Force 120 - runs smooth but no top end

[AdamLotz]

Hey guys - <br /><br />I just picked up a '95 boat with a 120 Force outboard. (assuming the engine is a 94-95 but I can't find any identification) This was a 'little old lady' boat - the Dr. I bought it from literally used the boat for 7 years of just driving up and down the intracoastal.<br /><br />Now, here's the thing. The engine starts up right away. It idles great. Runs to 3000 rpm with no complaints. The problem is - top end just isn't there. Even wide open the most I got out of it (trimmed up) was an indicated 3800 rpm. It felt like the throttle linkage might have been out of adjustment, but confirmed yesterday that it was okay. <br /><br />What's my next step? Fuel pump? Fuel filter? Carbs?? Is there anything I can look for? I'm mechanically inclined but rebuilding the carbs on my own would be out of my area of expertise... before I fork over a wad of $$ to a mechanic I'd like to rule out the obvious.

 

[DJ]

Re: Force 120 - runs smooth but no top end

Most likely, you are not running on all four cylinders.<br /><br /><br />Remove the spark plugs and keep track of which cylinders they came from. Do they all look alike? If not, you probably have carb problems. You can rebuild them with one of these.<br /><br /><br /> http://www.outboardrepairs.com/manuals/ <br /><br />Once you get it running right. You should do this.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000006

 

[AdamLotz]

Re: Force 120 - runs smooth but no top end

I'm 95% positive I'm running on 4 cylinders - although I've never had a 4 cyl two-stroke before, I can't imagine that it would idle and start so well if it weren't...??? It certainly doesn't have any sort of dramatic miss, as it will run up and down the intracoastal all day long between 1000-2000 rpm.<br /><br />I'm going to try to pull the spark plugs tomorrow, the boat didn't come with a trailer (doh) so until I find one, working on it is a little more difficult. (currently it's sitting at a friend's dock)

 

[roscoe]

Re: Force 120 - runs smooth but no top end

You would be suprised how well they can run with one cylinder out. Well, until you increase the load on the motor, as in trying to increase the speed.

 

[WillyBWright]

Re: Force 120 - runs smooth but no top end

They'll actually run noticably smoother on 3 than 4. Naturally it won't develop full power on 3. Regarding the carb kit referral, each carb feeds 2 cylinders. If either of those cylinders is running well, then it can't be the carb. Looking at the plugs will be the biggest bit of info we can get to help you. Let us know ASAP what you find.

 

[AdamLotz]

Re: Force 120 - runs smooth but no top end

Ok guys, well, first off someone should have warned me these plugs have no electrodes. Scared the crap out of me when I pulled the first one and there was nothing there. hahaha.<br /><br />All 4 plugs looked the same - a little black and oily but not bad.<br /><br />I did a compression check - came in at around 147/147/135/147. (3rd cyl down was about 10 psi low)<br /><br />As far as I can tell, all 4 cyls are firing. I pulled off one plug wire at a time and generally speaking the idle was worse with any of them pulled than it was with all of them on. (obviously this involved me shutting it off / restarting / balancing off the back of the boat so it wasn't 100% foolproof but I think it was accurate)<br /><br />Next steps? PS: the only other "unusual" thing that I've noticed about the engine is that, in neutral, if I grab the throttle linkage and push down to rev the engine, it will rev a little bit, but trying to go more than 1/3 throttle I've had the engine just abruptly die on me. ?? Seems odd, but the controls won't let me go more than about 1/10 throttle in N so maybe it's normal?<br /><br />Also I sprayed a bit of seafoam in the carbs and had it smoking pretty well, aside from a couple backfires (one of which somehow knocked me into gear, that was fun) that seemed to go smoothly.

 

[chuckz]

Re: Force 120 - runs smooth but no top end

If the engine was driven by "a little old lady" it's probably carboned up. Check the first forum (Enginge FAQ) for a decarb procedure.

 

[14rudy]

Re: Force 120 - runs smooth but no top end

adam, check the fuel system for restrictions, cloged lines,fuelfilter. a restriction would limit the rpm under load. replace the plugs, easy cheep fix. check carb for a main jet restriction. good luck.

 

[AdamLotz]

Re: Force 120 - runs smooth but no top end

Replaced the plugs, but won't have a chance to take it out to open water probably for another week or two. <br /><br />Humor me here guys, I've got a service manual on order, but when talking about fuel restrictions in the carbs - am I literally just looking for gunk buildup?<br /><br />I couldn't get the carb covers off this past weekend, I didn't have the right size hex bolt to remove them, so couldn't actually look inside.<br /><br />PS: on further inspection, I realized that the boat hasn't been registered since 2002! So there's a good chance it has actually been run less recently than I thought. I put in 20 gals of gas and threw in some random stablizing additive, may go through the invovled de-carbing process next weekend weather permitting.

 

[BrettNC]

Re: Force 120 - runs smooth but no top end

That is exactly what you should be looking for- any kind of build up. Thoroughly clean the carbs. Make sure that you are getting spark to each of the plugs. The ignition timing must advance with the throttle, so it might act funny if the throttle opens without the advance mechnism adjusting with it. Check the timing with a timing light to make sure it is adjusted properly- refer to the manual. The motor may not have the correct size propeller for the boat. If all else fails then look into that.

 

[DJ]

Re: Force 120 - runs smooth but no top end

As mentioned previously-decarb it.<br /><br />See link for instructions/benefits.<br /><br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000006 <br /><br /><br />Yes, it will NOT rev to full RPM in nuetral. That is normal. It is a designed in rev limiter to keep all the parts under the hood.

 

[bigbluedog]

Re: Force 120 - runs smooth but no top end

actually, i had a 125 force that did the same thing... turned out to be a power pack. i replaced it and off i went. running great.

 

[bellybuster]

Re: Force 120 - runs smooth but no top end

What is a power pack? I am having a simalar problem. Is there more than one? And if so, how did you know which one?

 

[imported_bjs]

Re: Force 120 - runs smooth but no top end

my 1998 120 force same problem had water in the gas might drain and try it worked for me.

 

[Tech2123]

Re: Force 120 - runs smooth but no top end

My 1985 125 Force did the same Idled Sweet but no more then 3000 RPM replaced the Startor (After LOTSO Ohm Meter testing with repair manual) a mUST have! New stator and im on my 4th weekend NO problems! These engines love to eat Stators! so dont rule it out the Ohm meter test! is EASY!