Hi there. Just registered to contribute with a bit of my personal non technical experience, since I've been reading posts with a lot of options and solutions, and taking and not giving is not something I enjoy even if I'm the one with the benefit.
So first of all you will all excuse my english because it's not my native language so, sorry for any mistake in advance.
I've been a rider since I was 16 of course I could only ride 50 cc in my country. I did for 15 years till I got tired of every 35000 km when I was lucky had to replace pistons and two stroke stuff. So I decided to go for a Honda and after my license I bought a Honda CB 500 and what a mess "she" was in. After lots of sweat time and money I got "her" where I wanted(better running than brand new) unfortunatly "she" turned into a pile of junk when some drive rear ended me on a red light (the car went to junkyard too and lucky I didn't). So when everybody thought I was through with motorbikes I thought otherwise and found myself a '99 CBR 600 F4 with 18000 km(If I'm to die let it be on something I really enjoy). Problem solved!!! It was as new... Till it started to stall and almost misfiring when on a red light. Same symptoms as discribed on several posts I've read. Here we go to the main. Since my 1st bike I've been kind of taking a beat on motorbike troubles I didn't panic. It seemed the solutions and symptoms would all match to my personal problem. But experience thaught me that if you can only guess what the problem is you can't know for sure (can't scale a storm just by the height of the waves). Here is what I did and still in progress. First the stalling problem started and it felt like as if timing wasn't correct or fuel was igniting randomly. Then I noticed the throttle wouldn't have a quick almost instant response as it should= there was delay and on that delay was somekind of misfiring that lead to stalling. So I ignored that problem because I couldn't locate it, and if there's a problem it can only get worse. Now my bike really stalls and hesitates so I went to wiring and fuel lines spent some time measuring charging capacity and all that was posted here and some other forums... When the cooling fan starts its cycle it's useless trying to go it'll definetly stop. Theory of not enough power to the spark plugs is correct but I found something that I didn't see before. In the direct ignition coil where the spark plug fits if you're not taking your time you wont notice that the coil might be deffective. Inside the coil there are two springed wires that grip onto the spark plug thread in my case they are still there but worthlessly since the only thing holding the spark plug is the outside rubber which means the current is jumping from the coil to the spark plug therefore not enough power symptom mentioned and experienced here by everybody that has the same problem specially when cooling fan is on. As for the hesitation problem I think it's somehow an independent trouble. Because if you pay enough attention to it you will notice the almost misfire resembles lack of fuel(tending to lean) but also a false air intake(air bypassing carbs=too much air=lean mixture). When i had the CB 500 i got that same trouble it wouldn't respond instantly the iddle was unstable( constant adjustement was required)... So I got new insulators and forgot to tighten one them... Cylinder nē1 was crazy and nē 2 was trying to balance the whole thing. So the best way to check for air leaks is to take parts on your hands and closely inspect them... Hope it helps, and don't expect to find the trouble for the first time, it's not the same as replacing some brake pads because you don't know the source of it... Finally do forgive if it's a too long post or inapropriate.

 

Welcome aboard Hondaowner. Thanks for giving back. ;-) You make some good points.

Its good to be able to share our experiences & glean benefit from them, & hopefully all help each other.

 

From what I've been reading here it looks like desperation comes 1st... And that's quite a valid reason to start spending money on parts without pin pointing the problem... The trusty mechanic even though bikes are his everyday won't sometimes locate the problem because it's a random fault and client can't afford hours and hours on diagnosis, it'll be interpreted as incompetence or picking the pocket...Faults are the hardest to fix since there's no way to reach them except by trying method on modern bikes think it's already possible to connect to a diagnosis pc and check out troubleshoot codes but those won't pin point the fault, they'll be readings of an event that caused something to fail (example: FI light ocurred on some awkward condition that doesn't mean the injectors are good to throw away or lambda sensor is). As for the ignition coils the same happens on a traditional ignition system, spark plug pipe maybe damaged, the supressor (internally- that thing that looks like a fuse) or the clip that holds to the top end of the spark wears/rusts out due to vibration, engine heat or weather moist from a hard winter... Oops sorry I do forget writing. Thanks for the warm welcome.

 

If you know you have a bad coil or more, then replace those first. If the coils arent distributing fire correctly it doesnt matter how much fuel or air your getting. It will not run right.

 

What I did last saturday before replacing ignition coils... Picked up a small unloved flat screw driver and pushed the clips out a bit till they hold the top of the spark plugs on the 3 affected coils, on the top rubber collar area put some tape around the coils to expand the collar a bit and fitted the back in place, reassembled everything fired it up (wash hands of course)and after the cycle fan started went for a ride on a heavy traffic road. I like a smooth take off and on medium weight bikes you don't need the throttle so it was the perfect place to try it out. Results... Even the smell exiting the exhaust is different the cooling fan doesn't start so often and the bike doesn't heat up my legs so easily. The next step and not now (because I'm currently out of budget) is to replace all four coils. There's a personnal theory behind that: Coils, Light bulbs and almost everything that works together must be replaced like one part, it's the same as buying new shoes to skip the original comparison that may sound rude. Summarizing: If it weren't for those worn out clips inside the coils they'd be perfectly functional.

 

As for carbs check I did find those insulators a bit on the loose side and not yet cracked which means a minimal air leak. It turns out the rubber shrinked a bit after some years due to regular engine heat so I just retighten the braces.