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Author Topic:   2000 Mercury 135-HP Bogs Under Load

cworthy posted 07-20-2009 09:13 PM ET (US)
I have a 2000 Dauntless 18 with a 135-HP Mercury. The engine will bog down at 1,800-RPM and stall if throttle is not pulled back. This occurs only when the engine is not idled for about five minutes before going WOT. If I am running OK and cut the engine for just a few moments, it must be idled for another five minutes before WOT. After idling, it runs great and will even pull a water skier out of the water without issue.
I have read previous posts and tried the following remedies without success: inspected the fuel filter and fuel pump; installed a fuel water separator; and cleaned the carbs. Any thoughts to assist me? Needless to say a very frustrating. Any help with the [solution to this problem] would be much appreciated. Thanks to all.
Tom W Clark posted 07-20-2009 10:21 PM ET (US)
Which Mercury 135 HP motor are we talking about?
cworthy posted 07-20-2009 10:26 PM ET (US)
[The motor is] a 2000 V6 two-cycle saltwater model and is not an OptiMax. Thanks again.
Tom W Clark posted 07-20-2009 10:31 PM ET (US)
That sounds like a fuel restriction. Idling th e motor reduces the fuel demand enough for the fuel delivery system to regain pressure.
When this problem occurs, is the fuel primer bulb unusually soft or collapsed?
cworthy posted 07-20-2009 10:33 PM ET (US)
[The primer] bulb is soft.
Tom W Clark posted 07-20-2009 10:36 PM ET (US)
OK, don't jump to conclusions, proceed by process of elimination.
Run the motor on a portable fuel tank. If the problem do not appear, you can proceed with trouble shooting a fuel restriction in the boat's fuel delivery system.
cworthy posted 07-20-2009 10:43 PM ET (US)
Thanks [Tom]. I am not terribly handy with motors and will probably have a mechanic do this. Is the process to disconnect the existing source and hook up the [portable] straightfoward, relatively?
Tom W Clark posted 07-21-2009 10:19 AM ET (US)
It is terribly simple to connect a remote fuel tank to your motor. Be sure use a portable with a 5/16" or 3/8" fuel hose.
cworthy posted 07-21-2009 02:58 PM ET (US)
Tom--at what point do [I] use the existing delivery system? [Should] [I] start at the primer bulb or use a different bulb?
Once again much appreciated. Thanks.
Tom W Clark posted 07-21-2009 03:01 PM ET (US)
No, disconnect the fuel hose at the motor and connect the portable tank there.
I am not familiar with the 2000 135 but my 1989 Mercury 150 has a quick disconnect fitting on the motor (which I have always thought strange).
Most motors of this size have a barb at the motor the hose fits over and is clamped to. You want to be sure you have the test hose clamped on perfectly tight as well.
cworthy posted 07-21-2009 03:17 PM ET (US)
OK. [U]nderstood. Will I need a new [primer] bulb?
Tom W Clark posted 07-21-2009 03:20 PM ET (US)
Most portable tanks have a fuel hose and primer bulb already attached.
cworthy posted 07-26-2009 06:21 PM ET (US)
I ran a test on the portable tank this weekend and continued to experience the bogging down at 1,800-RPM unless the engine was idled for approximately five minutes before going WOT. Pulled the plugs and the three on the port side were a bit cleaner on the threads. Evidence of water in the cylinders? After idling is the water pushed out by fuel pressure? Just a gasket or could it be more serious?
cworthy posted 08-10-2009 09:46 PM ET (US)
[This article was originally posted as a new discussioin in a separate thread. Please do not start a new discussion only to follow up on a previous discussion. I have deleted the orphan thread and moved it this original discussion--jimh]
I previously posted regarding my engine that will bog down at 1,800-RPM and stall if throttle is not pulled back. This occurs only when the engine is not idled for about five minutes before going WOT. If I am running OK and cut the engine for just a few moments, it must be idled for another five minutes before WOT. After idling, it runs great and will even pull a water skier out of the water without issue.
I have read previous posts and tried the following remedies without success: inspected the fuel filter and fuel pump; installed a fuel water separator; and cleaned the carburetors. At a reader's suggestion, I ran off a portable tank and the [problem] continued.
I pulled the plugs and the threads on the three on the port side were clean. Could this be water intrusion into the cylinders? A buddy even suggested that it may be the electronic choke; I am not too familiar with this.
Any thoughts are greatly appreciated!
jimh posted 08-11-2009 03:48 AM ET (US)
Generally operation at idle speed for five minutes will be enough to get the engine temperature to rise to the 140-degree range. Perhaps the problem with the engine bogging down on acceleration is related to engine temperature.
In observing a spark plug's condition as a diagnostic indicator, you generally look the electrode tip and the ceramic insulator surrounding it, not the threads of the plug body. The threads of the plug body should not be protruding into the combustion chamber.
Plotman posted 08-11-2009 05:21 PM ET (US)
I had a 150 version of this engine and had a similar problem. There is an in-line fuel filter under the cowling. I cleaned mine out and had no more problems.
cworthy posted 09-20-2009 06:53 PM ET (US)
I had a different mechanic take a look at the bogging down [motor]. He says that the [cause] is low fuel pressure, and, that after it has idled for a few minutes, the pressure is sufficient until the engine is turned off. His diagnosis is that the floats in the carburetors need to be adjusted. He also informed me that once the engine begins to bog, press the choke and additional fuel is added to the engine. I tried the choke fix and it worked like a charm. Does anyone foresee [a problem] if I do not adjust the floats and just choke [the engine] when it bogs? Will the cylinders run lean? Additionally, the [cylinder pressure] registered at 95- to 105-[PSI], which he indicated was low, and my engine has "about a year left" because of this. As such, he did not recommend spending the money to adjust the carburetors.
Any thoughts are much appreciated.
Pat
jimh posted 09-21-2009 07:37 AM ET (US)
When you measure the peak pressure in each cylinder with a pressure gauge, which is often called "a compression check," the readings are usually evaluated on how much variation there is among cylinders, not on the absolute value of the readings. One benchmark for comparing pressure readings among cylinders is the range should not be more than 15-PSI. Your readings are within 10-PSI.
As for the absolute value of the readings, the measurement can vary due to variations in the gauge used, the technique used, and the condition of the engine. If a mechanic uses the same gauge and the same technique, and collects a history of readings on many engines, he may develop knowledge of the measured value that an engine in good condition will exhibit. If a mechanic with that background measures your engine and tells you that the readings are low, based on his experience and background with that type of engine, this is a reasonable interpretation of the data. It would be hard to second guess his interpretation, since we have no idea of the particular gauge he used, how he used it, or what the normal reading for an engine of your type might be.
As for continued operation of the engine by using the fuel enrichment circuit to overcome a lack of fuel supply by the carburetors, that sounds like an awkward solution and a tedious way to operate the motor.
Unless your motor has been abused, it seems extremely unusual that a motor from year-2000 would already be on its last legs. A typical two-cycle outboard motor can generally last for decades if given reasonable care and fed quality fuel and lubrication.
jimh posted 09-21-2009 07:52 AM ET (US)
I do not understand the diagnosis you were given regarding "low fuel pressure" and it being caused by the carburetor floats.
First of all, the fuel in a carburetor is not under pressure. It sits in a reservoir (a "carburetor bowl") which is vented to the atmosphere, so there cannot be pressure contained in that reservoir. In fact, there is negative pressure, or suction, because the fuel is pulled from the reservoir by the air passing through the carburetor throat. Fuel is pulled out of the reservoir and metered into the air flow via an orifice or jet.
There is some pressure in the fuel system from the action of the fuel lift pump. The pump pulls fuel from the fuel tank by negative pressure (or suction) and lifts it to the engine. Then fuel flows under a slight pressure from the output of the pump to the carburetor bowls. An inlet valve operated by a float in the carburetor bowl admits fuel to the bowl as needed to keep the fuel level in the bowl constant. If there were low fuel pressure, the remedy would be to replace the fuel pump.
jimh posted 09-21-2009 07:56 AM ET (US)
A little more research on your c.2000 Mercury V6 135-HP engine revealed that it is a 60-degree V6 2.0-liter block. I believe this is quite a famous engine in the Mercury line, often used in racing, and respected as a durable and high-performance engine.
Before abandoning this engine because its cylinder pressure readings were low, I would try some de-carbon remedies. Add some solvents to your gasoline to remove carbon deposits. In some cases poor cylinder pressure is caused by carbon deposits on the piston rings. Removing some of the carbon can often restore higher pressure to the cylinder.

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Author	Topic: 2000 Mercury 135-HP Bogs Under Load
cworthy	posted 07-20-2009 09:13 PM ET (US) I have a 2000 Dauntless 18 with a 135-HP Mercury. The engine will bog down at 1,800-RPM and stall if throttle is not pulled back. This occurs only when the engine is not idled for about five minutes before going WOT. If I am running OK and cut the engine for just a few moments, it must be idled for another five minutes before WOT. After idling, it runs great and will even pull a water skier out of the water without issue. I have read previous posts and tried the following remedies without success: inspected the fuel filter and fuel pump; installed a fuel water separator; and cleaned the carbs. Any thoughts to assist me? Needless to say a very frustrating. Any help with the [solution to this problem] would be much appreciated. Thanks to all.
Tom W Clark	posted 07-20-2009 10:21 PM ET (US) Which Mercury 135 HP motor are we talking about?
cworthy	posted 07-20-2009 10:26 PM ET (US) [The motor is] a 2000 V6 two-cycle saltwater model and is not an OptiMax. Thanks again.
Tom W Clark	posted 07-20-2009 10:31 PM ET (US) That sounds like a fuel restriction. Idling th e motor reduces the fuel demand enough for the fuel delivery system to regain pressure. When this problem occurs, is the fuel primer bulb unusually soft or collapsed?
cworthy	posted 07-20-2009 10:33 PM ET (US) [The primer] bulb is soft.
Tom W Clark	posted 07-20-2009 10:36 PM ET (US) OK, don't jump to conclusions, proceed by process of elimination. Run the motor on a portable fuel tank. If the problem do not appear, you can proceed with trouble shooting a fuel restriction in the boat's fuel delivery system.
cworthy	posted 07-20-2009 10:43 PM ET (US) Thanks [Tom]. I am not terribly handy with motors and will probably have a mechanic do this. Is the process to disconnect the existing source and hook up the [portable] straightfoward, relatively?
Tom W Clark	posted 07-21-2009 10:19 AM ET (US) It is terribly simple to connect a remote fuel tank to your motor. Be sure use a portable with a 5/16" or 3/8" fuel hose.
cworthy	posted 07-21-2009 02:58 PM ET (US) Tom--at what point do [I] use the existing delivery system? [Should] [I] start at the primer bulb or use a different bulb? Once again much appreciated. Thanks.
Tom W Clark	posted 07-21-2009 03:01 PM ET (US) No, disconnect the fuel hose at the motor and connect the portable tank there. I am not familiar with the 2000 135 but my 1989 Mercury 150 has a quick disconnect fitting on the motor (which I have always thought strange). Most motors of this size have a barb at the motor the hose fits over and is clamped to. You want to be sure you have the test hose clamped on perfectly tight as well.
cworthy	posted 07-21-2009 03:17 PM ET (US) OK. [U]nderstood. Will I need a new [primer] bulb?
Tom W Clark	posted 07-21-2009 03:20 PM ET (US) Most portable tanks have a fuel hose and primer bulb already attached.
cworthy	posted 07-26-2009 06:21 PM ET (US) I ran a test on the portable tank this weekend and continued to experience the bogging down at 1,800-RPM unless the engine was idled for approximately five minutes before going WOT. Pulled the plugs and the three on the port side were a bit cleaner on the threads. Evidence of water in the cylinders? After idling is the water pushed out by fuel pressure? Just a gasket or could it be more serious?
cworthy	posted 08-10-2009 09:46 PM ET (US) [This article was originally posted as a new discussioin in a separate thread. Please do not start a new discussion only to follow up on a previous discussion. I have deleted the orphan thread and moved it this original discussion--jimh] I previously posted regarding my engine that will bog down at 1,800-RPM and stall if throttle is not pulled back. This occurs only when the engine is not idled for about five minutes before going WOT. If I am running OK and cut the engine for just a few moments, it must be idled for another five minutes before WOT. After idling, it runs great and will even pull a water skier out of the water without issue. I have read previous posts and tried the following remedies without success: inspected the fuel filter and fuel pump; installed a fuel water separator; and cleaned the carburetors. At a reader's suggestion, I ran off a portable tank and the [problem] continued. I pulled the plugs and the threads on the three on the port side were clean. Could this be water intrusion into the cylinders? A buddy even suggested that it may be the electronic choke; I am not too familiar with this. Any thoughts are greatly appreciated!
jimh	posted 08-11-2009 03:48 AM ET (US) Generally operation at idle speed for five minutes will be enough to get the engine temperature to rise to the 140-degree range. Perhaps the problem with the engine bogging down on acceleration is related to engine temperature. In observing a spark plug's condition as a diagnostic indicator, you generally look the electrode tip and the ceramic insulator surrounding it, not the threads of the plug body. The threads of the plug body should not be protruding into the combustion chamber.
Plotman	posted 08-11-2009 05:21 PM ET (US) I had a 150 version of this engine and had a similar problem. There is an in-line fuel filter under the cowling. I cleaned mine out and had no more problems.
cworthy	posted 09-20-2009 06:53 PM ET (US) I had a different mechanic take a look at the bogging down [motor]. He says that the [cause] is low fuel pressure, and, that after it has idled for a few minutes, the pressure is sufficient until the engine is turned off. His diagnosis is that the floats in the carburetors need to be adjusted. He also informed me that once the engine begins to bog, press the choke and additional fuel is added to the engine. I tried the choke fix and it worked like a charm. Does anyone foresee [a problem] if I do not adjust the floats and just choke [the engine] when it bogs? Will the cylinders run lean? Additionally, the [cylinder pressure] registered at 95- to 105-[PSI], which he indicated was low, and my engine has "about a year left" because of this. As such, he did not recommend spending the money to adjust the carburetors. Any thoughts are much appreciated. Pat
jimh	posted 09-21-2009 07:37 AM ET (US) When you measure the peak pressure in each cylinder with a pressure gauge, which is often called "a compression check," the readings are usually evaluated on how much variation there is among cylinders, not on the absolute value of the readings. One benchmark for comparing pressure readings among cylinders is the range should not be more than 15-PSI. Your readings are within 10-PSI. As for the absolute value of the readings, the measurement can vary due to variations in the gauge used, the technique used, and the condition of the engine. If a mechanic uses the same gauge and the same technique, and collects a history of readings on many engines, he may develop knowledge of the measured value that an engine in good condition will exhibit. If a mechanic with that background measures your engine and tells you that the readings are low, based on his experience and background with that type of engine, this is a reasonable interpretation of the data. It would be hard to second guess his interpretation, since we have no idea of the particular gauge he used, how he used it, or what the normal reading for an engine of your type might be. As for continued operation of the engine by using the fuel enrichment circuit to overcome a lack of fuel supply by the carburetors, that sounds like an awkward solution and a tedious way to operate the motor. Unless your motor has been abused, it seems extremely unusual that a motor from year-2000 would already be on its last legs. A typical two-cycle outboard motor can generally last for decades if given reasonable care and fed quality fuel and lubrication.
jimh	posted 09-21-2009 07:52 AM ET (US) I do not understand the diagnosis you were given regarding "low fuel pressure" and it being caused by the carburetor floats. First of all, the fuel in a carburetor is not under pressure. It sits in a reservoir (a "carburetor bowl") which is vented to the atmosphere, so there cannot be pressure contained in that reservoir. In fact, there is negative pressure, or suction, because the fuel is pulled from the reservoir by the air passing through the carburetor throat. Fuel is pulled out of the reservoir and metered into the air flow via an orifice or jet. There is some pressure in the fuel system from the action of the fuel lift pump. The pump pulls fuel from the fuel tank by negative pressure (or suction) and lifts it to the engine. Then fuel flows under a slight pressure from the output of the pump to the carburetor bowls. An inlet valve operated by a float in the carburetor bowl admits fuel to the bowl as needed to keep the fuel level in the bowl constant. If there were low fuel pressure, the remedy would be to replace the fuel pump.
jimh	posted 09-21-2009 07:56 AM ET (US) A little more research on your c.2000 Mercury V6 135-HP engine revealed that it is a 60-degree V6 2.0-liter block. I believe this is quite a famous engine in the Mercury line, often used in racing, and respected as a durable and high-performance engine. Before abandoning this engine because its cylinder pressure readings were low, I would try some de-carbon remedies. Add some solvents to your gasoline to remove carbon deposits. In some cases poor cylinder pressure is caused by carbon deposits on the piston rings. Removing some of the carbon can often restore higher pressure to the cylinder.