See full version: Mercury Carburetor Adjustments
4. Then, turn idle screw clockwise / tighten or close until the mixture starts getting to lean (too much air) and the engine will stutter / backfire, seem as if it is about to give out. Loosen the idle screw from that point 1/4 to 1/2 turn out. here
1. Loosen idle screws counter clock wise or from a lightly seated position 1 to 1 1/4 out. more
Propeller size - the larger the propeller size, the more resistance it will transfer to the engine, so the final idle sound may be high if your prop is too big.
Propeller pitch - the higher the pitch, the higher the resistance and vice-versa; this also may increase the RPMs and isle noise if you have an incorrect prop size. [links]
2. Start up engine and ensure the engine is idling properly (not backfiring, warmed up). If it is not correct, you may have to adjust the idle stop screw. My Merc 650 is suppose to idle at around 600 RPMs. Check the service manual for your particular engine. more
Please note I take no responsibility if you burn your engine out. It is better to be slightly rich than lean. If you are running lean, you run the risk of not supplying enough lubrication to the pistons. You be the judge of what is too lean. If the plugs are white, or no fuel / oily substance on the spark plug, then you are more than likely lean. Again better to be rich than lean. here
First, let's pinpoint exactly what's going on. We're not talking about a knocking engine or one that idles rough or stalls. We're talking about engines that start easily and accelerate smoothly, but then, after a few minutes at a steady speed, either surge in speed or misfire, causing the car to "buck." If that's your experience, then there are a number of things you can check out first before heading to a mechanic.
Whatever the cause, if your car's engine is misfiring or surging, it will prompt error codes to appear in your OBD-II Diagnostics system. These codes can cause you to fail your local vehicle inspection, or at the very least can result in that alarming orange glow to appear on your dashboard: the Check Engine Light. The good news is that, in many cases, an engine that is running poorly can be repaired for very little money.
Performing maintenance tasks like replacing worn spark plugs, inspecting plug wires, or even replacing an old, partially clogged fuel filter can make a huge difference in how well your engine is running. This can also save you a bundle of money, because even an hour of diagnostic time at your local repair shop can put the smackdown on your wallet. But if you've kept up with your maintenance and your engine is still acting up, read on for possible causes and fixes.
The list of symptoms and possible causes below should help you get a better idea of what's causing your engine to act up. If you see a symptom that looks familiar, read on to find out what a possible fix can be. Nothing is set in stone, of course, but a cheap fix is always preferable to an expensive repair bill. Look over all of the symptoms and fixes to be sure you're working with the one that most closely describes your situation.
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This article was co-authored by Hovig Manouchekian. Hovig Manouchekian is an Auto Repair and Design Specialist and the Manager of Funk Brothers Auto, a family-owned business operated since 1925. With over 30 years of experience in the automotive industry, Hovig specializes in the process of auto repair and maintenance. He is also very knowledgeable in common automotive issues and needs including engine repair, battery replacement, and windshield accessory and maintenance. Hovig's knowledge and hard work have contributed to Funk Brothers Auto winning Angie's List Super Service Award for five consecutive years.
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Merc Models 1966 & Earlier [links]
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