Any Ideas, Mecury 50HP

slangley · 08 August 2003, 12:23

Having a bit of trouble with my engine ( Mercury 50HP SN: 9233460 ). I suspect it is a problem with one of the carbs. I am about to strip them down and have a look. On one of the carbs. the mixture screw has no effect whatsoever. You can turn it in or right out and it makes no difference to the running of the engine. The engine also cuts out after about 10 mins use and is worse at full throttle. Onece it cuts out it is very difficult to start again and then runs very badly. It also holds back and coughs if you put more throttle on.

Any help would be much appreciated.

Steve.

Mosser · 08 August 2003, 16:31

How old is that engine by the way?
It seems you have converged on one of the carbs for a reason.
Is this because you found that adjusting the mixture screw on
the other two carbs caused a difference in the running of the
engine?

tue · 08 August 2003, 18:06

just because the mixture screw makes no difference doesn't mean it has to the carb

. It could be any number of things from faulty spark plug, to lack of compression. I would suggest a spark and compression check on all cylinders. There should be no more than 10psi difference between cylinders on the compressions.

gavin · 08 August 2003, 19:17

Mixture screws air screw are particuarly sensitive,I think you are looking in the right direction,I had a yam before which wouldnt idle when warm and was a pig to restart, I turned the screw in all the way and out its correct turns, it instantly cured the problem, 1 and a quarter I think, for the yam, you need to find out what is correct for each of your 3 carbs, Is it possible the orificae behind the spring loaded screw is blocked or gummed up, presenting no change when you turn the screw.Remove the screw stretch the spring and check for blockages,refit the screw and set correctly, remember these screws often vibrate open it can be a problem with high revving cheers gavin

slangley · 08 August 2003, 22:13

There are only 2 carbs on this engine and not 3. If I play with the mixture screw on 1 of the carbs it changes the running of the engine dramatically. On the other carb it makes no difference at all. It is a twin carb engine.

I suspect the carbs just because the feeling I get when it goes wrong. It just feels like fuel. I have experienced it in cars before. I am very new to boat engines but used to fix cars years ago. All the compressions are ok and the spark seems regular and strong. The higher I push the throttle the worse it gets. I have checked timing and that is Ok. I now have both the carbs in bits and currently soaking in some carb cleaner fluid. Everything looked Ok but I did notice that the floats were completely different settings on both.

gavin · 09 August 2003, 09:07

I was thinking of my old engine which had 3 carbs, is the motor twin cylinder as well as twin carb, or does one carb feed 2 cyl, this might explain different float settings was there much crystalised orange powder in the carbs or where they pretty good

slangley · 09 August 2003, 17:24

It is a twin carb 4 cylinder engine. It appears that I had 2 problems. The carb did have quite a lot of dirt in it which I have cleaned out. My running problems were caused by a thing called a 'stator'. Not a cheap part. I went and bought one and then had to pick myself off the floor when they told me the price, £231. It looks like this will cure all my problems.

I will keep you posted.