Hi Everyone,

I have an '87 cbr600f hurricane with a yoshimura exhaust. I got it for free from a friend. He says that he used to race it at the track with a special fuel and that it is jetted for that fuel. Right now it runs very rich and pumps out a lot of smoke from the exhaust and goes through gas like crazy. How do I know how to re-jet it? Is it just the mains or the idle jets that need to be replaced as well? Do I replace the entire jet or just the tip that screws off from the longer piece on the main jet? Does it matter that I have the yoshimura can on it - can I just put the stock jets on it? (i'm planning to put a stock exhaust on it anyway, as the yoshimura is too loud). I know these are a lot of questions but they all kind of play into each other...

Thanks,
Aujax

 

If you're putting a stock pipe back on, just replace all the jets in the float bowl with stock stuff, and set the fuel mix screws to 2.5 turns out for a starting base. while you're at it, measure float height.

 

you should be fine putting the stock jets back in it. check both the pilot and the main. also pull off the bell on top of the carb to see if it has an adjustable needle jet. if it does, the clip should be on the 2nd, or 3rd clip position from the top. put the mixture screws back to stock position or readjust as needed.
loud pipes save lives.

 

Sorry, physics 101 disproves this. vehicles forward of you generally will not hear the sound waves from your pipe, as the exhaust is aiming rearward, and sending the sound along with gases toward whoever is behind you, so really only the person behind, or possibly to the direct side of you, will hear it. beyond that, the loud pipes save lives thing is a myth.

 

If you are putting the stock pipe back on then YES, go ahead and put stock jets back in it as suggested. And YES, you just need to take off the screw-on tip of the jet. There will be a number stamped on the side of it. Stock jets are .105. The idle jet most likely has not been changed, but you might as well check anyway. It's off to the side of the main jet, and the whole thing will unscrew from the carb assembly. It should be a .035. And, as recommended, check to see if the needles have been changed; if they have a circlip and some grooves on them they are not stock needles. Stock needles don't have a clip system at all.

Have fun!

 

thanks everyone. I think the yoshimura is a slip-on. how do i know what main jet size to use with it? (i will probably ride with it on until i can locate a stock muffler.)

 

Here are a couple of good sites for general carb info as well as jet set-up.

Hope this helps.

http://www.motorcyclecruiser.com/tec...ion/index.html

http://faq.ninja250.org/wiki/How_a_c...arbs_explained

http://www.factorypro.com/magazine/H...trider97t.html

 

You really need to just open it up and find out what's in there. Knowing is half the battle. It could have a dynojet kit in it, which is aftermarket needles, slide springs, and jets, or a factory pro kit in it, or stock needles, etc. You just never know. So, in order to get it right you need to find out first what you're working with.

Stock Keihin jets for the 32mm carbs that came on the bike in 1987 are 105s. If you have stock needles and the Yoshimura, maybe you need to go a little bigger, like 108s or 110s or something. But even that's only a guess. It depends on a lot of things, like the pipe and the intake and if there's anything else that's been done to the bike that you don't know about. So get those carbs out of there and find out whatcha got!

 

First thing before you do anything is see if your airbox is drilled out, if it is, youd be wasting your time changing jets unless you bought a new airbox lid.

If its not, then yes go ahead and change it back to stock. But youre going to also possibly run into some issues. 1 if its a dynojet kit (marked by DJ in front of the jet size number) You will need to buy either a used or new set of slides as the lift holes are drilled out when a dynojet kit is installed, as well as if the needles are adjustable, you will need new needles as well.

Once that problem is taken care of, you need to first determine what size main jet is in it, and go from there. Odds are the pilot jet is still a 35 as neither factory pro or dynojet provide new pilot jets in their kit, but like mentioned check it anyways.

Now a few things to consider before rejetting,
1. Is the bike firing all 4 cylinders?
2. Is one of the floats bad? (ie Stuck open, have a hole in it)
3. Could one of the needles and seats be worn?
4. I have also seen obstructions in the fuel rail cause flooding as well.

 

Thanks everyone,

well, i've had the carbs off several times and did a thorough cleaning. It is firing on all 4 cylinders, at least some of the time. I think i'll buy four rebuild kits to make sure the jet needles, float needles and main jets are all stock. I think all the floats are good, but will check again. what is the fuel rail?

i think the lid of the airbox is drilled out. can't i just fill those holes with some epoxy?