1994 Mercury 150hp rough start, rough idle, rough running under 2500rpms

[rtrevino]

Hey Everyone, I need everyone help to diagnose a problem with my 1994 150hp 2-stoke outboard motor. At times is hard to get it started cold and warm. Once it is running it has a rough and shaky idle up to 2500 rpms, after that it run much better. I can take it to 45mph and runs smoothly. I had changes all 6 spark plugs, check current on coils and cables and seem to be okay. I also put new fuel/mix, new water separator and fuel filter; still fails. When chatting with a guy at the boat shop he told me that it might need the carbs rebuilt. Had anyone experience anything like this? All help is highly appreciated.

 

[Chris1956]

It could be dirty or mis-adjusted carbs. I would first verify the link and synch is correct. Next take a compression test. If both are good, carbs are logical next step.

 

[rtrevino]

It could be dirty or mis-adjusted carbs. I would first verify the link and synch is correct. Next take a compression test. If both are good, carbs are logical next step.

Hey Chris, thanks for your tips. You are right, I'll check the needles settings. have not done that.

 

[Chris1956]

Gee, needles setting is just one part. Idle circuits can get dirty. High speed jets can get clogged or partially clogged as well. this can lead to melt down. Clean the entire carb, replace all gaskets, and if in doubt, the inlet needles. You should be able to get new floats for that carb as well.

 

[rtrevino]

Gee, needles setting is just one part. Idle circuits can get dirty. High speed jets can get clogged or partially clogged as well. this can lead to melt down. Clean the entire carb, replace all gaskets, and if in doubt, the inlet needles. You should be able to get new floats for that carb as well.

Thanks again for your help.

 

[rtrevino]

UPDATE: So I decided to take it to a local marina and have it checked. After 3 days I picked to boat and they told me that all it needed was a linkage adjustment. Compression was okay and that It should be just fine. I left happy and eager to take it to the lake. That weekend I took it to the lake, get it set. then I crank it. 1 time, 2 3 ...10 times!! Back fires, spits. Nothing. I took me 10 minutes to get it started. But the back fires gave me a clue. Timing. I did notice that they adjust the Idle adjustment screws good 4mm in. almost all the way in. My lake visit sucked.

So I decided to take things into my own hands. I order t timing light from ebay and got to work. I removed the fuel line, spark plugs, ground the wires, release the throttle link. First I checked for the maximum timing at crank speed at WOT. Lucky I got reading of 21 deg.BTDC (my motor decal show this should be the setting), which let me know that I was doing things right. Next I checked for idle timing which according to the decal on the motor it should be 0 -9 deg. ATDC. When I cranked the motor there I could not even make a number out of the reading. I decided to set the screw half way. I cranked the engine again a now I got 10 deg ATDC; the setting was way off!. I decided to set it half way to 6 deg. ATDC. Connected everything back and... Wow! it started within the 1 second. I found that the Idle speed was a little slow so I adjusted the screw slowly until i got a satisfactory speed. I tried it over and over and it started nicely every time. yeah! BTW I also did a Carb sync which was 2 mm offset.

Now, I still feel like the idle speed is a little rough, it shakes a little, but now bad. I did notice something and I need you help on this one...

I had never paid attention to the fuel filter when engine is running. I have a clear in-line filter and I notice that when the engine is idling the filter is not fully full. The pump is like spitting the gas into the filter; not fully full and it forms some sort of vortex. Is this the way is should be? Just is case I order a replacement kit for the fuel pump. Also I'm going to check if the the engine idles better if I play around with the carb needles a bit. I'll keep you guys posted.

 

[rtrevino]

BTW. I was reading a Mercury Service Manual about setting the fuel mixture screws and I am a bit confused here. It reads...
..If the fuel mixture adjustment screws are moved for carburetor cleaning, reset at 1-1/2 turns ( 1-3/4 turns on WMH "4-_A" and "6-_A" Carburetors)...

Does this means that carbs 4 and 6 have a different setting? I thought they all go for 1-1/2 turns.

 

[Dukedog]

tha screws are for fine tunin'.. your on tha right track... as for "idle timing" tha boat needs ta be in tha water, in gear (on tha trailer is fine)... set tha timing at where ever tha motor idles best for you and tha motor (not luggin' or loading up) for idle speed.... don't even hook up tha timing light......

 

[rtrevino]

tha screws are for fine tunin'.. your on tha right track... as for "idle timing" tha boat needs ta be in tha water, in gear (on tha trailer is fine)... set tha timing at where ever tha motor idles best for you and tha motor (not luggin' or loading up) for idle speed.... don't even hook up tha timing light......

Awesome. thanks again.

 

[rtrevino]

Update and Conclusion: Okay guys. So I took the boat to the lake today. After the last adjustment I did to it started within 5 second. Nice. Still a little shaky. After letting it warm up I started adjusting the screws. I started at 1- 1/2 (all six) turns and turning then in 1/8 turn at a time for all six carbs. As I started to turn them in the RPMs Started to increase slowly, also the engine started to run better and less shaky. As the RPMS hit 1500 I had to adjust the Idle timing screw to slow down the RPMS a bit. My final setting ended in exactly 1 full turn from the seated position. If I go any further in the engine will hesitate and will not rev when I manually open the throttle. So the final setting was all 6 Carbs at 1 turn out from the seated position. Engine starts within a few cranks cold and 1 crank when warm. It will idle and go WOT with no problem.

I hope that this posts will help someone with their engine adjustments. Happy fishing.

 

[cvflyer]

I'm having similar problems but not quite to the extreme you were. Starting is tough, and idle is rough. If I bump the enricher (push the key in) when it starts struggling at idle it comes back to life. I have been pondering the fuel mixture screws.

 

[Chris1956]

rtrevino, you have discovered that the idle screws need to be a bit rich and the idle a bit rough on the Mercs in order to have smooth acceleration. That is true on your V6 and on the older inline motors as well.

Getting 6 carb idle mixtures set properly is a good feat. You deserve a slap on the back and a beer in the hand....

 

[rtrevino]

Thanks Chris1956, a beer was always on my hand while troubleshooting.

 

[Dukedog]

Getting 6 carb idle mixtures set properly is a good feat. You deserve a slap on the back and a beer in the hand....

good for you...that's just one of tha reasons tha wmh's only hung around 'bout 5 years.....