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Author Topic:   High fuel rate 1989 Johnson 3cyl 70 HP

Sfef84 posted 05-30-2012 11:41 AM ET (US)
Just installed fuel flow sensors for my 19 Raider with twin 1989 Johnson 70HP outboards. The readings at idle are 1-1.5 gal/hr EACH. It doesn't seem like the motors should be burning an average of 2-3 gal/hr at idle.
Preface:
-The Lowrance manual states that each sensor is factory calibrated to 3% accuracy.
-No smell of gas under cowling
The consistent readings (port and starboard) lead me to believe that calibration is not an issue.
What can cause high idle fuel consumption?
What should be the idle/wide open fuel rate (for a single 2 stroke 70hp Johnson)?

newt posted 05-30-2012 12:47 PM ET (US)
I was planning on replying to your other thread after using my boat with twin engines and Lowrance EP-60 fuel flow sensors installed, but forgot to check the flow rates or grab my log book this past weekend.
Hopefully tomorrow night I will run the boat and compare notes with you. In the mean time, this is what I have noticed about the Lowrance sensors.
First thing to check is that the sensors are configured for port and starboard and that you are not inadvertently reading combined fuel flow from both. I mention this, because my sensors came factory configured both as starboard. If you have already done this, then disregard the following: Be very careful when changing configuration settings for those sensors. DO NOT delete the sensor from whatever head unit you are using to read the data. Once you delete the sensor, it will never again show up when you scan for devices, and the only fix is to send it back to Lowrance for a replacement.
Second, I question the instantaneous accuracy of these sensors with carburetor engines. My fuel flow readings jump all over the place. Perhaps this a result of the pulsing in the fuel lines due to the crankcase pressurized fuel pump, or the VST filling up and draining to the carburetors. I don't know the reason, just that I have noted fuel flow and fuel economy readings are too sporadic to get good real time info without doing some mental averaging. I have not found a way to set up the sensors to sample less frequently or average the flow for a few seconds. If you figure this out, please share.
I would suggest that you try averaging the data yourself and see what you get for idle fuel consumption. Try resetting your fuel used to zero, then after a measured amount of time take down your fuel used value and multiply it out to see what you would burn in an hour. For example, reset the fuel used, idle your engine for two minutes, then multiply your fuel used times 30 to see what your hourly rate would be. This would at least confirm the accuracy of the instantaneous values you are getting.
I will have more to add in a couple of days.
Sfef84 posted 05-30-2012 01:38 PM ET (US)
Just the response I'm looking for!
OK:
Setup: I noticed that both of my sensors show up as Port on the device list. Each sensor has it's own IP address. Stupid question: does the physical name on device list matter?
RE: totalizing; Its not totalizing form both sensors because on the HDS dashboard, I added Port fuel flow and Starboard fuel flow to the screen and when ONLY the port is running I get a reading on the Port fuel rate and 0.00 on the Starboard fuel rate window. When both motors are on, the total fuel rate for vessel is around 2.5-3 gal/hr
At WOT; My GPS SOG is 37-39 mpg with a GPSecon of around 2 mpg
(never looked at the gal/hr for each motor at that speed but simple math equals about 10 gal/hr per motor.
Cruising at 28-30mph gives me the best economy at around 2.78mpg with a total range of 175 miles (63 gal tank). USCG rule of thirds puts me at almost 60 miles before returning home. Not too shabby.
The idle and trolling speeds are what kill me. At 0-6 mph my economy averages 1.3 mpg with both motors on. With one motor off and trimmed out of the water, the economy improves to about 2-3 mpg.
What kind of whaler/engine set-up do you have?
newt posted 05-30-2012 02:21 PM ET (US)
I have a Revenge 25 with twin Johnson 150's.
From some limited notes I have on hand:
At WOT, I am burning a combined 34+ GPH.
At 1250 RPM, each motor burns 3.5 GPH
I always shut down one engine (but leave it in the water) when at no-wake speed. My best fuel economy at no-wake is not much different than at cruising speed - 1.4-1.6 miles/gallon.
Your numbers do not appear to be wrong, given that your engines are less than half the displacement than mine.
Regarding setting up your sensors - the physical description is necessary even thought they have separate IP addresses. If both sensors are set to Port, than both readings will contribute to Port. Try running only the starboard engine and you will probably see the fuel usage show up as Port. Your vessel usage and Port usage will always read the same if both sensors are set up as Port.
newt posted 05-30-2012 03:07 PM ET (US)
Just wanted to add that you will want to physically unplug one of your sensors, so that you can configure the remaining one correctly (port or starboard). Then, by default, when you plug the other sensor back in, you will know which motor the un-configured device belongs to.
sosmerc posted 05-30-2012 07:57 PM ET (US)
I would guess that WOT fuel consumption for each engine should be around 7 gph. Idle should be 3/4 gph each. Where are your flow sensors mounted in relationship to the engines?
Sfef84 posted 05-31-2012 10:56 AM ET (US)
Newt- Good advice. When installing, I connected both senders to the network and then powered up the head unit.
sosmerc- The senders are after my water separators.

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Author	Topic: High fuel rate 1989 Johnson 3cyl 70 HP
Sfef84	posted 05-30-2012 11:41 AM ET (US) Just installed fuel flow sensors for my 19 Raider with twin 1989 Johnson 70HP outboards. The readings at idle are 1-1.5 gal/hr EACH. It doesn't seem like the motors should be burning an average of 2-3 gal/hr at idle. Preface: -The Lowrance manual states that each sensor is factory calibrated to 3% accuracy. -No smell of gas under cowling The consistent readings (port and starboard) lead me to believe that calibration is not an issue. What can cause high idle fuel consumption? What should be the idle/wide open fuel rate (for a single 2 stroke 70hp Johnson)?
newt	posted 05-30-2012 12:47 PM ET (US) I was planning on replying to your other thread after using my boat with twin engines and Lowrance EP-60 fuel flow sensors installed, but forgot to check the flow rates or grab my log book this past weekend. Hopefully tomorrow night I will run the boat and compare notes with you. In the mean time, this is what I have noticed about the Lowrance sensors. First thing to check is that the sensors are configured for port and starboard and that you are not inadvertently reading combined fuel flow from both. I mention this, because my sensors came factory configured both as starboard. If you have already done this, then disregard the following: Be very careful when changing configuration settings for those sensors. DO NOT delete the sensor from whatever head unit you are using to read the data. Once you delete the sensor, it will never again show up when you scan for devices, and the only fix is to send it back to Lowrance for a replacement. Second, I question the instantaneous accuracy of these sensors with carburetor engines. My fuel flow readings jump all over the place. Perhaps this a result of the pulsing in the fuel lines due to the crankcase pressurized fuel pump, or the VST filling up and draining to the carburetors. I don't know the reason, just that I have noted fuel flow and fuel economy readings are too sporadic to get good real time info without doing some mental averaging. I have not found a way to set up the sensors to sample less frequently or average the flow for a few seconds. If you figure this out, please share. I would suggest that you try averaging the data yourself and see what you get for idle fuel consumption. Try resetting your fuel used to zero, then after a measured amount of time take down your fuel used value and multiply it out to see what you would burn in an hour. For example, reset the fuel used, idle your engine for two minutes, then multiply your fuel used times 30 to see what your hourly rate would be. This would at least confirm the accuracy of the instantaneous values you are getting. I will have more to add in a couple of days.
Sfef84	posted 05-30-2012 01:38 PM ET (US) Just the response I'm looking for! OK: Setup: I noticed that both of my sensors show up as Port on the device list. Each sensor has it's own IP address. Stupid question: does the physical name on device list matter? RE: totalizing; Its not totalizing form both sensors because on the HDS dashboard, I added Port fuel flow and Starboard fuel flow to the screen and when ONLY the port is running I get a reading on the Port fuel rate and 0.00 on the Starboard fuel rate window. When both motors are on, the total fuel rate for vessel is around 2.5-3 gal/hr At WOT; My GPS SOG is 37-39 mpg with a GPSecon of around 2 mpg (never looked at the gal/hr for each motor at that speed but simple math equals about 10 gal/hr per motor. Cruising at 28-30mph gives me the best economy at around 2.78mpg with a total range of 175 miles (63 gal tank). USCG rule of thirds puts me at almost 60 miles before returning home. Not too shabby. The idle and trolling speeds are what kill me. At 0-6 mph my economy averages 1.3 mpg with both motors on. With one motor off and trimmed out of the water, the economy improves to about 2-3 mpg. What kind of whaler/engine set-up do you have?
newt	posted 05-30-2012 02:21 PM ET (US) I have a Revenge 25 with twin Johnson 150's. From some limited notes I have on hand: At WOT, I am burning a combined 34+ GPH. At 1250 RPM, each motor burns 3.5 GPH I always shut down one engine (but leave it in the water) when at no-wake speed. My best fuel economy at no-wake is not much different than at cruising speed - 1.4-1.6 miles/gallon. Your numbers do not appear to be wrong, given that your engines are less than half the displacement than mine. Regarding setting up your sensors - the physical description is necessary even thought they have separate IP addresses. If both sensors are set to Port, than both readings will contribute to Port. Try running only the starboard engine and you will probably see the fuel usage show up as Port. Your vessel usage and Port usage will always read the same if both sensors are set up as Port.
newt	posted 05-30-2012 03:07 PM ET (US) Just wanted to add that you will want to physically unplug one of your sensors, so that you can configure the remaining one correctly (port or starboard). Then, by default, when you plug the other sensor back in, you will know which motor the un-configured device belongs to.
sosmerc	posted 05-30-2012 07:57 PM ET (US) I would guess that WOT fuel consumption for each engine should be around 7 gph. Idle should be 3/4 gph each. Where are your flow sensors mounted in relationship to the engines?
Sfef84	posted 05-31-2012 10:56 AM ET (US) Newt- Good advice. When installing, I connected both senders to the network and then powered up the head unit. sosmerc- The senders are after my water separators.