FJ 1200 3CW fuel issue (pump or relay or something else?)

[mikkorna]

Hello,

I have ridden with my 1990 3CW about 10 000 kilometers in 2 years.

Last summmer (2023) I had strange issue with fuel supply; Bike was running well for several months with constant use but one day the fuel pump provided too much fuel and the extra fuel leaked from the overflow hoses to the ground while I was driving. This sympton was only on one day. I cleaned the electrical plugs (fuel pump and relay) and after that I hadn't faced the issue anymore on summer 2023.

This year the same issue has occured several times. I ordered new fuel pump and it worked well couple of days but now the same issue occured again. Can it be the fuel pump relay or is it more likely something with the wiring as I face this issue only now and then? I will have a new relay soon but I was wondering if that helps as the bike works well most of the time?

PS. When changing the fuel pump I noticed that the hoses were installed with wrong aligment (wrong hose to "IN" marked hole) but the bike has still worked well 2 years before I now changed the pump couple of weeks ago...

Thanks in advance for any kind of assistance.

[FJmonkey]

The fuel pump is not likely the problem, you are getting fuel. The valve seats in the carbs are worn or have some crap holding one or more slightly open. They are the main control to prevent the carbs from flooding. The open hoses are vent lines and need to be open. Might be time to get your carbs cleaned. Rand and sons at RPM does a great job if you want to go that way.

[mikkorna]

The fuel pump is not likely the problem, you are getting fuel. The valve seats in the carbs are worn or have some crap holding one or more slightly open. They are the main control to prevent the carbs from flooding. The open hoses are vent lines and need to be open. Might be time to get your carbs cleaned. Rand and sons at RPM does a great job if you want to go that way.

I still think the problem is with electrics as the pump clicks too often when the problems occurs. If the carbs were bad I think I would have the flood all the time?

Today I drove about 60km and there was no symptons.

[FJmonkey]

Think about it this way.

What stops the pump from pumping when it is powered, other than a 5 secondish time-out when the engine is not running?

The answer is pressure. When the floats rise in the carbs due to a FULL condition, it forces the plunger up and stops the flow. The fuel pump only has one input other than power. Either it can pump, or the pressure is too great and it cannot. The next suspect is also a KNOWN suspect to cause this problem. The floats and seals.

Some have managed to unstick a float by different methods.

Keep at it, you will find it and fix it.

[mikkorna]

Think about it this way.

What stops the pump from pumping when it is powered, other than a 5 secondish time-out when the engine is not running?

The answer is pressure. When the floats rise in the carbs due to a FULL condition, it forces the plunger up and stops the flow. The fuel pump only has one input other than power. Either it can pump, or the pressure is too great and it cannot. The next suspect is also a KNOWN suspect to cause this problem. The floats and seals.

Some have managed to unstick a float by different methods.

Keep at it, you will find it and fix it.

Thanks. I think I believe you now Maybe I have to start with the new needles to to carbs as I don't have any information when those are changed last time.

That is a job I can't(and don't want to ) do by myself but I have couple of goods bike services here in Finland also for older bikes