Help, my 90 TLRD is a dog

[Whitedog]

I have a 90 hp TLRD on my Nautic Star 1800. Boat and gear = about 2000# ready to fish. Swinging a 17" Stiletto I could only get about 4400 rpms out of it. Switched to 15" Stiletto I get 49-5000 rpms with motor trimmed out. My last rig was a Hydrasport 1700 same setup about 300# heavier. This boat had a Johnson 90, a 17" SST and would turn 5700 rpms and smoke the snot out of this Yamaha. Any sugggestions short of getting a Johnson as replacement would be appreciated

[tripleb]

Hey Whitedog,

You might want to raise the motor one hole on the transom.

Edited for content

[Ken]

Whitedog,
5000 rpm for that Yammie is right at mid-range for max 4500-5500 per the manual - should be ok.
The cavitation plate of the lower unit should be riding right at the top of the water surface when on plane and trimmed out - not below the surface which would add more drag.
When was the last time the motor was tuned? Spark plugs, carb cleanout, timing checked, compression? Check the carb linkage to make sure the throttle is going to max.
Good luck [img]smile.gif[/img] ,
Ken K

[Whitedog]

Yamaha is new, 3 months old. Throttle appears to open all the way, as for timing I don't have a clue. I guess I need to drag it all the way back to the dealer (50 mi) for a checkup.

[Bazooka Joe]

I have a 2004 Yamaha 90 on a Smokercraft 16 ft which previously had a freshly overhauled 88 hp Johnson. I'll see if I can help.

First question, what is the max hp that your boat is rated for? I think the Yam 90 might have its hands full if not mounted on a boat with somewheres close to 90hp as the max rated power.

Next, what speed are you running? By the tach numbers you stated, you should be about 31-32 mph, which seems quite slow and I can see why you'd be unhappy compared to the OMC which was running 43-44ish mph. I am assuming that even if the tach is wrong, your boat is going substantially slower than the Johnson 90 could push it. (what year Johnson 90, btw?)

The book says to run the Yam 90 at 4500 to 5500 rpm, but I think I would have been VERY unhappy with propping my Yam on my boat to be WOT at 4500 or even 5000. I think you will be MUCH happier with the motor if you prop to upper 5K as the Yam 90 continues to make nice power to 6000rpm and rev limits at 6200.

However, thinking about trying to hit those rpms, it seems scarey to think that you would be running a 13p prop. Something has got to be wrong, IMO.

Also, yes, the Yamaha 90 is NOT going to run with a healthy OMC 90. For my application, the Johnson could tear the Yam completely apart on holeshot and still push the same boat about 3-4 mph faster.

The Yam does have good midrange power and runs & idles very good. It's just a light on off-throttle response until 3K rpms or so, and is not as strong on top.

Something else of note, I installed Boyesen reeds and it helped the motor idle better plus boosted the lower rpm power. W/ the Boyesen reeds, it comes on the power at a lower rpm. $75 very well spent, IMO.

I currently run a 16P SS prop on the Yam for skiing and it does good on skiing holeshot and runs about 42 mph at 5900rpm. For fishing, I run a 17p SS which runs out in the upper 5K, but is marginally at best for pulling a skier.

Good luck with it and keep us posted what you find out.

[Whitedog]

The Boat is rated for 115. According to Yamaha most applications for this weight or type boat usually require a 15 to 17" prop. It could be a timing advance issue? Hole shot is pretty decent, my problem arises @ about 4000 rpms. The motor maxes out about 44-4500 trimmed down. trimming up to max brings it to 5k. At this level I get a lot of back spray over the transom and a roostertail of about 2'. The motor is mounted so the cavitation plate is even with the lowest point of the transom. I'm thinking that I may be experiencing a lot of drag @ this setting. Would raising the motor an inch or two make much of a difference? By the way, the Johnson was a '96 model. I think that Johnson looked @ 90 hp in its rear view mirror.

[tripleb]

Hello Whitedog,

As long as you are not currently experiencing any cavitation issues, moving the motor up one hole will reduce drag and probably increase RPM's. This drag reduction and RPM increase may increase your WOT speed.

[Bazooka Joe]

Whitedog,

The 90hp OMC, according to Bass & Walleye boats' test, turned about 91 hp @ 5200 rpm while the Yam 90 spun the same 91 at 6000 rpm. However, at 5100 rpm, the Yam 90 only produced 81 hp. This was from their 90hp comparison test in 4/97. The Yam is basically unchanged since then, I believe.

Back to your motor....

Ok, since the outboard pulls out of the hole properly, then that eliminates a whole bunch of potential problems in the powerhead mechanics. I don't know what ignition adjustments are available. Unlike a lot of outboards with those contraption inter-related linkages from hell, the Yam is a simply arm back to the brain box. Not a whole lot to adjust I think, but look closer, there might be.

It sounds like you have something weird with either the hull or rigging which is causing a whole bunch of drag, which maybe prevents the front end from lifting up out of the water properly.(?) Does the boat seem to plow or does it dry out and get back on the rear of the hull properly? (guessing at the problem w/ the information given)

The back splashing you describe is from the solid water (coming off the bottom/back of the boat) hitting the front of the lower unit above the cavitation plate. This could mean that the motor needs to be higher on the transom.

More questions...

Does the prop seem to blow out at full trim? I'm guessing not, or else you would be hitting full revs rather than the 5000 rpm.

Is this a new boat which has never been rigged before?

How does the motor sound? The Yams typically sound pretty eager to pull. Keep in mind that the Yam is 3 cyl so it will not howl like the 4 cyl OMC.

If you bought this boat rigged, I would take it back to the dealer and see what he can do for it. If not, (or the dealer is clueless) then keep trying some things and we'll try to help.

One other thing to brighten your outlook on the Yam 90- It has a VERY cool choke system. Pay close attention to the choke instructions in the manual. Basically, there is NO choke for the operator because the motor's choke system is all automatic. You simply keep the throttle closed and spin the motor until it fires because the brain box system pulses the choke by itself according to engine temps. Pushing in the key switch serves no purpose, other than to exercise your casting wrist. Aside from the extra spinning to start a cold engine, the Yam 90 will start almost like an EFI once warm. This was a HUGE improvement over my old OMC 88hp which almost always needed the high idle lever flipped, and would blow a huge cloud of smoke on a warm engine warm up.

Also, one more thing- if your idle seems rich and/or it stammers too much, you can adjust the fuel screws by removing the brass idiot plugs to gain access. Makes it very easy to adjust for cooler temperatures.

Good luck with it!

[Whitedog]

Joe,
I'm Thinking it might be a rigging problem. The boat plows along until I start to trim up. By this I mean the motor is not tucked under but has a little outward trim to it. When I trim out all the way it starts acting correctly. With the present setup I occaisionally lose a bit of hookup on fairly sharp turns in choppy water. When this happens I'll turn 5500 rpms but I don't have a solid hookup. It is a new boat rigged by the dealer. I think tomorrow or Friday I'm gonna jack it up an inch or so and give it a whirl.

[Whitedog]

Well,
I raised the motor 1 hole and then took it out on the lake. Water was pretty choppy with a 10 mph southeast wind blowing. Rpm ran up to 5200, with 2 grown men, 3 batteries, *****ing mtor and about 20 gals gas. No problems noted except once or twice I lost hookup in bouncing turns. Motor performed slightly better. Previously I experienced what I would call a lot of drag until I trimmed out. This phenomena is markedly decreased.. I spoke with Marcus @ Powertech props and he recomended switching to a semi cleaver type prop that would be easier to turn than the stiletto. All things said I believe the mounting change and upcoming prop change may get me to the magic 5500+ rpm range.

[tripleb]

Hey Whitedog,

Glad you took my advice Actally, I had to do the same thing with my 90 ..... even though the cavitation plate was already above the bottom of the boat, I raised it one more hole and the RPM's pick up, speed picked up, and I had little to no "blow-out".

[SteveE]

Interesting thread...I've been dealing with a lot of the same issues with a 90TRLD on an '04 Blue Wave 180VBay. WOT with a PowerTech 17p gives 4,700rpms (boat tach) 5,000 (shop tach), 37mph (gps) trimmed nearly full up, with 2 people, full fuel, fishing tackle, etc. Dealer says the 17p is what they have found to be the best prop for this rig and the rpms are within the operating range. One "prop guy" says dealer is basing this on a test load a lot lighter than typical fishing load and a 15p prop is the answer.

Something Bazooka mentioned about back splashing makes me wonder if motor height could be part of the issue. I see a lot of back splash at all trim settings. This model boat has what is called an "engineered pocket" at the stern, I call it a box tunnel (the stern is recessed 12" or so) so I'm not sure where the cavitation plate should really line up. The motor is presently in the lowest hole.

I'm just wanting to get the optimum performance but more particularly don't want to damage the motor from low rpms or lugging.
Any suggestions or ideas (particularly with this model boat or this type stern) would be appreciated.

[Ken]

Steve,
Since you are able to get 5000 rpm out of that 90 Yammie at WOT and trimmed out, I don't think you are "luggin" the motor at all.
You could drop down to 15 inch pitch and the max rpm would probably go to 5500. That would get you a quicker hole shot, but I don't think much increase in mph top end.
With the motor WOT and trimmed out, have someone check the position of the cavitation plate. It should be just on top of the water surface. There should not be any water running over the top of it. You want the motor mounted as high as you can w/o the prop ventilating (blowing out) when you WOT and trim out for max speed.
How much does your hull weigh? If it is more than 1100 pouds (dry), then that 90 Yammie is doing a pretty good job already to reach 37 mph. What is the max rated hp for the boat? If it is more than 90 hp, then 37 mph is about all you are gonna get with the 90.
Good luck [img]smile.gif[/img] ,
Ken K

[SteveE]

Ken: Good point about checking the position of the cavitation plate while running. I guess that tells the story on correct motor height regardless of stern type/design???

Dry wt. of this boat is 975# and max. h.p. is 115, so maybe my numbers are "as good as it gets". Hole shot as I would describe it is okay, 4-5 seconds to get on plane and top speed is fast enough for this old fisherman. Really happy with the Yamaha.

If checking the cavitation plate while running indicates the motor is low, is moving the motor up as simple (or as difficult) as removing the 4 mounting bolts and lifting the motor (by the ring attached to the head under the cowling) to the next hole position?

Thanks for the suggestions and I hope things are getting back to normal (post Rita) on your side of the State.

[Whitedog]

Steve,
First I think the Yamaha 90 may be overated in the horsepower category. I have had many people that sell Yamaha along with other brands say that Yamaha just doesn't have the cajones that Mercury or Johnson/Evinrude has. I will say that the Yamaha is a well made and reliable engine. That aside to raise your motor you can do what I did. Lower the tongue of your trailer to as low as you can get it. Place a large wooden block such a a 4x6 under the skeg of your motor. Back the upper transom bolts out and loosen the lowers. Using the trailer jack slowly raise the tongue until the bolts line up with whichever setting you wish. some will say you can damage the skeg this way, but the Yamaha 90 is a relatively light motor (261#) and is easily moved.

p.s. Boating life magazine did a test of a Blue Wave 18 V bay and 90 hp Yamaha. Their test revealed 42 mph @ 5600 rpm turning a Power Tech 16p prop.