Automixing VRO issues Mercury LightningXR

[1530dean]

Hi All,

I would like to let everyone know the issues I have had with my Mercury 40hp lightning xr 2 stroke outboard and why I have decided to remove the Automixing VRO and to premix instead.

I have been having to deal with a bogging down issue with the engine almost since the day I bought the boat late last year.

On my last trip out about 2 weeks ago it died as if it had run out of petrol and was very difficult to start and appeared to be flooded. When I did manage to get it started it would only let me idle back to the boat ramp and would always bog down when I put on the throttle.

This issue would never show itself on the ramp only in the water.

After purchasing the boat I made sure to give it a service, I replaced the lower unit oil and impeller, thoroughly cleaned all three carbies and replaced petrol pump gaskets and manifold o'rings, replaced the fuel line and bulb, cleaned the tank and checked the in line fuel filter and the siphon filter from the tank all ok.

The compression is good on all 3 cylinders (app 105psi on all cylinders), all the voltages checked out according to the manual for this engine which is actually a Tohatsu.

I even went through and completed the adjustment of the timing and synchronisation so it is as per the manual.

Whenever I checked the spark plugs they would always appear very oily so I assumed the engine must be getting too much oil.

Last weekend I replaced the spark plugs set the jets to 2 1/2 turns and the engine would start easy but as I revved it would begin to sputter and cough and would just about die at idle unless i gave it another rev.

At idle it would surge and would behave like it was chocking and blowing a lot of smoke.

As a last resort I decided to bypass the oil injection and feed the fuel straight from the output of the fuel filter into the carburetors and wow what a difference..!

Looking at how the whole oil injection mechanism is working it turns out that it is not possible to meter the fuel oil ratio accurately since there is such a long delay in the fuel line from the point at which it is mixed to the carburetors.

Increasing the throttle suddenly and then decreasing the throttle only serves to exacerbate the problem.

In my opinion the engineers that designed the Automixing mechanism solution in hindsight should be metering the oil to the carburetors the same way the fuel is being metered via the the intake manifold vacuum.

My feeling is that the Automixing solution the engineers have provided was developed as an after thought and would strongly recommend anyone with this mechanical mixing set up to consider converting their engines.

I would look forward to any of your comments, if you have had to deal with these same issues then at least checking your spark plugs should reveal the same issues I have been dealing with also.

 

 

 

Edited July 24, 2017 by 1530dean
Wrong data

[Mullatt]

I had a 50HP Mercury some years back that I also had constant problems with along the same lines that you have mentioned above. It went on for years and even though various mechanics reckoned they had fixed the problem, it never was. One day I was out at Burrinjuck Dam when the motor had issues (again). I noticed that there was a Marine service bloke there so went in to see him......long story short after he kept the boat for a week or so, he came back to me and said the problem was the automix and that he disconnected it (as he had done to other Mercs he said). He claimed it was a common known problem (funny how no other mechanics ever picked it up). After that, the motor was fine for the rest of the time that I owned it!