I recently bought a 2000 F4 that had been stood for approximately 18months. After installing a new battery and flushing out the tank I turned her over and fuel was gushing from the carb drain hose and so I suspected one of the floats had become stuck.

I then went about taking off the carbs and giving them a good clean. I took all the floats out and cleaned the chambers on the fuel side including floats/valve/pin etc. I then checked the vacuum chambers and cleaned the jet needles and replaced the diaphragm carefully.
After reassembly I turned her over and there was no more fuel gushing from the drain hose

She idles fine on full choke but then as soon as you turn the throttle she cuts out (even when warm). It’s possible to get the revs going a little bit by caressing the throttle gradually but she doesn’t run smoothly and then when you drop the revs to idle, she’ll cut out.

I’ve read lots of posts on here but nothing has worked for me yet. Originally I thought it was a vacuum/fuel issue. But all the vacuum lines are as they should be; all the carb clamps/hoses are tight. I’ve had the carbs off a second time to make sure all the diaphragms are seated correctly. I’ve installed a brand new set of spark plugs and air filter. I then checked the ‘slow jet’ to make sure it was clear of any debris. I noticed these were screwed all the way in (I hope this is right?). I also fiddles with the idle screw, but this didn't help. The issue remains.

Does anybody have any suggestions as to what the problem may be or what I should try next? Please state anything obvious as these problems are usually caused by something silly! But I’m thinking the problem is caused by it being sat for many months, or by miss-assembly.

Thanks in advance, Howard

 

The screws that you mention are probably mixture screws and shouldn't be screwed all the way in. Back them off about half a turn then in again gently, to just seat them. Now turn them out 3 turns as a starting point. Warm the engine up to normal operating temperature, then see if the idle is ok. If it is a bit erratic, turn each mixture screw in or out by exactly the same amount and listen to the engine to see if it speeds up or slows down slightly. You need to set each screw the same to achieve the best idle speed of around 1300 rpm. If this doesn't improve things, take the carbs off and turn them upside down and check the float heights, by measuring the distance from the face of the float chamber, without a gasket, to the top of the floats. This distance should be 13.7 mm +- 0.50 mm. There should be a small metal tang that you can bend gently to lower or lift the floats. Be careful not to break these tangs off! LOL! It sounds as if you are not getting enough or too much fuel and having the floats set at the wrong height would cause your problem. There could of course be other reasons for your poor running CBR, but try my suggestions first. At least you'll know it isn't the float heights or mixture screw settings that are the reason. Hope it works out, but get back to me if not.

 

highwaypatrol has you on the right track..
but honestly it took me three full cleanings on my carbs with 150 psi compressed air to really get everything out.. and my bike had been sitting for as long as yours or maybe a tad more.. actually i had scrap the sides if the fload needles with my thumb nail because it sat so long and some crud built up on them and they wouldnt move freely..anyway after the third full cleaning my bike started running right and been driving it ever since everyday for the last six weeks.. oh and the reason why i answered this is because my carbs had the same sysmtems.. gas coming out drain plug.. anyway it all cleared up..just dont lose your cool.. youll get it.. just imagine if you sent it to the dealer..
what that that bill would look like..
just to add something highway was saying, if the bike is piped it most likey has been jetted too, so turning your screws out three turns as a starting point is good , but if its jetted i think it will actually be an extra turn "4"to allow more fuel to go through..
jay..
ps.. once get this squared.. come answer my post on suspension..

 

This is a helpful thread, mine is having the same problem. I got a bike, replaced the engine, but I used to carburetor off the old engine. It spews out gas off the Y connector going into the right side of carb. I already cleaned the jets and checked the floats, but now im going to do a complete tear down, and try by turning the screws to you guys recommendation. Useful information thanks guys

 

Just to clarify, are you guys talking about the 'Pilot Screw' or the 'Slow Jet' as depicted in the following image?

 

The slow jet should be fully seated. The pilot screw is what is used to change the air/fuel ratio from idle to around 1/4 throttle. I'm not sure how many turns out the base setting is on your bike, but on mine for example the base settings are 2.5 turns out from seated. Lightly snug each pilot screw down and then back out each one the appropriate amount of turns which will get you in the ball park. You still have to fine tune the mixture according to the service manual.

Your problem to me sounds like there is still debris in one or more of the jets causing it to run lean. The best way to clean them is to remove each slow jet and spray it out with carb cleaner & compressed air.

After making sure the carbs are clean and the mixture adjustment is set correctly it will hopefully start and run well enough to check the sync. This is also very important since if the carbs are out of sync far enough it will run like crap no matter what you do. As far as backing out the mixture screw more because it has a jet kit it's not necessary. The jet kit replaces the main & needle which is not affected by the pilot screw as it mainly controls the mixture in the idle circuit (slow jet).

 

thats why i said it took me three full cleanings... tahoeriders description is dead on, unless the bike has had larger jets installed already, if so you'll need to turn the pilot screws (4) one in each carb out, more than what is the normal stock setting..
For instance my bike was piped and jetted when i bought it recently and i did a cleaning now i have two identical 95 900's that exactly the same on my pilot screws the stock one was two and half turns out and on the jetted one it was 3 1/4 to 3 1/2 turns out to allow more gas and air.. look when you get it all figured out you will be on top of the world my friend.. and you'll know how it all works.. which is nothin g but good for you..
jay