Boat falling on its face at WOT

[wesleycharlessmith]

Hello Everyone, long time lurker and first time poster. I have a 1986 Bayliner Capri with a force 85 motor that I assume is the same year as the boat. I just got the boat and am having a little trouble with it. The problem is when I am out on the water the boat will go fine at low to about half throttle but when I go wide open the boat sputters and ends up stalling out. I have cleaned the carbs and put new seals in them. I checked the compression and all three cylinders are at about 125#. The boat has fresh fuel. I am using a 50:1 mixture with Penzoil marine 2-cycle oil. I pulled the fuel pump diaphragm and there appears to be no holes in it.

My question is about the two screws on the outside of the carbs. The ones where the air box attaches I pulled out and cleaned. I then adjusted them as recommended on this site to about 7/8 turns out from lightly seated. There is another screw on the outside that I think is the air screw, is that the correct term? I cant find anywhere on how to adjust this one so I have not taken it out to clean it. Is it possible that this may be gunked up causing part of my problem? Can someone please tell me how to adjust this screw so I can take it out and clean it. I have a Seloc manual but I dont see in there anything about this adjustment.

 

[Jiggz]

The idle fuel air mixture screw (brass screw on each of the carb) should be set no less than 1 turn from lightly seated. This is to make sure you have enough lubrication during low speeds. Improper setting on this screw can result in catastrophic damage to the engine due to lack of lubrication.

There are two common reasons why the motor falls on its face at WOT.

1. Improperly set timing
2. Lack of fuel delivery to the carbs.

Since this motor is new to you, validate the timing first before going for the more complicated troubleshooting. Search the forum for "Static timing" you should find procedures on how to do this.

As for the lack of fuel delivery, I highly recommend you install a clear fuel filter between the fuel pump outlet and the carbs' inlet. This is more for troubleshooting than a fuel filter. With this you can actually tell if the fuel pump is delivering enough fuel to the carbs during high speed ops. If not, then it is time to troubleshoot the fuel system.

 

[jerryjerry05]

The air screw is on the top of the carb it's encased in the metal of the carb.
What 2 screws did you adjust?
​You can't add pics until you have 3 posts so use Shutterfly to add pics of the carb.
​
The 86 air screw might need to be adjusted further out??? Maybe??
One of my customers, 86/85 his carbs needed to be at 2 1/2 out?
The air screws have nothing to do with wide open operation.

The tank vent might be clogged with bugs??
The inline connectors on the fuel hose might be bad and sucking air?
The fuel hose might be bad from age or Ethanol??
The carbs high speed jet might be clogged?

The fuel might have water in it?
​Unhook the fuel line at the pump and draw off some fuel in a glass jar, check for water?

The timing doesn't usually change unless you change it.
​It doesn't "jump time" like a car.
Check the plastic connectors on the linkage.

​Lastly, check the overheat buzzer for operation.
​Might be getting hot??

 

[wesleycharlessmith]

Ok, so I replace ALL the fuel lines including the supply hose and it seems to be running a little better. Here are photos of the adjustments I am trying to learn to adjust. The first 2 photos are what I call the "side" screw, where should I adjust this one too? The second 2 photos are what I call the "front" screw. I have not taken the side screw out because I didnt know where to adjust it so there may be some gunk in there. How do I adjust this one and which one should I do first?

https://wesboat.shutterfly.com/pictures


As far as the overheat buzzer goes I dont know if mine is working. With the key off I get 0 volts at the orange and only wire coming from the switch. With the key on I get 12.2 volts at that same wire. When I start the boat there is no buzz or anything or at any time while I am running the boat. Does this sound right?

 

[SkiDad]

you don't adjust the ones on the sides - you adjust the 3 in the front - start at 1-1/4 turns out and then adjust from there - most people recommend not going below 1 turn out.

see this link: http://forums.iboats.com/forum/engi...-on-a-75-150-chrysler-or-early-force?t=431021

 

[wesleycharlessmith]

Ok, thanks Ski for the information. I found a guide to testing the overheat sensor and it does test fine. I just bought a timing light so in the morning that is my next step. If that doesn't show any issues I am going to open the carbs again and try to clean them again. There is a screw where the bowl bolt goes in, do I need to remove that to clean the carbs? If so, how do I adjust that one? Thanks guys, I am off to learn how to check the timing!

 

[jerryjerry05]

There are NO adjustments other than the air screw on the top of the carb.Pic 3
​The screws (pic 2) are jets and don't need any help or adjusting.
​Neither does the jet in the bottom of the bowl.
A shot of carb cleaner in the jet will clear any gunk.

​Timing: IF??? no one had touched it(adjusted) then it probably is OK.

​2 things you should adjust(if needed) the air screws on the top of the carb.
The idle screw on the bottom of the towershaft if the idle is too low.

​Otherwise don't mess with it.

​Your digging into things that might cause more damage than good.
​The falling on it face is probably a fuel delivery problem and not timing.
​If it runs good at 1/2 throttle then the carbs are probably ok.

If the timing is adjusted wrong it can burn up the motor.

 

[wesleycharlessmith]

Thanks Jerry for the information. At what RPM should I set the idle sitting in the driveway with muffs on in neutral? I am going to check the timing and despite my best efforts of searching online I am still unclear as to which mark to set it to. This is my understanding of what I should be doing:

Ground spark plug wires
Remove spark plugs (optional but I am doing it)
Put a jumper wire at the neutral safety switch
Turn the engine over at WOT

My flywheel has 4 marks on it, three that are very close together and one to the right. Which one should I be timing to in the driveway with no load?

Thanks again guys

 

[wesleycharlessmith]

Here is a video of my setup:

https://youtu.be/JhJe6WQasi0

Is the timing adjustment backward? If so, that would indicate to me that someone has monkeyed with it in the past?

 

[wesleycharlessmith]

Ok, so I just did a timing test in the driveway and it is showing up at the single line to the right of the three lines. If I'm not mistaken this is the TDC line and it should not be there. In the driveway I should be at the right line in the group of three, correct?

 

[SkiDad]

Yes it looks like your timing adjuster is backwards - but I suppose you can see it the timing is correct how it's setup that way you don't have to mess with it.

Actually that would be fairly correct for just idling. But you cannot test timing on these boats when running in the driveway - you have to test them while cranking at full throttle (but not running) - I'll post a few links on what you need to do.

https://www.youtube.com/watch?v=o1HmYyOQFW8&t=23s

http://forums.iboats.com/forum/engi...ler-outboards/616464-carb-and-timing-tutorial

 

[jerryjerry05]

It's called a static timing and done while the motors off.
​The adjuster IS backwards???
Fix that. You might need to remove the flywheel??

​The single line is for finding TDC.
Mainly used when you think the flywheel key has been sheared.

In the video: he needed to remove the plugs after grounding the wires.
​If not it won't spin easy.

Also the first few posts in this forum have good info on thing to help your motor.
READ THEM FIRST!!


The adjuster isn't backwards.
It can be adjusted while at WOT. Sorry

 

[wesleycharlessmith]

Hey guys, I found a video online and I think I have it fixed. It seems the linkage from the tower to the carb cam was way off. I havent tried on the water yet but it is running much better in the driveway with muffs. I just bought a tiny tach (the marine version) and I am wondering how many times an '86 force 85 sparks per revolution. Does anyone know?

 

[Jiggz]

It's a two cycle engine so it's one spark per rev.