Does anyone know how the fuel pump is supposed to work/feel in a 1994 CBR900RR ?
Mine is kicking in every 2-3 seconds, like pulsating in a low frequency when idling and if I rev up the engine a bit the frequency of the pulsation increases, Is it supposed to work like that? If I remove the pump from the bike and test it on the bench it will pump continuously. What could be the issue here or is it normal? Please advise

 

This is how it works - it pulses in relationship to the RPM of the motor.

 

You also need to remove fuel-pump relay and ignition-system to bench test. Here's how connections go:

Ignitor --> fuel-pump relay --> fuel-pump

Fuel-pump relay is triggered by same ignition-pulses that fires #2 & #4 ignition-coil. Then relay amplifies signal and powers fuel-pulp with higher-powered pulses.

At idle & low-RPM, when there's small fuel demands, there's fewer pulses per second and small flow of petrol. At higher RPM, there's need for more fuel and there's more pulses per second. Quite an ingenious solution!

 

Dannoxyz - Thanks for the explanation, an ingenious design indeed :-)
This is really interesting, now since the fuel pump relay is triggered by the same pulses that goes into the ignition coils I think the pump should "tick" with a bit higher frequency than once every 2 or 3 seconds - right? This would equal to 20-30 pulses per minute. Say the bike is idling at 1000rpm and due to the ignition systems nature the plug is fired twice for every cycle (spark + wasted spark) so we should get about (1000 pulses :60 seconds) 16-17 pulses per second, right? What am I missing here?
Short video where you can see the" fuel squirt frequency" when idling: https://photos.app.goo.gl/TtDGqmVxgbGrs8Zo8

I do not seem to have an issue with fuel flow from the pump when testing on the bench, when pump is directly fed with 12V to the terminals but the issue (if it is an issue?) seems to come into play when the pump is installed and the command pulses from the ICM start to dictate the pace of the fuel system.
Please comment - should the pump operate at a higher frequency than 20 - 30 times a minute at idle?

Thanks!

 

What problem are you trying to fix / understand? Might help to inform your question.

 

Pump is reciprocating design with toilet plunger that goes back & forth. Final control layer is mechanical clicker on bottom, similar to old style ignition systems. Voice-coil/solenoid on click accumulates relay pulses unil there's sufficient power to generate one click. Pressure in output fuel-line also affects how much force is required to generate one click/one pump. All this leads to variable number of relay-pulses needed for one pump click.

https://cbrforum.com/forum/stickies-...l-pump-102151/

Good upgrade to improve reliability of pump is replace mechanical clicker with solid-state version. Someone here did write-up, but I can find it. Here's another guide.

http://www.ktm950.info/how/Orange%20...itsubishi.html

 

If you're having issues with fuel-delivery into engine, inspect petcock, fuel filtre and carbs next. You can do bypass test and squirt 2-3cc petrol into airbox, wait 30-sec for it to vapourise, then start bike.

It bike's been sitting for more than 3-months, most likely carbs are clogged and needs complete disassembly to every last nut, bolt and individual component for restoration.

 

Hi Al, good point.
The problem I have is that the engine dies after a while. It seems like the bike is not getting fuel and I wanted to understand how the fuel system works and if the carburettors are getting enough fuel. I have dismantled the carbs and cleaned them, new filter, no kinks on the fuel pipes but I was wondering if the fuel flow from the pump, when installed, is sufficient or not

 

Thanks Dannoxyz !

Yes I have cleaned the fuel system very carefully, All components has been cleaned, the carburetors has been dismantled completely and every component has been cleaned in ultrasonic bath, 2 times actually. There is free passage for the fuel, new filter has been assembled as well.
The symptoms my bike has is like it is running well sometimes but very often it feels like it is only firing on 3 cylinders or less, then recovering again and eventually dies completely. If I wait for a minute the bike may start and I can get it back home .. barely. I have new plugs, coils, cables, ignition key socket+cables, new killswitch... just for the record. .I have not made a thorough diagnosis of the pump itself or the relay but I will jump on that now, Thaks for the links and info!
Stay tuned :-)

 

Run it with the fuel cap open - you would be shocked how many times the air vent gets blocked and causes exactly this problem.