motor trouble or boat trouble

[aqhunter]

I recently bought a 1987 mercury 40hp 2 cylinder. The motor had not ran in a little over a year. So I started with new gas, spark plugs and compression check(both cylinders were over 100psi). The tiller handle didn't move smoothly so I took it apart and cleaned the old greese off and put back together. I also put in a new water pump. The motor seems to be running fine now but I am only getting about 15mph. I have tried moving the tilt rod and have seen no real change. The boat is a 16ft crestliner. I have done some modifications to the boat (new floors, casting decks) and added some weight with everything I have done. Maybe added about 200lbs. The bottom of the boat is painted with bed liner because of a leaking problem I had. So there could be many problems with the boat and motor not getting the mph it should. I had older twenty horse on it before and was able to get 11mph with the all the modifications to the boat.

Could it be me not putting the lower unit or tiller handle back together right? (tiller handle seems to be fine with looking at it in neutral)

The bed liner on on the bottom of the boat causing to much drag?

The added weight?

Or the motor is just not running a full capability?

[wastewaterguru]

You need to know the RPM the motor is getting to. Borrow a timing light with tach lead from someone and check out your rpms at wide open throttle. That's a key part of the troubleshooting process.

[upnorth]

Did you paint the outside of the hull with bedliner? That could easily cause a fair amount of extra drag. Bottom of the boat needs to be smooth.

[aqhunter]

I will try the tach. I hadn't thought about that. Thanks

Yes I did paint bedliner on the bottom of the boat. Wasn't really thinking it would cause any problems at the time. Should have thought more about it before I did it.

[motownmasher]

for sure the bedliner is adding quite a bit of weight, but many people do this to their boats. (mostly jets in shallow rivers to protect them) havn't heard this affects the performance noticably, and have considered doing this as well.

[fish_eat_sleep]

Correct me if i'm wrong here, but i always assumed the bed-liner process was supposed to be applied to the interior of the hull only.

And 200 pounds of additions to the boat is like having an extra guy and gear all the time. For a 16 foot tiller that is a noticeable difference in performance.

My 16ft with a 50hp is fine with 2, but with 3 guys it just doesn't want to go like it did before. I believe that the bed-liner mixed with the 200 pounds of extra weight could limit to 15-20mph. especially because i had a 1974 Lund s16 with a 25hp. (feather light boat with benches) and at best we got 13mph with 2 people.

[Dragonsm]

I agree with others on starting with the RPM of the motor. The motor may/may not be propped right for your boat. I played with props on my boat (16 ft. Mr Pike with a 50hp evinrude) and with the right prop I was getting 32-34 with 2 guys and gear....and it didn't decrease much with a 3 guy with no gear who's looking to learn to fish.

[Capt. H (Ret.)]

I don't think it is the bedliner material. That stuff doesn't weight that much once it is applied.

Mike

[midex717]

I agree with upnorth as to the bedliner affecting the smoothness of the hull. A few years ago we had a 20' Searay in a slip on Prior Lake. In some years the algae growth on the bottom of the hull was so dense that the boat had a very difficult time planing out. I had to load the boat on its trailer, take her to a car wash, and clean the hull with nasty muratic acid, then she would plane out normally. The bottom of a hull is similar to the airfoil of a wing, it needs to have a clean laminar flow over its surface, if there is too much disturbance of that flow excessive drag is produced.

[aqhunter]

I was able to get the boat out today. I installed a digital tach to see what the RPM's were. At full throttle I am able to get 19mph at 4550 rpms. I had no fishing gear and was by my self. Not sure what the rpms are suppose to top out at full throttle. Put I am still hoping to get some more speed.

[clKiekhafer]

I would say the RPM's should be between 5,000 and 5,500 for you motor.

[BoxMN]

Spun hub?.... This sounds sort of like it, but maybe your rpms might be higher if spun hub.

[wastewaterguru]

You WOT RPM's should be close to 6000 for that motor. I would recommend taking off the air box and visually making sure the butterflies in the carbs are opening all the way at the WOT position. You mentioned you took apart the tiller handle so you want to eliminate the possibility of not getting that back together right.

If they are opening all the way, then you need to drop at least 2 pitch sizes on your prop.

[delcecchi]

I think the WOT on that motor is spec'd at 5000 to 5500