1998 90hp Force: Possible carb issue? need advice.

[Seawolf_504]

I have a 1998 90HP Force in good shape, but have been having, what I think, are fuel related issues.
Same ol story, Purchased the boat used and it is in pretty good shape. At time of purchase engine cranked up fine and idled on a hose no problem.

First couple times out in the boat everything was fine, but then started having issues getting the engine to turn over, maintain idle (cranks up but soon stalls out), and running out of sync or vibrating at max throttle as if one cylinder is not firing correctly. You can back the throttle down a little and engine smooths out, but doesn't produce enough pwer to get up on plane.

I've tried replacing all the fuel lines internally and externally, replaced entire fuel/water sep assembly with bigger 10 micron filter, have tried sea foam, new plugs, etc. After every replacement or fix I run it on hose and it runs perfect. Get it to the ramp and it runs ok at first, but then gradually starts having the same symptoms.

Boat was purchased with a full tank of fuel and owner says he always used stabil and proper oil mix. I pulled several fuel samples on the inlet side of filter and fuel has no sediment or water. It's also the correct tint showing proper fuel/oil mix.

I have managed to run the majority of the fuel out, but still have about 1/4 left. My gut tells me it's carb related and I need to rebuild them. My question to you guys is does this sound like a carb issue to you?

The thing that bugs me is the fact that after I replaced hoses or spark plugs or something else it would run fine at first, but then start acting up. If the carbs were gunked up wouldn't they run crappy consistently from start to finish?

I work as an Aircraft Mechanic and my experience is with Jet engines, not small carbs. Believe it or not I am a little intimidated by them. lol I just want to make sure before I dive into this project that I am actually looking at the right thing. Also, if I get the carbs rebuilt and everything synced up again, will running that last 1/4 of old gas negate all the work I did, or would it be safer to fill up the tank with fresh gas and mix it with the old? It costs so much to have the tanks dumped on these things I'm just trying to keep it cheap.

I have my carb parts kits on the way and hope to get started next weekend so let me know what you guys think. I tried to keep this short, but it's hard to describe exactly what the engine is doing without going into detail so I apologize for getting long winded.

At least I didn't just leave a message saying, "Engine inop" lol

 

[tjello327]

Re: 1998 90hp Force: Possible carb issue? need advice.

I would get a spark tester and test spark on all cylinders. Sounds like you are loosing a cylinder now and then. If you do a spark test, don't crank over the engine without any of the spark plug wire grounded. You can fry the CDI boxes.

 

[pnwboat]

Re: 1998 90hp Force: Possible carb issue? need advice.

As a general rule, whenever I get a motor that it new to me, I check the compression, replace the fuel pump diaphragm and water pump impeller. The fuel pump diaphragm and impeller are relatively inexpensive, easy to do and are showstoppers if they fail. Compression is also important on a 2-stoke motor. Readings should be no more that 10% difference from lowest to highest reading. If you've already replaced the fuel pump diaphragm, then it wouldn't hurt to look at the carburetors.

The carburetors are very simple. Generally you don't have to do much to them. No need to dis-assemble every single part, unless you see something obvious. A little carburetor cleaner, compressed air and you're good to go. Most important thing is to replace the needle valve assy., and get the float height set correctly, replace the fuel bowl gasket, and set the idle mixture. Idle mixture screws are usually 1 to 1 1/4 turn out from lightly seated. If you've got a lot of gunk inside the carb, you may have to do a more extensive cleaning.

As far as the gas is concerned, I would just fill it up with some fresh gas/oil and mix it with the old. Also under "Force & Chrysler FAQ and other great information", first topic listed at the top of this Forum, there is a subject called "Synchronizing carbs and timing". It will explain how to perform a "link and sync" so that the carbs operate properly. Good luck!

 

[Seawolf_504]

Re: 1998 90hp Force: Possible carb issue? need advice.

Yeah thanks. I did a search before posting and did find the sync thread, which I printed out and will use along side the SELOC book I bought for the motor. I'm used to manuals with a little more "Dumbed Down" instruction, but between the sync thread and the book I think I will be ok. I did not think about the fuel pump diaphragm and will go ahead and replace that too. I think autozone sells those compression check tools for cheap so I will pick one up.

A friend took his Yamaha 2 stroke in for the same symptoms and ended up spending $800 parts and labor. I can't justify spending that much money, although cheap in boat repair terms, on something I have the ability to do myself for a fraction of the cost especially having the internet at my disposal. I have this thread bookmarked and will report back when I'm done and let you guys know how it went.
I will also try and take some photos for the guys about to tackle this as well. Thanks again.

 

[pnwboat]

Re: 1998 90hp Force: Possible carb issue? need advice.

Can't predict for sure what your experience will be with your motor. One good thing is that it does have the Mercury CDM ignition system. Personally I like it better than the older Prestolite CDI ignition system. Much easier to trouble-shoot because it's modular and not many wires to trace. All in all, I think once you become familiar with this particular motor, you'll find it relatively easy to work on. I have many friends that have late model 2-stoke, 4-stroke engines that have to rely on Marine mechanics/shops for repairs. I just smile and offer my condolences. I have a 1988 125Hp Force motor that has been running flawlessly for years thanks to the help I've received on the Forum....knock on wood.

 

[Seawolf_504]

Re: 1998 90hp Force: Possible carb issue? need advice.

Just an update I ran a compression test today and all 3 cylinders were sitting at 120 psi.

 

[jbp84]

Re: 1998 90hp Force: Possible carb issue? need advice.

That motor has one carb. I've owned my boat two or three months and its doing the samething. I bought a extra coil I've swapped coils around dissasembled the carb on it twice inspect for gunk, rebult fuel pump,new fuel filter, new ngk plugs was told they like champs better bought set of those. Been to one mechanic no prob found,the other let me boat set in the rain for a week and another guy wanted to look at it and see if he could find it swearing it was carb related. I've learned that boat mech are a diff breed of people they seem to not care