1976 75 HP stinger loses power

[awjens]

My 75 HP stinger idles fine, but wont runn at full throttle. It bogs down and stall if I hold throttle. Compression 120# on all three. New plugs. At idle i disconnected plug wires on at a time, all seem to be hiting. What is a link and sync? How common is a blown head gasket or exhaust gasket. Pumped the biulb at WOT, no change, still quits. I thought I saw water on the plugs. Tank was drained and cleaned. cHE=CKING CARBS TOMORROW.

 

[jtexas]

Re: 1976 75 HP stinger loses power

On checking the carbs: there's really no point. Every carb I've ever rebuilt, I never once visualized the problem. Either it was in a tiny passage, or worn float valves you can't really eyeball 'em & tell they're bad. Removal & reinstallation is the hardest part of rebuilding. Might as well get the kits & do it right.

blown head gasket or exhaust gasket = lost compression, so you've ruled that out.

You're describing a classic symptom of dirty carbs, specifically the high speed jets which don't affect idling. But bad compression or bad spark could contribute to your symptoms, and those are quick & easy to test for, so generally a good idea to do those first.

Get an inline spark tester (less than $10 at autozone), set the gap at 7/16", clip it to the block, attach the plug leads (one at a time) and look for spark while cranking. If it won't jump a half-inch gap in the open air without a spark plug, it won't fire in the hole under heat & pressure.

Make sure the carb throttles stay parallel and end up horizontal (not beyond) at WOT, and that the choke plates stay open except when the choke is engaged.

Then rebuild the carbs.

Link & sync is the process of syncronizing the carb throttle valves with each other and with the spark timing advance. For the full step by step you really need a manual. Sometimes (not always) after a carb rebuild, nothing else changes and there's no adjustments to make during your link & sync.

 

[doghunter9]

Re: 1976 75 HP stinger loses power

Just had the same problem with my 50hp,
get a spray bottle and remove the air box, At WOT spary pre-mix into each carb in intervials and the motor shold pick right up if you got High speed trouble, find the bad carb get a rebulid kit and you'll be back up and running.

 

[jtexas]

Re: 1976 75 HP stinger loses power

First, don't take the motor back out on the lake and run it just for that premix spray test. Your motor gets its lubricating oil from the fuel, so whichever cylinder is starved for fuel is not getting lubricated.

And never but never rev your motor over 1500 or so on the muffs, for a couple reasons: one is thermal runaway; the motor can literally tear itself apart before you can get it to stop, read more about it here: http://forums.iboats.com/showthread.php?t=194958 The other is because backing off the throttle reduces the amount of lubricating oil in the cylinder, but without a load on the propeller, the RPMs don't drop immediately. You get a brief moment of inadequate oiling.

Second, don't bother rebuilding only one of three carbs. If one is dirty enough to drop out at high speed, the others are dirty enough to cause lean burning, which leads to elevated combustion temps and eventual catastrophic piston failure.

Besides which, start to finish (cowl off to cowl on), if you spend two hours on one carb, you can do three in about 2 hours and 15 minutes. Kits are cheap.