Complex problem with my Yamaha, need some help

**FurFlyin** · 05-18-2018, 07:55 PM

Long story but I'll try to just hit the highlights with the pertinent info.

Bought a boat last fall. It's got a 1998 Yamaha 115 V4 2 stroke on it. The boat is an Xpress H56 with Hyper lift hull. I took a boat mechanic with me to check out the motor before buying. He noticed that the prop shaft was slightly bent. Ended up buying the boat, the mechanic had a machine shop cold straighten the shaft. I put a 20P Laser II prop on this spring to help with bow lift as I added on to the front deck this winter before recarpetting. Boat ran great, then about 2-3 weeks ago the lower started ticking. Got worse and got loud. I removed the bottom plug and there was metal all over the plug. The oil looked like metallic paint. As luck would have it, the mechanic who I paid nicely, in cash last fall to check and go through my lower, dismissed having anything to do with the lower unit failure, without so much as the courtesy of looking at it. He diagnosed his lack of responsibilty for the problem over a text message.

So I order an SEI lower and install. I also put on a 6" jack plate. I did the 5 hour break in exactly as described. During this period of running, I worked up to 2500 RPM's and while running at that speed the motor started spitting and sputtering. I thought I had sucked something into a carb, or thought that maybe water got through my water seperating filter. After a few minutes of spitting and sputtering, everything levels back out. I do the 6-10 hour break in exactly as described, the motor runs fine. When the time comes to finally give her full throttle I did and the motor was VERY sluggish. As in it took upwards of 45 seconds - 1 minute to get on plane and the top end was turning around 4200 RPM's.

Since the motor spit and sputtered, I assume the loss of power is a carb issue. I removed both carbs, tore them down and cleaned them. I removed every jet that had a screw slot across it, cleaned them and reinstalled. The floats looked good as did the needles. I decided since the motor was 20 years old I would replace all the fuel lines from the motor to the carbs, including a new OEM primer bulb and also installed a new OEM fuel pump.

I took her back out and it did the same exact thing. I ran the jack plate up to the max and it did the exact same thing. I removed the jack plate, put the motor back on in exactly the same hole position as it was in prior to the lower replacement. The motor did the exact same thing. A buddy of mine suggested that I try a 16 pitch prop to get my RPM's back up so I did.

The motor jumped up on plane and topped out at 5400 RPM's, but I lost 8 mph. Dropped from 45-37.

I decided that the new SEI lower must be the wrong gear ratio. I checked my old lower and it's a 2:1. SEI only lists a 2:1 for my motor so I dropped it this afternoon to check it. I checked and double checked and it's indeed a 2:1 as well.

So, that means that I've lost power, somewhere, somehow, right?

Compression on all 4 cylinders is 120-122. I tested spark with a gap tester this afternoon set on 7/16" and all 4 are jumping that gap well. The fuel system is spotless with all new lines. The idle timing is spot on. I have not checked the WOT timing yet but will. There is no fuel being spit out the front of the carbs so I think the reed valves are okay.

I am at a loss here. Granted I'm not a boat mechanic but I'm a fairly mechanical guy. I don't have all the testers and such, and I've scheduled an appointment at a reputable Yamaha mechanic shop, but that's over 2 weeks from now.

Does anyone have an idea what the cause of this could be or what else I can check? This sounds like one of those $1000 "we can't find an issue" problems on the horizon to me.

But, a new but same gear ratio lower unit on the same motor, with the same prop, should turn the same RPM's and run the same speed, correct? What am I overlooking?

**"G"** · 05-19-2018, 03:07 PM

Try a 19 pitch prop

Sent from my SAMSUNG-SM-G891A using Crappie.com Fishing mobile app

**FurFlyin** · 05-19-2018, 05:25 PM

Originally Posted by G";3637002]Try a 19 pitch prop

Sent from my SAMSUNG-SM-G891A using [URL="http://r.tapatalk.com/byo?rid=87936

Crappie.com Fishing mobile app[/URL]

That's just going to cause me to lose RPM's. The point of the whole story is that the boat ran fine with a 20 P prop before changing the lower. Now it won't even remotely pull a 20 and a 19 wouldn't be much better. The 16 is running 5400 at WOT where the 20 was running 5400 at WOT prior to the lower going out.

**Cray** · 05-19-2018, 06:36 PM

I don't want to sound like a jerk here, but your story has me confused. Your mixing the not running right with a prop and lower unit issue. Is the motor running right now and did you fix that problem? If motor is up to snuff and running like it should then you have a gearing issue. But first it needs to be running right then progress to the other problem. If motor is not up to snuff it can't pull either prop up to what it should.

**doggone** · 05-19-2018, 07:47 PM

Quote
"The motor jumped up on plane and topped out at 5400 RPM's, but I lost 8 mph. Dropped from 45-37. "

That sounds like the hub is spinning some. 5400 rpm should be close to top rpm for this motor. And from what I have read on that combination 45 to 50 should be closer to top end. And I don't think you could change the setup enough to drop the top end that much with the same prop unless you did something really funky. That leads me to think the prop is slipping on the hub some.

Quote
"I worked up to 2500 RPM's and while running at that speed the motor started spitting and sputtering. "

That could be a lean condition or a firing problem. Since you changed all the fuel related stuff that leads me to believe an intermittent ignition problem. THAT is where the hard part comes in. If you run it on muffs and have a something to see if if its firing right on all cylinders at different rpms ,then you can figure it's still something with the fuel.

I have something similar happening with my V4 Johnson since last time out. I have to figure it out...like you I have some mechanical aptitude and experience with mechanical things but not the training and experience a good mechanic has and all the tools . I may be headed to the shop too if I don't figure it out.

**FurFlyin** · 05-19-2018, 09:56 PM

No offense taken Cray, it's confused the crap out of me.

The motor was running great when the lower went out. I put the new lower on, and did the break in starting at 1500 rpms and slowly working up to 3500 over a 5 hour period. The motor ran great that whole time, other than about 5 minutes towards the end where it spit and sputtered. When it got time to throw the coal to it, there was no power. Not coming out of the hole or at top end. I couldn't turn over 4200-4400 RPM's.

In my mind, the most likely culprit was the new SEI lower, since that was all I had changed on the motor.

I finally think that I figured out the problem this afternoon and it was something so simple that an experienced mechanic would probably have found it in the first 5 minutes of checking the motor. When I did a leak down test today, while I had the motor turned to TDC1, I looked at the piston and it was coated in wet, black oil residue. The plugs were real wet too. I guess the problem was the motor being overly loaded with oil residue from basically idling for 5-6 hours. I did a "decarb" and put new plugs in and it completely changed the engine. I haven't swapped back to the larger prop yet but it will over rev now with the small one on. I couldn't run over 2/3 throttle. At 2/3 throttle I was turning 5800 RPM's and I didn't leave it there long and sure didn't want to go over that. I "think" it's back to where it will now turn the 20P prop at 5400, just like it would before the old lower turned loose.

If I go out tomorrow after church or Monday it will have the 20 pitch prop on it. If it doesn't run good, then it's just about got to be electrical because it ran at more RPM's with less throttle today than it has with the smaller prop on it.

**Cray** · 05-19-2018, 10:31 PM

Sounds to me like you solved your problem. Oil soaked plugs will do it every time. I was going to say that with that motor on that hull you should be turning with a light load in the neighbor hood of 5500-5700 at optimum for that motor and should have been turning the 16 at about 6800. If she still only pulls 5400 max trimmed out I would seriously consider running a 19 to got max rpm up around 57-58 then loaded she should drop to around 5500-5600. Good luck. Believe it or not sounds like about ready to just go fishing instead of working on it.

**FurFlyin** · 05-19-2018, 10:42 PM

Thanks for the info and I'll believe that not working on it part when I see it. LOL

I left out part of the whole story on purpose just to condense it to pertinent info. I had ordered a 6" jack plate the day before the lower went kaput. I installed it while I was waiting on the lower to come in. Due to all the problems, in an attempt to get everything back as close as I could to before I had problems, I took the jack plate off. I'm sure a jack plate puts more load on the motor, but having said that, if I drop to a 19 pitch prop and get to 5500-5600 do you think I can gain any performance if I put the jack plate back on?

I need to get more of the bow of this boat out of the water to maximize performance. The spray is coming up about even with the console. Too much boat in the water at WOT. I put a "bow lifting" stainless prop on and it helped hold up the bow more, but it still needs a little more help to completely keep from porpoising. Turning more RPM's might fix that, but do you think the jack plate would help?

**"G"** · 05-20-2018, 09:41 AM

Just a thought.....Going way back now....bent prop shaft....what ever it hit to bend the prop shaft ....the force could have sheared the key in the fly wheel ...yep way up at the top of the motor...Possible key shear and Fly wheel moved a little and wedged by broken key. If so...your timing is off. This could be the cause of your performance problem.

**Cray** · 05-20-2018, 09:48 AM

Adding the Jackplate should give you more bow lift. The setback actually gives your motor more leverage to lift the bow. Watch close that you don't get it to high and lose water pressure. It takes a little time and effort to get one right but worth it in the long run. Start out with cavitation plate even with bottom of hull, make a good run with a couple of from dead stop to plane. Then move it up 1/4 inch and do it again. Move up a 1/4 at a time until you experience some blow out when trimming up or on jumping up on plane. One thing it should do is allow you to ride a little higher out of the water at a slower speed. Good luck, just remember take your time.

Thread: Complex problem with my Yamaha, need some help

Thread Tools

Display

Complex problem with my Yamaha, need some help

Tags for this Thread

Posting Permissions