Outboard - Carb leaking

[Ecosse120]

I need a bit of help, my old Tomos outboard would not go above about half speed it just bogged down. So far I have stripped and cleaned the carb (4 times), cleaned the fuel pump and checked the fuel lines. It is now better but when reved up I noticed a stream of fuel coming out of the top of the carb, I therefore adjusted the float level, it may be better but is still leaking fuel from the air hole. Any help much appreciated as the boat went in on Friday and I can't sail until the outboard is fixed.

 

[KellysEye]

I don't know the make but did you renew any gaskets or O-rings? Please can you explain where the hole is on your outboard. On our carburettor the air is controlled by the choke on the front side of it. Or even better a picture.

 

[FWB]

This has happened to my outboard. It was the needle valve sticking or not seating.

 

[VicS]

I need a bit of help, my old Tomos outboard would not go above about half speed it just bogged down. So far I have stripped and cleaned the carb (4 times), cleaned the fuel pump and checked the fuel lines. It is now better but when reved up I noticed a stream of fuel coming out of the top of the carb, I therefore adjusted the float level, it may be better but is still leaking fuel from the air hole. Any help much appreciated as the boat went in on Friday and I can't sail until the outboard is fixed.

If you have adjusted the float level correctly take a look at the needle valve and seat.. ... It cannot be closing properly if the carb is flooding.

may be just some crud on the seat . may be damaged but rescueable, may be cream crackered

 

[Boathook]

I need a bit of help, my old Tomos outboard would not go above about half speed it just bogged down. So far I have stripped and cleaned the carb (4 times), cleaned the fuel pump and checked the fuel lines. It is now better but when reved up I noticed a stream of fuel coming out of the top of the carb, I therefore adjusted the float level, it may be better but is still leaking fuel from the air hole. Any help much appreciated as the boat went in on Friday and I can't sail until the outboard is fixed.

When I had that problem it was caused by dirty fuel and required all 3 carbs to be removed and cleaned. Took the Fowey marine engineer around 5 hours, mainly as we were afloat on a visitors buoy.

 

[macd]

As VicS writes, it's probably the float valve, which shuts off the fuel supply when the float has risen to the appropriate level. It's either cruddy or worn. If it's not working correctly the mixture will be excessively rich, plus you'll get the leak described. Sometimes a light tap on the float bowl with, say, a spanner will fix it, but it sounds like you have a more chronic case.

The only likely cause, as suggested, is a duff seal where the float bowl meets the body of the carb, but usually the fuel level is below this joint so there should be no continuous leak if the carb is level.

 

[oldharry]

I know these engines: fuel coming from the air vent is as VicS rightly diagnosed the needle valve not closing, or the float itself is sticking. As you have already adjusted the float level this is less likely, but with the bowl off, check the float is not sticking anywhere in its movement.

To check the valve, hold it shut and using the fuel line bulb, pressrise the fuel system. There should be no trace of fuel leaking through with it held shut. Check the fuel valve rises and falls in its housing freely. Sometimes just rotating the moving part against its seating is enough to clear and free it off.

You notice the fuel flow from the carb more on revving the engine, because it has an engine operated fuel pump which increases fuel pressure and flow as the engine goes faster.

 

[FWB]

Lakesailored twice in the same thread.
Is this a record

 

[Ecosse120]

Thanks for all your help. I have stripped the carb again and the leak was coming from the air release on the top. It is still not working correctly, would it make any difference if I put in fresh fuel (rather than last Novembers fuel)?. It always starts first time and goes up to about half throttle with no issues at all. I am running out of options and skin on my knuckles !

thanks

 

[VicS]

Thanks for all your help. I have stripped the carb again and the leak was coming from the air release on the top. It is still not working correctly, would it make any difference if I put in fresh fuel (rather than last Novembers fuel)?. It always starts first time and goes up to about half throttle with no issues at all. I am running out of options and skin on my knuckles !

thanks

Fresh fuel might make it run better but if its starting easily then the fuel is probably OK. I find if fuel is stored in full, sealed metal cans it is OK from one season to the next, although in practice I always filter the stored fuel and use it mixed 50:50 with fresh.

Any deterioration in the fuel is going to have no bearing on the leaking/flooding issue.

If fuel is overflowing from the float chamber air vent then the needle valve is not controlling the flow into the carb.

Various possibilities include

Float sticking
Float punctured if hollow or other wise not floating properly
Float not adjusted correctly ( but I'd doubt you could set it so far out that the carb will flood)

Needle valve not seating properly

needle valve worn

Can you post a diagram of the carb?