CBR 600F2 1991 - 1994 CBR 600F2

Honda cbr 600 f2 surging

  #1  
Old 09-30-2014, 08:52 AM
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Default Honda cbr 600 f2 surging

I have a 1993 Honda CBR 600 f2 and i am about at the end of my teather with it, i bought it in March 2014 and have had nothing but problems, the bike seems to surge over 50mph, also when i shut off the throttle then open up again its hesitates quite bad.
I bought the bike with this problem and spent many hours trying different solutions and searching the internet to no avail.
It has a micron link pip and end can but i have been told by 2 independant garages that it DOES NOT need re-jetting.
So far i have
Cleaned and synced the carbs about 3 times
Replaced inlet rubbers
Replaced fuel tap and filter
Oil/filter
Spark plugs
Rectifier
Vacuum line from cyl. #2 to fuel tap
Clean all electrical connectors and soldered any damaged wires
Carb cleaner through fuel tank.
I am on the verge of selling the bike as i have literally has enough of it now so any help would be greatly appreciated.
 
  #2  
Old 09-30-2014, 11:28 AM
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The vacuum nipple from cylinder 2 should be plugged, and the vacuum line from the petcock should be connected to the nipple to the left of cylinder 1, which you can see on the left side of the motor - that vacuum port should be used for the petcock when the bike is being run, and ALL other ports should be blocked, when you're not using a synch tool.

You mentioned that bike mechanics said it did not need re-jetting - did they tell you what they are basing that on? The only way for them to know this, is if they KNOW what size jets are installed, as well as the needle clip and pilot settings, in conjunction with the exhaust used, and the intake setup, i.e., what type/condition of air filter being used.

Since you're new here, and I don't know your level of carb-tuning knowledge is, I will have to ask some basic questions... don't be offended!

Different people have different ideas about/experience with cleaning carbs, but when YOU cleaned the carbs, did you:
1) Remove the main jets, main jet holders, jet needles, pilot screws, and pilot jets, and soak all these in carb cleaner? (minus the tiny rubber O-rings that go in with the pilot screws)

2) Remove the vacuum-operated slide piston/diaphragms to inspect the condition of all 4, and have them OUT of the carbs while spraying or soaking the carb bodies?

3) Did you make a note of the size of the main jets and pilot jets, as well as making a note of how many turns out, from lightly seated, the pilot screws were originally set at? Did you make a note of the jet needle adjustment settings? (some aftermarket needles are adjustable via needle clip positions, and there are shims that raise the needle as well - if your needles only have one clip position, then they are likely stock, and only adjusted by number of shims under the needle.)

4) With all the rubber parts removed (carb cleaner dries out, expands, and eventually renders rubber O-rings/seals useless), did you spray carb cleaner into every orifice, verifying that the cleaner came out at the other end of it's passage, and then later blow the same passage out with compressed air, to be certain that ALL passages were completely clean?


Other important questions are:
a) Do you have the original F2 airbox, without holes, cracks or other damage, and what type of air filter is installed? Is it an OEM-type paper air filter, if so, is it in good condition? Is it a high-flow aftermarket filter, like a K&N, BMC, or UNI, and if so, has it somewhat recently been cleaned and re-oiled?

b) Is the exhaust header stock, with only the slip-on being aftermarket, or is it an aftermarket header?

c) Have you tested for a vaccum leak? A simple way to do this, is to start up the motor and just get it warmed up a LITTLE bit (not to hot, so as not to start a fire), and with the motor idling, spray a little carb cleaner around the base of each carb, where the boots join them to the motor, from each side, to see if the idle changes at all - if the idle does change, then you know you've got a vaccum leak, which is allowing the spray to be sucked in.

d) Have you checked out the choke circuit, verifying that the cable is indeed connected correctly, and that when you move it back and forth, the slide moves in accordance with this, and the plungers return to their closed position when the choke is not in use?

e) What is the condition of the spark plugs? Are they new, and properly gapped? If you have not replaced them, have they been pulled and checked, to verify they are not toast, or fouled-out from richness?


A lot of questions, yes, but there are a lot of factors involved!
Carb tuning is no picnic to the unacquainted, and it can take a lot of trial and error - if the issues with the way the bike is running are totally consistent, and not intermittent, then it IS very likely that the issue is air/fuel related.
IF (this is a big "if") the garages you've consulted with know that the current jetting/settings are correct for your air filter and exhaust setup, and this IS an air/fuel issue, then something else has got to be at play... it could be a vacuum leak(s), bad plugs, malfunctioning choke, damaged slide piston diaphragms, issues with the floats/float valve seats, etc.

This is why fuel injected bikes can be so much easier to live with!! I'm NOT saying carbs are impossible, far from it, because once you DO have them dialed in, if the system is kept clean and stable, your bike can scream like a banshee!! Both of my F2s do!! Well... I just sold the F2 race bike on Sunday, but you get what I'm saying!
 

Last edited by JNSRacing; 09-30-2014 at 12:01 PM.
  #3  
Old 09-30-2014, 12:54 PM
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Thanks for the reply, its a standard airbox with what looks to be a good condition standard filter, with no damage to either, i tried hooking the vacuum upto cylinder 1 but still the same, the spark plugs have been replaced and gapped recently, i did check for leaks around the intakes using that method and was no apparent leakage. I completely stripped the carbs down to every last part, i'm not 100% sure about the settings for the jets i always thought you just nipped them up or they would vibrate out of place, i double checked the jets against the manual and are standard. I just have standard headers with a small micron link pipe and end can. I took the spark plugs out this afternoon and all 4 are a sort of tan colour so the fuel mixture appears to be correct, i am a car mechanic and had colleages look over it with me and as far as we know we have checked everything we can think of including the coils. The very last straw is going to be a standard end can to see if thats the problem.
 
  #4  
Old 09-30-2014, 12:56 PM
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Sorry forgot to add that all diaghrams are in good condition
 
  #5  
Old 09-30-2014, 02:06 PM
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Got it Marc!

So the air filter just has a paper element, right?
You said the jets are standard, to confirm, are the mains 135, and the pilots 38?
Do you recall if the jet needles had just one clip position, or multiple, and do you recall how many shims were under the clip?

How about the fuel screws? Were they also removed for cleaning?
If so, when you put them back, after seating them lightly, how many turns did you back them out? Also the way those screws go back in, they would have, in the following order, a small spring, washer, and O-ring on each, before being screwed in - were all of those components present?

If you reach into the throat and push the slide pistons up into the cavity, do they go up and then return freely and easily?

It sounds like your issues are only under load, if I understand correctly - does it start and idle just fine?

Did you check the choke operation? Since you could be either too lean or too rich (I would have to ride the bike myself to be able to tell) if the choke is stuck, that would be giving you too much fuel in all circuits, at all speeds.

You're right about the jets just being tightened firm enough to not vibrate free, but obviously not "gorilla'd" into place, for sure, but the one exception is the fuel screws. Some folks have cleaned F2 carbs, or others of the same general construction, several times, and never touched those screws - they are the ones I was asking how many "turns out" they are set at.
From the factory, there are little soft metal protective caps over the "D" shaped screws, to prevent them from being messed with... just to make sure we're on the same page with those screws, this is what I'm talking about:



For what it's worth, if you've got an OEM paper filter, and a stock header, you shouldn't have this degree of trouble, due to a slip-on, but just out of curiosity, is it mega-short, with little to no packing, or is it, let's say, 12 inches or longer, and at least quiet enough that you don't suspect that it is totally gutted?
 
  #6  
Old 09-30-2014, 02:41 PM
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I removed the fuel screws completely and they all went back in order/ the order they came, will double check with the order you say they should be but there is no caps over the top of them. I have tried adjusteing these fuel screws from 1 1/2 turns upto 3 turns (half turns at a time) But each time it makes minimal if any difference. My exhaust is i assume standard length as its over 12 inches and sounds sporty but not aggressive.
The Jet sizes you mention sound very familiar but i didn't actually fully look into the choke side of things i just checked they moved freely which they do.

I appriciate you can't fully get the extent of what it's doing exactly but its so annoying/frustrating. The surging is not to the extent where its unridable but it just makes riding it unpleasant.

The bike idles just fine and rides perfect unto 50 mph with instant throttle response.

The jet needles had only one seating position and if i recall correctly had 1 metal shim and also a plastic one. Each diaghram moves freely and all return to the normal seating position
 

Last edited by Marc Storr; 09-30-2014 at 02:57 PM.
  #7  
Old 09-30-2014, 03:28 PM
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So does the problem really seem to accompany a particular speed, or is it at a particular RPM in a higher gear, that just happens at that speed?
I mean, if you were to start in first, and go wide open throttle to redline, through the first 4 gears, at what RPM is the issue rearing it's ugly head?

One way you can try to determine rich or lean, that is if this is even an air/fuel issue, is this: let's say you're running lean in the main circuit (about 7500 to redline) - you're full throttle, and when you get up to 8,000rpm or so, it begins to stutter, and "fall on its face" - if letting slightly OFF from wide-open throttle then allows it to pick up speed, and increase in RPMs again, where it initially couldn't rev past, this is an easy sign of a lean condition... this is just an example, but in that case you would need to go up a main jet size, and run it again.

In your first description you used the term "surging", and if it seems to be surging or "hunting", the way I perceive these terms, I would actually be leaning more toward you running too rich.
This is why I initially brought up the choke circuit, but if you can see the plungers going back in after you disengage the choke, then they're probably not stuck.

You already checked primary and secondary coil windings, right? And one thing I don't remember if you answered earlier, is the consistency of the issue - is it at all intermittent, or is it pretty much "like clockwork"?

Anyway, definitely try to bang through at least your first three or four gears at WOT, and see if it's a consistent RPM where the issue comes about, which would be at quite different speeds course.
 
  #8  
Old 09-30-2014, 03:58 PM
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Sorry i didn't make it fully clear as i was on my phone but now on my desktop.
The bike will start up fine when cold with the choke and after a few minutes will idle fine.
If i rev the bike up in neutral you can slightly notice a little choking/ cough around 7000-7500 rpm.
A couple of months ago i found a decent size crack between my headers where they join underneath, i welded it up and since then there is a split second high pitch 'screech' around 7000rpm in all gears and neutral.

When riding it doesn't matter how much throttle i give it along as i'm accelerating it is fine, its when i back off the throttle a little to 'cruise' above 50mph its like somebody is nipping the fuel line and creates like a on/off/on/off effect.

When riding above 50 mph if i snap the throttle off then back on quick it 'goes' 'stop' 'goes' all in a split second as if its hesitating, this is quick a major issue when changing gear.

I can hard accelerate through all gears with no issue upto whichever speed i need. And feels like 100 % power with no 'bogging' or spluttering under WOT

I've noticed its more of a high speed problem rather than a rpm problem as the optimum point on which it 'surges' is around 70mph but the problem is i don't rev the bike above 6-7k really in lower gears when cruising i just aim for 6th

The problem is persistent and not intermittent, its been like this since i purchased it in march.

Since replacing the inlet rubbers between the carbs and head the bike seems to runs a lot smoother at lower speeds and also idles at the correct rpm (1200100 RPM according to the manual) as before that anything less than 1400 RPM it sounded a little lumpy and wanted to die. I have done a carb sync since replacing them as well .
 
  #9  
Old 09-30-2014, 04:58 PM
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What are your fuel screws currently set at?
Now that you've described this in perfect detail, I would think that maybe slightly richening the fuel screws and needles (maybe one shim), might resolve this, but that is IF the exhaust situation isn't to blame, I mean it seems like too much of a coincidence to NOT suspect that! Can you feel any sort of an exhaust leak, even after the repair attempt?

By the way, I have two OEM F2 headers that are undamaged, if you suspect that this exhaust may still have a leak, or fear that the weld may be disrupting the flow at that point, or something... I'd be happy to sell you one really cheap, just so you could eliminate that possibility.
 
  #10  
Old 10-01-2014, 06:33 AM
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I have the fuels screw set at 2 turns out, i can't feel/ hear any sort of leak from or around the headers.
The high pitch screech i mentioned only came about after i repaired the front pipe which is kind of strange, i am still tempted to purchase a standard end can to eliminate that.
I am going to turn the fuel screws out 1/2 turn today and test it on the way home from work
 

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