Carb Jetting Question
 

Hey All, I'm new to this forum. I just traded a running buell blast for a 94 CBR F2 that wasn't running, I also have a 2008 FZ6. It is currently running, came with a yoshi slip on, stock jets (I checked), stock air filter.

My plan for the bike now is to check/adjust valves (if needed), jet and tune the bike properly, and a carb sync once the tune is good, then oil change/new tires/new plastics. So my question for the forum is this, does anyone have a similar setup to me and if so what jet sizing do you use? I live in upstate NY, ~0-1200' above sea level.

Would it be best for me to buy a jet kit, leaning towards Factory Pro (but curious what everyone else uses), or just buy the correct jet sizing and some shims for the needle (if I know which size will work)?

I'm also looking for new plastics, has anyone had experience with the Ebay fairing kits? If so thoughts?

Thanks,
-Rob

First off, welcome to the forum Rob. :icon_beerchug:
Just to clarify, are you saying the F2 is now currently running, and has the Yosh slip-on, and stock jets/air filter? If the answer to this is yes, then the stock 135 mains and jet needle shim setting will be just fine for just the slip-on... if you had a full high-performance exhaust system, from headers to can, and/or a high-flow air filter, like a K&N, UNI, BMC, etc., then you might need to make some adjustments, but bear in mind, that no two setups are exactly alike.

Bottom line - leave well enough alone, when it comes to the jets - do a thorough carb cleaning, make sure your pilot screws are adjusted properly, install a clean OEM paper filter, and see how it runs... more than likely, if there are no other performance-affecting issues with the bike, it'll run like a 90hp 600 should!

Just as a for instance, though, I'll tell you what I'm running:

In the race F2, I have a K&N filter, Two Brothers race header mated to a shortened Yosh RS-3 carbon fiber can, stock cams and ignition timing, and I'm running 142 main jets, agressively tapered Factory Pro jet needles with the original shim, set one clip below middle (raising needle), and the pilot screws are all right at 3 turns out... its hard to keep the front wheel on the ground.

My street F2 has a BMC filter, stock headers (though not for much longer! :p), a shortened Yosh R&D slip-on, and bone stock internals, and I'm also running 142 mains in those carbs, with one additional shim on the stock jet needles and the pilot screws are at about 2 7/8 turns out... it's a little easier with this bike, but still takes some work to keep the front wheel down.

Good luck with your work on the bike, and surely you don't have to be instructed to create a project thread, and post some pics of what you got going on!! :icon_mrgreen:

Oops, forgot to comment on this...

Do a search on the forum for "Hong Kong fairings", and you'll surely find a few threads with talk about them - the are definitely a "mixed bag". I suggest this search, because nearly all of the cheaper plastic kits on eBay are from China.

If you read through my "Phase 1" thread, starting about 1/2 way through the 2nd page, you can see what my experiences were... I posted several other times here and there, later in the thread as well, regarding issues/resolutions with the HK fairings.

Thanks for the reply and greetings.

Bike is running with yosh slip-on, stock air filter/jetting.

I did a quick carb clean in the bike to see if it would run before I started putting money into it. The previous owner spayed carb cleaner into the carbs to try and get it to run :icon_fryingpan: so I was checking to see if it would run. I did test compression also checking for blown head gasket and it looked good. I plan on doing a thorough cleaning when I'm doing valves.

The bike is running, rough. The bike seams to have no power when starting off in first gear until about >4k, as in its very doggy/hesitant and sometimes studdery. A friend of mine who use to work on older bikes says he thinks is because of the sync. I'll try and post/link a video of it idling and you can't hear it not sounding ideal. I'm also use to EFI not carbs... :icon_denk:

I've read that even with an exhaust slip-on that the jetting sizing/needle height should be adjusted because the bike is running leaner than before, but you can get away with running stock jetting. The engine will just run "hotter"...?

Does a BMC air filter add noticeably more power throughout the power band with a slip-on or is it only noticeable with a HP full exhaust? And I do understand that every bike is different when it comes to jetting/tuning. So from what you're saying if I do replace the stock air filter with something like a BMC filter, like this:BMC Air Filter - Standard / Street, Race and Carbon Fiber versions available for 1994 Honda CBR600F2 - 2WheelPros.com then I'd need to retune/jet the carbs? I'd plan to tune the bike how Factory Pro calls out: CV Carb Tuning Procedures

I do plan on making a build/work thread throughout the whole process.

Honestly, people worry too much about synching the carbs - I'm not saying don't do a sync, but it is most definitely overrated, meaning, it is most often not needed... I have two F2s, one with 27K, and one with 32K, and in both cases, the sync tool was an unnecessary expenditure, as they needed no adjustment. Don't get me wrong, I love buyin' me some tools, but it was just not needed.
You can check to see if a sync is really needed, and get decent results, carefully using some feeler guages and checking the butterfly openings from one carb to the next.

OK, so at about 4K, the bike comes to life - that's when your jet needle circuit kicks in - if we assume it pulls hard everywhere but under 4K, in all gears, then we could isolate your issue to the pilot circuit.
When you cleaned the carbs, how thorough were you? Did you first check the fuel screw settings, and then remove those screws for thorough cleaning? Also, did you pull the actual pilot jets to clean them and their passages?
It's possible they are not set right - a recommended starting point would be to turn them all in until their lightly seated, then turn out 2 1/4 turns (I think, for a 49 state bike - it might be 2 1/8 - check the manual).

Yes, leaner will be hotter, but to get things right, those procedures are what needs to be done in order to "dial it in"... welcome to carbs!

Actually, what I'm saying is don't change the air filter to something that will require you to tinker with it more than necessary - OEM-type paper filter will be just fine, unless you just really want to pull the carbs off quite a few times while you experiment with different settings, ride/dyno, repeat.

Your low RPM issue is most likely your pilot circuit, so start there, and see how things go.

For what i get out of carbs your slow jet is for idle and low speed, jet needle is for mid range to high and the main jet is for high rpm chaos. What happened to myself once was i cleaned the carbs and did not seat the jets in all the way so they became loose and fell out, there went all my power right at the 7k-8k mark, just some food for thought.

Thanks for the advice, I really appropriate it. I'll be keeping the stock air filter then, when I cleaned the carbs out I did not clean the fuel screws/those passages but I will when I do valves. I do think I have the fuel screws out way to far now that you mention it, out about 2 3/4 turns...

I built my carb sync too, wasn't going to be paying $80+ for one :icon_lol:

Again thanks for the help,

-Rob

For sure, all of those items must be removed in order for you to know that the carbs are thoroughly clean, the fuel screws, pilot jets, main jets, and needle jets... you can soak those items in carb cleaner, in addition to spraying carb cleaner in all the metering holes for the corresponding fuel circuits. Let the carb cleaner sit in those passages, and then use compressed air to blow them free - be careful with the air, as until you learn what holes are on the other end of each orifice you blow air into, you could end up with a face full of carb cleaner! :icon_saywhat:
As you do learn what holes lead through what passages and to what holes, you can repeat the process until you feel confident there's no debris/gummed up fuel in them.

Some caution when doing the cleaning:

1. Unless it is specifically designated as such, most spray carb cleaner is not safe for rubber parts, so make sure the slide diaphragms, the float needles, the tiny O-rings on the fuel screws, and the float bowl seals do not come in contact with the carb cleaner - they will dry out and expand, and you will potentially have to replace these items.
2. About those tiny O-Rings mentioned above - when you remove the fuel screws, they will each have a small spring, and very small O-Ring and washer on them - take note what order they come out, and make sure they don't get lost.

Like kingtut mentioned, make sure your jets are screwed back in tight - they are brass, so you've got to be careful not to jack them up, but if you're using screwdrivers with the appropriate blade size for each jet, you should be able to get them quite tight without damaging anything.

Good luck!