Tried Everthing to Fix Fuel Pressure on 99 90hp Johnson

Bwil

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Apr 11, 2016
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14
Boat ran great for a year before trash got into fuel filter, making boat run rough and shut off. I rebuilt carbs, adjusted floats, replaced intake gaskets, cleaned tank and it has never been able to go without bogging and starving. I think there is not enough pulse pressure to operate fuel pump. Compression is 100-105 on cylinders. Below are other things tried:

- Install gauge between pump and carb with clear hose to verify pressure and air bubbles (low in my case with new and old pump, no bubbles for me)
- Bench test pump using proper procedure (good in my case)
- Test vacuum between pump and tank (high indicates restriction. I used MityVac to test. No restriction for me)
- Install new pulse limiter and check that pressure coming from fitting/hose when cranked (helped some in my case, but pressure not real strong)
- Check pulse limiter hose going to fitting on pump for leaks, cuts (good for me)
- Run off portable tank with hose directly to pump (didn't make difference for me)
Here is link to test video:
https://youtu.be/I63im862224
 
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flyingscott

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Apr 8, 2014
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That motor does not sound good need the model #. What have you done with the ignition especially if you have the OIS system a bad sensor will cause that problem. Also recheck the compression that seems low if it's a looper.
 

Bwil

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Apr 11, 2016
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Compression checked twice. No test to ignition. Model is J90Pleeb. Pressure should not go from 3 to 0. Not sure why its doing that. Next test will be with temp electric pump regulated to 4psi bypassing vro. Want to test if engine runs right with correct pressure.
 

flyingscott

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Instead of hooking up a electric fuel pump just pump the primer and see if it changes. You will see fuel pressure fluctuate in a carbureted motor it is not a regulated system. Because the floats in the carb open and close needle valve it causes a fluctuation in pressure. Is the motor flooding a bad needle valve in the carb will cause excessively low fuel pressure because it never seals or a bad float and or float bowl. You seem to be fixated on a fuel pump that bench tested good might be time to look at some other possible issues.
 

Bwil

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Apr 11, 2016
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No real noticeable change when pumping bulb, just me so did not try while driving to see if I could plane. Bulb helped keep boat on when trying to shut off. New floats and needles on rebuild. System holds pressure from bulb when off so floats/neeedles working.
 

ondarvr

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Apr 6, 2005
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11,527
No real noticeable change when pumping bulb, just me so did not try while driving to see if I could plane.

If there's no change when squeezing the bulb, then the fuel pump is working, but you need try it at the RPMs where it's bogging.
 

Bwil

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Apr 11, 2016
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Thanks, I will try that and let you know how it works this weekend hopefully
 

Bwil

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Apr 11, 2016
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Ok, kept the electric pump on since there was nobody to drive while I pump bulb. It delivered 3,5 psi constantly. I plugged off the limiter hose so vro pump did not work. The fuel is mixed 50:1. Still no power to take off. Engine never shut off. Plugs are oil fouled bad so think I will try new plugs. I guess weak ignition or enough fuel not making it to cylinder????
 

slimdaddy45

Seaman Apprentice
Joined
Jul 11, 2007
Messages
45
Dont sound like its hitting on all four could be plugs is the plug wires on right could be flywheel key throwing could be sheared just a tad unscrew the flywheel nut and look to see if it is that motor is missing
 

racerone

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Dec 28, 2013
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????----Well, there is no flywheel nut on that motor and there is no flywheel key !
 

juno pierrat

Petty Officer 1st Class
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Dec 14, 2013
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355
learned something new early today, looked at parts diagram, no flywheel nut, 5 bolts, WOW
 

Bwil

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Apr 11, 2016
Messages
14
Wires are on correct, ran all last year with this setup. Will have check ignition next time out. Tganks for replies.
 

Bwil

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Apr 11, 2016
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Starting to think my floats could be the issue...I adjusted the closed height to proper spec but the open height was maybe 1/16 outside the range. I had to bend the tabs on float to adjust as I installed the nylon gasket in kit under the needle seat. This seat gasket was not on my carb when disassembled and in last working order. This is the only variable I can think of. Maybe its running too lean from extra float drop????
 

Tim Frank

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Jul 29, 2008
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Did you actually remove and check the high speed jets when you R&Rd the carbs?
 

flyingscott

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Apr 8, 2014
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Starting to think my floats could be the issue...I adjusted the closed height to proper spec but the open height was maybe 1/16 outside the range. I had to bend the tabs on float to adjust as I installed the nylon gasket in kit under the needle seat. This seat gasket was not on my carb when disassembled and in last working order. This is the only variable I can think of. Maybe its running too lean from extra float drop????

I don't think the float drop is causing you problem float height is much more critical than drop. Unless you have no float drop
 
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Bwil

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Apr 11, 2016
Messages
14
Finally some progress...I can get on plane now, but not full throttle. I did not install high speed jets on last rebuild (rookie move). I rebuild carbs, cleaned base and screens ALL OVER AGAIN. I flushed fuel system before hooking up to carbs THIS TIME and noticed particles from what had to be the fuel lines after the filter (figured particles must be whats making it starve and bogg). Installed new hoses and flushed again to make sure fuel clean, then finished hooking up. Electric pump still hooked up, I will hook original pump back up and test again to see if high speed can be reached...will let you know!
 

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