Re: 85hp Ok I give up.....................................
Ok! You got me curious so I ran some theoretical nimbers to see if your tach was reading correctly. So: And remember, this is all theoretical, not actual:
If you have a 2 to 1 gearcase in your 85, then at 3800 rpm with a 19 pitch prop, you should get somewhere near 31.7 MPH. With a 17 pitch prop, you should get around 27.5 MPH.
If you have the 1.78 to 1 gearcase, these numbers should be respectively34.6 and 30.0 MPH.
With the 2 to 1 gearcase, at 5500 rpm you would expect around 45 MPH.
I arrived at these numbers by taking engine rpm and dividing by gearcase ratio. Multiply by pitch to get inches per minute and factor in about 10% prop slip which the prop forum guys seem to think is average or reasonable. Convert the inches per minute to miles per hour (easy way, 60 mph is 88 feet per second)
Ok! having arrived at these numbers, neither your speed or your tach reading would seem to be greatly out of line since you claimed 28MPH at 3800 RPM.
So therefore, we must assume--oops there's that word again-- that there really is something wrong with your engine.
Now we have apparently covered the more likely things so I'm going to throw out a few of the less likely things.
1st. Check the carb linkage tie bar. that is the flat aluminum bar on the side of the carbs that links all three together. the three pieces of this bar are held together with thin metal clips and sheet metal screws. If these screws work loose -and it doesn't need to be much-- you could have 1 or 2 carbs not opening fully with the bottom carb. Replace the sheet metal screws and clips with two small bolts and nuts. Tighten them well with all three carbs closed and the cam not touching the lower throttle roller.
2nd. Take off all three carbs and using a pencil flashlight look in the holes and see if you have any broken reeds. These engines will start and run with several broken reeds. they will even idle, but when asked for full power, too much gas blows back through the missing reed(s).
3rd. Has the engine ever been taken apart? Check the 4 bolts holding the front plate to the block at the center cylinder. 2 are above and 2 are below; one of them usually holds the lower starter bracket also. They have 9/16 inch heads. These are 4 of the 8 main bolts that hold the crankcase halves together. If they come loose--and again, it doesn't need to be much--they will allow the case to flex while running and gas to bleed between cylinders. Enough that the engine will only put out about half or less of it's rated power. They should be torqued to 270 INCH pounds. If they are really loose, you can tighten them and probably get good results, but the best thing to do is to break down the engine, clean the flanges and re-assemble with new sealer.
4. Check for air leaks and bad gaskets around the bypass port covers, the puddle drain system (The flat plate with black hoses behind the linkage tower) The gaskets sealing the manifold to the block and sealing the reed blocks to the manifold. Check for broken hoses in the drain system and the fuel pump (one short thick hose from the block to the pump). And just for the hell of it, check that the fuel pump pressure hose is not clogged, leaving the pump to function on only one stage. While you are at it, replace the diaphragm. These engines will also function with only one stage of the fuel pump working, but again, not at full rated HP.
Now, when you had the head off, you would have seen scored cylinders so we can eliminate that, However, worn pistons that don't seal properly at the lower end will reduce pumping efficiency and of course, if you don't pump the gas from the crankase to the upper cylinder, the engine can't make horsepower. It's the same effect as if you had a smaller engine.
At this stage though, if you have done linkage and carb syncronizing and timing I suspect you either have massive air leaks or one or more broken reeds.
