CBR F3 fuel pump flooding
 

I pulled the carbs off and gave them a very thorough cleaning. After install, the fuel pump goes nuts now and makes gas pour out of every bowl. I'll pull the carbs again and check the float needles, but maybe there's something wrong with the fuel shutoff relay?

Any help appreciated.

you can try bypassing the fuel pump all together. Just connect directly from your tank and see if the issue persists. That will tell you if your issue is pump or carb related.

I used an IV style fuel bladder to feed gas to the carbs while I was balancing them, and if I held it too high the bowls would overfill. From my understanding, the fuel pump shuts off when the current draw from the pump gets high, caused by the strain of the pump pumping against the closed needles, so if the needles aren't seating properly then the pump never shuts off.


I have a sneaking suspicion that it could be leaking from bad o-rings at the T-joints between the carbs...

Just to put a final update to this thread, it was the t-fitting o-rings that were leaking. Float valves sealed up great.

Check vid for diagnosis video -->

Thats a common issue for these carburetors, the O rings get old and brittle. If you move them in any way, they'll start to leak. Glad you found the cause.

I got the bike back together and balanced the carbs. It runs awesome, very good throttle response. I tried tuning the pilot screws with the tachometer procedure outlined in the manuals, but there was no rpm swing when adjusting the pilots.

I started with 2 turns out. Idle at 1200
Intake/filter on and all piping done up.
Rpm would only drop when I bottomed out the pilots, other than that it would only fluctuate maybe 20 rpm...

I dicked around with it for an hour then just set it based on throttle response. Best was 1.75 turns out and my IR thermometer measured very even temps across all the exhaust tubes. ~280F

Anyone got any recommendation on how to fine tune these stupid carbs?

Are you using a bench tach? When doing carb work I find that to be much more useful than your bikes tach as it is far more accurate. Since the gradients are more spaced out you will see small changes in greater detail.

Also, always remember to bring the rpm back to 1,200 withe the idle adjustment knob after each carb.

No I'm using one of . Induction tach off one of the spark plug wires. Seems to work pretty well, refresh rate could be better but it works for idling. The rpm would swing maybe 30 max between pilot open and closed.

I've never used one of those before. Try this. Instead of using the plugs, there is a terminal on the back of the instrument cluster. Try attaching the wire to that. See if that works. I have no idea if it will or not, but it's worth a try.

Here's a video of how the tach looks when its working, go to ~4:40 (not my video). I can't connect it to the dash I don't think. And I can hear the engine rpm change.

The issue I'm thinking, is the step in the procedure that says turn the #3 carb pilot screw in gradually until the engine speed drops 50 rpm. The only way I could possibly get a 50 rpm drop is by bottoming out the pilot.
I'm not having a tach problem I just can't get the pilots to cause an rpm change. **** I'll just go build a sniffer with a wideband and do it my way!