85hp Force RPM problem

[collegefund]

HI eveyone, I have a '87 Bayliner '17 Trophy center console`with a 85 Force out back. I got the boat from a friend and he has owned it for years with the same problem.... The boat fires up and runs great, it has new plugs, 120 psi of compression, and spit shine carbs and ive ran some Seafoam thriugh it. Problem is it wont turn past 3300 RPM in the water (28 mph tops by myself), and i also have a problem with it stalling when I put it in gear if i dont quickly give it gas. In neutral it runs about 1100 and about 8 or 900 in gear once I keep it from stalling. The carbs are opening all the way and ive revved it to 5000 in the yard. The prop is pretty ate up from corrosion, the propeller reconditioning place said its probally a 17 pitch but it measured out to be about 16.... he also said that the prop is not why im not reaching max RPM. What do you think the problem is? Any help is GREATLY appreciated!

thanks,
George

 

[jerryjerry05]

Re: 85hp Force RPM problem

Is the throttle linkage opening all the way?Move the throttle all the way and see if the carb pickup cam is at the end of the throttle arm.
No load rpm means nothing.
It sounds like a prop problem.That boat should have a 17 or 19 pitch.If you can't find any marks on your prop, then go to a dealer and see if they have a loaner prop(some do) to figure out what you need.
Good luck J

 

[john from md]

Re: 85hp Force RPM problem

In my opinion, you are running on two cylinders. Here are some reasons why that can be happening.

1. One side of a CDI unit is intermittant.
2. One coil is intermittant, perhaps after it heats up.
3. You have a head gasket leak to the water jacket. These will still show compression.
4. Your timing is too retarted.

The reason that you notice it in the water is because it is there that you are putting a load on the engine.

First check the timing and the carb/timing sync.

Next hit the water and run the boat up to speed and then kill the engine without coming back to idle. Watch out for back wash coming over the stern. You can minimize this by turning as soon as you cut the power. Now examine your plugs. Look for the one that is super clean as that is the one that is either not firing or is getting cleaned by steam from the water leak.

If you suspect a cylinder but are not sure, swap the coils and if that doesn't make a difference, the CDI units.

And get a decent prop. They are always for sale on ebay.

Hope this helps,

John

 

[collegefund]

Re: 85hp Force RPM problem

Ok ill give that a try tomorrow, I might be able to get a new prop today so if I can Ill check the timing and repleace the prop and go from there. It would seem strange to only be running on two cylinders tho, only because it runs so smooth at any RPM.... it just basically seems like your not giving it that much gas but the carbs are opening all the way via throttle lever

 

[collegefund]

Re: 85hp Force RPM problem

Ok, so i checked the timing and its right, but I did find the the wiring for the CDI and coils was all wrong according to the diagram on the top of the motor. Before i got into that though I checked the spark on all 3 cylinders. When running i removed the #1 and a noticable drop in rpm occoured , I removed #2 and it barely changed the idle, when I removed #3 it would just shut off. I did this several times, I removed the plugs and noticed they all seem to have the same nice blue spark when turning over. I then rewired it to the diagram and figured it might fix the problem but it didnt, I tried swapping coils, and since the rewire, the #2 cylinder is now using a different CDI box so that would eliminate either of those. After looking at the plugs and hearing the engine with different spark plugs removed ive come to the conclusion that if cylinder 3 is functioning at 100% then #1 is between 80-90% and #2 is maybe 20%... plugs look accordingly, 3 is cleanest and 2 is dirtyest. I cant help but see the Reed valves as the problem, unless the stator/trigger for the CDI box is somehow sending a delayed signal to the #2 cylinder???