120 HP Johnson Bogs down

[Fishing PoleLuck]

My 120 HP Johnson runs fine but after awhile bogs down an won't speed up again.

 

[racerone]

Model # is ?------Did this issue start suddenly ?----Checked for water in the fuel. ?---Overheating and going into S.L.O.W.

 

[Fishing PoleLuck]

Thanks for your help Racerone,
I just bought the boat it's a : [h=1]1990 Johnson VJ120TLESB 120hp Outboard Motor[/h] I am restoring it. Only been in the water a couple weeks now. Taken it out 4 times and each time runs great for awhile, a few miles, then bogs down & won't speed up, shutters if I try to speed back up. Before I put it in the water, I put in a new impeller & both Thermostat, put in new water separator filter. Took off the VRO pump put on a new fuel pump & hand mix oil & gas. I don't think it's overheating, but yes he goes slow. I disconnected the key alarm, when I turn on the key it beeps like it should then without the motor on, after a few minutes it beeps a solid constant sound, so I pulled the wire too it. I'm going to hook up a temperature gauge to see if it is overheating. I bought a lazier heat thermostat..I'll check with that also.

 

[boobie]

Do a cylinder drop test on it when it's acting up. You may find out something.

 

[ecu1984]

Have someone pump the bulb while it's bogging down and see if it picks back up.

 

[ct1762@gmail.com]

sure sounds like an overheat alarm to me

 

[Fishing PoleLuck]

Thanks everybody for your help. I Ran a Temp test today. I think over heat is the Problem. The Port 2 cyls. ran an avg of 130* to 145* while the Starboard side 2 cyls. ran an avg. of 90* to 100*. I didn't run it out long enough to see if it bogged down again. Now I have to find out why one side runs so much hotter! What could be plugged or what can I do to get more water to flow on the Port side?

 

[racerone]

What fuel pump was put on ??----Part # of the pump ?----Pictures of the pump ?----With those temperatures it does not appear to be overheating to me.-------Help yourself and post your compression numbers here.-----Then tell us if spark will jump a gap of 3/8" ( 1 cm ) or more on a test device.----Test run with a timing light hooked up one cylinder at a time to see if a cylinder has spark issues.------Look into each carburetor bore with a strong flashlight and compare fuel coming up the main nozzle at full throttle.-----This should be easy to figure out.-----Perhaps you bought somebodies problems here.

 

[Fishing PoleLuck]

[h=1]Fuel Pump for Johnson Evinrude OMC used on many 25-125hp engines from 1997-2005 Part # 438559 It's a Pulse Pump to replace the VRO. I hand mix the oil. Good compression of 135 lbs on all 4 cyl.[/h] I don't understand why one side runs hotter than the other? I replaced all the plugs w/new and the old ones looked wet & brownish like they should! I am going to use Seafoam to clean the carbs so i'll check for fuel flow then. I'm going to have to run it till it goes into the bog down and check the temp. on the heads to see if it overheats.

 

[racerone]

438559 may not be able to keep up with fuel demand of the big V-4 looper engine.

 

[Bosunsmate]

Its odd the starboard bank is running so cold yet youve put in new thermostats. Id swap them and see if the temp issue changes bank, occasionally a new thermostat will be faulty. If its not that then id be looking to see if the last owner has modified the system in some way, or one of those cylinders is not firing right

 

[ct1762@gmail.com]

as stated, the starboard side is up higher and thus gives water a tougher time reaching the top. are you getting your port and stbd sides mixed up? if not, make sure the grommet around the t stat is in good shape and not leaking, letting too much water cool the motor down on port side. that motor is 125-152 degrees at 900rpm, about 160 at the highest at wide open throttle so your temp on port side looks perfect