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Mercury 9.9 2 stroke crankcase +/- pressure question

newb197

newb197

Contributing Member
I am experience a running issue and seems to be fuel related. This motor has an integral fuel pump and crankcase ports(upper/lower) to operate it. Question: when you apply vacuum or pressure to the top port there is no restrictions. The bottom port allows vacuum but no air allowed to enter, is this correct? Is this a one way port? Im thinking there is restriction here, am I wrong? When I start it, I must keep the idle air adjust fully shut or will not run.
Thanks for reading.
 
Fuel pumps on outboards are very reliable and simple.------Is the running issue something that started suddenly ? -Have you done a compression test ?
 
Yes 100+ on both. This motor ran beautiful. started out a shift(on the handle) problem. Replaced violently stretched cables and shift shaft retainer was missing, nver touched fuel system except to remove bottom crankcase hose to get at the shift area. I ran the outboard after and ran beautiful up and down the river. I did notice after I had not rehooked the bottompulse line, soI rehooked it(not running). Tried to start two days later and this major problem started. I tried to put compressed air into both of these port/pulse line connectors at the block, bottom one would not take air? clogged?
 
The small hoses have to do with the recirculation system of a fuel / oil mix.-------Caburetor may have ports to run the fuel pump.-Post pictures of the pulse lines so we know what you are attempting to do.
 
Yes, on the 9.9 the fuel pump "pulse" comes through a channel in the carb.

There is three termination points on the bleed lines.

The bleed line that goes to the lower crank case connects to a check valve that should let oil/gas "out" (of the crankcase) into the line.

The bleed line that comes from the base of the carb scavenges leftover oil/fuel from the base of the reed cage. Likewise there is a check valve there that lets oil/gas "out" into the line.

Both the above lines connect to a T connector and the third bleed line takes the feed from both of those up to the top of the crank case to lube the upper main bearing/seal (upper crank).

If the check valves are shot you can end up with a an extremely "rich" situation which can appear as a flooded engine.

When you failed to re-hook the bottom line it should not have caused any fuel delivery issues. If the check valve was functioning properly it simply would have "misted" oil/gas into the lower cowl and you would get a slimy film similar to an "engine fog".

Likewise, the line that was normally connected there would have "dripped" goop that was scavenged from the reeds and your upper bearing would have got a limited amount of lube (the open hose would have been the "easy way out".

Now, if your motor won't start at all I'm fairly certain (without having the motor in front of me) that the bleed lines are not to blame, or certainly not solely to blame. Suspect that whatever the real issue is, is coincidental...
 
Correct - NO check valve on the upper crank fitting - 1 on the lower crank and one behind (under) the carb that scavenges from the reeds.

Since they are "one way" (out) when the upper crank case pressurizes it can't force the "goo" back to either the reeds or the lower case - the valves won't let them so in effect the bleed lines become pressurized. When it's "sucking" whatever is in those lines gets fed to the upper bearing/seals (vacuum created in the bleed lines pulling from the reeds/lower crank)..
 
Thank you Graham. Seems I misspoke, was actually running rich or even richer we'll say when adjusted out. The recirc lines where in fact coincidental. Little ball bearing in the primer assembly was found forced down into the spring. Apparently the carb was dissatisfied with this. Was even more dissatisfied when I then dropped and lost the ball bearing. So most components being worn I got a carb kit, but to get that little ball bearing too you have to order a second kit almost identical to the first. so.. lots of extras. Good stuff. Thanks everyone.
 
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