1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

[jwh0171]

Here is the deal. I have a 1997 Bayliner 1600ls open bow with a 1997 Force Outboard 90hp. When I take the boat out it starts right up and idle's great. I get out into the lake and run it. It runs great for about 30 minutes. After that the boat runs good at low speed but at full throttle it just wont do anything like it should. It stays at about 2500rpm. Its basically like the boat is at half throttle. I am not sure if it is flooding but when I stop the motor and tilt the motor up fuel starts running out the front of the carbs. I have replaced the primer bulb and fuel line. After the boat sits for maybe 30 minutes I start it up and it runs great again but after another 30-45 min of running it, it does the same thing. I have replaced the fuel filter and the tank is clean with fresh gas with proper mixture. (not a fuel quality problem). New Champion factory plugs. I am also wondering if anybody has any input on any plugs that give better performance (ngk, bosch). The only other thing I just noticed while looking at things in my garage is that if I push the key in to choke the motor it is not really doing anything. It makes a faint pop noise but not the standard clicking noise of an automatic choke. Could the problem be the choke is sticking and flooding the carbs at high rpm? if so what causes the choke to stick.

Thanks in advance for your input,
JH

 

[Frank Acampora]

Re: 1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

That engine does not have choke butterflies. It has an enrichment valve in between the carbs and this valve is much quieter than a normal choke slamming the butterflies closed. It also has an over-ride button --usually on top--that you push if the valve fails. What this valve does is take fuel under pressure from one bowl. It then squirts it into the manifolds--usually through fittings in the mounting flanges.

The full throttle could be fuel or could be ignition. You may have a bad pump diaphragm so replace it as a matter of course. Then, if the problem still exists, check all plugs for spark while the problem is happening and the engine is warm. It is possible that there is a heat related short or breakdown in the system that only occurs when the engine is well heated. Possibly in the stator.

No particular brand of plug works better than any other. As long as they are working, stay with the Champions. If they ever wear out and if you prefer, use NGK. I have used NGK, Champions, and Autolite. All gave the same performance, but I like Champions for no real reason.

 

[jwh0171]

Re: 1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

Can the enrichment valve go bad. I did locate this and saw the button on the top. I still think that it was making a different sound previously. How does the valve "choke" the motor without messing with the air/fuel ratio like normal butterfly choke. What is the purpose of the override button. When you say pump diaphragm do you mean the fuel pump diaphragm?

 

[roscoe]

Re: 1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

The enrichment valve pours extra fuel into the manifold, thus making the mixture richer.

If the enrichment valve goes bad (they usually stick closed), then you use the "override" button. This will manually open the valve and pour fuel into the manifold.

In either case, you must pump the primer bulb first to pressurize the system.

Yes, the fuel pump diaphragm. If it is leaking, it will leak extra fuel thru the back, directly into the crankcase, causing a cylinder to flood out.

These have a habit of wearing out, as they were not alcohol resistant, and our fuel now contains ethanol.
Rebuild kit is about $15. New kits are ethanol resistant.

 

[jwh0171]

Re: 1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

Another thing I did not mention is that the primer bulb does not feel as hard as it should. The bulb is good and all my quick disconnect's are new. Could a failure of the diaphragm cause this? How do I know if the enrichment valve is bad? it does squirt gas when the button is pressed manually but not sure about when the key is pushed in. Can you test that by disconnecting the fuel outlet hose from the valve and press the key and if it squirts it works? Could a bad fuel pump diaphragm cause good idle power and great full throttle power for 30-45 minutes of operating the boat and then stop working?

Also, do you know of a good website to purchase parts online?

Thanks a lot,

 

[CharlieB]

Re: 1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

It is possible that your fuel tank vent is restricted, taking that long to pull enough vacuum on the tank so as to restrict fuel flow.

 

[jwh0171]

Re: 1997 Force 90HP Outboard Runs great at idle but not up to par at full throttle

I dont believe the vent is restricted because it is a onboard fuel tank with a built in vent. I did think of that and loosened the fuel fill cap while I was on the lake and it did not make a difference.

Just took the boat out this morning and it fired right up and ran great but after 30 minutes of boating I kicked the motor back up when I put it on the trailer and gas just started to run out again. Ran good but only ran the boat for 30 minutes. Before taking the boat out I took the fuel pump off and disassembled it and cleaned it. Looked pretty good. Put it back together and put it back on. All fuel lines look good.