Issues w/ 9.9 merc 2 stroke

[DJ76]

Well, took out my little boat into raritan valley today cause of the nice weather to do a little trout fishing...well my motor is acting up again.  Been having this issue for awhile was wondering if its something stupid on my end or maybe a worse issue.  Any insight would be appreciated.

Motor is a 90/91 Mercury two stroke 9.9hp.  I have been having issues with it running for maybe ten or so minutes...dying out (like its starved for fuel) and then once I prime it it starts right back up...then...repeat the problem.  Well finally it just doesn't want to start anymore. With this said, this only happens when the fuel tank is half full (~3 gallons).  I've opened the valve on the tank thinking its a vaccum issue, I've replaced the fuel tank with a brand new one, I replaced the fuel line, primer bulb, and the connection to the motor.  I checked the screen on the fuel tank end and also checked the fuel filter and was clean.   I'm scratching my head here.  I've tried moving the tank to different positions thinking maybe the fuel line in the tank is not reaching the fuel...I've tried different octance ratings.  Now, if I go place another 2-3 gallons of gas in the tank she runs fine with no stalls...until I hit the halfway mark.

I'm thinking some type of vaccum issue, no?  Could it be a fuel pump...which only works and 3/4 to full tank of gas?

thanks in advance for any feedback

 

[Reckless]

Weak fuel pump? My reason for saying that the more fuel you have in the tank you say it is ok. The  full tank gives more head pressure. Pump doesn't have to work as hard. You said you replaced the lines and tank. Loose connection? Sucking air?

[DJ76]

Fuel pump...thats what I'm leaning towards as well. But I wasn't sure about why the fuel pump would work better at full than half full gas tank.  In all my years of handling equipment usually when the fuel pump goes, its gone. Its not I'll work when the conditions permit type of thing.  But I have no experience with boat motors (obviously).

And yes,  from the tank to the motor is all brand new (within six months). Fuel line, fuel tank, bulb, connectors.  I wanted to make sure I wasn't sucking in air, losing pressure, somethings clogged, etc.


A little more background.  when its running right before its about to stall out I can see the primer bulb collapse.  Reason I know is I figured if I'm not getting enough fuel I'll try squezing the bulb...well I can't its collapsed.  so I normally plug and unplug the fuel line that goes to the motor (sorry don't know the technical name  ) so the primer bulb 'pops' back out.

[Reel Time]

 might sound simple enough but,,,,fuel prime bulb going right direction or any other one way valve?


 if its collapsing the bulb i would guess the pump is good, and have to be a feed problem, maybe just a coincidence and the new tank has a piece of crap clogging the intake line?




 if it comes down to it, maritime matt is rumored to be topnotch and reasonable, plus he's a sponsor,, either way i'm sure he'll chime in with some tips to throw in and check

[Reckless]

Bulb collapsing agree probably not the pump. You need to check between the tank and the bulb. Is the line in the tank ok?

[DJ76]

might sound simple enough but,,,,fuel prime bulb going right direction or any other one way valve?

 if its collapsing the bulb i would guess the pump is good, and have to be a feed problem, maybe just a coincidence and the new tank has a piece of crap clogging the intake line?

yes..checked bulb direction...could be a coincidence but clog would have to pass through screen on tank fuel line an that was clean when checked this afternoon.   man my irish side is popping up again...murphy's law i guess.

[DJ76]

Bulb collapsing agree probably not the pump. You need to check between the tank and the bulb. Is the line in the tank ok?

seems to be yes.


i think I'm going to fill tank all the way up again and see if I get the problem of the engine shutting down.  perhaps its another problem altogether

[Andys Delight]

Debris in the fuel line or tank. Most of the time it is in the tank. It will get sucked up against the intake line not letting fuel pass.  Also try opening the fuel tank first if the bulb collapses.  If the bulb pops to normal when you do it's a venting issue. Lastly, make sure all your hoses are tightly clamped and not sucking air anywhere. 

[DJ76]

Debris in the fuel line or tank. Most of the time it is in the tank. It will get sucked up against the intake line not letting fuel pass.  Also try opening the fuel tank first if the bulb collapses.  If the bulb pops to normal when you do it's a venting issue. Lastly, make sure all your hoses are tightly clamped and not sucking air anywhere. 

will do thx

[BigAl13]

Is the vent on the center cap of the tank open? Maybe stupid but you never know. If it was closed air would not get into the tank to keep the fuel flowing and once the pressure went down because of consumption it would choke itself out.

[IKAT]

I see you have replaced the tank and the connector to the engine--Did you check the line from the back of the fuel line connector to the pump for any air leaks? Just saying

Had this problem with another engine--when the line heats a little it collapsed and got the restriction in fuel flow--just saying this because it was just a bad line when it got warm it collapsed when you are running for 10 minutes. Also it shut down when you give it gas as going to wot.

My .02

Good luck

I know this dosen't solve the half tank issue-could still be faulty fuel pump.

Hey D--If none of all this helps-don't go up Cherry St.-could be an altitude issue--Just Kidding Bud

[DJ76]

hopefully later on today i'll give it a walk through here on dry land.  i'll stick the motor in the large barrel i have and go to work starting with the basics.   i'll try and do one thing at a time so i can have a process of elimination.  thx for all reply's...i'll post back later on (hopefully) and let you all know how i make out.  i really appreciate it

[IKAT]

Hey D just 1 note

Putting it in a barrel sometimes will not give you a true reading of whats going on--if the engine is not under pressure/torque as in running in the water-certian symptoms may not show up

Take care

[DJ76]

Hey D just 1 note

Putting it in a barrel sometimes will not give you a true reading of whats going on--if the engine is not under pressure/torque as in running in the water-certian symptoms may not show up

Take care

yep, thought I could cheat.  Tried running it in the barrel to replicate the problem...no go. ran it for like twenty minutes and she runs and sounds fine. although I couldn't put her into full throttle cause i'd have no water left.  Guess I have to take it out to the lake again and get her back into the water.  Not sure I'm going to be able to do that today.

maybe i should just go out with full tank of gas...that will give me all day on the water anyway (use the trolling motors a lot) and I don't have to worry about it.  Now if this problem happens with my new 20hp yahmaha i'm really going to go nuts.

[IKAT]

Here ya Bud --if you need a hand just email me --be glad to help -I'm about an hour from you

Need to have the problem there when checking

Later

IKAT

[wb]

Fuel pump is good, it's probably the fuel line from the tank to the primer, or the primer itself. I have seen brand-new bulbs NFG right out of the bag, usually the check valve sticks and "checks" in both directions. Stick to the OEM bulbs. Lines too, unless you have a source for a quality, reinforced, ethanol-resistant aftermarket lines. Also as was said before could be restriction/contamination in the tank, but unlikely....

Good luck. 

[DJ76]

thx again everyone.  really appreciate all the feedback.  Have to get the wife from the airport tomorrow so getting the boat into the water is out. If I happen to put the boat in the water and then I'm late to pick her up you'll never here whether or not i solved the problem!

[Pops Soul]

Dj know I'm a little late hear on the subject, but I had the same problem on my 25 merc. your secondary needle valve is sticking. This jet opens when the carb float drops down. If you pull the carb and drop the bowl, the needle sets above the lever that the float rests on. If you take some very fine sand paper or steel wool and polish the needle jet to let it open and close with out sticking you should be fine. I have a Seloc Manuel if you need me to I can try to scan the pages and send them to you. Let me know

[DJ76]

Dj know I'm a little late hear on the subject, but I had the same problem on my 25 merc. your secondary needle valve is sticking. This jet opens when the carb float drops down. If you pull the carb and drop the bowl, the needle sets above the lever that the float rests on. If you take some very fine sand paper or steel wool and polish the needle jet to let it open and close with out sticking you should be fine. I have a Seloc Manuel if you need me to I can try to scan the pages and send them to you. Let me know

wow...great info.

You were only having these issues at half tank as well?  I'm actually curious what causes this...assuming has to do with pressure in tank once its at the halfway mark???

[Pops Soul]

Actually I was having these issues know matter what Level the tank was. I found some small air leaks in the fuel system. I replaced the fuel line from tank to motor, I replaced the fuel filter and bowl. I replaced the suction line in the tank. Made sure the vent on the tank was working right. Played with the carb adjustments. The bitch of the whole thing is I had to be in the water and run the boat for it to happen.