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  1. #1
    Join Date
    Jan 2010
    Location
    decatur, alabama, morgan
    Posts
    4

    Default 1988 Johnson 175 GT fuel starvation

    Hello I have a 1988 Johnson GT 165 model number J175stlccm. My problem I'm having is at higher RPMs there is a fuel starvation. Things I have done so far.
    Replaced VRO pump(mixing 50:1)
    Checked Pulse Limiter
    Replaced spark plugs
    Rebuild carbs
    Replaced primer bulb 3/8 from tank to motor. I've tried 3 different ones.
    Replaced all fuel lines in motor
    Replaced inline fuel filters
    Checked tank vent. Have ran motor from a portable take with same problem.
    Replaced water pump
    Checked Spark
    I have also done a decarb on the motor it needed it pretty bad.
    Checked compression 75PSI across all cylinders.
    Took apart VRO pump and inspected and tested per testing procedure. Tested good.
    I have 2 clear inline fuel filters installed. One before the VRO pump and one after pump before it goes into the carbs.
    When running on muffs I can watch the gas being pumped into the fuel pump filter stays fuel. The filter after the pump gas is being pumped into in but filter never gets full even at idle. But motor never stalls. Once I but motor in water and under load. Same thing idles great can run motor up using the cold start gas flow increases from pump never stalls. When it's in gear up to about WOT throttle about time boat wants to get up on plane it just bogs and dies out. I can manually pump it to keep it running somewhat but doesn't help much. I know the fuel pump gets its pulse from the crankcase but I can't find any problems anywhere.

  2. #2
    Join Date
    Oct 2019
    Location
    Near Folsom Lake in Northern CA
    Posts
    362

    Default Re: 1988 Johnson 175 GT fuel starvation

    If your compression guage is accurate your motor needs to be rebuilt. Find another guage to rule that out.

  3. #3
    Join Date
    Jan 2010
    Location
    decatur, alabama, morgan
    Posts
    4

    Default Re: 1988 Johnson 175 GT fuel starvation

    Ok I have checked compression with 3 different gauges 1st gauge read 80 on all cylinders.
    2nd gauge read 83 on all cylinders and 3rd gauge 75 on all cylinders. I was told these were low compression motors and that the compression was good fir a 33 year old motor. My neighbor has a 150hp same year and his compression is 84 on each cylinder and he said it's always been that way ever since he bought it 15 years ago. I may have been miss informed but all my research online dies say these are low compression motors. The manual doesn't say what the compression should be.

  4. #4
    Join Date
    Oct 2019
    Location
    Near Folsom Lake in Northern CA
    Posts
    362

    Default Re: 1988 Johnson 175 GT fuel starvation

    I could be wrong but I think an outboard built in 1988 should be around 120. I've heard many outboards built in the 60's had compression down in the 75-80 psi range. Hopefully others with more knowledge than I will provide their opinions.

  5. #5
    Join Date
    Oct 2019
    Location
    Near Folsom Lake in Northern CA
    Posts
    362

    Default Re: 1988 Johnson 175 GT fuel starvation

    Having said that low compression affects starting and low speed operation more than high speed operation.

    How did you check the spark?

  6. #6
    Join Date
    Jan 2010
    Location
    decatur, alabama, morgan
    Posts
    4

    Default Re: 1988 Johnson 175 GT fuel starvation

    Spark was checked with inline spark tester at idle speed. Also pulled spark plug wire while at idle to verify spark on each cylinder. Notice engine change each time plug wire was removed for each cylinder. I did notice while trouble shooting a flywheel magnet has came unglued and shifted over so there is large cap between 2 magnets and no gap between the other. I'm in the process of removing flywheel to reattach magnet but I don't think thus could cause a fuel problem. I did notice while checking the carbs. I placed my hand over all 3 carbs not completely covering it and can feel and hear good amount of air being pulled in. Reeds look good also. I then placed hand over each carb for a brief second and can get fuel to come out of the top and middle carb but none out if the bottom. Could I have a stuck needle in this carb not allowing enough fuel to it. Motor runs fine in idle on muffs and in water under load. On muffs I can Rev the motor o problems never dies only reving for maybe a min. In water under load can Rev motir to higher RPMs no problem problem only seems to come when under way trying to get on plane.
    Last edited by btowe05; 07-20-2021 at 03:44 PM.

  7. #7
    Join Date
    Oct 2019
    Location
    Near Folsom Lake in Northern CA
    Posts
    362

    Default Re: 1988 Johnson 175 GT fuel starvation

    Sounds like your bottom carb needs attention.

  8. #8
    Join Date
    Jan 2010
    Location
    decatur, alabama, morgan
    Posts
    4

    Default Re: 1988 Johnson 175 GT fuel starvation

    I inspected the piston and cylinder walls today. All look good except for the large amount of carbon build up. Noticed that the head gasket on #5 cylinder had deteriorated. I now have 2 head gaskets on order. I did notice on the starboard head #3 cylinder there seems to be some pitting on the concave part of recover. That the piston goes into. What would cause this?not any on the surface to mounts to the block. Should I just replace the head or would it be OK for now until it get the fuel related problem solved. I found one on Ebay fir 60.00 but don't really wont to spend the money if I can't get the fuel problem solved. Tve piston and cylinder wall on #5 and all others look good you can how ever tell there has been some water infiltration on the starboard head. The motir was given to me so don't have alot of money in it at the moment but if it's nor worth fixing I'd rather just cut my looses and repower.

  9. #9
    Join Date
    Oct 2019
    Location
    Near Folsom Lake in Northern CA
    Posts
    362

    Default Re: 1988 Johnson 175 GT fuel starvation

    Pitting can be caused by a foreign object in the combustion chamber. If the head is pitted but not the cylinder it's possible the piston was replaced at some time. I would not replace the head due to pitting. If there are sharp edges on any of the pit marks just smooth them out with a dremel type tool and/or sandpaper. Is the bore standard or oversize? At this point I would focus on the bottom carb.

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