Adjusting speed jets.?

Question

If your carbs have adjustable slow speed jets, post another question on how to set 'em when you get to that point?

I brought my boat to a friend of a friend, had a compression test completed, he stated I had low compression on one of the cylinders, however in the same breath he wanted to buy my boat....kinda fishy...if you know what I mean.

This motor has done this before and I just cleaned the carbs and it seemed okay for awhile, the boat has sat for awhile...so heck I dont know....its just a old old fishing boat.

However, its a great boat at that, tri haul, 1990 90hp yamaha, power tilt, it will fly across the water...just need some help in trying the find the problem.

Answer 1

Ask for the specific compression numbers of each cylinder.  If the lowest is within 5% of the highest, that's great.  If the difference is 7%, that's pretty darn good.  If it's 10% up to, say 12 or 15%, you have a good chance that the cause is a sticky ring due to carbon build-up, and the compression can be recovered with a de-carb.  Even very low compression on a cylinder could be something simple as a head gasket - you can't tell without pulling the head for a visual inspection.

If you need a step-by-step for a decarb, ask in another question (not trying to give you the run-around - it's just that it'll make a really long answer even longer).

Here's the slow-speed needle adjustment procedure - this is kind of generic for 2-stroke carbed outboards, I'm pretty sure it will work just fine on the yammy:

Before you start the engine, s***w the needle valve in until it seats gently, then turn it out one and a half turns.

Start the engine and use the hi-idle lever to adjust the RPMs where it will just stay running. Then start turning the needle valve in 1/8 turn at a time, pausing to let the engine respond. As you turn the valve in, RPM's will increase. Each time, lower the hi-idle lever to just keep the engine running.

Eventually you'll hit a point where the engine will start to die or spit back - at that point, back the s***w out 1/4 turn. You'll find the smoothest running somewhere in that last 1/4 turn.

With a multi-carb engine, don't try to do them all at once...just get the first one going best you can then do the next.  You might have to iterate back through them again.

Once it's set, you won't need to change it until the carb requires rebuilding again.

Answer 2

try a fuel filter,new plugs....correctly installed ....after you clean the carbs again