Merc 150 2 Stroke Carb Start and Idle Problem Cold Engine

[cvflyer]

Please bare with me as I have compiled some info for my problem...

I have a 1999 150HP 2-stroke carbureted outboard (blue water series) 0G912981. I am having some issues starting and idling at different points during a day on the water. When starting the motor for the first time I squeeze the primer bulb until it's hard, set wide open throttle in idle, trim the motor to level with the water line and choke for about 15 seconds. If I follow this process it usually starts within 1-3 cranks. Sometimes I have to choke 2-3 seconds between each crank attempt. I immediately bring the power back to a medium throttle setting in idle once the engine fires. If I don't run the engine for about 1-2 minutes at a medium power idle power setting then it will die. After it seems to warm up then it idles great. We can also shut down and restart just fine at this point.

A similar sequence of events happens after the motor is off for more than 15 minutes. I usually choke for 3-5 seconds with the throttle set at wide open in idle. When the motor starts I immediately bring it back to a medium idle power setting. However, if I bring it back to regular idle it will sputter and die. Once we run for about 5 minutes at anything over true idle we can return to idle with no trouble.

Outside of starting and idling the engine runs fine.

The carbs were rebuilt 3 years ago by a dealer and the boat has accumulated less than 30 hours since. As far as I know the starting and idling issue did not improve after the carb work. The plugs were replaced at the same time. I pulled all the plugs today after the motor cooled and they looked ok. I also checked the fuel filter and it was clean.

Any suggestions are greatly appreciated!!!

 

[Dukedog]

sounds pretty typical with non-electronic controlled carburetor motor in "cold water"...

 

[merc150]

I had the same problem with my 2003 150 motor turned out to be a broken reed valve. Take the airbox off the and run the motor on muffs and see if there gas spraying back out the carbs then you have a broken or chipped reed valve

 

[rtrevino]

Before you start taking parts apart, check timing. Check the 'primary pickup timing or idle'. For this engine should be 0 to 9 deg. ATDC. I also have a 150hp 2 stoke that was hard to start and had back fired. After syncing it started within the first cranks. Also do a Carb Sync before checking timing.

 

[Dukedog]

doubt its reeds or timing... either will act up warm or cold at idle.. Merc150, consider yourself very lucky with a broken reed (if it was a production steel reed) and not have any internal damage.. didn't see anything 'bout a backfire? .. carbureted Mercs have a mind of their own with "cold starts" and warm up... don't think there are any two that like tha same cold start sequence and warm up...some jus take a little longer than others ta get warm (water temp is a big part) for whatever reason.. I have found a way over tha years that "most" like more than normal recommendations...

pump bulb till firm
trim motor all tha way "in"
push enrichner and start at same time till motor "spits, belches", may even start, then release key
trim motor ta level, slightly raise fast idle,
start motor "without using tha enrichner", ya might have ta jus "bump" tha enrichner a tad here....it takes a lot more fuel than most think ta start a cold, carbureted Merv V6.....

may need ta use fast idle till warm...extra minutes ta warm is lots less expensive than hammerin' ona "cold motor"........jmo

 

[cvflyer]

So after some tips on here and some additional online reading, I found that bumping the enricher (key) will keep it from dying at idle power. What I am still trying to figure out though is that on the first start of the day it only needs 1-2 minutes to warm up. After we ran around for about 30 minutes yesterday, we shut down, had dinner, fired up, and warmed up for about 5 minures. Put it in gear and it was fine at first. We were coming up to the boat ramp in idle forward and it started trying to die again. Bumped the enricher every time it sputtered and it kept running fine. In fact, it helped enough that I could feel the boat accelerate slightly in gear each time I hit the enricher. Is there any adjustment I can make to help solve this issue? It gets to be a circus trying to bump the enricher while you are trying to throw docklines and squeeze into a slip, dock, or ramp. Should I adjust the idle RPM screw (not sure if there is one) or idle mixture screw?

Thanks again for the pointers!

 

[racerone]

On cold start the key is to be --PUSHED IN WHILE CRANKING IT OVER---and not before !

 

[Dukedog]

that's hard ta try ta diagnose ona key board.. some type of idle circuit fuel delivery with tha carbs maybe.. tha only thing outside tha carbs that control fuel is a thermal valve on tha starboard head. it normally only does anything when tha motor is cold... all three carbs should be tied together with a 1/4" tube (starboard side) that will have a tube from tha bottom carburetor going back to tha valve.. other than that idle is controlled by carb idle circuit and idle timin'....gl