Fuel leaking out of carbs when primed hard

[Nial]

Hi there<br /><br />I just installed a new fuel filter/water separater for my 1976 Merc 850 and to test it wasn't leaking I primed my fuel bulb as hard as it would go. I then noticed fuel dripping from the right side of the cowling. I pulled the cowling off and carb cover and found a heap of fuel pooled below the carbs which was draining out the side of the cowling. Should this be happening, do my carbs need rebuilding? It only happens when the engine is not running and I prime the bulb really hard. The fuel then slowly continues to run out of the bottom carb jet. Can anyone shed some light on wehter this is only happening because I'm priming the bulb too hard and the carb is overflowing or is something busted inside my carb causing it to leak. The engine also develops a loss of power after being switched off, once it is running around for a bit it will go fine but then problem will return when switch off and on again. Engine details are :Merc 850 Thunderbolt Blue Band Merc Eng No. 4366928. 4 coil electronic ignition NO DISTRIBUTOR<br />Thanks<br />Nial

 

[Laddies]

Re: Fuel leaking out of carbs when primed hard

It's not unusual for carbs to leak when primed hard, if it runs with out leaking your fine

 

[Texasmark]

Re: Fuel leaking out of carbs when primed hard

You know it's the job of the float and shut off valve to control the gas level in the bowl...preventing leakage. I think the ability of the valve to seal is in the range of 5 or 6 psig max, normally. If you really get to squeezing that bulb it's easy to speculate on 10 or 12 psig which very well could, and apparently does unseat it.<br /><br />Mark

 

[Nial]

Re: Fuel leaking out of carbs when primed hard

Thanks for the replies. Could I have damaged the float and valve at all by priming it this hard? Is it worth pulling the carbs out and rebuilding them?

 

[Laddies]

Re: Fuel leaking out of carbs when primed hard

No, that won't damage anything, test run it before tinkering

 

[timmathis]

Re: Fuel leaking out of carbs when primed hard

Some of the old mercs you have to prime like that to get them to start. You almost flood them by forcing the fuel by the needle valve with extra hard pumps of the bulb.<br />Tim

 

[LubeDude]

Re: Fuel leaking out of carbs when primed hard

Also, if the engine is still tilted it will leak fuel when you pump the ball hard.<br /><br />When was the last time you rebuilt the carbs?

 

[Clams Canino]

Re: Fuel leaking out of carbs when primed hard

Irrelevent when... the behavior is normal.<br /><br />-W

 

[Nial]

Re: Fuel leaking out of carbs when primed hard

Not sure when the carbs were last rebuilt, I haven't done it in the 4 years i've owned the motor but they seem in reasonable condition. I'm thinking i've buying the bits i need to rebuild them just to have on hand for when I have some spare time to do it. Where's a good place to get them from? I found a whole kit on oldermercs.com but it was $56 US and I would need to of them. This site has the needle & seat and gaskets pretty cheap but doesn't sell the float. Should I replace the float?

 

[Nial]

Re: Fuel leaking out of carbs when primed hard

I should add the engine is not tilted at all, its straight up while this happened. I'll drag is outside tommorrow and start it up before I take it for a run. Should be fine I'm guessing, starts easy enough. <br />Also I should add I just installed a Navman fuel transducer for my navman fish 4200. It states that the fuel transducer will create a backpressure on the fuel system. Here are the stats for it : Back pressure* generated by the fuel sensor on the feed line: ½ inch/mercury with a 19.8 US gallons/hour (75 litres/hour) consumption, 1 inch/mercury with a 39.5 US gallons/hour (150 litres/hour) consumption.<br /><br />Could this any effect on my carbs?

 

[Laddies]

Re: Fuel leaking out of carbs when primed hard

NO!