Yamaha 75hp 4stroke owners, and a few other OB’s.

i was reading this on another site, and they are discussing which motors come from the factory detuned with something as simple as a restrictor plate, and how to change it…

like a 75hp 4 stroke yamaha, to a 90.

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IF it is an EFI, 4 stroke, yes. The ecu will adjust the fuel and timing for the added air flow.

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You can do the same on a Yamaha 50 hp 4 stroke and make it a 60. Remove number 6.

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resetting the ecu after making changes.

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ntropy: Try disconnecting your start battery for about 5 minutes. That causes the ecu to re-learn all the flows. Your ecu may still retain the low speed fuel and air curve of a 50hp motor instead of the 60hp. Try disconnecting the battery for 5 minutes, then run it like you stole it for the next few trips out. Just like a car, these motors have a “learning” ecu. You need to make it brain dead so it re-learns. If that does not cure it, try removing the mass air sensor and cleaning the calibrating wires with brake parts cleaner. DO NOT USE carb cleaner, it contains oil and will re-coat the wires and cause bad flows.

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http://www.refugeforums.com/refuge/showthread.php?t=771608&page=4

maybe it will help someone out on here.

This is sweeeeet! Can hardly wait to do this to my F75!! This is what my 1650 Nav needs! Thanks alot Perch!!

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This is sweeeeet! Can hardly wait to do this to my F75!! This is what my 1650 Nav needs! Thanks alot Perch!!

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Rangerski

Let us all know how it works for you. I’m sure lots of guys will be interested.

There goes the mfg’s warrinty

Does that work on all 4 stroke EFI outboards? Like a 2003 60 Johnson?

Thats quite alright with the warranty, it’s a Yami! Besides it’s a 5 minute deal to remove restrictor plate and 5 minutes to replace I will be sure to let everyone know how it works after some additional research and the Rainy River run….. No need to take any chances yet…

Interested in tuning yammie’s check out the HydroTech website. They do some crazy things with outboard motor’s.

Not sure I would do this to my personal motor.

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This is sweeeeet! Can hardly wait to do this to my F75!! This is what my 1650 Nav needs! Thanks alot Perch!!

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here is a reply from one of the guys that did this to a yamaha 75 four stroke.

perch_44 wrote:

That is it! US-1 is the man. I did this to my 75 last year. With a 15 pitch prop at 75 I was seeing 33-34 mph. With a 19 pitch prop with the restrictor plate removed I was seeing 46mph. Nice little change to say the least. Be careful removing the restrictor plate, it is a tight fit.

Still debating about the 10″ jackplate????????

and remember, you will probably have to go to a higher pitch prop, as your rpms will increase with what is on there now, and you will probably hit your rev limiter.

the guy that is posting most of this – 1995 US1 on the refuge forums, is an ex factory mercury tunnel hull racer, and holds numerous records. and still works with Mercury’s development team.

he also is the guy that created the new reed sets and instructions on how to turn certain 40hp mercury 2 strokes, into 66 hp machines, for like 600 bucks, and retain all reliability in the motor still.

if he says something will work, and still be reliable, i would trust him as much as any service tech at any shop.

something else that has been brought up, is the fact that most manufacturer certified service techs know these little tricks, but have been threatened of being stripped of their certifications if they disclose them.

I’m very happy with my 75 Yami and dont want to mess with any of it!

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There goes the mfg’s warrinty

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you can always put the restrictor plate back in, and no one is the wiser.

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Does that work on all 4 stroke EFI outboards? Like a 2003 60 Johnson?

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I will ask him for you, and let you know.

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I’m very happy with my 75 Yami and dont want to mess with any of it!

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the 75 yamaha uses the same block and carbs, cylinder specs, stroke, everything as the 90, they simply choke it down to 75hp.

just like the early 2000’s 40hp 2 stroke and 4 stroke mercs. they use the same block and internals as the 60hp model, they are just “detuned”.

this happens a lot more then people think. another example, on a 35hp vanguard on surface drive mudmotors, if you put a carb spacer plate, hotter plugs, more open exhaust pipe, and a different governor spring, you can get that motor to about 45hp in like 1 hour of your time, and about 300 bucks.

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this happens a lot more then people think.

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Definitely. On my new boat is a 150 Verado. The specs on the Verado are identical to the 175 and 200 Verados. It’s a different ECU. That’s all. Now I just need to find a wrecked 200 Verado and get the ECU out of it.

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this happens a lot more then people think.

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Definitely. On my new boat is a 150 Verado. The specs on the Verado are identical to the 175 and 200 Verados. It’s a different ECU. That’s all. Now I just need to find a wrecked 200 Verado and get the ECU out of it.

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Ebay maybe?

OK, I did some digging relative to my 75hp Optimax. Here’s a snapshot of the parts screen, sure ‘nuf, #17 is an insert in front of the throttle body.

Hmmmmmmmmm?

HRG

Wonder if there are any options on my 2001 F80 which is the same as a F100 basically but these are carb motors.

So is this only EFI’s? I have a Merc 4 75 carbed with CA emissions. Any advice?

i threw the questions out there for everyone, i’ll let you know what i find out.

I saw that, thanks Perch!

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This is sweeeeet! Can hardly wait to do this to my F75!! This is what my 1650 Nav needs! Thanks alot Perch!!

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here is a reply from one of the guys that did this to a yamaha 75 four stroke.

koldfront kraig wrote:

That is it! US-1 is the man. I did this to my 75 last year. With a 15 pitch prop at 75 I was seeing 33-34 mph. With a 19 pitch prop with the restrictor plate removed I was seeing 46mph. Nice little change to say the least. Be careful removing the restrictor plate, it is a tight fit.

Still debating about the 10″ jackplate????????

and remember, you will probably have to go to a higher pitch prop, as your rpms will increase with what is on there now, and you will probably hit your rev limiter.

the guy that is posting most of this – 1995 US1 on the refuge forums, is an ex factory mercury tunnel hull racer, and holds numerous records. and still works with Mercury’s development team.

he also is the guy that created the new reed sets and instructions on how to turn certain 40hp mercury 2 strokes, into 66 hp machines, for like 600 bucks, and retain all reliability in the motor still.

if he says something will work, and still be reliable, i would trust him as much as any service tech at any shop.

something else that has been brought up, is the fact that most manufacturer certified service techs know these little tricks, but have been threatened of being stripped of their certifications if they disclose them.

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Going with a 19 pitch prop would make the motor troll to fast.

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There goes the mfg’s warrinty

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you can always put the restrictor plate back in, and no one is the wiser.

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I talked with Don Nelson this past weekend at the Skeeter Boat Center open house. Don is one of the lead technicians with Yamaha through the factory. I discussed this concept with him in general terms to get his honest take on modifying these motors in this manner.

Here’s what he told me. You can definitely get more horsepower out of a Yamaha this way. Pulling the restrictor plate will increase the air flow to the motor. The Mitsubishi made ECU’s do not have the ability to “re-learn, be re-programmed or remapped” by anything the owner can do. I asked him about unplugging the battery to “clear” the ECU. He laughed and replied “they’re not clock radios.”

So, you can pull the restrictor which will result in more airflow and a leaner mixture which will make more power. He also stated one could expect to see very high cylinder temps due to the lean condition and that the alteration would likely result in a catastrophic failure at some point down the road.

I also asked if a technician would be able to tell if someone had removed the restrictor and later replaced it before bringing it in for warranty work. His reply was “definitely.”

He did go on to offer a way one could make a 70 into a 90, etc., in a way that wouldn’t cause damage. He said all you would need is the ECU out of a 90 and to remove the restrictor on the 70. Bingo. Fast outboard, no lean condition.

I share this to give someone considering this mod some “from the factory” info regarding the alteration. If you still feel confident in making the mod, knock yourself out. I was curious about the process myself and since it sounds like going down this road comes with some serious risks I thought it best to share it with everyone here at IDO because motors aren’t cheap and a modified motor would definitely be rejected from warranty coverage.

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I’m very happy with my 75 Yami and dont want to mess with any of it!

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X2 After reading James’ and Koldfront’s posts

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There goes the mfg’s warrinty

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you can always put the restrictor plate back in, and no one is the wiser.

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I talked with Don Nelson this past weekend at the Skeeter Boat Center open house. Don is one of the lead technicians with Yamaha through the factory. I discussed this concept with him in general terms to get his honest take on modifying these motors in this manner.

Here’s what he told me. You can definitely get more horsepower out of a Yamaha this way. Pulling the restrictor plate will increase the air flow to the motor. The Mitsubishi made ECU’s do not have the ability to “re-learn, be re-programmed or remapped” by anything the owner can do. I asked him about unplugging the battery to “clear” the ECU. He laughed and replied “they’re not clock radios.”

So, you can pull the restrictor which will result in more airflow and a leaner mixture which will make more power. He also stated one could expect to see very high cylinder temps due to the lean condition and that the alteration would likely result in a catastrophic failure at some point down the road.

I also asked if a technician would be able to tell if someone had removed the restrictor and later replaced it before bringing it in for warranty work. His reply was “definitely.”

He did go on to offer a way one could make a 70 into a 90, etc., in a way that wouldn’t cause damage. He said all you would need is the ECU out of a 90 and to remove the restrictor on the 70. Bingo. Fast outboard, no lean condition.

I share this to give someone considering this mod some “from the factory” info regarding the alteration. If you still feel confident in making the mod, knock yourself out. I was curious about the process myself and since it sounds like going down this road comes with some serious risks I thought it best to share it with everyone here at IDO because motors aren’t cheap and a modified motor would definitely be rejected from warranty coverage.

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he is a yamaha tech…. numerous people have stated that you yamaha revokes factory certifications if its known that they divulge this information.

I understand your viewpoint james, but too many techs and dealers do not fess up to things like this, for lots of different products.

just like how Guide Series rods are made with St Croix blanks. good luck getting someone at gander to admit it.

or that the new bow i just bought isn’t the same as a Diamond Marquis, just because of the private label name on it.

it would be interesting to hear opposite viewpoints from the two sources though. a yamaha factory tech on one side. and a factory racer who has done this type of thing for years.

I hear ya’. I definitely kept the BS detector set to high gain. Nothing registered on the meter.

The biggest point for me was that the Mitsubishi made ECUs could not re-map themselves under any circumstance. He went on to name a couple sensors that would be needed to be able to do that, if the ECU was designed with that capability, but those sensors aren’t even on motors of this HP. Apparently the dominant sensor is a throttle position sensor. And that sensor is completely incapable of making any kind of adjustment for air volume. It just knows that at a given throttle position the motor gets X amount of fuel. Increase the air flow without adjusting fuel delivered at a given throttle position… and you’ve got problems. And that’s the scenario on the yamaha motors. Other motors might be completely different.

Again, tweak away if you’re out of warranty or if you think the motor can handle it. I was definitely curious myself.

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just like how Guide Series rods are made with St Croix blanks. good luck getting someone at gander to admit it.

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PS – St. Croix hasn’t made the Gander rods in a long, long time. But you’re right, at one time they did. But it has been many years. Most of the people working at Gander were still fishing snoopy poles and wouldn’t have been around back at that time.

Interesting, I just called the dealer and inquired about the P/N for both the ECU and throttle body and they are identical for the F75 and F90. This tells me with the restricter plate removed the powerhead would now be a 90. The last thing I would like to be certain about is if they actually program these ECU’S after installed accordingly? I will let ya know what I find out. Also it no one would comment on if this is possible or any info…. It’s olny a $600 diff. from 75hp to 90. My tub is rated for a 75 when the same rig with a counsel can have a 115? Thats what gets me

As some one who had to replace an ECU this spring (defective), I can add a few tidbits of information to this post.

You would be amazed at what the diagnostics computer can tell you about a motor(and how you use it) when they get you hooked up. Youre not going to “hide” anything from that computer readout.

The ECU is a plug and play installation. No tuning required for my 115. I did my own installation with no trip to the dealer.

I don’t get it… whats the big deal if your just going to gain a couple miles an hour?

It seems like a lot of risk for the return your getting.

The part numbers are not identical for the f90 verses the f75 ecu F75# is 6d6-8591a-11-00 F90# is 6d8-8591a-11-00