moved up?
Second, my top speed at WOT is not impressive; unfortunately I don't remember the exact number. The [concern] arises however after I have been at or near WOT (basically above 4,500) and then return to a cruising RPM between 3,000 to 4,000. The engine begins to run rough and revs up and down usually of fluctuations of about 400 to 500-RPM. While this is going on, the maximum speed the engine can reach is about 3,500-RPM (regardless of how far the throttle is pushed higher). I was wondering if anyone had any ideas about why this might be happening?
Thanks,
Greg
gakirby posted 01-11-2011 10:34 PM ET (US)
Just to add some possibly useful information. My prop is marked "17K" and is painted black. It has dings in it so I assume it is aluminum not SS (am I right in assuming this?).
tedious posted 01-12-2011 07:19 AM ET (US)
First off, get a new mechanic, because that one doesn't know what he's talking about. For starters, try getting the anti-ventilation plate about an inch above the keel line, when trimmed level. You want the A-V plate above the water when you're on a plane, not plowing through it like you have now. You're definitely giving away some speed and mileage with your current setup.
Regarding the WOT then cruise [behavior], please give some more information:
What is your WOT RPM?
If you stay at WOT, does the problem occur, or do you continue to run fine?
Does the problem go away after running for a while at cruise? If not, what do you do to make it go away?
Interesting problem--I was tempted to say you've got a cylinder dropping out, possibly a bad coil that overheats at WOT, but that wouldn't explain the surging. I'm thinking maybe too much fuel going into the motor at WOT, and then you're burning off the excess once you're at mid-throttle.
Tim
jimh posted 01-12-2011 08:13 AM ET (US)
Typically the Yamaha propellers marked "K17" and painted black are made from stainless steel.
jimh posted 01-12-2011 09:14 AM ET (US)
It is not recommended to continue using propellers whose blades are deformed or damaged. A propeller whose blades are damaged will be out of balance. Rotation of an out-of-balance propeller on the propeller shaft can cause damage to the propeller shaft seals and bearings. Repair of the propeller shaft seals and bearings will be much more expensive than repair of the propeller. This makes repair of the propeller a wise investment.
It is difficult to make judgments about the performance of a boat-motor-propeller combination when the propeller has damage. A propeller with damage will not perform in the same way as a similar propeller without damage.
Tohsgib posted 01-12-2011 01:35 PM ET (US)
Sounds like you need to go through the carbs, do so before it blows up.
gakirby posted 01-12-2011 05:28 PM ET (US)
Thanks to everyone for your replies!
Tim, I'll be sure to adjust my engine height myself this spring once the couple feet of snow outside disappear. My WOT RPM is about 5200 and although I don't stay up there for much more than about a minute at a time, the engine seems to run fine staying up at WOT. To make the issue go away I generally throttle down and shift into neutral and then slowly throttle back up to cruising (about 3500 RPM). This will usually make it run smoothly although sometimes the RPM surging will return.
Jim, thanks for the information that the K17 prop is likely SS. I've checked online and prop repair seems much more cost effective than buying a new prop.
Does anyone have any experience with prop shops that did a good job for a reasonable price that I would be able to ship my prop to? (I noticed a few places had promotions going on during January offering between 15-25% off the repair price) Am I better off just taking my chance with a local prop shop? (I live in CT)
John from Madison CT posted 01-12-2011 07:00 PM ET (US)
A 17" pitch is the right prop for that engine/hull combo.
Jefecinco posted 01-12-2011 07:45 PM ET (US)
A local prop shop should be fine.
Butch
Tom W Clark posted 01-12-2011 07:56 PM ET (US)
Greg,
The "K" in Yamaha props simply means it is for intermediate gearcase motors. "K" Series props have a 4-1/4" hub diameter.
Both the Yamaha Painted Stainless Steel propeller and the Yamaha Aluminum propellers are painted black (though some Aluminum are painted white) and have very similar shapes. All the other Yamaha stainless steel propellers are polished.
Removing the prop and feeling its weight will tell you very quickly if it made of aluminum or stainless steel.
Yes, the "17" refers to the pitch and for either the Yamaha Painted Stainless Steel or the Yamaha aluminum 17 is *probably* what you want.
If you use a Stiletto or Turbo brand prop, 17" is to much and you'll need to drop to 15"
If you choose a Yamaha three blade Performance Series prop you'll want the 16" pitch.
It is critical to repair or replace any pro that gets a ding. Selecting the right propeller is also critical to the performance of your boat and also to the life of your outboard, but you cannot select the best prop for you needs until your motor in running properly and I suspect something is wrong with it.
From you description is sounds as it may be loosing a cylinder, but Nick could be correct and it is a fuel delivery problem. It is bets to get it sorted out before doing any propeller testing.
As to the motor mounting height, your mechanic is dead wrong. I would be more surprised if it were not so common to hear experienced mechanics and long time dealers continuing to mount outboard motors far too low.
I suspect part of the problem is simply that the very experienced riggers who you would expect to know better actually are grounded in their training from 20 or 30 years ago when propeller design was nothing like it is today and motors did need to be mounted lower. Things have changed.
A Yamaha 90 on a Montauk can be mounted one or two holes up depending on the prop being used. It should NEVER be mounted all the way down on the transom.
My brother-in-law has a 1989 Montauk with a classic Yamaha 90 on it. The motor is mounted two holes up and uses a 19" Yamaha Painted Stainless Steel propeller. It works just fine.
Waterwonderland posted 01-12-2011 08:42 PM ET (US)
Stainless Steel props behave differently than Aluminum props so you must discover what prop you have since it will affect how you mount the engine.
gakirby posted 01-13-2011 10:40 PM ET (US)
Thanks Tom. I'm planning on having my prop repaired locally by H&H Propeller. And I'll bring my boat to the mechanic in the spring and have him try and figure out why it's not acting normally.
Once everything's in order I'll raise up the engine a hole or two and see how it performs. If I need to I'll then check out some of the props you posted in another thread Tom.

quote:
- 13" x 17" Yamaha Painted Stainless Steel, part # 688-45930-02-98
- 13-1/4" x 16" Yamaha Performance Series, part # MAR-GYT3B-V4-16
- 13-1/4" x 15" Stiletto Advantage 4.25, part # D 811315
- 13-1/4" x 15" Turbo Turbo 1, part # DT-13215
Also I hope its a simple fix for the engine. Thanks to all for your suggestions.
-Greg
gakirby posted 01-14-2011 09:16 PM ET (US)
Someone from The Hull Truth forums suggested [the cause of the poor performance of the outboard motor] might be [due to] carbon build up. It was suggested I do [an insane procedure in which an enormous of amount of solvent in used in place of gasoline as the fuel in the hope of dislodging carbon particles and anything else in the combustion chamber], as they referred to it. This season I had the gas tank replaced and I have a new plastic tank now. Beforehand I had a old Pate tank installed by the previous owner. Could my engine be the victim of the degrading fiberglass in the old tank? Not sure how long it was in use, I only used it for a month before replacing it but my guess is it was from 2001 when the engine and all rigging was replaced.
jimh posted 01-15-2011 09:21 AM ET (US)
If you had a fuel tank made by Pate Plastics, and if you had fuel in the tank which was a blend of gasoline and ethanol, then you may have had problems with the fiberglass resins of the fuel tank becoming dissolved into the fuel. Usually these problems result in clogging of fuel filters in the downstream portions of the fuel system. Usually you find that fuel filters have a gummy residue in them. You should check the fuel system to make sure it is not contaminated. Since your motor was built c.2001 its rubber components should all be tolerant of ethanol-gasoline blended fuel, but it is not unheard of that 11-year-old rubber components in a fuel system need replacement.
Yamaha has a fuel additive product called RING FREE. Yamaha recommends using RING FREE as a method to reduce or eliminate carbon build up in the combustion chamber. If I owned a Yamaha motor I would follow the recommendation of the manufacturer, use the product the manufacturer recommended, and generally follow that regime of treatment.
There are various other fuel additives which have been reported to be effective as solvents for dissolving or dislodging carbon particles in the combustion chamber. Use of these solvents has been recommended in various concentrations. In most cases a single can of solvent is used, applied in a combination of full-strength application and diluted application by mixing with the fuel. Procedures which call for use of six cans of the solvent and recommend direct application of an entire can of solvent in each cylinder are excessive. I would not recommend that, and you won't find any such recommendations like that published here.
This discussion is getting more into the diagnosis and repair of an engine running problem, not the optimization of boat-motor-propeller performance. Perhaps you should start a new thread in REPAIRS-MODS to further discuss the repair of the outboard motor.
Tohsgib posted 01-17-2011 11:03 AM ET (US)
The guy on Hull Truth is a moron.
tedious posted 01-17-2011 01:43 PM ET (US)
Greg, with the additional details you provided, especially that about the Pate tank, I think I'd start with rebuilding the carbs. If that hasn't been done for quite a few years, it's probably time anyway. It's not a big deal to do yourself, and it should cost you in the neighborhood of $35 per carb for the parts. If you go to a mechanic, it should take no more than a couple of hours labor, if that.
Tim
L H G posted 01-17-2011 09:15 PM ET (US)
Also remember that it has been pointed out several times on CW that the engine only puts out about 82 HP to begin with. Yamaha's calling it a 90 was a real stretch, but it sure helped sales of this incredibly popular engine. I would say the most top end you're going to get out of it on a smirked Montauk would be 40-42 MPH. Both the 90 Mercs and OMC V-4's were more powerful engines.
TommyWhaler posted 01-18-2011 09:06 PM ET (US)
Just out of curiosity, wouldn't a jack plate eliminate the mounting problem, since you can adjust the motor up or down?
Tohsgib posted 01-19-2011 12:18 PM ET (US)
Have you done a compression check?
ScooterCO posted 01-19-2011 04:05 PM ET (US)
Sound very familiar.
I had the exact same setup and same problems. It was the pate tank causing the issues. Installed a micron fuel filter. Had carbs cleaned twice. Ran ring-free thru motor.
It was running great last fall. I did notice that my motor would not go to red line unless I trimmed it up more than I could feel that was necessary.
Good luck.. But I am sure you need a good carb cleaning.
Jorgen posted 01-23-2011 07:04 AM ET (US)
You have some greath advices here sofar, all mentioned is good, however, I would advice you to start with the basics:
*Check the sparkplugs to see if ok and no carbon is set.
*Check if your air intake is free and clear.
Hang the motor on hole 3 from top (3th hole) than check RPM
If engine doies not run around 5700 RPM, take the carbs apart and re-work them.
good luck

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Author	Topic: Yamaha 90 on classic Montauk
gakirby	posted 01-11-2011 10:33 PM ET (US) I have a 2001 Yamaha 90 on my 1989 classic Montauk. Overall I love this combination but throughout this past boating season my engine had been acting up. Reading other threads regarding this boat-and-motor combination has led me to believe that at around 3,800- to 4,000-RPM my [MONTAUK] should be reaching about 30-MPH. What I am experiencing however is that I get about 22- to 23-MPH at 3,600- to 3,700-RPM. I think I have two [concerns]. First, the boat came with the engine mounted on the lowest mounting hole, meaning that the cavitation plate is level with the bottom of the hull when the engine is trimmed level. I've learned through this site that raising it up a hole or two can improve performance by reducing drag. I talked to my mechanic about this and he made fun of me saying that he mounts them on the lowest hole as well because that is how the cavitation plate is supposed to line up. Who is right? How high up should the engine be if it should be moved up? Second, my top speed at WOT is not impressive; unfortunately I don't remember the exact number. The [concern] arises however after I have been at or near WOT (basically above 4,500) and then return to a cruising RPM between 3,000 to 4,000. The engine begins to run rough and revs up and down usually of fluctuations of about 400 to 500-RPM. While this is going on, the maximum speed the engine can reach is about 3,500-RPM (regardless of how far the throttle is pushed higher). I was wondering if anyone had any ideas about why this might be happening? Thanks, Greg
gakirby	posted 01-11-2011 10:34 PM ET (US) Just to add some possibly useful information. My prop is marked "17K" and is painted black. It has dings in it so I assume it is aluminum not SS (am I right in assuming this?).
tedious	posted 01-12-2011 07:19 AM ET (US) First off, get a new mechanic, because that one doesn't know what he's talking about. For starters, try getting the anti-ventilation plate about an inch above the keel line, when trimmed level. You want the A-V plate above the water when you're on a plane, not plowing through it like you have now. You're definitely giving away some speed and mileage with your current setup. Regarding the WOT then cruise [behavior], please give some more information: What is your WOT RPM? If you stay at WOT, does the problem occur, or do you continue to run fine? Does the problem go away after running for a while at cruise? If not, what do you do to make it go away? Interesting problem--I was tempted to say you've got a cylinder dropping out, possibly a bad coil that overheats at WOT, but that wouldn't explain the surging. I'm thinking maybe too much fuel going into the motor at WOT, and then you're burning off the excess once you're at mid-throttle. Tim
jimh	posted 01-12-2011 08:13 AM ET (US) Typically the Yamaha propellers marked "K17" and painted black are made from stainless steel.
jimh	posted 01-12-2011 09:14 AM ET (US) It is not recommended to continue using propellers whose blades are deformed or damaged. A propeller whose blades are damaged will be out of balance. Rotation of an out-of-balance propeller on the propeller shaft can cause damage to the propeller shaft seals and bearings. Repair of the propeller shaft seals and bearings will be much more expensive than repair of the propeller. This makes repair of the propeller a wise investment. It is difficult to make judgments about the performance of a boat-motor-propeller combination when the propeller has damage. A propeller with damage will not perform in the same way as a similar propeller without damage.
Tohsgib	posted 01-12-2011 01:35 PM ET (US) Sounds like you need to go through the carbs, do so before it blows up.
gakirby	posted 01-12-2011 05:28 PM ET (US) Thanks to everyone for your replies! Tim, I'll be sure to adjust my engine height myself this spring once the couple feet of snow outside disappear. My WOT RPM is about 5200 and although I don't stay up there for much more than about a minute at a time, the engine seems to run fine staying up at WOT. To make the issue go away I generally throttle down and shift into neutral and then slowly throttle back up to cruising (about 3500 RPM). This will usually make it run smoothly although sometimes the RPM surging will return. Jim, thanks for the information that the K17 prop is likely SS. I've checked online and prop repair seems much more cost effective than buying a new prop. Does anyone have any experience with prop shops that did a good job for a reasonable price that I would be able to ship my prop to? (I noticed a few places had promotions going on during January offering between 15-25% off the repair price) Am I better off just taking my chance with a local prop shop? (I live in CT)
John from Madison CT	posted 01-12-2011 07:00 PM ET (US) A 17" pitch is the right prop for that engine/hull combo.
Jefecinco	posted 01-12-2011 07:45 PM ET (US) A local prop shop should be fine. Butch
Tom W Clark	posted 01-12-2011 07:56 PM ET (US) Greg, The "K" in Yamaha props simply means it is for intermediate gearcase motors. "K" Series props have a 4-1/4" hub diameter. Both the Yamaha Painted Stainless Steel propeller and the Yamaha Aluminum propellers are painted black (though some Aluminum are painted white) and have very similar shapes. All the other Yamaha stainless steel propellers are polished. Removing the prop and feeling its weight will tell you very quickly if it made of aluminum or stainless steel. Yes, the "17" refers to the pitch and for either the Yamaha Painted Stainless Steel or the Yamaha aluminum 17 is probably what you want. If you use a Stiletto or Turbo brand prop, 17" is to much and you'll need to drop to 15" If you choose a Yamaha three blade Performance Series prop you'll want the 16" pitch. It is critical to repair or replace any pro that gets a ding. Selecting the right propeller is also critical to the performance of your boat and also to the life of your outboard, but you cannot select the best prop for you needs until your motor in running properly and I suspect something is wrong with it. From you description is sounds as it may be loosing a cylinder, but Nick could be correct and it is a fuel delivery problem. It is bets to get it sorted out before doing any propeller testing. As to the motor mounting height, your mechanic is dead wrong. I would be more surprised if it were not so common to hear experienced mechanics and long time dealers continuing to mount outboard motors far too low. I suspect part of the problem is simply that the very experienced riggers who you would expect to know better actually are grounded in their training from 20 or 30 years ago when propeller design was nothing like it is today and motors did need to be mounted lower. Things have changed. A Yamaha 90 on a Montauk can be mounted one or two holes up depending on the prop being used. It should NEVER be mounted all the way down on the transom. My brother-in-law has a 1989 Montauk with a classic Yamaha 90 on it. The motor is mounted two holes up and uses a 19" Yamaha Painted Stainless Steel propeller. It works just fine.
Waterwonderland	posted 01-12-2011 08:42 PM ET (US) Stainless Steel props behave differently than Aluminum props so you must discover what prop you have since it will affect how you mount the engine.
gakirby	posted 01-13-2011 10:40 PM ET (US) Thanks Tom. I'm planning on having my prop repaired locally by H&H Propeller. And I'll bring my boat to the mechanic in the spring and have him try and figure out why it's not acting normally. Once everything's in order I'll raise up the engine a hole or two and see how it performs. If I need to I'll then check out some of the props you posted in another thread Tom. quote: - 13" x 17" Yamaha Painted Stainless Steel, part # 688-45930-02-98 - 13-1/4" x 16" Yamaha Performance Series, part # MAR-GYT3B-V4-16 - 13-1/4" x 15" Stiletto Advantage 4.25, part # D 811315 - 13-1/4" x 15" Turbo Turbo 1, part # DT-13215 Also I hope its a simple fix for the engine. Thanks to all for your suggestions. -Greg
gakirby	posted 01-14-2011 09:16 PM ET (US) Someone from The Hull Truth forums suggested [the cause of the poor performance of the outboard motor] might be [due to] carbon build up. It was suggested I do [an insane procedure in which an enormous of amount of solvent in used in place of gasoline as the fuel in the hope of dislodging carbon particles and anything else in the combustion chamber], as they referred to it. This season I had the gas tank replaced and I have a new plastic tank now. Beforehand I had a old Pate tank installed by the previous owner. Could my engine be the victim of the degrading fiberglass in the old tank? Not sure how long it was in use, I only used it for a month before replacing it but my guess is it was from 2001 when the engine and all rigging was replaced.
jimh	posted 01-15-2011 09:21 AM ET (US) If you had a fuel tank made by Pate Plastics, and if you had fuel in the tank which was a blend of gasoline and ethanol, then you may have had problems with the fiberglass resins of the fuel tank becoming dissolved into the fuel. Usually these problems result in clogging of fuel filters in the downstream portions of the fuel system. Usually you find that fuel filters have a gummy residue in them. You should check the fuel system to make sure it is not contaminated. Since your motor was built c.2001 its rubber components should all be tolerant of ethanol-gasoline blended fuel, but it is not unheard of that 11-year-old rubber components in a fuel system need replacement. Yamaha has a fuel additive product called RING FREE. Yamaha recommends using RING FREE as a method to reduce or eliminate carbon build up in the combustion chamber. If I owned a Yamaha motor I would follow the recommendation of the manufacturer, use the product the manufacturer recommended, and generally follow that regime of treatment. There are various other fuel additives which have been reported to be effective as solvents for dissolving or dislodging carbon particles in the combustion chamber. Use of these solvents has been recommended in various concentrations. In most cases a single can of solvent is used, applied in a combination of full-strength application and diluted application by mixing with the fuel. Procedures which call for use of six cans of the solvent and recommend direct application of an entire can of solvent in each cylinder are excessive. I would not recommend that, and you won't find any such recommendations like that published here. This discussion is getting more into the diagnosis and repair of an engine running problem, not the optimization of boat-motor-propeller performance. Perhaps you should start a new thread in REPAIRS-MODS to further discuss the repair of the outboard motor.
Tohsgib	posted 01-17-2011 11:03 AM ET (US) The guy on Hull Truth is a moron.
tedious	posted 01-17-2011 01:43 PM ET (US) Greg, with the additional details you provided, especially that about the Pate tank, I think I'd start with rebuilding the carbs. If that hasn't been done for quite a few years, it's probably time anyway. It's not a big deal to do yourself, and it should cost you in the neighborhood of $35 per carb for the parts. If you go to a mechanic, it should take no more than a couple of hours labor, if that. Tim
L H G	posted 01-17-2011 09:15 PM ET (US) Also remember that it has been pointed out several times on CW that the engine only puts out about 82 HP to begin with. Yamaha's calling it a 90 was a real stretch, but it sure helped sales of this incredibly popular engine. I would say the most top end you're going to get out of it on a smirked Montauk would be 40-42 MPH. Both the 90 Mercs and OMC V-4's were more powerful engines.
TommyWhaler	posted 01-18-2011 09:06 PM ET (US) Just out of curiosity, wouldn't a jack plate eliminate the mounting problem, since you can adjust the motor up or down?
Tohsgib	posted 01-19-2011 12:18 PM ET (US) Have you done a compression check?
ScooterCO	posted 01-19-2011 04:05 PM ET (US) Sound very familiar. I had the exact same setup and same problems. It was the pate tank causing the issues. Installed a micron fuel filter. Had carbs cleaned twice. Ran ring-free thru motor. It was running great last fall. I did notice that my motor would not go to red line unless I trimmed it up more than I could feel that was necessary. Good luck.. But I am sure you need a good carb cleaning.
Jorgen	posted 01-23-2011 07:04 AM ET (US) You have some greath advices here sofar, all mentioned is good, however, I would advice you to start with the basics: Check the sparkplugs to see if ok and no carbon is set. Check if your air intake is free and clear. Hang the motor on hole 3 from top (3th hole) than check RPM If engine doies not run around 5700 RPM, take the carbs apart and re-work them. good luck