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Old 05-05-2017, 02:18 AM   #1
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Default 3.0 Merc Spring Start Issue

1999 Maxum SRL 1900
Had problems last year and got carbs redone which seemed to fix the problem in the fall. I put 1.5hours on without issues in fall after carbs fixed.
So when I pulled it out this year got everything ready it started great turned over 2nd time and idled around 900rpm for 12-15mins then sputtered and stalled out.
Now will start but wont stay running for more then 5 seconds.
Since this happened i filled tank with fresh gas 85L
(I know very little about carbs)Took top of carb off could not move the flap. Started it at about 1500rpm and got back to the flap and I could keep it running if i played with the flap moving it slightly but as soon as i let go it would stall out. Ran this way for a few minutes.
Anyways before I take it to someone for $150 hr is there some diy things I can try keep in mind I do not know much about carbs. I would like to learn but do not know anyone and can not find many videos about them. Thanks for any help.
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Old 05-05-2017, 02:45 AM   #2
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Flap? Are you referring to the choke plate?

On the side of the carb is the electric choke with three screws, you may need to loosen them to adjust choke. When the engine is cold and you pump the throttle the choke should close to about a pencil diameter opening. As the engine heats up the choke should open till straight up. Go to the Documents section of this site to get the mercruiser manual for your engine as it has a section for the carb.
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Old 05-05-2017, 02:59 AM   #3
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yes choke plate. like i say im a noob sorry.
So when cold and engine not started if i pump it the plate should move or it moves after its started? So sounds like just choke adjustment? When i was manually playing with the plate it was running at around that pencil width but as soon as i let go it went straight up again. I will have a look tomorrow at it again.

I should also note the 1st time it stalled out i thought it was just out of fuel (thought it had more) this is why i filled it up and then the problems began.
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Old 05-05-2017, 03:30 AM   #4
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When the engine is cold the closed choke limits the amount of air with results in a higher fuel to air ration or a richer mixture to keep the engine running. As it warms up the choke opens and the air to fuel ration leans for the correct operating condition. A computer on a fuel injected engine does this by controlling the fuel injectors to richen the mixture when cold.

Yes you can manually close the plate and since the engine would then run this seems to be the problem. If you held it until the engine warmed you should be able to let go and the engine should continue to run.
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Old 05-05-2017, 03:39 AM   #5
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I would look at the possibility that the fuel filter is plugged!
The chock should have been fully open after it ran for 10 to 12 minutes!
Check the fuel filter first!
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Old 05-05-2017, 04:00 AM   #6
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There was about 2 hours between the time it stopped after running great (thought no fuel) so it would have cooled down for 2 hours. i have been looking at the manual and will attempt to adjust the choke but just so i understand i take the 3 screws off and turn it left for less choke and right for more choke? I want more choke i guess? Can the choke work perfect like it did 2 hours before for the 12-15minutes it ran to later not work like suspecting? I dont know if i did run out of fuel but it took 85 liters and im pretty sure thats my tank size. could this have caused problems?
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Old 05-05-2017, 12:38 PM   #7
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You just need to loosen the three screws not remove them. No the choke should not go bad in a day but since you said closing the plate helped I don't know if was ever set correctly. Don does have a good point if the gas tank ran low crude may have clogged the filter or carb. This would lean the mixture as well. There should be two filters, a spin on one and a cartridge one in the carb where the fuel line connects.
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Old 05-05-2017, 02:26 PM   #8
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Thanks. I will try to find them. Do they need replaced or can they be taken off and cleaned to test this therory? Closing the choke plate would allow it to ru. With a clogged or ad fuel filter? Thanks again for the help going out to stay playing with it soon.
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Old 05-05-2017, 03:59 PM   #9
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The spin on filter will need to be replaced it's constructed like an oil filter so no way to clean. The carb filter can be cleaned if the screen type and not a paper element, however these are cheap and if you are going through the effort to remove it just put a new one in.

Glad to help.
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Old 05-05-2017, 05:06 PM   #10
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ok took the top part of carb off cleaned it all up put a new fuel filter in carb put all back together.
Started up and ran for about 30 seconds good at about 1000 rpm then stalled out again. So question about the choke plate before starting it i could wiggle it to move a few mm from the closed (flat)position. After running it for the 30 seconds its straight up in open position and i cant move it without the throttle engaged. Is this normal? I did not do anything with adjusting the choke yet.
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Old 05-05-2017, 05:27 PM   #11
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After it ran for 30 seconds did it just die on its own or did you do anything such as pull the throttle back to idle?

The choke should be open this fast but it is normal that you cannot move it under this condition.
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Old 05-05-2017, 05:30 PM   #12
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No I did not pull throttle back. It started to sputter so I tried to give it a little throttle then died right away. Now when start it will turn over then stop instantly. I have not had time to change the other filter but going to try to get that done this morning.
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Old 05-05-2017, 05:51 PM   #13
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So I just tried with extra help to hold the choke plate again at about that pencil width opening and it would run as long as we held the choke on as soon as let it go slightly it started to stall. We let it run for 3 or 4 minutes like this at 1200rpm. As soon as pulled throttle back slightly it stalled. Can start again with some throttle 2500rpm it fires anything less won't. But will stall out every time unless we hold that plate.
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Old 05-05-2017, 06:01 PM   #14
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This also does seem similar to the problem last summer before the carb rebuild. But then I had it in the water so could start with higher throttle and give it full throttle and it would go and stay running with throttle. But cannot try this in the driveway.
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Old 05-05-2017, 07:17 PM   #15
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Sounds like the idle circuit of the carb is not delivering fuel. Are the idle adjust screws about 2 1/2 turns out?
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Old 05-05-2017, 08:29 PM   #16
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i just went out and did this have not tried starting
idle mixture needle i just set as - until lightly seated then 1 1/4 turns out
idle mixture screw in neutral - back out until no longer contacting then in until just contacts then 2 more turns?

should both be 2 1/2?
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Old 05-05-2017, 08:43 PM   #17
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So with those settings above it started and would idle fine 10mins (happy face)right at 1000rpm. Went to give it touch more throttle and stalled out right away. Sad face
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Old 05-05-2017, 08:53 PM   #18
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2 1/2 turns each it idle fine. But can't pull back to neutral with out Rpm dropping and stalling out. So guess this is problem if only I knew where the scews need to be exactly. If I pull the throttle back until 800ish rpm any more it stalls. What should I do with screws when I'm at that 800?
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Old 05-05-2017, 08:55 PM   #19
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Ok that is just a rough setting to start from. Refer to the 3.0 manual for further adjustments which involves setting the rpm and timing to get it right.
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