2001 Mercury 90 hp 2 stroke Premix gas after carb clean?

brianyo

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So I have a 2001 2 stroke 90hp serial 0T262997 with a mysterious misfire/rattle at low rpm that leads to stalling. I changed the rectifier as per a lot of research into this engine to no avail. So I proceeded to clean out the carbs in hopes it would help. My question is that, after a carb cleaning on these oil injection engines do I need to premix the fuel? When I reattached all the fuel lines and primed the bulb, the fuel filter seems to be filled with just straight gas and no 2 stroke oil. I was going to start the engine, but now im thinking that possibly my fuel pump isn't mixing the gas right which would cause this issue? This is my first outboard and im trying to learn it all on my own. I have read the entire service manual, but can't seem to find any info on it. Thanks in advance.

Current procedure: changed rectifier and replaced connections going to yellow wires(melted), decarb with seafoam (2 runs), new fuel filter, new marine starting battery (old owner had a dying deep cycle which I believe caused the issue), new spark plugs, fresh gas, cdm jump all checked out fine (7/16 in) & resistances, compression (cold 120, 122, 122; warm 122, 125, 125).
 
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wn6ngp

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Aug 12, 2012
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When you cleaned the carbs did you unscrew the idle jet needles? Hopefully counted the number of turns and cleaned those ports with carb cleaner. I have that same motor and I had a stumble on acceleration. Moving one carb idle screw a 1/4 turn solved the problem.

If you had an oil injection problem then the motor would have seized up at high rpm. However, I don't think it would hurt anything to do a premix after cleaning. As a matter of fact after I cleaned my carbs I used straight sea foam which is mostly diesel fuel and naptha to clean out remnants of old fuel. It smoked like all get out and it had very low power (wouldn't accelerate). Then I switched over to straight fuel and it ran fine.

Using premix along with injection shouldn't hurt anything. They recommend doing that for the initial break in period when the motor is new.
 

brianyo

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I actually didn't do that, I did write down the number of turns it originally had though. Ill take them out and shoot some cleaner in them. Going by the manual it should be lightly turned all the way in and then backed out 1 full turn for top carb and then 1 and a half turns for the bottom two. Thanks for the advice, ill clean them now and check!
 

brianyo

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Well ended up cleaning out the idle adjustment screws and then put them at first to what the manual suggested and then to what I had originally. Engine still is running very rough, ever more so than it had before. I picked up a timing light to try to figure out if it is an electrical misfire vs fuel system. Only issue is I dont want to damage the motor while I idle it. Any suggestions? The local marine places here have a 2 week wait apparently.
 

flyingscott

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How did you clean the carbs? The rectifier will have nothing to do with the idling.
 

GA_Boater

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What the idle RPM?

The screws still need adjusted with the motor in the water. All the settings you used are for the initial setting to get the motor running enough to do the in water adjustment.
 

brianyo

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I took all of the carbs out, checked to make sure the floats were good in a tub of water, took a pressurized air can and blew all of the openings, then took a carb cleaner can and sprayed down everything. The carbs were honestly pretty clean. I did end up taking off the fuel pump and found a bunch of plastic tubing(?) inside of it where the check valves were. I reversed the plastic discs and cleaned the inside of it. Hopefully this helps, gotta run it now. Here is a picture of the stuff I found.
 

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brianyo

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Alright, well the engine is 100% idling better. It is definetly running rich, but thats something that will just take some fine tuning on the water or possibly using a carb sync tool. Thanks for all the help!
 

MH Hawker

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I took all of the carbs out, checked to make sure the floats were good in a tub of water, took a pressurized air can and blew all of the openings, then took a carb cleaner can and sprayed down everything. The carbs were honestly pretty clean. I did end up taking off the fuel pump and found a bunch of plastic tubing(?) inside of it where the check valves were. I reversed the plastic discs and cleaned the inside of it. Hopefully this helps, gotta run it now. Here is a picture of the stuff I found.

thats remnants of the liner in the gray fuel hose
 

brianyo

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You're right, I took the fuel hose off and some more chips came out. Guess i'll be paying walmart a visit because I think it keeps leaking into the fuel pump. Anyone have any tips with balancing these carbs? I have the top one running too rich I believe because the engine keeps stalling with a big fume of smoke every few minutes. I made a little manometer and have been trying to precalibrate it before I take it to the launch. It seems like the vacuum on the top carb is pulling a decent amount more than the bottom two carbs, which I feel like might be correct? When idling, the top carb hits the black line with the other two equally lower. I tested the meter with dosing syringes and its surprisingly accurate. I feel like i'm at least getting in the right direction.
 

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