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Mercury 40hp 2stroke 2cylinder seapro running on 1 cylinder at idle

T

Timconijn82

Member
Hello my name is tim from The Netherlands.

I just bought a Mercury 40hp 2 stroke 2cylinder seapro.
Now i have noticed that when at idle my motor runs on 1 cylinder .
I have pulled the top sparkplug wire and still runs the same . I have change the sparkplugs en switched the coils. Still the same result.
Now i have noticed that when i pull the sparkwire from the sparkplug, i still hear sparks in the cap so it does spark..And when i pull the top sparkplug out it,s greasy and darkblack (to rich in fuel) . And the bottom sparkplug looks good. Also it smokes heavy until 1quarter of gas. From 1quarter gas till full throttle there is no problem and runs great.

What do you guys think it is.
1, reedvalve
2, condensator
3, stator
4, something else

I just wanna know so i can import the parts and replace it . But i dont want to buy the wrong parts
 
Well i swaped the complete kit (cdm module ,wire ,cap) from the top to the bottem . So i could see that it works . But with the same result. Still a the top cylinder that doesnt burn correct
 
You didn't mention model# and year, carbs or fuel injectors? It almost sounds like low speed nozzle issue in the top carb or improper adjustment. I see carbs that were "tinkered with" often trying "fix" idle problems. A good cleaning and resetting to factory specs may solve the issue, if it has carbs.
 
So, you have spark. If it runs great from 1/4 throttle on up, sure sounds like fuel delivery. You mentioned you cleaned the carbs - how did you do that?
 
I have pulled it apart and cleaned everything with brakecleaner and with the adjustable screws counted the rotations and but it back together the same way . . Al the jets everything ..but still the same results after the rebuilt . So i think then it must be the reed valve . Thats the only thing i think it must be ....but parts need to be imported so i wanna know for sure . Or else its 250 euro spend for nothing
 
I feel your pain; in a similar boat with my '92 Merc 40 2 stroke not wanting to idle; been buying carb parts in anticipation of cleaning them including new tank to engine fuel line and primer bulb; carb gasket sets; fuel filter; diaphragm kit for the fuel pump; did you do anything with the fuel pump and fuel filters?
 
I did clean the fuel filter .. but not the fuelpump. But i dont think thats the problem ,because there is just 1 carb and the bottom cylinder works great. The only thing that separate them is the reed vales and inlet manifold
 
I'm starting to lean on the bad top seal idea. Easy enough to fix: remove the flywheel, trigger coil, stator and change out the seal.

Forget the carb. If it was the problem BOTH cylinders would be screwed up.

Jeff
 
Ok but when the topseal is broken . Will it still run at other throttle positions. Because after a quarter of gas it runs great . Its only the low rpm. And with a bad reed valve (its 1 reedvalve per cylinder packed in 1part) the bottom cylinder reedvale works good and the top one spills to much fuel to idle good (causes smoke ,to much fuel to burn, wet and greasy sparkplug)
 
Its recording to factory specs. And i also think it,s the reedvalve. But if i want to replace it . I have to import it at 250€€ . With no refund if thats not the problem
 
Hi.
Is it just me but do I see something changing on primer bulb when going on WOT? Going empty?
Where does bulb hosing connects? Can it draw extra fuel from priming bulb causing rich mixture at idle?
 
Wel i have checked the primebulb at WOT but that,s not the problem .. So when i came back i pulled of the carb and reed valve . But there seems nothing wrong with it . And made a video of the reed valve
 
Just to make sure we are talking same bulb. In your vid about time 1:00 going wot that bulb goes "white"
Any way it's easy to check by pinching the hose between bulb and intake with pliers while idling

Capture.JPG
 
Well i understand what you see..but i think thats it,s the reflection of the sun or something . Because when i test it yesterday i even pushed the button at idle and it just stalled. And if it was leaking as you sugested ,it still don,t explain why only the top cilinder misfire,s. Because there,s only 1 carb and the prime bulb injects in the front parts of the carb
 
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