1999 75hp Fuel Prime Issue

[pshelfo]

Have a 1999 Force/Mercury 75hp 2-stroke 3 cyclinder andhaving an odd fuel issue. prime up bold and it is hard, motor starts fine but will eventually stall out and bog down from fuel starvation. Primer bulb goes soft and if you prime it up, starts but eventually dies and can‘t get give it any throttle. Thought was fuel air leak and have replaced the fuel tank plastic tub, anti shiphon, hose to primer bulb, primer bulb, hose to to quick release, hose to fuel filter and hose to fuel pump. Nothing has fixed the issue, inserted a clear line and there were some tiny bubbles that came out of fuel pump side and was worried flow is not occuring. Rebuilt fuel pump a year ago with a kit when this problem only happened after fishing for a while then trying to move spots. Motor is definitely losing prime and carbs are getting starved. At a loss of what to try next. Worried that it might be fuel pump as there was a big bubble in the clear line thst
that just stayed there. Would have thought fuel flow would pull that though.

 

[markhodges78]

It definitely sounds like the fuel pump .. have you checked the fuel pressure?

 

[racerone]

The fuel pump is driven by a crankcase PRESSURE pulses.------Not the same as cylinder compression !-----Posting cylinder compression numbers may offer a clue on motor condition.

 

[pshelfo]

Continued saga. I took boat to mechanic twice. First visit said bottom carb float was stuck and a crack in a T-fitting. Second visit said spark plug wire that was arching and my top carb bowl was leaking. I have replaced everything from the fuel tank pickup to the fuel pump (put in a new fuel pump). Got boat back on water and still having issues. Very hard to start, once it does I have rev it, baby it with choke. When I try to get on plane it struggles like it is starving for fuel. I pressure the choke in and it get a little life but stall out, eventually I can get it on plane (might stall out a few times). When I get it on plane and WOT it runs great. Then it sit while I fish, fires right up on crank, then dies out. Then have issues getting it to start, have prime bulb to I rev it idling, slam it in drive to get it up on plane quick. I am at loss and not sure if this is carb rebuild situation or what else could be causing it to starve for fuel. It almost seems like it get flooded fast and then when I put it under load it starves for fuel until it pressurizes to a point - then all is good. Any suggestions very welcome. Dropped $1400 on mechanic bills and not wanting to waste more.

 

[flyingscott]

Sounds like the motor is lean. Does it have low speed screws?

 

[racerone]

Any compression numbers?----Or do you feel that is a waste of time ?----What did your mechanic do for $1400 ???

 

[pshelfo]

I took it in for a few things but for the fuel issues he fixed a stuck float, re-worked a kinked fuel line, fixed a cracked t-fitting, tighten a leaking carb bowl, checked one bowl and it was clean, adjusted sync and link and found a cracked plug wire and covered it with silicon since he did not have the part. it appears to have been all labor and each time he says it is running well. But that is without back pressure. I have assumed he checked compression but not sure. I don.t know if it has low speed screws and have to check. What is confusing me is it runs fine when you finally get it up and going. If it was compression or something major would expect it not to run good at WOT. No happy with the mechanic and that is why I am trying to get help. I have stared at the motor while it is running in idle and no leaks or anything odd. It appears to idle pretty well.

 

[pshelfo]

I worked on the motor some more today and ran compression tests. All three cylinders are sitting at 120 foot lbs give or take a pound or two. Since compression looks good I went around and looked at everything. Boat starts fine when cold, it won't idle long in driveway. When I first primed I pushed it hard till I could not any more - fuel came out of the bottom carb - not sure if this is normal. After it starts the primer bulb won't start hard so I think that is still the issue but have not idea where. I have replace everything from fuel tank pickup all the way to fuel pump minus the quick connect. Any ideas on how to troubleshoot this?

 

[racerone]

There is no need for the primer bulb to be hard once motor is running.---This confuses / baffles a lot of folks !

 

[pshelfo]

Okay that is very helpful information which rules one thing out. When the engine is not on the bulb appears to stay hard after I prime it. I noticed that while it was running the fuel filter appears to slowly drain out (or just have less in it) when idling. When I rev it it seems to fill up a bit but there is always an air bubble sitting on top. Is this normal?

I have been toying around with carb rebuild at this point as I don't know what else to look at.

 

[QBhoy]

Hi. Very much sounds like your float is sticking. Give her a proper carb clean and try again. I’d also make sure the fuel line is going the right direction and it’s not able to draw air from its fittings too. Check the arrow is going the right direction on the primer bulb.
Also wondering about the fuel filter you have installed too. What type is that ? Make sure the fuel piping is going the right way through that too. Check the fittings in and out of that. If it’s one of the cheap small things that you usually might fit to a lawnmower…ideally throw it out for a proper one…or at least check the arrow for the direction of travel is correct. All the best.

 

[pshelfo]

I finally got around to rebuilding the carbs and giving them a good clean. So far engine appears to be running better in that it did not stall out in idle. However, it seems to now be running hi RPM at idle. I read to loosen the sync & link clamp screws, let it re-set closed and then tighten them up again. The other thing I am wondering is if I need to reset my fuel mixture screws. It was odd that the top was set at 1 1/4 turns out and the middle and bottom where 1 1 3/4 turns out. I not sure if this is the correct setting. I put them back as is but wondering what they are supposed to be set as. Appreciate all the help!

 

[pshelfo]

Today I reset the sync and link and the idle seems much better. However after all the work I have done, I still have the same darn issue where the boat runs and seems to starve from fuel and crap out. Looking at the fuel filter (which is mercury brand) when idling it seems to empty out most of the way which makes me scratch my head as the entire fuel system and hoses are new. I did not purchase a mercury OEM primer bulb when I first started having the issue (picked up an aftermarket at Academy Sports). I am wondering if the part I got is bad or something. Really scratch my head on this one as if I keep pumping the bulb the motor appears to stay on.

 

[racerone]

The bulb is a simple manual pump.----Sounds like the pump on the motor is not working.----The bulb does not need to stay hard when motor is running.

 

[brodmann]

If you cleaned the carbs and cleared out some blockages or trash inside, it's expected that you may have improved fuel delivery and that would require some adjustmets. Often the mixture screws are used to adjust for little issues inside the carbs.

 

[pshelfo]

Thanks for the reply. I have already replaced the fuel pump with a new one 1/2 into the job. How do I set the fuel mixture screws? Is there a standard I need to set these for this motor? I have been looking about the internet and not found any instructions for this motor. Regards,