125 hp exhaust boot missing plastic insert

[erosenwinkel]

I posted earlier regarding possible exhaust leakage causing engine to die from lack of fresh air (worked fine with cowling off, would die when I put it back on). I checked the exhaust boot, all looks soft, pliable and hole free. I am missing the plastic insert, is it necessary? What is its purpose?
I purchased a handheld digital tachometer, painted my flywheel black on the edge and attached the reflective sticker. A WOT I get a reading of 4800 rpm, my understanding is that it should be around 5500 rpm. By adjusting carbs and following the sync procedure should this bring up the rpm's (assuming that I have optimal compression in all four cylinders, good fuel mixture etc...) When I purchased the outboard pretty much everything was monkeyed with so I am trying to muddle my way through.

 

[foodfisher]

Re: 125 hp exhaust boot missing plastic insert

Mine doesn't have one (plastic piece) '86 - 125. The hose part fits well into the concave receiver on the leg. No leaks, runs well. If you see no leaks in the leg, key word, no, then you've another problem. Plugged air intake ( disentegrated cowling insulation)plugging it, a rag stuffed in it, or ?another exhaust leak.

 

[Frank Acampora]

Re: 125 hp exhaust boot missing plastic insert

The plastic ring keeps the tapered end of the boot circular in shape and uses the spring pressure to firmly push it into the seat. Is the spring there or missing too? While the boot MAY work properly without either or both parts, it will certainly seal correctly with them, and you do seem to have an exhaust aspiration problem. Occam's razor: The most obvious solution to a problem is usually the correct one!

Engine RPM is dependent upon many factors, including prop pitch. If you are doing 4800 now, synchronizing timing and carburetion may not give any more RPM and speed. We need to know what size boat the engine is on and what pitch prop it is swinging now. Anyway, that engine is rated to run between 4500 and 5500 RPM at full throttle with the rated horsepower developed at 5000 RPM. It is within range and not far off the max HP RPM at all.

 

[erosenwinkel]

Re: 125 hp exhaust boot missing plastic insert

The Boat the 1258x5a is pulling is an 18.5' Bayliner Capri with a prop pitch of 17. I don't think it is waterlogged, had plug out overnight with the front end up and very little if anything dripped out overnight (evaporated if anything). Rebuilt over the winter as I have stated before (got it hot before I learned it was water cooled . Started with new plugs a month ago. Put in fuel additive that Mercury dealer suggested to combat the ethanol. Doesn't smoke very much at all. Although, I did notice last night when I was taking the cowling on and off trying to figure this out there was some "some" exhaust that wafted out of the cowling. I suppose 1/2 the amount as a smoker would exhale. Engine has plenty of power and sounds smooth and even, no vibration. If if weren't for the stall at idle going into forward I would say it was perfect. Thanks a bunch for all your patience and advice.