1999 Force/Merc 75HP 3 Cylinder 2-Stoke Rough Running Issues

[pshelfo]

Been struggling for over 6 months working to troubleshoot fuel/idle issues with my 75HP outboard. All started when boat started to stall out when getting to dock in reverse and then, hard to start and dying out sometimes getting on plane. Fast forward to now I have exhausted my knowledge and repairs and not sure what to do next. Had another older post but this one is focused on latest situation.

Current Situation. Motor very hard to start but does eventually. Have to really rev and warm up to get it stable and once at that point appears to idle okay. Giving it some throttle runs very rough, chokes on itself with puffs of smoke, and is hard to get on plane - sometimes dies out like it is staving for fuel and then a pain to start. But on on plane with WOT runs great with no issues. Until you turn off and let sit - cycle repeats.

What has been fixed or checked:
- been to boat mechanic twice (no luck)
- fixed a cracked t-fitting on carbs
- fixed stuck float
- ran hi concentration of SeaForm through
- compression perfect on all three cylinders
- fixed arching plug wire
- new starter (was shorting and burnt a few wires which were repaired)
- rebuilt carbs, sprayed the heck out of them, cleaned permanent jets with paper clip. Floats look good,
- adjusted sync and link - idle rpms seem fine.
- adjusted carb fuel mixture screws to a 1 & 1/4 turns out, tried 1 &1/2 with no luck. Previous setting was a little odd with one carb set higher at 1 & 3/4 out.
- replaced entire fuel delivery hose system from fuel tank pickup all the way to carb hoses (including primer bulb, fuel filter, fuel pump with the only exception being quick connect.

This is a real head scratcher as I don’t see anything wrong. Maybe it is mixture issue but it runs good at WOT and crap if you are revving on muffs or on lake. With new starter should be kicking over quickly. Prop is dirty with black carbon buildup so I see It not happy, 6 months of messing and still have not gotten a handle on things.

Appreciate any and all help as not many want to work on the old motors.

 

[Faztbullet]

What is this perfect compression numbers?

 

[pshelfo]

Sorry. All three cylinders are sitting at 120 foot lbs give or take a pound or two.

 

[pshelfo]

Today changed all three spark plugs and still very hard to start in driveway. This is a real head scratcher. Any ideas of what to check next.

 

[Chris1956]

Check fuel pump diaphragm for a hole. If it has one, it will flood the cylinders with raw fuel.

Using a paperclip on the carb jets is very bad, as it can easily change the size of them. You might see if you damaged them.

 

[QBhoy]

Amazed to read that a “mechanic” has seemingly gone to all that chargeable (to you) trouble and effort…but failed to remove and properly clean the carbs. Sounds like he’s danced everywhere around about them though. The thinking that seafoam is an alternative to a good and proper carb strip down and ultrasonic clean…is crazy, I think. I don’t mind a bit of seafoam through the fuel occasionally…but an alternative to the above mentioned…it certainly isn’t.
I see the mention of him rebuilding the carbs..then spraying the hell out them..and seafoam. Hate to be cynical…but these things mentioned together and with association…don’t generally fit perhaps. Along with the mention of adjusting settings separately. Of course…should he have actually stripped the whole lot down…then put everything in a US cleaner, then ensure all is well…whilst rebuilding and setting up again…please forgive and ignore the above.

 

[pshelfo]

Thanks for the replies and assistance. Answers and clarifications:
- I originally rebuilt the fuel pump but decided to buy a new one (which I installed but did not help)
- I did not use a paper clip on the jets (that was my wording mistake) but rather on the nozzle tube. I saw a you tube video to try and clean and won’t do that again.
- twice taken to a boat mechanic who fixed and adjusted things but never did a carb rebuild.
- after dropping cash on mechanic I first tried sea foam and then I rebuilt carbs myself.
- when I say I sprayer the heck out of them I meant I used carb cleaner and throughly and repeatedly hit every hole and pass through with cleaner and compressed air.
- I put the fuel mixture screws back to what they were prior to carb work.
- I am going to check the choke solenoid maybe adjust my starting sequence,
- I see the bottom carb bowl leaking and looks like gasket did not seat right. Have to fix this first.

 

[flyingscott]

What is your starting procedure? Using the choke? Fast idle lever?

 

[racerone]

Does spark jump a gap of 3/8" on the 3 leads , yes or no ?-----Has the battery been load tested , even if new ?---Flywheel key checked ?----Water pump impeller changed every 5 years ?----Water in the fuel ?-----Factory fuel pump installed or an Amazon special ?

 

[pshelfo]

Starting procedure is prime bulb, put throttle and 1/2 way, press choke a couple of times, turn key and hold choke at same time if needed. I read I am supposed to turn key and then hold chock in for 8 to 10 seconds and then try and start using the same procedure. Am going to try that.

 

[pshelfo]

• Not sure about the spark gap jump as I have the marine plugs without the electrode j-hook. I might have to buy one of those testers.
• Battery load I will test and see what it says.
• Flywheel key checked - not sure what that is but will check.
• Water Impeller - yes (did it a year ago).
• Water in fuel - new fuel but I am thinking to install an inline filter to address if there is water in the tank.
• Fuel pump - aftermarket.

Thanks!

 

[racerone]

Testing spark has nothing to do with the sparkplug itself.----Test the spark with a tester or make one with some wire / cardboard / glue.-----If flywheel key is sheared the timing will be off.

 

[BWR1953]

...Current Situation. Motor very hard to start but does eventually. Have to really rev and warm up to get it stable and once at that point appears to idle okay. Giving it some throttle runs very rough, chokes on itself with puffs of smoke, and is hard to get on plane - sometimes dies out like it is staving for fuel and then a pain to start. But on on plane with WOT runs great with no issues. Until you turn off and let sit - cycle repeats...

Have you tried running it on the water without the cowling in place?

 

[pshelfo]

Was able to work on boat today and had some success. Took carbs off again and fix fixed the gaskets which stopped the bottom carb leak. I noticed that on two of the carbs the float needle was stuck. Reset all of them gently. Also took or the jets, spayed with carb cleaner and put them back (they looked good). Checked the choke solenoid and with key on and pressed in, only a tiny drop of fuel comes out of the top tube which goes to the engine. I think I have a bad choke solenoid and looking to replace.

Did not start up easy but after 8 to 10 times it lit. Engine did not stall out running 10 to 15 min which is great. Idle was very good with no issues. When I give it some juice it handles it but chokes and puffs some. I turned my idle screws from 1 and 1/4 out to 1 and 1/2 out and "may" have made it a little better but hard to say. A movie is worth a thousand words so I attached good idle and rough rev. Not sure if it is idle mixture or perhaps water in fuel tank.

 

[flyingscott]

You need to hold the choke in until it starts. Bumping the key does nothing if the motor is not turning over.

 

[brodmann]

When you rebuilt the carbs did you order carb kits? I've attached a link to a blow up diagram of your carbs. Did you remove the plug #2 and clean the passages in there. That's part of your idle circuit. The kit will contain the replacement plug. That's pretty critical stuff under that plug for a smooth idle and the ability to rev up until the main jets start supplying the fuel. Running great at WOT means the main jets are clean. A rough idle, or difficulty getting up to around 2,000 RPM's is a sign of an idle circuit issue with the carbs.

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[pshelfo]

Shoot I did not. I have the plug but was not sure how to remove. That was a miss on my part. How does that plug remove and install?

 

[Chris1956]

That plug is listed as a welch plug. They are convex and when replaced are normally pressed (or tapped) flat and sealed with wife's nail polish or RTV silicone. Getting them out usually damages them.

That looks like it covers the top of the emulsion tube. Maybe you can clean it from the bottom?

 

[alldodge]

Folks a side track question.
Comment came into the Mods that this is a Force motor and not a Merc. It does look like a Force, and Force was made by US Marine for Bayliner until 1999.

What say you?

 

[pshelfo]

This particular motor is really a Merc behind the scenes even thought it has some Force tags.