1992 Johnson 90 bogs down at hig RPM

[Jupiter]

My suntracker 24 will start and run great up to about 3500 RPM. At 4000 RPM it will bog down. If I squeeze the fuel tank primer bulb it will recover, but only temporarily. If I pull back the throttle it will continue to run fine at 3500 RPM. I changed the fuel filter and the down steam fuel line, but did not change the symtoms. The advice I have seen so far leads me to suspect the VRO fuel pump. A rebuild kit is $30 and a new pump $400. If I rebuild the pump is it possible that the electric motor driving the pump could be weak?

 

[kenmyfam]

Re: 1992 Johnson 90 bogs down at hig RPM

Sounds like either an air leak in the fuel line somewhere or the fuel pump failing.
Electric motor ??????
Welcome to iboats

 

[Jupiter]

Re: 1992 Johnson 90 bogs down at hig RPM

Sounds like either an air leak in the fuel line somewhere or the fuel pump failing.
Electric motor ??????
Welcome to iboats

I don't fully understand how the VRO fuel pump works. Does the fuel pump operate by an eletric motor or is it driven mechanically? What allows the pump to supply enough fuel at 3000 RPM but not 4000+ RPM? What checks are there to determine if the problem is an air leak?

 

[tashasdaddy]

Re: 1992 Johnson 90 bogs down at hig RPM

the Vro pump is mechanically driven, by air pressure pluses from the crankcase. do you have 3/8 fuel line to the motor, any kinks in the fuel lines, when was the last time the carbs were properly clean, and used rebuild kits. rarely is it the fuel pump. is the vent open on the fuel tank?

 

[kenmyfam]

Re: 1992 Johnson 90 bogs down at hig RPM

I don't fully understand how the VRO fuel pump works. Does the fuel pump operate by an eletric motor or is it driven mechanically? What allows the pump to supply enough fuel at 3000 RPM but not 4000+ RPM? What checks are there to determine if the problem is an air leak?

May well not be the pump as TD says.
If the diaphram starts to fail then less fuel will get through to the carb's. Maybe enough to continue to run at lower rpm but not enough to run at the higher end. These were the symptoms that I had when my old VRO pump started to fail.
Does not mean that is your particular problem though.
You could do a fuel flow test if necessary but if the carb's have not been serviced for a while you should do them first. Check for venting and fuel line kinks though as TD says.

 

[Jupiter]

Re: 1992 Johnson 90 bogs down at hig RPM

May well not be the pump as TD says.
If the diaphram starts to fail then less fuel will get through to the carb's. Maybe enough to continue to run at lower rpm but not enough to run at the higher end. These were the symptoms that I had when my old VRO pump started to fail.
Does not mean that is your particular problem though.
You could do a fuel flow test if necessary but if the carb's have not been serviced for a while you should do them first. Check for venting and fuel line kinks though as TD says.

Venting is good and no fuel line kinks. The fuel/VRO pump rebuild kit seems like a inexpensive alternative to a new pump. It look fairly easy to rebuild. Does anyone have experience with rebuilt or rebuilding these pumps?

 

[kenmyfam]

Re: 1992 Johnson 90 bogs down at hig RPM

Rebuilding is not a difficult thing to do. However as stated earlier this may not be the issue.