My newest jet problem---UPDATE---

Well, after getting my new rig (1648 with 50 hp jet), it ran like a champ for 2 months. It would absolutely fly, and it would jump on plane in less than 2 boat lengths. But over the last few weeks, performance has been lagging. My boat takes forever to get on plane, and as it gets on plane, it cavitates like crazy. I mean terrible cavitation!!! The boat then runs fine for a few minutes, and starts to bog down, and i notice that I lose speed. Part of the problem is leaves getting stuck in the intake. Every time I stop to fish, I clean the grill, which is always clogged with 25+ leaves. But I do believe there is a bigger problem. I recently checked the gap between the impeller and the housing, and it was right at 1/32. It might have gotten jarred by a hard hit, but I just can't believe it. Anyone have similar problems? Suggestions??

Problem Solved! Thanks to the help of Joe Troutt, from Troutt and Sons, I was able to fix the problem. It seems I have a bad electronic rev limiter, and whenever I would give the boat full throttle, it would make the loud skipping noise (what I originally thought was cavitation). I unplugged the rev limiter, and took my boat out today, and it worked like a charm. So, my next step is to order a new one from mercury and install it over the Christmas holidays. For the time being, I am going to be running without the rev limiter, but I am going to have to practice self control, to keep from using too many RPMs

As always, thanks for the suggestions and input given. Hopefully this can be a learning experience for everyone on the forum

I am no expert, but I will give you a few suggestions that I have found to cause the problems you list. If you have a tunnel hull with a piece of UHMW from the tunnel to the motor it could be bent. Also have you checked the grill bars to make sure they are straight. It could be the impeller key about to go bad and slipping a little. When you had the impeller out checking the clearance did you file it to make sure it had good sharp edges. Hope this helps and let us know what you find so we can all learn.

More to check......
Could also be that your bearings for the impeller are going bad. Take measurements from the shaft to the outside of the housing all the way around the impeller. If they are not the same..then check for movement. I had lower bearings go out and had somewhat similar issues. When mine stopped though...it left me dead in the water and bound up.

I don't own a jet but is it possible the colder water this time of year affects jet outboard performance on top of the leaf problem? Colder water is harder for a motor to push??? :?

89Suburban said:

I don't own a jet but is it possible the colder water this time of year affects jet outboard performance on top of the leaf problem? Colder water is harder for a motor to push??? :?

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Good thought, but I doubt that's it. All the jet does is suck it in and push it back out. Mine has been working just fine too. (sorry...not trying to correct anyone)

89Suburban said:

I don't own a jet but is it possible the colder water this time of year affects jet outboard performance on top of the leaf problem? Colder water is harder for a motor to push??? :?

Click to expand...

Doubtful - I have actually had the performance of my jet PICK UP during the cooler months. Probably due to the denser, colder air (verified by GPS). If there is not a fuel starvation problem I would check to make sure everything is OK in the lower unit (as has already been suggested above).

Dave

The cooler water should make the jet run better. It may not be a jet problem, it sounds like possibly a carberateur
problem. ( the bogging down, that is ). If it did not cavitate before, something has physically moved or there is something in the intake. Good Luck.

Thanks for all the input. Yesterday I took off the intake and checked the distance between the impeller and the casing. It was fine. I also checked the fuel filter and the spark plugs in case it was an obvious problem. Took it to the lake, still had the same problem. So I spoke with a few knowledgeable people about the topic today. Everyone I talked to said it does not sound like a powerhead problem. They have all told me there is some sort of cavitation problem, which is just hard to believe, but they all think that is it. Even though nothing has changed since I last ran it (and it worked fine), I am going to adjust the plate that helps the water flow from the boat to the intake. If that makes no difference, I am going to to try pounding out the dents on the bottom of the boat. I think the fact that it is a cavitation problem is a good thing, it is easier and less expensive to fix, unless I have to buy a new boat! I will update the progress, hopefully I can get everything worked out before my big duck hunt in 2 weekends.

Are any of the dents on the bottom new? Have you recently impacted something? It doesn't take much of a dent in the right (or wrong) place to disrupt the flow into the intake causing cavitation problems. I know of others that have had the same problem. Make sure there is no "hook" near the back of the transom.

One more question - Do your trailer bunks end before or after the transom when the boat is on the trailer? If the trailer is too short for the boat it can cause too much pressure being put in the wrong places causing the above mentioned "hook".

Dave

I have not added any new dents, holes, or even scratches to my boat in the last 2 months. That is why its so weird to me. How can it be cavitating now, when it didn't used to cavitate, yet I havent done anything to the boat!!!!

Any my bunks extend past the rear of by boat by 4 four inches, so I doubt that is causing a problem. Plus the trailer is built for the boat and it fits like a glove. Thanks for the continued interest. Hopefully I can get it figured out soon enough.

When you do figure it out.....please post your findings. Things like this, although very frustrating to you, help us all in the long run.

Here is a phone # that you might call if you can't figure it out. These guys are the leading experts in Missouri (IMHO) on jets, and very, very nice small town service. They might just have the right answer for you???

Trout & Sons 573-265-3456

Initially when I read this I thought it sounded like a power pack has gone bad. Sounds like you are only running on half of your cylinders.

With regard to the cavitation, could it be a redistribution of weight? Did you recently do something like relocate a battery, an anchor...add a trolling motor, anything that moved weight forward?

Fender, Thanks for the number. A number of my friends have boats from Troutt and Sons, and they have all recommended me to call them. I might do it if I cannot figure this out.

And no I have not redistributed weight. Everything is unchanged from when it ran perfectly. About the powerpack, I am not sure what that is, and i did initially think the actual powerhead was the problem, but according to the multiple sources I have talked to, they do not think it is in the engine, more likely the jet unit.

It will be a week before I can try to beat out the dents. Does anyone know if a hammer or mallet can beat out dents on a 100 gauge aluminum boat?

Many outboards have two sets of power packs. On older merc 6 cyl's each pack drives a bank of 3 cylinders. If you have one that is bad or greatly diminished, it will significantly reduce your ability to to get the necessary RPM's needed to get on plane. If in fact you are plowing a lot of water because you can't get on plane, it may be disrupting the flow of water needed to get to the pump foot.

Here is my input(not that I have the answer),but have you changed your trim.I've noticed with mine that sometimes when I trim too much it tends to cavitate more.

I'm also another Troutt & Sons customer.If it makes any difference.

kthmarks,
Thanks for that explanation. Due to some other recommendations, I am going to focus on the foot being the problem for now. If the dent repair and some other ideas do not pan out, I will be forced to assume it is the powerhead. Since I know very little about engines, I would have to take it to a mechanic for him to check out. If I do that, I will mention the power pack as a possible problem.

S&M,
I don't think it has anything to do with the trim. When I go to full throttle to get on plane, I have my motor trimmed all the way down to get the most suction of water. Once I get up on plane, I trim it up until it rides flat and drafts little water. Of course that was when it was working properly. I have tried throttling up with the motor in different positions, but it does not make a difference, the problem still occurs.

Thanks everyone for the input, hopefully I can get it worked out and I'll relay the info so if anyone has any future problems it can help.

Praying you get this solved and solved cheap. I know how frustrating it can be to have this problem. Hopefully it is something simple. I wish I had more suggestions for you, but all mine have been listed. Although I guess you could call outboard jets and see what they think it could be. Please let us know as we may have the same problem one day.

Look and see if the jet unit has some loose bolts holding it to the motor lower shaft. I had a prior jet that the mounting bolts came loose and it sure acted up. You may have to look close. The front one was tight but the back ones were loose and letting the back of the jet unit drop down about 1/8 in. You have to snug those from the inside.

Moelkhunter has a valid point here.As I've had the loose bolt problem with our Merc.See https://www.tinboats.net/forum/viewtopic.php?f=48&t=13749. I would think that they wouldn't have to be very loose to cause a problem.

moelkhuntr, S&M,

Thanks for the advice. I actually had a problem with those bolts in the past. I think I posted a thread about it, but I will sum it up really quick...

I was checking to make sure those 4 inner bolts were tight, and I over tightened one and it broke. I went through a long process to remove it, and I basically had to take apart the whole jet portion of the motor.

Anyway, I know those 4 bolts are tight as can be, and I actually checked them 2 days ago, just in case. Starting on Tuesday, I will be pulling up the floor, pounding out some dents, and re-positioning the piece of plastic on the jackplate, which directs water to the intake.