Re: 115 HP Carb rebuild
Here's the deal on carbs. rebuilding them is cake. Taking them off is yet another issue. I'm pretty sure your engine has a distributor and that causes problems getting to the nuts on the port side. removing the starter from the starboard side is a lot easier. These carbs can't be any simpler. Once you get 'em off I also recommend working one at a time, but there are several things you need to look for - are the floats a tan foam float? If so be sure and throw them as far as you can and replace them with news ones. The black ones are OK and would be what you'd get as replacements from a dealer today. Several years ago they tried hollow plastic floats - ahhhh well that didn't work out so well so they went back to the black ones. Anyway what ever floats you have check the height of the spring in the top of the float and set it to 3/32" from the top of the spring to the top of the float. If your float has a raised round area surround the spring ignore that as being the top of the float. When you replace your needle valves then you'll want to check your needle valve lever adjustment. It's a two lever setup and the main concern is the have the bottom lever perfectly level between the two pivots locations. (the top lever pivot from one side and the lower lever pivots from the other. Those are really your only adjustments outside the idle mixture screw. Oh yeah you'll have to remove the pivot pin on the bottom lever to replace the needle valve and the pin that it pivots on should only be removed from one side as it's serrated on one end to hold it in place. You'll need to look a little closely to see which end it is. Push or drive the pin out from the opposite end! One more thing you should check as well - each carb has it's own fuel line fitting, the bottom carb just has an elbow but the top and middle carb have Tee's. It's a good idea to remove at least one of the fittings to see if there's a trash screen behind it. If so remove it. Don't just clean it - take it out and throw it away. If you find one then remove the fittings from the other two carbs and take those screens out as well. The reason for doing this is it was a bad idea in the first place and that's in part because it's a multi-cyclinder engine being fed by multiple carbs. If one of those screens plugs up it won't necessarily cause a big running issue, but it could cause those two cyls to run lean. With the other cysl running normally it might not even be perceptible that is until the cyls that are running lean bite the dust! Oh yeah and don't do what a lot of people do and install a fuel filter between the tank and the engine. NOT RECOMMENDED on that engine! The fuel pump is NOT a mechanical device. It's only pressure and vacuum operated. A fuel filter on the feed side could become partially clogged and strave the engine for fuel. The only filter that Mercury recommends for inline between the tank and the engine is a water separtor type. A much bigger filter and a little more trouble to install as you need a place to mount the bracket assembly. Oh yeah a be generous with the idle mixture adjustment screws. A lot of earlier inline Mercs would work fine at a turn to a turn and a half from seat, but your engine would prefer more like two to two and a half turns from seat. It would be a good idea to see where they are first before taking them out like Bob recommended. Now there's one part to this task that can be rather daunting and that's sync'ing the carbs together. It's easy if you've done it as many times as I have and I don't know that I can really go into that here but suffice it to say that if they don't all open at the same time your performance with suffer.
Sorry for the long winded reply!
Happy boating.
John
Owner/Operator
UB&M
