MERCURY 70 HP - carby problem?

[tnankerv]

I am a complete neophyte - bought a 15ft 1/2 cabin with early 80's blue band merc 70 HP o/board last week. Worked fine on first 2 outings. Yesterday started OK but died when throttle applied. Primer bulb felt strange - tended to stay deflated on pumping. Air vent on fuel tank was open. So could it be that I have a carby problem? No chance to get it to a mechanic before Xmas - so will have to do it myself. Any suggestions for a sequence of checks? Many thanks

 

[JB]

Re: MERCURY 70 HP - carby problem?

G'Day, Tony.<br /><br />It sounds more like you have a primer bulb problem than a carb problem. The primer bulb should get firm as you fill the carb bowl.<br /><br />Borrow an alternate fuel tank and line and try that out. If that works, try your original fuel line with that tank.<br /><br />Let us know what you find.

 

[rickdb1boat]

Re: MERCURY 70 HP - carby problem?

Tony, try leaving the gas cap off and run it. If this works, your vent is clogged. If it does'nt work, replace your fuel line, connectors and bulb. Sometimes the valve in the bulb goes bad or an air leak will develop at the connectors.

 

[AndyL]

Re: MERCURY 70 HP - carby problem?

I agree with the others and belive it is more likely a problem in your fuel line however, I had an engine similar to yours (3 Cylinder) and had an intermittent fault with a carb that was intermittent. Ran it with all the covers and shields off until it manifested itself. Traced down to a faulty needle seat which would occassionally fail and cause neat fuel by the bucket full to flow into the engine. Go for the simple stuff first unless you have the spares readily to hand.<br />Good luck and Merry Xmas.<br />Andy

 

[tnankerv]

Re: MERCURY 70 HP - carby problem?

Thank you so much guys<br /><br />I actually had a look at it myself this morning before coming to work and thought it through like a person with a real brain. By thinking through the passage of the fuel to the motor (plus a lot of pumping and blowing) it quickly became obvious that the problem was in the fitting that joined the fuel hose to the tank. The housing for the bayonet on the tank was RS, stuffed, broke. So thanks JB, Rickdb1boat, and AndyL, you all had it right. Many things learned from this first encounter with the joys of boat mechanics: First is to think before I go asking other people for help and second that this is a brilliant forum for when my logic falls short. Thanks again