3800 rpm at WOT!!! Help!!!!!!

84 force 85 hp. Runs great, idles great, accelerates great,not reaching peak rpm. Only able to obtain 3800 rpm no matter which prop I choose 17 or 21. Checked spark, checked fuel delivery, checked compression,130psi, checked butterflies in carb, decarbed, checked reeds,replaced anti-siphon valve at fuel tank. Running out of ideas, can you guys help me out? Thanks!!!

Re: 3800 rpm at WOT!!! Help!!!!!!

If you have power trim, do the rpm rise if you raise the motor too far?

Is the motor mounted at the correct height? anti ventilation plate above the prop should be 1-2 inches above the bottom of the boat

All 3 cylinders are actually getting fuel into them?

What size/model/type of boat is it on?

I would think that one plug is not sparking, or on cylinder is not receiving fuel.

Re: 3800 rpm at WOT!!! Help!!!!!!

What Roscoe said.

Plus, something doesn't add up.

1. Not hitting on all three cyl's.

2. Too heavy a load? Even a 17" may be too deep for a heavy boat.

3. Poor set up.

Re: 3800 rpm at WOT!!! Help!!!!!!

Has this motor ever reached proper rpm for you?
Have you varified the tach accuracy?Borrow a portable tach from a marina for a test.What were the results when you changed props?What type of boat are you pushing?Does a little choke help at all?

Re: 3800 rpm at WOT!!! Help!!!!!!

Thanks for all the response!! The boat in question is a 1984 Bayliner 1710 fish and ski boat. 17' 10". I will check the anti-ventilation plate location. Does not have tilt and trim must place pin in proper location. This is the stock setup for this boat. Tach is the proper type for the stator arrangment. I have not verified fuel to all cylinders, but all the plugs look the same not wet but they are dark brown and somewhat gummy. The next thing I am going to try is a timing light at the lake to test each cylinder for spark at wide open throttle. Local mechanic suggested that I shine the timing light on top of flywheel at the three holes that a flywheel puller would bolt into. Says if I see six holes while viewing with timing light the modules are firing twice and this couild be my problem. Anyone heard of this test? As long as I have owned this boat it has not reached a higher rpm at wot than the earlier stated 3800. Thanks so much for you help.
Ron

Re: 3800 rpm at WOT!!! Help!!!!!!

You need to confirm the tach is accurate.It is not necessarily working correctly just because it is the correct type/setting.
You also need to get or check your service manual for proper timing procedure check syncronizing the throttle & ignition.Sometimes you can find a manual at the library.
Again what were the results when you tried the 17 and 21 inch pitch props?If there truly was no change then
almost certainly there is a tach problem.There should be around 400 rpm difference.

Re: 3800 rpm at WOT!!! Help!!!!!!

Thanks Spike,
You are correct I do need to confirm that the tach is reading correctly. Maybe I am expecting to much out of this engine. I do have a repair manual and have used it to guide me in adjustments of the carbs and to check the timing at idle. Have not been able to check the timing at WOT as of yet(need someone to ride shotgun) hard to do this alone. My manual does not say anything about syncronizing the throttle and ignition. Could you inlighten me on this I don't want to buy another manual unless I have no other choice. I also am planning to test for a high speed miss with the timing light when I can arrange for assistance. Again thanks Spike, your help is great.

Re: 3800 rpm at WOT!!! Help!!!!!!

This sync procedure is discussed in the carb section seperate from the ignition section.
Set timing according to manual.
Then disconnect the throttle rod (a horizontal rod that connects to a verticle shaft and the throttle cam) then move throttle cam until mark is alligned with center of roller( if 2 marks the roller should be between them).Loosen lock nut on roller and turn eccentric screw until cam just contacts roller in the position previously described.tighten the lock nut.
Move speed control to max speed position and adjust the length of the throttle rod so it can be connected with the carb throttles at max opening.
Once you have everything adjusted it is very important to get the motor operating within its reccomended rpm range.It must run at approximately
5,500 rpm wot with one person aboard.
Running below reccomended wot rpm is bad for the motor and could result in fatal damage.
Don't missunderstand once the wot rpm is correct it is fine to cruise at lower speeds.
Hope this helps.