How fast should I be able to go??

[jordy1380]

Ok, so I finally got my new boat, well, new to me..., out on the water the other day. It is a 17.5' lund with a '88 mercury 150hp xr4 outboard on it. I got up to about 31mph at wot according to the gps on my boat. How fast do you think a vessel like this with that hp rating on the outboard should be able to go? and if it's supposed to go faster, what are things I should check for any issues?

 

[Levinz11]

Re: How fast should I be able to go??

I'd reckon she'll go much faster than that if everything is running right? Is that boat even rated for 150hp? How many RPM's @ WOT?

 

[jordy1380]

Re: How fast should I be able to go??

It was a little over 3000 rpm at wot. The guy I got it from said that it went about 55mph but I never got up to that. 150 HP is the max rating for that boat.

 

[briangcc]

Re: How fast should I be able to go??

You're well under Merc's rating for WOT. I'd wager your RPM's should be in the 5-6k range. My 115 Honda was in that range and it pushed a 18' Bayliner around 50MPH. You're in a lighter boat with more HP so you should be hitting in the 50-60 range I would think.

Something is definitely amiss and needs to be checked. I'd start with fuel supply and prop.

Also what year boat? If its a matching '88, was it stored outside uncovered?

Yes, I'm taking a shot in the dark that your Lund *might* have some waterlogged foam increasing the weight of your boat and decreasing its performance dramatically... And if that's the case, how does your transom look?

 

[TurboM700]

Re: How fast should I be able to go??

That boat should run much faster then 30mph.

My dad has a 90 Lund Tyee that is 17ft with a Merc 135 black max. With a 5 bald prop she will run just under 50mph.

Your problem is in your engine RPM it should be double what its running at WOT. I wouldn't be surprised if you have a few weak cylinders.

 

[jordy1380]

Re: How fast should I be able to go??

The exterior of the boat looks fine. Its a '93 so the boat is a bit newer than the engine itself. My guess is there may be something screwy with the fuel supply because it starts pretty rough but once its going it never has a problem starting again. What should I check and how?

 

[TurboM700]

Re: How fast should I be able to go??

Fuel pump is on the motors on those. Any air leak in fuel lines will cause hard starting and poor running as the fuel pump is drawing air instead of fuel.

You can try running the motor off of small boat tank and see if its better.

Be carefully running the boat to much if you have an air leak in a fuel line you can cause the motor to go lean and burn it down.

I would first change plugs and check compression to very easy things todo.

Mike

 

[RogersJetboat454]

Re: How fast should I be able to go??

First order of business is to check compression.
If the engine isn't hitting solidly on all holes due to compression loss, no amount of fiddling with the fuel system is going to fix the issue. May also want to get a spark tester (found at your local parts store for roughly $8), and make sure all holes are getting a GOOD spark (the old spark plug against the block trick doesn't cut it).

If all is found to be satisfactory, dive into your fuel system.

 

[jordy1380]

Re: How fast should I be able to go??

Any suggestions a compression tester? Any type will do?

 

[Don S]

Re: How fast should I be able to go??

You should start a thread over in the Mercury & Mariner Outboards forum for your troubleshooting questions.

 

[RogersJetboat454]

Re: How fast should I be able to go??

Any suggestions a compression tester? Any type will do?

Best to get one that screws into the cylinders. The type with the tapered rubber boot you hold in the hole while cranking leave allot to be desired.

If you have one with the right adapter, give it a shot. If you want to buy one there are many choices out there. Some say the Harbor Freight tester works OK. Personally, I would probably go to Sears for one if I wanted to buy one from a brick and mortar store. Could always order one off the internet too.

If you don't want to buy one, but have a local Autozone near by, you can borrow one for free. You will need a credit card to put a deposit on it, but the deposit will be refunded when you return the tester to the store.

 

[jordy1380]

Re: How fast should I be able to go??

New thread started here: http://forums.iboats.com/mercury-mariner-outboards/boat-speed-question-604568.html#post4212025