97 90hp Force - fuel pump? - exhaust leak?

[vit13]

I have a problem with my 90hp Force. It was working fine until last weekend - it started normally first, I moved the boat to the dock and stopped the motor. When trying to start it again in a few min, the motor didn't start and the primer bulb went soft. After squeezing the bulb I was able to start the motor but it was running very uneven like one of the cylinders wasn't firing and with a lot of smoke. Smoke was smelling of oil/fuel and I could see some fuel in the water too. When going from fast idle to idle the motor was cutting off most of the time but when I managed to go to idle and then in gear, the smoke was gone and the motor started to work properly - high RPM, low RPM, neutral, back to forward gear etc. Once I stopped the motor all symptoms came back - smoke, running roughly, cutting off at idle. I checked the plugs - all three were wet/dirty, especially the lower one.

Where should I start to look? Is it fuel pump? Bad diaphragm? I have a service manual but it's not very specific on fuel pump repair just a few diagrams on common pumps used in Force outboards.

Thanks!

 

[pnwboat]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

I would suspect a needle valve in one of the carbs has gotten a piece if crud stuck on it preventing it from closing properly. This would cause too much gas resulting in a flooded engine.

A soft primer bulb is the classic symptom of a carb. needle valve stuck open, or the float level is set too high.

 

[john from md]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

You may also want to clean out the recirculating system. This consists of the small hoses on the side of the engine that are connected to checkvalves in the power head. The purpose of these is to return unburned fuel to the intake where it is sucked up and burned. This keeps the lower cylinder from fouling.

You should clean the passeges in the powerhead and the check valves with a powered spray like Deep Creep or Valve Tech. Let it sit overnight and then spray it out again. This should clear the carbon so that you don't have that build up of fuel that causing your starting problem.

Regards,

John

 

[vit13]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

Thanks! Will look for crud in carbs and recirculating system. Just before that happened I filled up the tank so it might be that something got sucked into the system. That probably makes more sense because if the fuel pump is bad there would be the same symptoms both starting and running, right? What else could cause the flooding when starting? Is primer valve another place I should check?

 

[pnwboat]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

If the primer solenoid was stuck open I doubt that the engine would run well at any speed. Easy enough to check. Pull the small hose off that goes from the solenoid to the base of the carbs with the engine running. Only time you should see gas coming out is when you push the key in to prime it.

One other thing. To prevent crud from entering the carbs you can get one of those inexpensive inline filters for 10 bucks or so and install it between the fuel pump and carbs. If you get one that has a see through body, you'll be surprised at what you see getting caught in the filter. Be careful of the cheap see through glass ones. Glass breaks if it lays against the vibrating motor.

 

[vit13]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

Checked the primer valve and it's not stuck I can see it going on and off as I push the key in. Fuel pump is also looks alright so I think the next thing to check is the carbs. Also I have located the fuel filter but its not a see-through type so I might have to just replace it, it's a 12 year old motor after all. Thanks again for the help!

 

[vit13]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

Was trying to identify what cylinder might be a problem and noticed one thing - the motor is idling better without the cowling. When I replace the cowling the problem is back. Could it be that exhaust is leaking inside the cover? What part could be leaking?

 

[john from md]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

There is a boot in the mid leg that channels exhaust out to the relief ports on the back of the leg. If this boot is leaking, exhaust will be routed back to the intake. The boot costs about $10 and is held on with spring clips.

John

 

[vit13]

Re: 97 90hp Force - fuel pump?

Re: 97 90hp Force - fuel pump?

Thanks, John! Could you help me locate this part? I can find it on earlier models like '94 90hp - that's #27, right? - but it seems that they have changed design and moved it somewhere else on '97 model Thanks!

 

[pnwboat]

Re: 97 90hp Force - fuel pump? - exhaust leak?

I believe the 97 model uses a Mercury lower end. It doesn't seem to have the small idle exhaust relief like on the earlier Force models. Only exhaust seal that I can see is a gasket between the block and exhaust plate #10 and a seal at the bottom of the exhaust tube # 13.


http://www.crowleymarine.com/mercury_parts/2009/140.cfm

 

[vit13]

Re: 97 90hp Force - fuel pump? - exhaust leak?

Removed the lower unit today to check the exhaust seal and it looks ok, but I found that there was some sealant applied on lower unit and mid section in the exhaust cavity and it's all worn. Not familiar with this motor, just got it a few month back - is it a standard procedure to put sealant there? Didn't see anything like this on my old Mercury and there is nothing in the repair manual either.

UPDATE: Yes, sealant must be applied there - Mercury 90 H.P. 65 JET has the same lower unit and some sealant #116 (?) is shown on the diagram. Must be some kind of high-temp RTV.

Also when I inspected the impeller, it turned out that water pump gaskets are both bad. Is it possible that WP is sucking exhaust? I'm going to replace the gaskets and see if that's the problem. Thanks for the help!

 

[pnwboat]

Re: 97 90hp Force - fuel pump? - exhaust leak?

When you re-assemble the lower unit you should re-seal with sealant. Highly unlikely the bad water pump gaskets has anything to do with exhaust.

Most of the time you would be correct in assuming that there is an exhaust leak since putting on the cover seems to cause a problem, however, since you don't have the exhaust by-pass boot on this model I would suspect that the cover was either moving or touching some wires in the ignition system.

Check all the ground wires where they are attached to the block and the plate that the coils are mounted on.

 

[vit13]

Re: 97 90hp Force - fuel pump? - exhaust leak?

Just in case it wasn't posted here yet - Mercury/Quicksilver Lubricants, Sealants and Adhesives tube ref #s. Tube ref #116 is Loctite 587 ULTRA BLUE RTV SILICONE SEALANT, p/n 92-809825.

 

[pnwboat]

Re: 97 90hp Force - fuel pump? - exhaust leak?

Forgot to mention, check the spark plug wires themselves. You should be able to put your hand close to the wires while it's running with no shock. If you get zapped then that wire is either bad or bad connection at either coil end or spark plug end. Maybe you can talk someone else in to doing that test...LOL.

 

[vit13]

Re: 97 90hp Force - fuel pump? - exhaust leak?

Inspected the wires and didn't see any obvious problem there. Will re-check while running, just need to find the right candidate for the job Anyway, I'm going to fix the water pump and reseal first, hopefully the rebuild kit will arrive soon. Thanks!

 

[cr2k]

Re: 97 90hp Force - fuel pump? - exhaust leak?

Wires could be a problem. Also check the stator wires to see if there is any connectivity issues there. With motor running gently move stator bundle to see if it has an effect on engine. Also with motor not running go from idle to full throttle and back checking wires and routing as they move for any chaffing or pinching or pulling.

We chased this problem for several hours one day. Finally figured out the wires were routed right but about 1/2" too long and caused the problem.

90% or carburetor problems are electrical in nature.

 

[cr2k]

Re: 97 90hp Force - fuel pump? - exhaust leak?

Wires could be a problem. Also check the stator wires to see if there is any connectivity issues there. With motor running gently move stator bundle to see if it has an effect on engine. Also with motor not running go from idle to full throttle and back checking wires and routing as they move for any chaffing or pinching or pulling.

We chased this problem for several hours one day. Finally figured out the wires were routed right but about 1/2" too long and caused the problem.

90% or carburetor problems are electrical in nature.

One other thing or maybe 2...Exhaust cover gasket or powerhead gasket for exhaust recirculating in to cover.

 

[vit13]

Re: 97 90hp Force - fuel pump? - exhaust leak?

The parts finally came and I have the water pump rebuilt and appled some RTV sealer as per LU diagram. Also I have thermostat and fuel filter replaced. The motor works fine as it was before the problem started - starting, idling, going into gear and back into neutral alright. I think the problem was the W/P gaskets or maybe the RTV sealer that was worn in LU.

Thank everybody for help!