old 7.5 Merc carb/fuel problem

[darnold]

I just got a sixties vintage Merc 75 with the Tillotsen carb from the previous owner who said that the engine ran, but that he had to keep it choked to keep it running. I am assuming that this is a fuel starvation problem due to leaks in fuel or vacuum line or a gummed up carb. I am not a mechanic but I do tinker with some succes. This motor is so old (though the compression seems ok) that I don't think it would make sense to take it for professional repair (as if I could get it scheduled before Memorial Day, anyway, the way the shops seem to be booked in this area). So, my question is: What should I check out and do first to keep the repair cost low and likely solve the problem? Thank you kindly for any help. David

 

[JB]

Re: old 7.5 Merc carb/fuel problem

Howdy DArnold.<br /><br />I agree that you have a fuel starvation problem. The first thing to do is decide if it is the carb or something in the system that feeds the carb.<br /><br />Remove the fuel inlet line from the carb and stick it into a bottle (plastic for safety). First pump your primer bulb to see if that squirts fuel into the bottle. Then turn it over and see if the fuel pump produces strong squirts into the bottle. Only if those two check out okay do you have a carb problem. If the primer or the fuel pump don't work you will know where to look for your problem.<br /><br />I would expect it to be a carb problem. Take the carb apart and clean every tiny passage with a wire or air under pressure. Reassemble and try her out.<br /><br />Let us know (on this thread) how it works out.<br /><br />Red sky at night. . .<br />JB

 

[Waco]

Re: old 7.5 Merc carb/fuel problem

If the fuel pump is working properly, I would pull the carb., take it apart, and soak it some quality carb. cleaner per instructions on can., then put it back together with new seals and gaskets. I worked on a 7.5 merc. last year, it was a 1970 model and had been sitting for over 10 years. After I went through the procedure described above, the motor ran like a champ.

 

[JB]

Re: old 7.5 Merc carb/fuel problem

Hmmm. Waco and I were typing at the same time. It doesn't matter. We agree.<br /><br />Red sky at night...<br />JB

 

[darnold]

Re: old 7.5 Merc carb/fuel problem

Thanks JB and Waco. I will test the fuel pump <br />tomorrow. The fuel pump on this engine is not <br />part of the carb (as I have seen on more recently made Mercs), but sits above it and takes a vacuum off a cylinder or the crankcase. Will let you know how it all goes.

 

[darnold]

Re: old 7.5 Merc carb/fuel problem

Took engine outside (brrr..) and checked the fuel line bulb and the fuel pump. Pumping bulb really shot the fuel through but the pump seemed to only dribble when I tugged the starter to turn the engine over. Had it in water barrel to protect the water pump but the engine didn't start. Have pulled the fuel pump and carb as well as the fuel line attachment which leaked. Will get parts for the carb and fuel pump for cleaning. It appears that there isn't much buildup in the filter or carb. I think the problem might be the leaking fuel attachment and or the fuel pump. Maybe the weather will warm up before I get it back together and try to run it again.<br />Question: How much fuel should come out of the fuel pump when the engine is turned over on pull. Thanks again.