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Old 06-19-2012, 12:12 AM   #1
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Default VERY night idle

I have a 4-Barrel webber carb. My engine (and carb) was completely rebuilt. It ran GREAT the first two runs out! The third time I went to take it out, it was a little hesitant starting. When it did start, it ran fine but the idel speed was VERY high - about 1800-2000 RPMs. I tried letting it idle, heating up, playing with throttle, no change. I could've it up, but it would never come down below 1800 RPMs.

My mechanic said it was most likely the spring that is supposed to pull the throttle back to its closed/idle position - saying it probably fell off.

I was just looking at the carb in the service manual and can find no such spring.

Any ideas where it is? Other theories? (My mechanic is an hour away - on land - I have no trailer!)

Thanks!

-BKG
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Old 06-19-2012, 02:04 AM   #2
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sounds like it might be a throttle spring that they usually attach to the throttle control rod to the engine someplace.....they usually don't show that spring as it can usually be mounted about anyplace....or there can be a rotational spring that mounts on the shaft of the throttle body...that spring might have popped off...either way your going to probably have to get to the boat's engine and maybe take the carbs apart....


SP
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Old 06-19-2012, 03:00 PM   #3
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Might also be the choke/fast idle mechanisum on the carb is hanging up......
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Old 06-19-2012, 03:19 PM   #4
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goto auto zone and buy a cheap 6" long spring, and connected it to the linkage to test it.

if the boat dose not throttle down, then its your automatic choke kick down wheel, which hangs on the side and holds the idle screw up to race the engine.

you can also knock it down by hand. I would guess your electrical choke is sticking, and it rotates the chock flapper and the kick down wheel. $30 part.
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Old 06-19-2012, 06:59 PM   #5
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I don't have an electric choke. It's a vacuum pull-off I believe.

Would this be the spring you were referring to?

spring_maybe.jpg
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Old 06-19-2012, 07:10 PM   #6
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What type of choke do you have? Is a manual pull type from the helm or possibly a hot air/spring type?

A manual choke may not have a fast idle mechanisum attached but all other types will. Basically, when the choke closes the linkage also activates a fast idle device that keeps the engine running fast until it warms up a little and the choke opens.

Another thing you might try to narrow things down is to remove the throttle cable from the carb linkage, then start the engine and see if it will idle down. With the cable detached you will be able to operate the carb's throttle with your hand.

Dan
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Old 06-19-2012, 08:19 PM   #7
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It is an automatic choke, controlled by a Vacuum diaphragm.

The manual is here: www.boatfix.com/merc/Servmanl/16/16B5R2.PDF
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Old 06-19-2012, 08:26 PM   #8
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disconnect the vacuum hose to the choke pull off and then run it.
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Old 06-19-2012, 08:44 PM   #9
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BK -

There are two different types of automatic chokes; 1) Electric 2) Stove and Coil. Both types use heat to relax a spring which makes the choke open. The electric choke uses electricity to heat the spring, the stove/coil uses heat from the intake manifold to heat the spring. If adjusted properly the choke will be completely closed when the engine is cold. Since the engine needs air to run the choke cannot remain completely closed when the engine starts so the choke pull-off diaphram is used only to crack the choke open once the engine starts.

Since your carb does not have an electric choke it must have the stove and coil.

Since you mentioned that the engine and carb are freshly rebuilt, and ran fine for the first couple of times, you might also look for a vacume leak, especially check the carb to manifold bolts.

Dan
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