Have a Problem
05-15-2007, 06:11 AM
#1
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Have a Problem
Hello All
After doing some checking on my K&B 7.5 Outboard for air leaks I notice that there is a small air leak.
Just below the Flywheel is located the Flywheel Collet and Front Bearing and it seems that this is where the leak is coming from. Mind you that with some amount of presure i can only see two very small bubbles after putting soap and water on it.
What seems to be the problem is... When I run the engine on the test bench it runs fine. will idol fine, has good pickup and will run at full throttle without any problem. All seems to work prefect.
Now when I go to the lake and start the engine it starts fine, I put it in the water and it idols fine, but after trying a few starts it dies and then it requires that the glow plug needs to be left on in order to keep running.
Any ideas or suggestions would be greatly apreciated as to what is happening and why. I have posted a few pics of the boat and motor if you want to have a look.
Thanks
Chris
After doing some checking on my K&B 7.5 Outboard for air leaks I notice that there is a small air leak.
Just below the Flywheel is located the Flywheel Collet and Front Bearing and it seems that this is where the leak is coming from. Mind you that with some amount of presure i can only see two very small bubbles after putting soap and water on it.
What seems to be the problem is... When I run the engine on the test bench it runs fine. will idol fine, has good pickup and will run at full throttle without any problem. All seems to work prefect.
Now when I go to the lake and start the engine it starts fine, I put it in the water and it idols fine, but after trying a few starts it dies and then it requires that the glow plug needs to be left on in order to keep running.
Any ideas or suggestions would be greatly apreciated as to what is happening and why. I have posted a few pics of the boat and motor if you want to have a look.
Thanks
Chris
05-15-2007, 06:17 AM
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RE: Have a Problem
I think?[&:] your motor is leaning out on you.Try to richened your carb alittle bit at a time to see if she straintens out on you.But one thing that hits my mind,If you got air comming out your crank,one bad crank bearing that has a bad seal and other is bad/warn out pistion seal=blow by,This would make your motor not to run right with a load on it.[8D]
05-19-2007, 01:30 PM
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RE: Have a Problem
I had a Tunnel Hull with a K&B 7.5 outboard.
it could be a bad bearing but before replacing the bearing(s), check how many turns you have on your high speed needle, turn it all the way in and come back out 3 turns, this will be a good place to start.
at 3 turns out she should be ritch, remember its better to be too ritch than too lean.
Tuning an engine on the bench is not recommended, the motor may run great on the bench at full throttle but as soon as you put the boat in the water it puts a load on the engine and all your settings is now out to lunch,
Like MissHydro said, more than likely you are running way too lean. So try that method I mentionned on top.
Once you found the right setting and you can keep her running on the water, you will know if she is now too ritch (runs with a spewting sound, or sore throat), than you can bring her in and FINE tune on the bench and lean her in slowly 1/16 to 1/8 of a turn IN at a time.
Keeping a reading on your engine temperature will also tell you if you are running too lean, also if you keep pulling the filament from your glow plug out every run is also a sign that its too lean.
Dan.
it could be a bad bearing but before replacing the bearing(s), check how many turns you have on your high speed needle, turn it all the way in and come back out 3 turns, this will be a good place to start.
at 3 turns out she should be ritch, remember its better to be too ritch than too lean.
Tuning an engine on the bench is not recommended, the motor may run great on the bench at full throttle but as soon as you put the boat in the water it puts a load on the engine and all your settings is now out to lunch,
Like MissHydro said, more than likely you are running way too lean. So try that method I mentionned on top.
Once you found the right setting and you can keep her running on the water, you will know if she is now too ritch (runs with a spewting sound, or sore throat), than you can bring her in and FINE tune on the bench and lean her in slowly 1/16 to 1/8 of a turn IN at a time.
Keeping a reading on your engine temperature will also tell you if you are running too lean, also if you keep pulling the filament from your glow plug out every run is also a sign that its too lean.
Dan.
05-19-2007, 09:15 PM
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RE: Have a Problem
You might want to put a new glow plug in it also. Plus from what your saying it sounds like you are just setting the boat in the water at idle and trying to go. If so this wont work you need to give it an underhand toss forward as your throttling the boat up to 1/4 or so
05-19-2007, 11:49 PM
#5
RE: Have a Problem
Usually a properly set needle for running will be almost too rich to keep running on shore without blipping the throttle, and will want to die or load up if you stay on idle.
I am not quite sure it would be a bad bearing problem, because K/B does not use sealed bearings. If a bad bearing is the cause it is gone past the point of being just the bearing, because the crankshaft would have already scared the front housing, where there is only a small air gap or clearance allowed between the housing bore and the cranshaft diamter. That is what provides the air seal. Front bearings are usually left open. No shields or seals.
The front of the crankshaft recieves oil from the carb being shut off quickly by the intake port closing, and continues to pump charge to the front of the crank until that rush is past and starts over again. The oil provides the seal along with a narrow gap. There is also a positive pressure inside the crankcase when past half throttle. This also helps lubricate or force intake mixture to the bearing.
If you are in doubt, you could remove the crankshaft and use grease on its nose where it is located in the housing - just behind the bearing and ahead of the intake port. It will not last, but will prove if it is the seal. It will run good until the grease clears out if that is truely the problem.
I am not quite sure it would be a bad bearing problem, because K/B does not use sealed bearings. If a bad bearing is the cause it is gone past the point of being just the bearing, because the crankshaft would have already scared the front housing, where there is only a small air gap or clearance allowed between the housing bore and the cranshaft diamter. That is what provides the air seal. Front bearings are usually left open. No shields or seals.
The front of the crankshaft recieves oil from the carb being shut off quickly by the intake port closing, and continues to pump charge to the front of the crank until that rush is past and starts over again. The oil provides the seal along with a narrow gap. There is also a positive pressure inside the crankcase when past half throttle. This also helps lubricate or force intake mixture to the bearing.
If you are in doubt, you could remove the crankshaft and use grease on its nose where it is located in the housing - just behind the bearing and ahead of the intake port. It will not last, but will prove if it is the seal. It will run good until the grease clears out if that is truely the problem.
