1997 force by Mercury not working at its best

[mochosla]

Hi,<br /><br />A few months ago I bought a 1997 maxum boat with a 120 HP Force by Mercury of the same year. The first few times I took the boat out it run very well with a top speed of 45 miles per hour. Then it happened, it started to loose power and would take off very sluggish. Then it would work fine. For the last 4 or five times that I have taken the boat out, it does not go any faster than 35 M/H with a sluggish take off.<br /><br />I have done the following:<br /><br />Replaced the spark plugs<br />Use hiest oct gas and best oil in the mix<br />Verified that all pistons are firing<br />Verified that all coils are working (to the best of my knowledge)<br /><br />I'm lost to say the least. I don't know what else to do so any help will be greatly appreciated.<br /><br />Thanks.

 

[WillyBWright]

Re: 1997 force by Mercury not working at its best

First, you're talking about a Force in the Mercury board. You'll probably be moved to the Chrysler/Force board. If you don't see any more answers here, look there.<br /><br />You could have a carb with a clog or a float valve stuck closed. Two carbs...four cylinders. The upper carb feeds the upper cylinders, the lower feeds the lower cylinders. Try running the motor with the upper two sparkplug leads removed. If it runs the same, the problem is probably the upper carb. Try the same with the lower two sparkplug leads removed. It could also be water in one or both of the carbs. Water is heavier than gas, so the lower carb usually gets water in it first.<br /><br />A compression test would be a good idea if you have a gauge. If not, I'd bet a someone you know has one. Otherwise, they're not very expensive. Expect the upper cylinder to read lower than the other three by 10psi or so. Heat rises, so they lowered the compression ratio in that cylinder to run a bit cooler. Otherwise, the readings shouldn't vary from each other by more than 10% or so.

 

[bluebyyou]

Re: 1997 force by Mercury not working at its best

I vote for getting the carbs cleaned out. Are you running out of a metal gas tank? Sometimes rust and other crud can get in the carbs. After doing the carbs I'd add one of those clear inline fuel filters.

 

[mochosla]

Re: 1997 force by Mercury not working at its best

Thank you both for your answers. I have already done the compression test. Three of the piston are @ 140, the last one is @ 135 PSI so the compression is good. <br /><br />A clugged carb sounds like a possibility as the boats sometimes will be running sluggish and it will start functioning fine just out of the blue.<br /><br />I have a built-in plastic gas tank so it should not be rust.<br /><br />I will attempt cleanning the carbs (I hope I don't mess it up even worst as I don't know how to set the jets right. Any input?<br /><br />Tanks again!!

 

[moderator1]

Re: 1997 force by Mercury not working at its best

Moving to Chrysler and Force Questions.

 

[jayvaughn]

Re: 1997 force by Mercury not working at its best

Do you know how much your boat weighs? I have a 1998 Tropy with a 1998 120 hp Force. My boat weighs about 2600 lbs. I have never been able to go more than 35 mph in mine. I know my compression is good as well. Does this sound right?

 

[mochosla]

Re: 1997 force by Mercury not working at its best

my boat is about 2500 pounds and I know for sure the boat will do 45mph with 5 people on it and a skier behind it. I've done it many times. My problem is fairly new (3 months). You should have your motor checked. Is it a 120HP as well?

 

[jayvaughn]

Re: 1997 force by Mercury not working at its best

yes it is a 120hp - 98 year on a 19' bayliner trophy center console... i get it to about 5200 rpms and 35 mph with only 1 person in it.<br /><br />how long is your boat? I wonder what my problem could be??? could my speedometer be wrong?

 

[mochosla]

Re: 1997 force by Mercury not working at its best

My boat is an 18' maxum. It could be your speedometer but I doubt it. When my motor is working fine you can feel the power. It takes off very fast. As I said, I use it for sking and fishing and I ussualy have 4 or more people on it for sking and there is no hesitation. How is your prop?

 

[jayvaughn]

Re: 1997 force by Mercury not working at its best

new prop - same as the original - i believe a 19 pitch aluminum... the only difference i can think of is the design of the hull between yours (ski boat) and mine (fishing boat)... I wonder if that can account for anything?

 

[walleyehed]

Re: 1997 force by Mercury not working at its best

mochosla, My 1800lb boat with a modified 115hp with an 18" SS Raker @ 5700 RPM will only do 46-47 GPS. Your speedo is WAY off.....2500lb. boat, 120 Force, 5 people on board pulling a skier....<br />IF...your boat would plane in that situation, it would suggest a very low pitch prop which would be IMPOSSIBLE to achieve 45 MPH....more like 30-32 at WOT.<br /><br />jayvaughn, if I may suggest, I would drop to a 17" prop to get where the engine should be run when you have a few people on board...that's a big boat, and a 15" prop might even be better...<br />5500RPM with 2 on board and fuel would be good.

 

[mochosla]

Re: 1997 force by Mercury not working at its best

Thanks walleyehed. Now that I think about it, I could be wrong. What I really wanted to say is that with 5 people my boat has a lot of power. I know for sure that it will do 30 to 35 mph when pulling the skier. When not pulling the skier it will do 45 (when working right). <br /><br />Somebody suggested that I replace the fuel pump diaphram and that that could solve my problem. I will try it this weekend.<br /><br />jayvaughn, I talked to a guy in one of my fishing trips who had a Bass boat, I think it was a Nitro with the exact same motor as mine and he told me that his boat will do 45mph easily too. <br /><br />I think you have a problem too.

 

[jayvaughn]

Re: 1997 force by Mercury not working at its best

not sure if you have ever seen a '98 bayliner trophy, but it is much different than a bass boat. It has a deep hull and pretty high sides... It is a "chunky" hull... I think that is what accounts for my speed... or lack of, should I say...

 

[walleyehed]

Re: 1997 force by Mercury not working at its best

mochosla, check all your fuel line connections as well...loose clamps, etc. Make sure your tank is venting as it should, and yes, the pump diaphram can make a slight difference is engines that are running "somewhat" normal to begin with.<br />Carb orfices are VERY small, and a spec of fly-crap can cause intermitent problems. Good Luck!

 

[WhiteHorse]

Re: 1997 force by Mercury not working at its best

Check your lower unit oil and see if the motor blew a seal and is mixing mud down there in the gearcase. Sometimes you pick up a piece of fishing string and it winds itself right around the prop shaft and pushes the seals out or cuts off the meshing surface. Oil is gets so thick down there with the water mixed in that it takes top end off the motor. <br /> Open the vent screw, then put a drainpan under it and open the drain screw. If the oil looks milky, creamy, etc. there's the culprit.

 

[mochosla]

Re: 1997 force by Mercury not working at its best

Actually, I just changed the gear oil last weekend and it looked very clean.<br /><br />Thanks for the advice though.

 

[Knightgang]

Re: 1997 force by Mercury not working at its best

Also, stop running hi-octane gas. Outbaords are designed for 87 octane. Change the octane and you change the ratio of gases in the chamber. Higher octane burns hotter and you could sacrifice some of the lubricating ability in your engine. Use 87, it will last longer.<br /><br />If you think you have carbon buildup, after you clean your carbs, run Seafoam thru it and keep it in your gas a a treatment.<br /><br />Good luck