Hello all.

A little background story: My bike, -91 Honda CBR 600F, was stored for the winter. It was started up atleast once a month. During winter I also washed it. After summer finally came, I went for a ride, and immediately noticed that it wasn't running as smooth as it should. I didn't bother that much though, but I only rode it for about 40 kilometers.

After a month or so (been very busy ) I went for another run, which went much worse. The bike was running rough, and acceleration wasn't like it should be. The bike also stalled a couple of times. When I got back home, I heard the camchain rattling unusually loud. Note: Camchain tightner (probably not the right word, but you get the drift..) was changed last year. The bike has 62 000 km on it, I'm pretty sure the chain itself is original.

The next day I started it up, and checked, that cylinder #3 wasn't firing (not getting hot). The camchain rattle was gone (Well, ofcourse there's always some noise with there bikes, but it wasn't loud) I checked the plugs and cleaned them, nothing looked bad, except #3's was a bit wet. I had changed all of them last year, and they only have about 1000km on them. After this I took off the carbs to have a look at them (never done this before, some of the hoses etc. were a bit confusing.. ), to see if they were maybe dirty or something. Everything was very clean looking (I checked the fuel chambers the valves inside), so I put it all back together and scratched my head a bit. I rechecked the spark plugs, and sure enough, #3 wasn't getting a spark. I tested it with another plug, and it worked, so I got to a shop and bought a new spark plug. After this the bike ran fine for a few minutes, I sighed in relief and went to bed.

So, next day, I was supposed to take the bike for a ride. It started well, but soon enough the rough idle came back, and engine was revving rough, so I checked the cylinder temps again: now #2 wasn't firing! Another failed spark plug. At this point, I knew it couldn't be this simple, because they were all very new spark plugs to begin with. I did go and buy a new plug again though, it ran fine for a while but again, #2 isn't firing. Didn't check, but possibly the spark plug broke again.

So, something is wrong, first #3 stopped firing because of broken spark plug (which was new to begin with), and after changing that, same thing happened to #2, which no isn't firing. Is it possible the camchain is so loose that it had messed up the valve sync or something?

 

no, a cam chain tensioner is not going to cause ANY of that. it's a CAM chain tensioner. a cam is a steel shaft that opens and closes. the timing for one cylinder is the same for all cylinders. so, you're valve timing on cyl #1, is going to be the exact same as #2,#3, and #4. a cam issue will not cause an intermittent misfire - ever. that's not to say it can't cause problems, but intermittent misfires, that will not be one of them. and a worn CCT can't cause that either. a CCT is there in order to maintain the tension on the cam chain so that a) it keeps the valve timing correct (we're talking possibly a degrees or two - not enough to cause any real performance issues at first) and b) protects the cam chain from being too loose, thus causing the chain to wear more and wear unevenly.


what i would do is buy all new plugs. once you change those plugs, run the bike. if one cylinder goes off again, then i would start to move plugs to different cylinders, in order to see if the misfire moves from cylinder to cylinder as you move the plugs. that will tell you if it's a plug issue, or if you should start looking at the coils.

i believe it has 2 coils right? cylinder's #1 and #4 on one coil that runs in wasted spark and another coil that operates #2 and #3?


and ^^^^ is when you're sure that the plug is not getting spark. if you have one cylinder running too rich via a stuck open/closed needle valve, or a mis adjusted pilot screw, etc - it could be a carb issue that's making it run too rich, thus fouling the plug

 

Thank you for your answer!

It has two coils, yes. I'm pretty sure it's just as you said, one coil operates #1 and #4, and the other one operates #2 and #3.

I'll go back to test the bike with changing the plugs to different cylinders. As I said, they're were all new to begin with (just about 1000km on them), and I've also bought new ones for #2 and #3 now. So I'll now change the plug from #2 to #1 and try to run it, and see what happenes. #3 is a bitch to change, without taking the fuel tank and air filter off..

I've tested the plugs like so, that I take it out, put it in the coil wire and ground it to the engine -> start the bike, see if there's spark. This is how I found that the #3 was broke, and later saw the same thing in #2.

Is needle valve inside the carb? Could you point me with a picture or something, which valve you mean?

 

oh, okay, you're testing plugs like that. i thought you had a mis, changed the plug, and it ran; so, you had determined that you had a bad plug. yes, that's a sure fire way to make sure the plug is or is not working. however, if a carb fouled the plug, it could ruin the plug. now that you have fresh plugs, i'd test them again that way, and make sure they work.

i would wear out the possibility of it being an electric problem before messing with the carbs. a)you've already started testing the plugs. b) it's very intermittent - most likely electric/ignition c) it's already moved once.

if you test the plugs, but think it could be a coil issue, you can swap those to see if it moves as well. after one of these plugs goes out, i'd test the coil. you said it went from #2 to #3, which would be on one coil. coils do have a tendency to go out. they're also not all that expensive - and aftermarket newer ones are very good compared to the old ones. if and when you do decide to swap coils to see if your misfire moves, remember, you have to switch everything over, you cant just swap plug wires. the coil itself is the only thing that moves, so the lead wire has to transfer, and then your plug wires have to transfer too.

like i said, i would have to assume that this is an ignition issue - that you were right on target with your approach. having said that, if you keep having problems after you tested/corrected everything ignition related, i would check the carbs. if it was sitting all winter, it could have some water or bad fuel in the lines. i dont know if you guys have ethanol in your gas over seas - but we do here, and especially on older bikes, it's a problem because it breaks down the fuel lines - and can cause clogs inside the carburetor.


your bowls in the carb start to fill up with fuel. the float (yellowish plastic thing that looks like a dumbbell) floats in the fuel via a hinge. once the level gets up to a sufficient level, the float presses on the needle valve. the needle valve closes and fuel stops coming into the bowl. this should be close to what your needle valve looks like (also called a float valve)




you just want to make sure the passage way is clean and the valve works. you want to make sure that the floats are free to move up and down. as you can see from the picture, one little piece of trash guming that up would make the entire system not work. also, make sure your jets are free and clear . and have your pilot jets been messed with before? if so, you could try backing them off a half turn or 3/4 of a turn to see if that leans out the rich cylinder

 

Thank you very much for your help so far.

Today, I worked on the bike again. I took off, cleaned, and switched the plugs for #1 and #2 cylinders. I also checked the vacuum line pipe (Atleast I think that's the one, I mean the other pipe that comes from the fuel tank and goes to the #1 cylinder), because I had to remove that earlier when I took the carbs out. The vacuum line didn't have the clamp on (that tightens it), but it wasn't really loose, so I don't think that had any effect.

After this, I started the bike. Now I must note here, usually, when I start the bike, I give full choke, start it, and let it run with the choke on (while I finish putting on my driving gear etc). This time I pretty much immediately took of the choke. The bike ran fine, on all cylinders. I let it run for a while, while parked, gave it some throttle and measured the temps of the exhausts coming off the cylinders.

Everything ran fine, except idle wasn't stable (but it has always been like that, more on this later). I went for a ride, lasting about ~30minutes / ~40km. The bike ran fine, acceleration was good and it didn't stall. I got back home, every cylinder was firing (measured the temps).

Now an idea popped into my head, is it possible that the bike is running a bit rich (hence the not perfect idle) and I've drowned the plugs with fuel when I've started the bike with full choke? As I said, this time I took the choke off right after the bike started.

About the idle, I've had the bike for almost two years now. I has always had a bit rough idle, jumping ~200rpm up and down. It sounds a bit like it misses some strokes or something, but nothing major. This is my first bike, so I have nothing to compare to, but my neighbor has similar bike (with same colors aswell) and as I've heard his bike, I think it's has much smoother idle. I haven't paid that much attention to it thus far, because I haven't had big problems with it but just now.

I know basics of fuel/air mix stuff, from my youth (Fiddling with Suzuki PV), but eventhough the basics are pretty much the same here, I don't really how how to adjust the mixture with CBR 600F. Which one is the pilot jet, does that handle the fuel/air mixture?

 

whoops, i mis-typed. i meant pilot mixture screw. your pilot jet won't matter that much so long as it's free.


your pilot mixture screw is what i meant to say. the pilot jet - it's a jet. no real adjustment there. but the pilot mixture screw was what i meant to reference.


its usually on the bottom of the carbs, forward of the bowls. each cylinder's carb has it's own pilot mixture screw. now, if they've never been messed with - they might have aluminum caps guarding them. you can drill them out. i know that drilling on the carbs sounds crazy, but they're little aluminum caps that will pop right off as soon as your drill bit bites. if you ever get a jet kit for your bike, it'll actually come with a bit because you need to pop those caps off in order to properly adjust the carbs.

anyways, the mixture screws are usually set in the middle or so. they usually have about 2-3 full turns of play each way (tighter and looser). if you loosen the mixture screws, it enriches the mix, if you tighten them, it'll lean out the mix. so i would suggest maybe tightening them a half turn or so. you'll want to check again on those exhaust temps - to make sure you don't see a significant raise in header temps (btw - infrared gun is my favorite diagnostic tool - good on you to have one!). and it mainly goes by how the bike feels. if it feels sluggish, i'd loosen those screw back up. if it still smells too rich, maybe go another 1/4 turn tighter

it also could be that you need a carb sync if you haven't done one. if you search the forum, there is a procedure for how to do it without the expensive tool. it'd be a good thing to do if you suspect one hasn't been done. that would clear up the rough idle for sure

 

I'm actually lucky enough to use my stepfathers garage, he has many handy tools I'll check those out, I'll probably take the bike for a cautions ride today, and be careful with the choke. And after that I'll try to change the mixtures to bit more lean, to see if it has any positive effect!

I'll also definitely look into the carb syncing, I've seen some info about it already, but haven't yet thought too much into it.

Thank you very much for you help so far, I'll report back after I've checked on the mixtures!

 

Zerby,

Members who let old threads die without a disposition report shall be subject to unspecified retaliatory measures...

Just kidding, of course! Came upon your thread during a search.

What was your outcome?

Best wishes.

 

I doubt you'll get an answer. It shows that he hasn't logged back on since he posted that last message, over 11 months ago.

 

Heh, luckily I had this thread on subscribe, and happened to see the email which notified me about new messages...

Not so luckily though, I've been so busy with work and stuff, that I hadn't had the time to ride or fix my bike. I've done one trip this year, and eventhough the trip went relatively fine (I was extra cautions with the choke), I had some difficulties with the bike after starting it after breaks (gas/food brakes). The bike was stuttering for a few minutes when accelerating, and even stalled a couple of times. After few minutes of running though, it ran fine again.

Well, after this I decided I have to fix the bike before any futher trips. Unfortunately I don't have time myself, so I'll have to take it to a shop and see if they can sync and adjust the carbs, hopefully fixing the problem.

I won't make any promises this time about reporting back But, I'll try..