This is a little difficult to follow, but if your saying that it misfires and stutters with the coke on that is normal. The choke is really an "enricher" to bring more fuel in for cold starting. Depending on air temp it may need to be on longer or shorter periods depending on how long it takes for the engine to warm up. Here in the northern part of the US my ATV (with same type carbs and choke system) can take a few minutes under choke before it is ready to go. In the summer sometimes no choke at all. Starting and warm will be different depending outside temps.

If you are saying that it runs (idles) better with choke than without, that is generally dirty pilot jets or incorrectly adjusted pilot screws. Most people when they tear down these carbs do not clean the pilot jets properly. They are the smaller jets next to the mains and they need to be taken out and cleaned with carb cleaner and a wire probe. The orifices are very small and gum up easily from poor fuel quality or sitting for long periods with fuel in the carbs.

 

The emissions "tech" suggested to me that because the NOx were at 0 that my bike was experiencing a lean misfire, which is the opposite of what happened. Lean mixtures cause NOx, and since I had 0, that would suggest a rich condition.

Right, I was just giving a very simplified explanation of how I knew the bike was running rich and not lean.

CorruptFile, after 4k RPM my bike runs like a champ. No breaking up, no hesitation, it just screams. It's everywhere else that's the problem. If I poured money into the bike I could keep it running like new, but it would be money poorly spent. Although I think the CBR F/F2 is a great bike with lots of pedigree, I have no particular attachment to it.

My airbox does have the two extensions and the filter is clean. I've also pulled the plugs and they suggest perfect mixtures - slightly rich with no fouling. I'm going to school for this kind of stuff (no MMI/UTI lol) so I'm not just shooting in the dark. At the end of the day it's an old cheap bike, and if I put the money into it I could get it to run exactly as it did new, but if I'm going to spend $3k to get a "like-new" 20 year old bike, I'd rather take the same cash and go fuel injected.

 

Was there a jet kit installed previously. You should have 103 or 108 (I can't remember) and 38 pilots. Check for the keihin logo too.

 

thoes two pipes are there, they dont exactly touch the pipes but they are there, i really dont know what else to try, so i am going to change the coils over to a set of stick coils and see how that works, then i will try proses of elimination, check everything,
does any one know what stick coils i use on my 88 600?

 

for my bike when i play with the choke while on it, it does run a bit better but it doesn't fix it but it runs a little better, the bike still sounds like it is dropping a cylinder every couple of seconds.

 

When it's dropping off a jug like that, try pulling the spark caps one by one to try to locate the exact cylinder that's giving you trouble.

I would hold off on the coils, doesn't sound ignition related.

 

thanks alot guys for all the input, it helps quite a bit.
you can only notice it dropping off when you are riding the bike,
it does have a little miss when just revving it up stationary

 

As asked earlier in this thread, did you put a jet kit in it? The aftermarket kits are suspect. This sounds like a transitional problem. The point where the main jets take over from the pilots...usually around 1/8 throttle, possibly a little more. You also have a problem at idle from what your saying...are the pilot jets clean (or are they aftermarket?). If aftermarket get the stock ones. Where are your pilots set. You also said you bench sync'd the carbs...if off a bit could cause this problem...vacuum sync them. Where are your pilot screws set? How did you adjust them? Were they taken out during cleaning? Are the washers and packing o-rings washers in there on the ends of the screws? Were they put in correctly? These carbs will run like crap without those o-rings because they suck air in there.

These carbs can be set-up to run perfectly with the right tuning, but they are very sensitive to mis-adjustment and dirt. Still sounds like this is a carb problem to me. I've seen this exact problem with carbs that were not cleaned properly, missing parts or mis-adjusted.

 

to my knalage there is no jet kit in the bike, i had the carbs cleaned and set uo by two difffernet shops and they were done on flow benches, one of the shops was a personal shop and the other was a well known motorcycle / atv shop.
so as for the adjustments and the settings i have no idea what they are set at.
and i can only assume that they were put together right.
can carbs wear out, just from over time, not the parts but the base?
could i have a faulty diaphragm? or would the bike just barely run if one was bad?

thanks

 

The slides can wear and diaphams go bad or crack. You can check this by running with the air box off and see if they are all moving properly (slides). You can also see if the sync is off (although not precisely) if they all move at the same time. If you really feel the carbs are set right, then do compression test and check the valve adjustments...but still sounds like a carb issue. The bodies of the carbs don't wear out. One other thing to look for is vacuum leaks. Carbs seated in boots, bad boots, hoses, etc.