blueskiiies
Cadet
- Joined
- May 7, 2004
- Messages
- 11
1981 15ft3in trihull <br />w/1967 75HP Battery alternator with points in distributor (cowl shows magnapower 85 but nameplate shows 75773 ser.# 3642)<br /><br />My dad bought it used and I dont know history except seven years ago when I ran it twice on the water. It ran good from what I remember but seemed to run out of fuel when trying to max rpm it from a hole shot. I believe I found float levels very low then but it was never ran it until about year ago. It also stalled sometimes when idling. Dont know if it was fouling plugs or idle too low.<br /><br />About a year ago, on muffs it seemed to rev up fine but wouldnt idle. Was fouling plugs and very rich smelling. Cant remember if plugs were getting wet. Found bad (half gone) lower crank seal. Tore down, honed cylinders and replaced Pistons and Rings with new (std.size). <br /><br />Now, after assembling and testing on muffs and in water, Im getting wet (fuel/oil) plugs after idling a few minutes. They also wet foul right away when cruising. Feels and sounds strong until misfiring starts to occur from plugs fouling. Plugs are wet before misfiring starts to occur after running briefly. It fouls the plugs sooner off idle than letting sit at idle.<br /><br />Rebuilt Tillotson carbs when I rebuilt the powerhead looked very clean inside found nothing wrong except two jets were .072 and one was .064. Specs. say .066 for all three so that what I installed. Top carb is different than others in style of bowl vent and high-speed air bleed but same throat size (1.5, 1 3/16 venturi ID). It also has a casting clock with 71 for the year 1971. Im guessing the original 85 HP got blown up and the powerhead was replaced with the 1967. It must have needed a carb at some point and someone put on the 1971. Maybe someone also changed the jetting to compensate for seal going bad?<br /><br />I checked each carb very carefully for clear passages (idle air bleed, idle ports, idle passage, idle pick up tube, nozzle, high-speed air bleeds, main jet).<br />Checked inlet passages for leakage into other parts of carb by pressurizing.<br />Looked for cracks or porosity in casting.<br />Made clear fuel bowl to see level of fuel in bowl. Get high but shuts off. Not sure where level should be.<br />Set float levels to .420using dial calipers (spec is 13/32 +/- 1/64 or .406 +/- .015).<br />Made sure good sealing between bottom of main well stem (below main jet) and inside of bowl at screw<br />Idle mixture screws do adjust and best setting is at 1 7/8 turns.<br /><br />Compression is about 140 all three cylinders when slightly warm.<br />Reed valves all looked okay<br />Timing set at 28 deg. WOT spec is 32.<br />Primer bulb gets firm and doesnt leak down with long squeeze. (I can feel when inlet needles shut of the fuel ).<br />No dripping inside of carb throats but throttle plates get wet off idle.<br />Fuel pump pressure teed in line. 3-5 sometimes goes to 7 psi.<br />Diaphram looks good.<br />Hoses from crankcase to fuel pump are dry inside.<br />Puddle drain reeds shut off properly.<br />New 89 octane fuel at 40:1 mix for break in. Began with 25:1.<br />Points set at .014.<br />Changed condenser to one from GM car (ran same). Changed it back as wrong condensor can pit points prematurely. Cap and rotor look fine.<br />New Plugs BUHW - manual calls for L20V or BUH. W is just for tungsten. L20V and BUHW have annular gap of .050 Plugs that came out were L77JC4s.<br />Plug wires ohm out fine and get a 7/16 spark gap.<br /><br />I tried setting the float levels 1/8 lower than spec but only the idle RPM went higher and still fouling the plugs.<br /><br />Plugged exhaust? When I had everything apart, I cant imagine missing that. They way I remember things are designed there isnt much constriction anywhere for carbon to close up. I dont think it would have the power it does either.<br /><br />My conclusion is that I still have the same problem there was before my dad got the boat. The previous mechanics must have richened it up to get it to run as good as it could to compensate for worn rings and seals. Then things got so bad it wouldnt idle. Now, since compression and crankcase seal are better, it cant tolerate the extra richness as much. I am thinking I need to downsize the jets. I struggle with this as I know they are the size they call for. But Im thinking, maybe they arent the right carbs. Maybe they are bigger CFMs (from the original 85) and even the standard 75HP jets (.066) are too big. But didnt they make 85HPs by bigger carbs with bigger .072 jets and bigger reed plate assys. Im confused.<br /><br />Ive tinkered with all kinds of engines. Cars, motorcycles, chain saws, powerwashers, weed whackers. This is my first outboard. This old one seems pretty simple. Really not that much to it. Cant believe its settings are that sensitive. Something is fundamentally wrong to wet the plugs. I believe Ive ruled out ignition or the fuel pump, so there is only one way extra fuel is getting in there; through main the jets.<br /><br />Maybe Ill try a set of L77JC4s that I can make a smaller gap (.030) to help rule out completely a weak ignition problem.<br /><br />Any ideas guys? Would like to know proper carb bore size of a 75 HP. Top carb is WB9B 316061-1 with 71 embossed on side. Middle and bottom are WB1B no other number.<br /><br />Thanks,<br />Mark
