jetting issues
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jetting issues - 10/8/2008 8:14:05 PM
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aujax
Posts: 12
Joined: 8/24/2008
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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
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RE: jetting issues - 10/8/2008 9:03:27 PM
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Hurricane rider
Posts: 624
Joined: 8/23/2008
Status: offline
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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.
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RE: jetting issues - 10/8/2008 9:40:50 PM
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Hurricane rider
Posts: 624
Joined: 8/23/2008
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quote:
ORIGINAL: tripicana
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.
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RE: jetting issues - 10/8/2008 11:23:43 PM
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Gogar
Posts: 255
Joined: 9/4/2007
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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!
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RE: jetting issues - 10/9/2008 9:29:05 AM
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aujax
Posts: 12
Joined: 8/24/2008
Status: offline
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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.)
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RE: jetting issues - 10/9/2008 1:57:40 PM
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Gogar
Posts: 255
Joined: 9/4/2007
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quote:
ORIGINAL: aujax
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.)
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!
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RE: jetting issues - 10/9/2008 3:27:01 PM
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tds94probe
Posts: 266
Joined: 10/18/2007
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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.
_____________________________
''''87 CBR 600F - K&N Filter, Drilled Airbox, FP Config 3.0 Jets, FP Ignition Advancer, Hindle CF Super Sport Slip On, JT -1 Front Sprocket, CF Race Mirrors, CF Tank Pad, Shaved Rear Fender, Shaved Front Fender, Nokya Ultra White 5000K Headlight Bulb
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RE: jetting issues - 10/9/2008 7:23:05 PM
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aujax
Posts: 12
Joined: 8/24/2008
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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?
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RE: jetting issues - 10/9/2008 8:30:05 PM
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aujax
Posts: 12
Joined: 8/24/2008
Status: offline
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Ok, well, got the carbs off. The pilots are stock 35''s. The mains are not dynojets, but are 120''s. The lid on the airbox is definitely drilled. I''m not sure about the float needles, but they look ok. Also, not sure if the jet needles are stock or not or what position they are in since I can''t get them out. The screwdriver and hex parts are stripped.
So, here''s my plan for now - seal up the holes in the airbox and go smaller on the main jets (105''s) and see how it runs. Next step is to replace the float needles and seats. thoughts?
-aujax
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RE: jetting issues - 10/9/2008 11:45:32 PM
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Gogar
Posts: 255
Joined: 9/4/2007
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NO NO NO:
My suggestions:
Leave the airbox alone, it''s not worth your time and not much is going to change there. The holes drilled in the airbox are not going to change your life much. If you''re really interested in going back to stock, get on ebay and save some heartache.
FIRST: The needles.
If you disassemble the carb and take the slide/needle assembly out, you SHOULD be able to get a phillips and stick it inside the black plastic slide and turn the plastic piece 1/4 turn to the LEFT, and then push the needle out from the other side. It''s a click-kind-of feeling, not an "unscrew" kind of feeling.
If you look at the needles, do they curve in and get really skinny (they taper very gradually kind of like an hourglass and at the end they''re about the size of a ball-point pen?)
OR: They don''t taper so much, and towards the end they have a definite angular cut at the last 1/8" and make a "pyramid" shape at the end of the needle?
The "hourglass" style is probably a dynojet-style needle. Especially if you found 120s in there, that''s a size that comes with the dynojet kit.
The style with the tiny "pyramid" taper at the end is stock. If you could get the needles out of the slide that would really help, but if you can''t, that''s ok.
REMEMBER, all this is just to really find out what you''ve got going on in there. If your airbox is drilled and you have DJ needles and DJ 120 jets and a Yoshi pipe, you might be in the ballpark, and maybe there''s some other issue in your setup.
IF you''ve got the carbs out, make sure they''re CLEAN as can be, and make sure all 10 holes are clear in the main jet (when you take out the whole jet.) Make sure all 8 holes in the idle jet are clear.
Take the floats out of the carb and get a little bowl or cup of gas. Put each float in the bowl of gas, and make sure both sides of the float actually "float" in the gas. Make sure the metal tab on the float is about parallel with the plastic arm of the float, that''s a good starting point for "float height." Make sure the black pyramid-shaped end of the float-needle is really , really clean. Take the float-needle-seat out of the carb and clean the little plastic filter that''s behind there.
Anyway, I"m rambling, but while you''ve got ''em out, try to find out EXACTLY what''s in there, and don''t waste your time on the airbox or the exhaust pipe, it''s not really at the heart of your problem. Good luck!
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RE: jetting issues - 10/10/2008 5:21:07 AM
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tds94probe
Posts: 266
Joined: 10/18/2007
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yea if youre running K120''s for mains with a drilled airbox and a yoshi pipe your bike is jetted properly, so this is not your problem. (Though with your current setup you could drop down to a K118 Main). But having a slightly larger main jet will not cause the problmes you described. Have you set your mixture screws yet? if not make sure you do as this controls your air to fuel ratio. (not the idle set screw). Make sure when you clean the carbs youre also blowing them out with compressed air to make sure all debris is out.
what your describing is definetly either a needle and seat issue, a float issue, or someone was messing with your fuel mixture screws way too much.
And what I meant by fuel rail was the pipes that connect the fuel line to each carb, there are 2 aluminium ones and 1 plastic in the center, make sure you pull out your needles and seats and blow compressed air up through them.
Also you dont necessarily want the metal tabs on the float to be parallel with the plastic on the floats. You want them to be adjusted to give you a float height of 9mm-1cm.
_____________________________
''''87 CBR 600F - K&N Filter, Drilled Airbox, FP Config 3.0 Jets, FP Ignition Advancer, Hindle CF Super Sport Slip On, JT -1 Front Sprocket, CF Race Mirrors, CF Tank Pad, Shaved Rear Fender, Shaved Front Fender, Nokya Ultra White 5000K Headlight Bulb
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RE: jetting issues - 10/10/2008 9:18:14 AM
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aujax
Posts: 12
Joined: 8/24/2008
Status: offline
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Thanks for all the info,
I opened the carbs up and thoroughly cleaned the float needle seats (which I had never done). They didn''t look especially dirty, but I used carb cleaner, a q-tip and a pipe cleaner. I also cleaned the little screens that go with them and the float needles themselves (again). I did notice a slight ring around one or two of the float needles. I looked at the floats and they are all set at the correct height.
I did notice one of my slow jets was loose - something i may have overlooked when I initially reassembled them! (OOPS!!!) I hope this is the real source of the problem. The metal caps over the mixture screws are still in place so I''m going to assume that no one ever messed with them.
The needles have that tiny pyramid at the end - so they must be stock, right?
When i did the initial cleaning I soaked each carb overnight in carb cleaner and blew them out with compressed air, so I think I''m covered on that front.
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RE: jetting issues - 10/10/2008 11:25:05 AM
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aujax
Posts: 12
Joined: 8/24/2008
Status: offline
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Ahhh! Success!!! It always seems to be the silliest and simplest things that cause the problem! I believe it was the loose slow jet - how could I have missed that???? The bike runs amazingly now. Only problem is a little bit of backfire when i decel - must be the idle screws. Anyone know if there''s any way to make a yoshi pipe quieter?
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