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wrench

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"Hi everyone...

This my fir

"Hi everyone...

This my first post, so hopefully I'll get a good response. I have a problem with my 2005 4.3 Mercruiser 190 hp. The engine will run-on after it has been run at a mild to high rpm. For instance, if we are out pulling the kids on tubes, or ski's and a rider were to fall off, you need to circle back to pick them up. Idling up along side of the person in the water, shifter in nuetral, we like to turn the motor off for safety sake. Shifter in neutral and idling for upwards of 15 seconds, turn the key off, and the motor runs-on like an old carburated car used to with the idle speed set too high. ( chugga, chug, chugga, chug). Turn the key back to run and the motor fires right back up a runs smoothly, wait 15 seconds and turn the key off and usually the motor will stop. Sometimes it may require the key on/off thing a second time. I had it in yesterday to have it winterized, (yes winter is on it's way), and talked to the tech about the problem. He said that maybe the idle is too high, but it runs at 750 in neutral, and he agreed that thats just about right. He suggested to shut it off in gear. I haven't tried that, but I shouldn't have to do that. It should shut off when I turn the key off -- period. He agreed. He also said that he couldn't make it do it while he had it running because he was running it on the muffs for water supply, and couldn't rev it up very high. It has a carb on it with quick start, so no choke plate. It has a solenoid for fuel enrichement during start up. No injectors that I know of. Next spring I will try turning the idle screw down a half a turn, but until then, does anyone know of a problem that these motors develop? I bought this thing used about 2 months ago. The whole boat is mint and it has about 30 hrs on it total. Give me an idea to chew on while the snow piles up outside.

Thanks
Wrench"
 
"Welcome Garth:

I am not fa

"Welcome Garth:

I am not familiar with the "quick start" carb. But 750 RPM seems too high in neutral. What is the RPM at idle in gear? 650 RPMs should be sufficient with engine under load at idle.

A float out of adjustment can allow excess fuel out of the carb when you turn off the key which will ignite from a buildup of carbon on the pistons and/or spark plugs. The carbon will glow red hot and ignite the fuel/air mixture.

Pull your plugs and examine them for carbon buildup. Plug color should be light tan/brown. White color shows the engine is too lean while black is too rich. If they are platinum plugs and covered in carbon, clean, check and regap if needed and reinstall them. If not platinum, install a new set.

Off branded fuel will not contain all the additives of fuel like Shell, Sunoco, etc. Marina fuel can be fine to use but I stay away from it due to the cost and unknown quality and age of it.

Next spring dump 2 cans of SEA FOAM into the fuel tank and fill it. It will remove any carbon builup while the engine runs. If you have the runon problem after half a tank of fuel, step up to 89 octane and see if it stops. If it improves but still has a little runon, step up to 91 octane. If no improvement, then its time to have the carb settings checked."
 
drop idle speed to 650 and tur

drop idle speed to 650 and turn mixture screw out 1/4 turn
 
"Garth,

I have a 2005 4.3 a

"Garth,

I have a 2005 4.3 also. I had the same problems along with hard to start and a lot of valve noise. I know the book says you can run 87 octane, but trust me the good stuff yields better results. I changed to ammoco 93 octane and all of the problems stopped. She runs like a cat in heat. H"
 
"Thanks for the responses.
He

"Thanks for the responses.
Hershel... now that you mention it, mine may also be considered a bit of a hard start. If its been sitting from one week to the next without being started, it takes alot of cranking to get it to fire up. 10 seconds of straight cranking. Let the key off, try again and it will fire right up. Then for the rest of the week end, it will fire up instantly every time. Its like the bowl in the carb goes dry during the week of non-use, and it has to refill with all that cranking. Never noticed any valve noise. I would/could move up to the better gas, but with our premium gas up here costing about $1.35 / liter (4 and a half liters in a gallon) that makes for an expensive week end pulling the kids around on the tubes. (thats about a $6 gallon) Next spring when the boat comes out of storage, I'm going to turn the idle speed down on it and see how it goes.
Thanks
Wrench"
 
"An old school method of remov

"An old school method of removing carbon deposits is to run some water thru the intake with the engine at high idle, like 1500-2000rpms. This can be risky if you put too much water to her, so I use a spray bottle and squirt a spray (NOT a stream) into the carb throat. This does not work well with engines with a catalytic converter, as the carbon flakes tend to block the matrix. Techron is also very good at removing these deposits."
 
Good old remedy Eddy. Just be

Good old remedy Eddy. Just be sure the engine is at operating temp. and to use really hot water so it will be sure to vaporize during the compression stroke. If you put the boat in the water then you can raise the RPMs for better carbon removal. A super shooter squirt gun works well.
 
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