Yamaha 4 stroke 4HP - carb keeps blocking up

tudorsailor

tudorsailor

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I have a Yamaha 4 stroke 4HP outboard. It lives on the stern rail so always exposed to the Mediterranean sun. I bought it new in 2007. It is used very lightly - which of course may be part of the problem. For the past three years I have had increasing problems with failure to fire after it has not been used for a few weeks. The fuel is from an external tank and not the little one inbuilt. I have had the carb cleaned twice this season and it seems blocked again.
The dealer from whom I originally bought the engine says that one gets flaking from the internals of an older engine and this can cause this recurrent problem. Naturally a cure is a new engine. Would others agree with this?
I have read various pros and cons about running the engine dry of fuel if it is to be left for a few weeks. Does this apply to 4 strokes?
Thanks
TudorSailor
 
I always run my Honda dry if it isn't go to be used for more than a few days by disconnecting the fuel line at he engine. I also try to run the Malta dry but don't always succeed and I end up with problems. Another thing to make sure is that the external tank is clean.
 
Are you using old fuel? And in the same "old" external tank, with the same old external tubing? Is there a fuel filter anywhere?
Older fuel gets water in it from the air... Plus probably looses some stuff to the air.
External tank may have gunk in it. If it has a vent - the vent may leak introducing gunk
The internal of the tubing could be crumbling.

The running it dry theory is that if you don't it evaporates leaving gunk. If you aren't - I'd try. If you are, I'd try not. Because the jury is out on effectiveness.
 
tudorsailor said:
I have a Yamaha 4 stroke 4HP outboard. It lives on the stern rail so always exposed to the Mediterranean sun. I bought it new in 2007. It is used very lightly - which of course may be part of the problem. For the past three years I have had increasing problems with failure to fire after it has not been used for a few weeks. The fuel is from an external tank and not the little one inbuilt. I have had the carb cleaned twice this season and it seems blocked again.
The dealer from whom I originally bought the engine says that one gets flaking from the internals of an older engine and this can cause this recurrent problem. Naturally a cure is a new engine. Would others agree with this?
I have read various pros and cons about running the engine dry of fuel if it is to be left for a few weeks. Does this apply to 4 strokes?
Thanks
TudorSailor
Click to expand...

It most definitely applies to 4 strokes .... not quite as acutely as two strokes but being in the Med accentuates the problem for both engine types.

The only "flaking" that would make any difference would be flaking inside the fuel delivery system .... which is probably all plastic .... or flaking inside the carb .... which is something I have never seen.

A small inline fuel filter in the hose just before the carb would be a wise addition of £1 if your inbuilt filter is a bit suspect.

Richard
 
New 4 strokes are picky, I have a couple 5hp Suzuki’s and if they aren’t run regular they play up, to the point I carry a screwdriver in the engine cases to drain the bowl which usually solves it (internal tanks and cleaned to death recently)
Get it going and give it a good run then run the carb dry for next time, wouldn’t buy a new engine, they are after a sale and a new 4stroke will do the same soon enough if it’s hardly used
 
seaangler23 said:
New 4 strokes are picky, I have a couple 5hp Suzuki’s and if they aren’t run regular they play up, to the point I carry a screwdriver in the engine cases to drain the bowl which usually solves it (internal tanks and cleaned to death recently)
Get it going and give it a good run then run the carb dry for next time, wouldn’t buy a new engine, they are after a sale and a new 4stroke will do the same soon enough if it’s hardly used
Click to expand...


Probably just needs the carb float bowl draining or running dry after use.

Modern fuel in a warm dry enviroment-like the Med- causes the lighter particles to evaporate away very quickly, leaving behind sticky residues which block jets and passages.

Adding a fuel stabiliser might help-but still drain or run the bowl dry.

Good luck.
 
Thanks all

Now an admission of incompetence. The engineer came to the boat and diagnosed the problem - this time - of the fuel line from the external tank not sending enough fuel. When one squeezed the priming bulb it did not get hard! I had a new line and bulb on board. Once installed, engine started beautifully.
So now I feel a bit foolish.
However advice to run dry still remains good advice. An additional inline filter is more difficult as there isn't really any room
Thanks
TudorSailor
 
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