WOT testing, where/how

gdean7 · Apr 24, 2005

Boat is almost ready to be run regularly. I need to test the WOT so I can tune the carburators properly. I know I have to test it in the water, but should I keep it in nuetral and put it in WOT or drive it around while in gear? Or tie it to a dock or something? I'm not quite sure what to do here. Advice is appreciated, thanks!!

eurolarva · Apr 24, 2005

Re: WOT testing, where/how

What kind of motor do you have? Please post model number make and HP.

gdean7 · Apr 24, 2005

Re: WOT testing, where/how

Oh, sorry. I have a 1985 Force 125 motor. 125 hp. On a 19 foot bayliner bowrider. Thanks!

Silvertip · Apr 24, 2005

Re: WOT testing, where/how

I'm not familiar with "Force" engines but generally high speed jets are fixed and therefore no adjustment is necessary or possible (other than replacing the jets). That also eliminates the need for WOT testing except to simply see how it runs and that can be done by simply going for a ride. Idle mixture is adjustable. One thing I do know -- rev the engine to WOT in neutral for very long and you and your kids can go on a scavanger hunt to find the pieces of the engine. Likewise, WOT when tied to the dock proves nothing. While the throttle may be wide open, the engine would be lugging and nowhere near its WOT RPM. The long and short of all this is that none of the three scenarios you posed are valid carb tune-up considerations.

gdean7 · Apr 24, 2005

Re: WOT testing, where/how

Okay. As I understood it, WOT was to test to see if your motor is in the proper range as far as what RPM's its supposed to be. And to change that, you're supposed to tweak the carbs. Perhaps I am completely wrong about this, but do you have any other ideas I can do to tune the carbs without taking it to a shop? There are 2 carburators on it, and it's much harder than a single, as i'm sure you know.

JB · Apr 24, 2005

Re: WOT testing, where/how

Set the carbs up according to your Service Manual, gdean7. If your engine is set up by the book what you tweak to change the WOT rpm is the prop pitch. By the way, never open the throttle all the way without a load on the engine. The probability of a thermal runaway and grenading it is high. Good luck.

Realgun · Apr 24, 2005

Re: WOT testing, where/how

Let me tell you what you need. A body of water big enough to run WOT at least 2-5 minutes. A tach and the boat ready to go. Warm it up first. Run it to WOT if the RPMs are higher than 5200 you are to low in pitch. If you are lower than 4700 you will want to go with a high pitxh prop. Yes you will need a tach to test this. The only tuning you need is to leave the engine OFF. look down the carb throats and be sure your butterflies are flat to the length of the carb body. The flat metal pieces should be flat with the top of the motor and apear thin like looking at a coin on edge. That way you know your carbs are set for that mode.

moderator1 · Apr 24, 2005

Re: WOT testing, where/how

Under 5000RPM is a big part of the trouble with these engines. I would shoot for nothing less than 5500, which would be perfect with a normal load.

gdean7 · Apr 24, 2005

Re: WOT testing, where/how

Okay, great, thanks all!

walleyehed · Apr 24, 2005

Re: WOT testing, where/how

Whats your altitude where you do most of your boating???

roscoe · Apr 24, 2005

Re: WOT testing, where/how

By Realgun, "If you are lower than 4700 you will want to go with a high pitxh prop." I believe Realgun made a mistake here. I'm sure he meant to say "If your rpm are below 4700, then get a lower pitch prop." A lower pitch prop will raise your rpm. A higher pitch prop will lower your rpm. Loveland Co, Elevation: 4982 feet above sea level.

walleyehed · Apr 25, 2005

Re: WOT testing, where/how

Need to drop 3 sizes on main jets for that engine to work as it should at that elevation. Fuel economy will go up as will your RPM...

gdean7 · Apr 25, 2005

Re: WOT testing, where/how

How do I drop main jet sizes? What would I go about doing there?

rottenray6402 · Apr 25, 2005

Re: WOT testing, where/how

This probably is no help at all but I've been messing about with boats for a lot of years and have found that there are a lot of things a person can do themselves such as replace spark plugs and change lower unit lube and so on. When you get to changing main jets for optimum running it is sometimes cheaper and always easier to take it to a honest shop and have it done. Chances are someone has a bunch of jets in their tool box drawer and would know which to use right off the bat.

roscoe · Apr 25, 2005

Re: WOT testing, where/how

From the Mercury parts site: http://www.mercruiserparts.com/Show...B4053/8.png&inbr=1215&bnbr=4&bdesc=CARBURETOR MAIN FUEL JET OPT. .092 1500 - 3000 FT. ( original part number FO14190 ) ( new part number 1395-5733 ) MAIN FURL JET OPT. .090 3000 - 4500 FT. ( original part number FO15406 ) ( new part number 1395-6247 MAIN FUEL JET OPT. .088 4500 - 6000 FT. part number F013193 MAIN FUEL JET OPT. .086 6000 FT. & UP number F013949

Silvertip · Apr 25, 2005

Re: WOT testing, where/how

Before you mess with main jets, make sure they have not already been changed. If the engine originally came from a low elevation to your location, or was originally delivered in your area, the jets may very likely already correct. Always make sure what you have or don't have before making modifications like this. You would be well advised to make a few test runs with an accurate speedometer or GPS. Note speed, engine trim setting, and RPM at wide open throttle. You need to get prop selection correct first. As pointed out earlier, a prop with less pitch raises RPM, one with more pitch decreases RPM. When you have that figured out, make some runs and check spark plug color. White insulator = lean, light tan = OK, sooty/blackish = rich.

Realgun · Apr 25, 2005

Re: WOT testing, where/how

Mod1 the Max RPM is 5500 for that engine. I was just checking the Seloc manual. I was thinking 5200. Now as to Altitude you will want 40 MAIN FUEL JET STD. .0937 SEA LEVEL - 1500 FT. 1 - MAIN FUEL JET OPT. .092 1500 - 3000 FT. - - MAIN FURL JET OPT. .090 3000 - 4500 FT. - This one >- MAIN FUEL JET OPT. .088 4500 - 6000 FT. - - MAIN FUEL JET OPT. .086 6000 FT. & UP Part number is what Roscoe has. Changing the jet will not get you any more RPM. It will however increase fuel economy.

Scaaty · Apr 25, 2005

Re: WOT testing, where/how

What am I missing here? He asked about WOT, and already were changing jets, and it aint even in the water yet! The only adjustment is in gear at idle at the dock so it don't quit changing gears. Then take it out (I have-among others-the same boat, only a cuddy). Anything 5200rpm (with all the junk and people left at the dock) up and above go have fun. Carbs are low speed adjustable only. Complicated procedure for adjusting the linkage, and even thats for low speed too, but it has to be done, and simple with a MANUAL...which you need. Seloc is good enough. Good luck!

Silvertip · Apr 26, 2005

Re: WOT testing, where/how

Robby -- The poster had the impression that some carb adjustments were necessary at WOT throttle. Everyone is trying to explain why this is/is not necessary and that there are other issues (like prop selection) to consider to get the engine in the proper RPM range. I'm not sure we've succeeded.

gdean7 · Apr 26, 2005

Re: WOT testing, where/how

Thanks all for your help! As said before, I'm completely novice at boats, and boating. And all of your help is greatly appreciated! I'm learning a lot from you all. By the way, I do have a manual, but the manual cannot put it in different words, as you all can, so I can understand it. So thanks for your help, and i'll give it a shot!

WOT testing, where/how

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