Diagnosing Fuel System Problem, Mercury 9.9-HP FOURSTROKE

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Author Topic:   Diagnosing Fuel System Problem, Mercury 9.9-HP FOURSTROKE

martyn1075 posted 07-11-2011 02:13 AM ET (US)
Are there any symptoms that would make a clear cut case [for the cause of running problems in a] 2006 Mercury 9.9HP FOURSTROKE Bigfoot [to be] a primer bulb or fuel pump? I started the engine and checked the bulb, which was clearly empty. I then pumped gas but instead was just getting only air. I bled the [fuel] system; [the results were] not much, but better. Engine wouldn't start, so I figured maybe the water filter had air, or the gas was not quite at the top, so I removed [the fuel-water separating filter]. [The level of fuel in the canister of the fuel-water separating filter] was low. After refilling the canister, I tested it before inserting back into the engine, and--bing--[fuel] was streaming out after I squeezed [the primer bulb] a number of times. Connected back [the fuel-water separating filter] to the engine, and [the engine] started after a few turns. I let [the Mercury 9.9-HP FOURSTROKE] run for ten minutes and it quit on me! Went back to look at the primer bulb--it was empty.
[The source of the problem] is the [primer] bulb--right?
The low pressure gauge was ON, so we can confirm [the source of the engine running problem is due to] a lack of [fuel]. Is [the lack of fuel] because the engine cannot suck the gas from the bulb because of a fuel pump problem? Or, is the bulb just not allowing proper flow to the engine?
Thanks
jimh posted 07-11-2011 07:43 AM ET (US)
If the primer bulb is sucked flat, this is an indication that there is an obstruction upstream. For more advice on primer bulbs and using them as a diagnostic indicator, see
Primer on Primers
http://continuouswave.com/whaler/reference/primer.html
jimh posted 07-11-2011 08:03 AM ET (US)
It is typical in a properly working fuel system for the primer bulb to lose some of its firmness as the engine is operating, but it should not lose all of its fuel. If the primer bulb has air in it, this is an indication that there is an air leak upstream of the primer bulb.
A simple way to eliminate the primer bulb and fuel tank as possible causes for the running problems on our 9.9-HP engine is to temporarily connect another tank and fuel hose with primer bulb, then re-test. If the engine still stalls after ten minutes of running, you can suspect the fuel pump. If the engine runs normally, the fuel tank and primer bulb were likely the cause.
martyn1075 posted 07-11-2011 11:59 AM ET (US)
Connecting an auxiliary tank is a good idea I will give that a try.
Thanks
Blackduck posted 07-11-2011 12:46 PM ET (US)
Try disconnecting the fuel line from primer bulb. Can you then pump fuel through your main filter, from the tank without any problems? I would suspect you might have a problem doing this, which would indicate a clogged filter, or fuel intake in the tank.
Tohsgib posted 07-11-2011 01:14 PM ET (US)
It might be a simple as the little diaphram pump can't suck it past the fuel-water filter. Your Owner's Manual might tell you not to use an in-line filter like my manual does. Again try an auxiliary tank and hose.
martyn1075 posted 07-18-2011 01:16 AM ET (US)
Problem solved, after replacing the bulb and line to the engine which did vastly improve the gas flow to the engine, it stalled and bulb went soft again. Took off the cowling and found gas spurting out of the tube that connects to the inline filter (white plastic cap) the hose was split where it connects to the nipple of the white cap. Improper amount of gas to the engine hence low pressure resulting in the engine stalling.

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Author	Topic: Diagnosing Fuel System Problem, Mercury 9.9-HP FOURSTROKE
martyn1075	posted 07-11-2011 02:13 AM ET (US) Are there any symptoms that would make a clear cut case [for the cause of running problems in a] 2006 Mercury 9.9HP FOURSTROKE Bigfoot [to be] a primer bulb or fuel pump? I started the engine and checked the bulb, which was clearly empty. I then pumped gas but instead was just getting only air. I bled the [fuel] system; [the results were] not much, but better. Engine wouldn't start, so I figured maybe the water filter had air, or the gas was not quite at the top, so I removed [the fuel-water separating filter]. [The level of fuel in the canister of the fuel-water separating filter] was low. After refilling the canister, I tested it before inserting back into the engine, and--bing--[fuel] was streaming out after I squeezed [the primer bulb] a number of times. Connected back [the fuel-water separating filter] to the engine, and [the engine] started after a few turns. I let [the Mercury 9.9-HP FOURSTROKE] run for ten minutes and it quit on me! Went back to look at the primer bulb--it was empty. [The source of the problem] is the [primer] bulb--right? The low pressure gauge was ON, so we can confirm [the source of the engine running problem is due to] a lack of [fuel]. Is [the lack of fuel] because the engine cannot suck the gas from the bulb because of a fuel pump problem? Or, is the bulb just not allowing proper flow to the engine? Thanks
jimh	posted 07-11-2011 07:43 AM ET (US) If the primer bulb is sucked flat, this is an indication that there is an obstruction upstream. For more advice on primer bulbs and using them as a diagnostic indicator, see Primer on Primers http://continuouswave.com/whaler/reference/primer.html
jimh	posted 07-11-2011 08:03 AM ET (US) It is typical in a properly working fuel system for the primer bulb to lose some of its firmness as the engine is operating, but it should not lose all of its fuel. If the primer bulb has air in it, this is an indication that there is an air leak upstream of the primer bulb. A simple way to eliminate the primer bulb and fuel tank as possible causes for the running problems on our 9.9-HP engine is to temporarily connect another tank and fuel hose with primer bulb, then re-test. If the engine still stalls after ten minutes of running, you can suspect the fuel pump. If the engine runs normally, the fuel tank and primer bulb were likely the cause.
martyn1075	posted 07-11-2011 11:59 AM ET (US) Connecting an auxiliary tank is a good idea I will give that a try. Thanks
Blackduck	posted 07-11-2011 12:46 PM ET (US) Try disconnecting the fuel line from primer bulb. Can you then pump fuel through your main filter, from the tank without any problems? I would suspect you might have a problem doing this, which would indicate a clogged filter, or fuel intake in the tank.
Tohsgib	posted 07-11-2011 01:14 PM ET (US) It might be a simple as the little diaphram pump can't suck it past the fuel-water filter. Your Owner's Manual might tell you not to use an in-line filter like my manual does. Again try an auxiliary tank and hose.
martyn1075	posted 07-18-2011 01:16 AM ET (US) Problem solved, after replacing the bulb and line to the engine which did vastly improve the gas flow to the engine, it stalled and bulb went soft again. Took off the cowling and found gas spurting out of the tube that connects to the inline filter (white plastic cap) the hose was split where it connects to the nipple of the white cap. Improper amount of gas to the engine hence low pressure resulting in the engine stalling.