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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10963
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Sir, I have 1986 or 87 30 hp Mariner. It runs well except

Customer Question

Hello sir, I have 1986 or 87 30 hp Mariner. It runs well except at low idle. It seems to be rocking and skipping a bit too much...i'm using 89 octane gas and star tron stabilizer
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. The idle jet is # ***** at the top of the carb stbd side. The jet should be adjusted in the water warmed up. The initial setting is 1.5 turns counter clockwise from lightly seated. Turn jet in till it just does seat then back it out 1.5 turns. Start engine and make small adjustments till you have achieved the best idle. Post back with if the engine doesn't run any better or runs better.
Customer: replied 2 years ago.
Thank you. Could you tell me about the two screws on the port side, one was up high and one was lower...
Expert:  Tan replied 2 years ago.
Sorry I meant port side. They only adjusting screw for idle fuel mixture # ***** port side top.Now the other screw # ***** is for idle speed.That won't cause the engine to run rough if out of adjustment on to slow or to fast an idle. Are those the screws you were referring to? Open this link for a diagram.
Customer: replied 2 years ago.
The reason I asked about the two other screws is it seems to be blowing a little extra smoke.
Expert:  Tan replied 2 years ago.
This could be due to the jet being adjusted to rich. Have you tried adjusting the idle jet? The only reason this engine would smoke is to much fuel, to much oil in the fuel or the engine is over heating. If the engine still smokes you need to check the engine temp. If engine isn't over heating be sure you arte mixing the fuel oil ratio at 50:1 or 2.56 ounces of oil to one gallon of gas.Then finally if the engine still runs rough we need to get a timing light and check the spark on both cylinders to see if you have an ignition issue. This should get you going in the right direction and solve your engine issue. Post back with questions and findings.

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