Merc 40hp 2cyl 2 stroke stalling issue. Help please

MystyBlue2

MystyBlue2

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Hi i went to buy my new motor today and the bloke had an issue with it, i havnt got the motor as it was not working properly and he says he will try and get it fixed before i purchase.

Im unsure of age but somewhere between 1996 and 2003 merc 40hp 2cyl 2 stroke elec start with the oil injection system.

He has put in new plugs fresh oil and fuel, stripped and cleaned out carb.

Will start first turn of key but dies shortly after. Only way we can keep it running is if we give it throttle on the linkage on carb.

It just wont run at idle, even when warm and back to idle it will hesitate then die after about 10seconds or so.

Any ideas on what this could be and any ideas on the mixture screw setting incase he has set it up wrong?

I really like the motor it is clean and tidy and will go well with my outfit but dont want a troublesome motor, is this an easy fix?

Cheers
 
If it's a good price and runs really well then it sounds like it's something trivial wrong with it, but what?
Could be carbs out of sync, one leaking air at the manifold, air/mixture screw, maybe float heigh settings or still a little crud in carb...etc
 
I dont honestly know theres no tach wired up to see exact RPM.

Could a faulty oil injection system cause this?, ive heard nothing but bad things about these systems.

The engine just wont idle, runs lovely at higher rpms with no hesitation or coughing and it has 160psi on both cylinders. Seems a really strong motor.

Could bad reeds cause this?

This has me and the seller both stumped.

Il ask if he will re clean the carb and set back to factory. Cheers
 
Sounds like the idle jet/route to the idle jet is blocked. If outboards are left unused for quite a while the carbs corrode a bit internally. It doesn't take much to block what is often a narrow tube. I had a Mercury 15Hp 2 stroke and the idle tube from the float chamber to the actual idle jet would block over the winter. It's easy to fix- take the carb to bits and clean out all the little orifices etc with some copper wire to avoid damaging any small holes. When you remove any mixture screws take a note first of how many turns needed to fully close them, so you can put them back in again and set to the same point. Took me a while the first time to find the pipe from the float chamber to the actual idle jet so patience. Otherwise it sounds like a good motor.
 
Does it cough and splutter just before it dies ? Does it instantly rev up from tick over without hesitation? If it does not suffer from the above then sounds like it's close to being a really good engine.
Oil injection should have nothing to do with it. What can happen with injection is the cable that operates it becomes slack so no oil on tick over leading to seizing.
Pre mixing the fuel and not using the injection system is a fool proof way of guaranteeing it always has oil.
You can take a carb apart multiple times and clean it and still have an issue yet the last clean fixes it !
How much over tick over does it need to keep running, a lot, a small amount ?
 
Starts first turn of key runs abit lumpy at idle soon as he applies throttle on plate on carb it instantly revs up super strong, as soon as he lets go and allows rpm to drop to idle it starts stumbling for 5-10 seconds then instantly cuts out, not really gradual but sort of sharply dies,

But then restart first time on key then super strong on higher rpm.

As no tach is fitted il take a wild guess and say 2000RPM he holds it at and runs super smoothly.
 
Im hoping its just a niggling easy fix as the motor is in excellent condition and for £900 on remotes with elec start seems fair, think it may need a new prop then a service before i winterize, but apart from that it is sweet. The compression readings are basically drawing me in as if any of you have read my previous threads ive had a bit of bad luck with my mariner 2 stroke with bad conpression.

I hope its just the normal annoying 2 stroke carb related issues. Il keep you guys posted. Thanks for all your help folks
 
Definitely sounds like the idle jet is blocked, I cleaned 4 carbs on 3 different engines on fri because of this problem. They will run at higher revs as then the carb uses the main jet to deliver the fuel.
 
If the seller manages to get it running and i purchase it, would anybody recommend to keep or remove the oil injection system and run 50:1 premix?

If so is this a hard job and it is safe to do? Read ALOT of posts and they are notorious for failing and causing major problems which is the last thing i need on a new to me motor after the issues i had with my previous motor. Cheers
 
Hi folks quick update, the guy/sort of friend of mine has given me the motor without needing payment and he said i can square him up if i get it sorted.

Now ive downloaded a repair manual and plan on removing carb and doing a full rebuild, ive been reading online and a common cause of the idle symptoms im experiencing is a faulty IAC valve...when i read on this it sounds very familiar with whats happening with this motor.

Can anyone tell me if my model even has a IAC valve and could this be a potential culprit?

My motor is a 1994 mercury 40hp 2cyl 2 stroke. S/N 0G083344

Any ideas on the best way to tackle this as the motor is a beaut apart from this issue and have not got the money to buy parts and chuck money left and right as order of elimination.

Thing is im not a mechanic nor have £60 per hour for a mechanic to rack up 6hrs diagnosing the issue then parts ontop.

Cheers folks
 
Im not sure you engine has one .. Your sure the throttle stop is set high enough to prevent stalling?
I presume it has 2 carbs?
It is something that is really hard to guess at whereas hands on makes a world of difference as can experience what is actually happening rather than a persons version of events..
Jets can have gum left on them even after cleaning causing all sorts of running problems.
 
Its a single carb and apparently he says the throttle is fixed and cant be adjusted to increase idle speed.

Yeah i totally agree that you need experience with this sort of stuff and i have none.

It is really keeping me awake and scratching my head as to what this could be,

He changed plugs, new fuel, cleaned carb and reset mixture screw to factory. I will be redoing the carb with new gaskets etc but after that im absolutely clueless. Thats why im thinking IAC as the symptoms on google are identical to this thread.
 
The throttle can't be fixed as in non adjustable. There is usually a screw that may have a spring around it with a rounded end. Basically it pushes against the slider in the carb increasing the revs.
It is possible someone has messed around with the carb and messed up a setting but sounds like the guy who sold you the engine has some understanding.
As I said earlier, You can take a carb apart multiple times and clean it and still have an issue yet the last clean fixes it !
I'm sure it will be something really trivial and cheap to fix.
 
Start with the carb and check every orifice, hole, tube, pipe etc. Rod through all the tiny brass tubes and jets. Make sure you can see through them.
 
Here is a very good test....

1) Buy some carb cleaner in a spray can (it is also flamble like petrol)

2) start the engine

3) Spray in some carb cleaner into the air intake of the carb with the air filter (it it has one) off.

4) If the engine increases revs then the idle jet is blocked as it is getting some 'fuel' ie the carb cleaner

5) If the engines get slower the carb cleaner is flooding the engine so the idle jet is not blocked.

6) I would also make sure that the float in the carb chamber is not split and full of fuel and also that the carb bowl gasket is good and not allowing air to suck in.
 
Are you sure also this has only one carb..... at 40 hp I would suspect 2 can you post a pic of the engine where the carbs are and also the serial number will help
 
Thank you i will do i posted my engine serial number a couple of posts above. Its definitely a single carb twin cylinder. I will post pics and serial number is...0G083344 its a mercury 40hp 1994 elec start long shaft.

Cheers folks
 
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