Logo
FULL SITE MENU

Merc 125 ob 2 stroke idle

B

bowhunterokie

New member
So long story but hopefully short.  2001 Merc 125 2 stroke, had some performance issues since owned (on mny 3rd summer now) last fall I hired a  mechanic and he recommended rebuilding the carbs since I couldn't verify when it had been done since I've only owned it for 3 summers now, during the carb rebuilding found out cylinder 4 had low compression (90psi). <br><br>

May 2022 installed new powerhead (did this instead of rebuilding the old one so everything was new).

Got everything in place, ran it on hose/muffs with no issues, took to the boat ramp and when I put it in gear it dies. Everyone pointed to lync and sync on the carbs, so I enabled the assistance of a shop to do that for me becasue I know there are alot of moving parts in there with 4 carbs.<br><br>

Shop did the lync and sync but said idle is at 1100 (verified this was on hose and muffs). Says "there must be something else wrong".  That was last week and today I stop by and the office manager says the tech was going to look at it again today and has built a setup to where he can get the lower unit under water (I recommended this to her after everyone started talking about the backpressure and idle in and out of water).  I don't if it still dies under load because the tech hasn't had it in the water.<br><br>

* New powerhead<br>
* Verified 130 compression on all 4<br>
* New carb kits<br>
* New inline filter and water seperator filter<br>
* new plugs last Fall<br>
* fresh gas with plenty of 2 cycle oil<br><br>

So I'm at a loss of what to do. Any ideas?
 
Yeah I think I found a DUD shop. They just called and my update was "tech doesn't know what it is and can't proceed any further". OK so to another shop tomorrow it goes. I am over frustrated. Just need to get going, High school tourneys start for my son in Sept.
 
Last edited:
I have a pair of 2+2 engines on my boat. 1100 rpm out of the water on muffs is about right. They idle way down in the water with back pressure. You're looking for 650-675 rpm in gear in the water. Forget about doing any adjustments to mixture or timing out of the water on muffs. These engines are completely different critters in the water. I have lots of experience with them. Bought both new in 1995 and still run great but I spent many hours getting them dialed in to behave consistently.
 
Texasmark said:
73222 is right on. Looks like he is quoting the manual verbatim.
Click to expand...

LOL, I know the factory manual backwards and forwards on these engines! I even managed to get the transition from 2 to 4 cylinders just being a "BIP" by getting the accelerator pumps gaps set properly.
 
Texasmark said:
73222 is right on. Looks like he is quoting the manual verbatim.
Click to expand...
<br><br>LOL, I know the factory manual backwards and forwards on these engines! I even managed to get the transition from 2 to 4 cylinders just being a "BIP" by getting the accelerator pumps gaps set properly. <br>
<br>
 
fitz73222 said:
LOL, I know the factory manual backwards and forwards on these engines! I even managed to get the transition from 2 to 4 cylinders just being a "BIP" by getting the accelerator pumps gaps set properly.
Click to expand...
I set mine tighter than the 0.020 (if I remember correctly) to get a quicker jab. The other thing is that I realized that the plunger is connected to a diaphragm so if you want a "squirt" of fuel, you have to "jab" the diaphragm.
With that said, coming up on plane, I firewall the throttle to get the squirt and then pull back to desired speed.....smooth as silk.
Other thing I do when idling for an extended period is to tilt the engine up slightly in the rear to keep unburned fuel from puddling in the area of the spark plugs. Sometimes the engine shakes a bit idling/slow speeds and I tilt the rear slightly and immediately it smooths out, smooth as silk having changed nothing else.
I learned about that back in a Mercury Mark 20 fishing motor posted in a sales brochure that was built with the crankshaft, not vertical as with most engines, but built to tilt the rear of the engine up 15* give or take, and they advertised that reason in the sales brochures. Made sense and for them to put out a series of fishing motors, for many years, tilted up like that, it must work.......did for me.
 
Back
Top