Impeller tolerance

[dhoganjr]

smackdaddy53 » 06 Sep 2014, 22:11[/url]"]I sure hope you are right bro! I was about ready to get a 90

I hope so too, you would love a 90 on there, but I know you are trying to keep the weight down. If you don't figure it out, definitely get it checked out by your marine shop. I'm almost sure it's going to be something with the adjustments.

I know the pump is pretty straight forward, just couldn't get it all to add up. Very few adjustments and it either works or doesn't. When you said it was running good I never thought about that end of it. #-o

 

[smackdaddy53]

Yeah, I want to draft as little as possible. I should have built it a little more scantily but I like sturdy.
We will see tomorrow! Thanks

 

[dhoganjr]

Nothing wrong with sturdy, I get ribbed all the time for having a river barge.

 

[Tbradley]

What about the setback of the jack plate? Should he have a splash plate to help direct the water to the intake? Maybe it's going over the foot?

 

[JL8Jeff]

I wonder if it's your linkage or cable adjustments. I have a 1994 Mercury 60/45 jet on my Lowe 1652 tunnel jet and it flies at WOT. Maybe your gate isn't adjusted properly.

 

[smackdaddy53]

No way water is going over my foot, when the motor is straight the front edge of my foot is about 1" from my tunnel and when it is turned either way the corner of the foot actually goes over the edge of my tunnel a little.
Jeff, how much does your boat weigh compared to mine? Mine is pretty stout.
I am taking it to the mechanic tomorrow to synch timing and carbs and get everything set right as far as WOT and getting max rpms. We will see from there. I am about at wits end with it and thinking about just ordering a brand new Yamaha F90 Jet

 

[smackdaddy53]

dhoganjr » 06 Sep 2014, 20:34[/url]"]One question come to mind, do you have a tachometer on there to verify that you are turning max rated rpm's .

I was thinking the same thing. At WOT for that motor you should be running between 5000 & 5500 RPM. My motor runs 5250 at WOT.

What size is your tunnel? It looks pretty big to me in the photo.

My tunnel is EXACTLY the same dimensions as a local guy has Alweld build jet tunnels for his shop where he has been rigging, running and selling outboard jet rigs for over 20 years. I actually went to his shop and measured his tunnel and fabbed mine exactly like it. He runs 4 stroke 60/40's on his 1552's but they are flat bottoms bare bones and he gets well over 30mph out of his rigs.
19" wide on bottom, 14" wide on top, 28" long, 2 3/4" deep, flat for the last 12". The only notable difference is it looks like his jet foot actually tucks under the leading wdge of his tunnel if you look at the picture. I am going to drag my boat to his shop tomorrow and see what he thinks the flaw is. I just set my height like everyone recommended on here, my tunnel hits right at the front grate pin hole. Is that possibly too high for mine? I know every boat is different and my design is not textbook but in theory it should work, I guess I have to just find out how!
Here are two pictures of mine and his.
Mine-

His-

 

[JoshKeller]

im willing to bet you have a cylinder that isnt firing or getting fuel..

 

[smackdaddy53]

One more good pic of mine

 

[smackdaddy53]

im willing to bet you have a cylinder that isnt firing or getting fuel..

I had the compression checked and it was 118, 118, 117.
New plugs, motor sounds good from what I can tell.

 

[JoshKeller]

verify you're getting spark/fuel on all 3 cylinders? keep in mind with a jet, theres no real resistance like a prop and it can sound like its reaching plenty of rpm with a cylinder down.

 

[smackdaddy53]

I definitely can't rule it out at this point. I am sure the mechanic can isolate the problem tomorrow.
I pulled the plugs today and they were all dry and looked the same but who knows. I had to replace the oil warning sensor module so who's to say the CDI is not shot? At this point $250 is a drop in the hat, if it may fix it I will try it!

 

[dhoganjr]

Since you mentioned replacing the oil warning sensor, I don't know if this one has the technology or not, but if they set a fault code it limits rpm's to around 2000 until reset.

 

[dhoganjr]

Those intake fins should feed the pump with little if any cavitation. If it was you would know it, the rpm's would rise sharply with injected air until the pump loaded again causing it to surge. Exhaust sound would drastically change also.

 

[JL8Jeff]

I think my hull is listed as 425 lbs but I have the center console and some extra weight up front. But it's pretty light compared to some of these well equipped boats. It reall sounds like you are not getting the top speed out of your motor.

 

[smackdaddy53]

I don't think this motor has a computer, it is a 1997 Merc 60.

The cylinder misfiring has me thinking about what I have been seeing.
The air intake had some 2 stroke residue inside after the first time I ran it and I cleaned it out with brake cleaner and after the second run it did the same thing.
When the motor is idling I can see it jump every now and then hard enough for it to move the steering wheel each time. This may also explain the wobble causing the impeller to contact the liner.
The motor also sounds like a bearing may be going out now, probably from running it with a misfiring cylinder.
When I got the motor the shop said the compression was 118, 118, 117 and it was written by each spark plug too. The bearing was totally gone and the liner and impeller were chewed up from the bearing allowing the shaft to drop. I wonder if all of this is tied together?
Im taking it to the mechanic her in about an hour and we shall see what he finds. It is all coming together now and sounding a lot like I'm going to get this one running, sell it and buy something else, maybe a Yamaha F70 Jet.

 

[smackdaddy53]

No available mechanics today, dragging it 80 miles to a jet guy that knows his stuff at 8 in the morning. Hopefully all goes well.

 

[JL8Jeff]

I tried to GPS mine tonight but it was windy goining upstream and the batteries were dying in the portable GPS so I got around 26 mph going upsteam into the wind before I lost the reading. It was cruising along on plane at 18 mph at 2/3 to 3/4 throttle easily. I don't normally run full throttle and it was starting to porpoise before I was getting the full reading anyway so I had to back out of it. My motor was beat up during Sandy and I'm surprised how well it still runs. I hope you have a simple issue like some sensor keeping you from getting WOT properly.

 

[LarryMc]

After you posted the measurements, I can see that your tunnel isn't too big. In the photo, it just looked bigger than most jet tunnels. As for your height adjustment, all jets won't work with the height set even with the front pins. Mine is set even with the leading edge. Any higher and mine will cavitate. I don't think that cavitation is your problem though. If your pump was cavitating, it would over rev and you would hear the difference in the sound your motor makes. I'm in agreement with the guys that think your problem is that your motor isn't reaching full RPM.

 

[smackdaddy53]

So far we found pinholes and a crack on plug boots. When we went to grab the plug wire with the plug pliers with it running they were arcing to the pliers robbing spark. About to put some new boots on and see what happens.