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Old 07-26-2007, 2:13 PM   #1
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Running too lean?

Hello all!

I own a 88 Honda CBR 600 F1 Hurricane. It has a Vance & Hines "Chrome" slip-on and a K&N filter, everything else is stock. I do not believe the prior owner had the bike rejetted for the slip and filter. When I purchased it one month ago it ran fairly well exept in mid-range 4-5k. The exhaust krackles in mid-range and during engine braking. Since then I cleaned the air filter and know have a new problem. After cleaning the filter, it realy bogged in mid-range. So I was driving on the freeway which is when the engine usually seems to want more fuel or less (wont run smoothly) and slowly moved the choke on when all of a sudden, the motor smoothed out . If I keep the choke on while I ride it runs like a champ . However, when I come to a stop, it revs around 2-2500k which if very fast.

Knowing that when I ride with the choke positioned at the half-way point the motor runs exelent through all rpm's at all speeds (execpt the fast idle at stops), is making me believe that the Vance & Hines Chorme slip-on and K&N is effecting the fuel to air ratio. If I understand correctly, if the choke is on and it runs great, that means there is normally too much air and or not enough fuel. This would most likely tell me that the prior owner did not rejet.

Is there a simple way to fix this?
Is there a fuel to air mixture screw on the carbs?
Can I damage the engine by keeping the choke on ?

Thanks for your feed back....
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Old 07-26-2007, 5:02 PM   #2
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Running too lean?

I also noticed that when I removed the air filter and can see the black boots over the carbs, there is a small brass tube located next to each boot. It looked like each boot had a small extention on the outside that would cover these brass tubes. Only one was covered and the rest werent because the boots were rotated such that the cover is not clocked close enough. (cant rotate the boots as they are bolted down).

So I am thinking of covering the uncoved tubes with a small rubber boot. (like the ones that cover the bottom of a dish strainer or something). If these tubes suck in air, this could also be the reason for running lean right?
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Old 08-01-2007, 5:43 PM   #3
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Re: Running too lean?

I hate carbs. Some of those nipples are meant to be plugged and some arent so I would get a manual and check on that. I dont believe the K&N and slip on would cause that much drama. When you choke the bike it gives A LOT more fuel to the engine than when it just runs normally. So I would pull the carbs off, take them to get cleaned and have them check the jetting, or if you know about carbs do it yourself. I wouldnt think you'll damage the engine by keeping the choke on BUT its possible the fuel washes all the oil of the cylinder walls, if its getting that much fuel. Get a manual.
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Old 08-03-2007, 1:02 AM   #4
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Re: Running too lean?

there is also an idle "screw" that let's you do minor adjustments to the fuel mixture. it should be on the left side just below the fuel switch. that's where mine is located. i have an F3 so it may be a little different, but not too much. i'll look through my manual and see what it says and keep you posted. i'm not sure how many changes took place between those years but it could get you pointed in the right direction. getting the carbs cleaned and syncronized is a good place to start too. good luck, keep us posted.
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Old 08-03-2007, 1:33 AM   #5
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Re: Running too lean?

Pull the carbs, have them cleaned and the jets replaced with the correct ones. The slip-on and filter will make the bike run lean.

Your issue started after you cleaned the filter. A clean filter allows more air through and thus you need more fuel.

You also might want to get rid of the K&N as it doesn't do much. On some bikes it actually reduces power over the OEM.
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Old 08-03-2007, 11:34 AM   #6
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Re: Running too lean?

Hello again. I could not find any documentation in the manual or online forums about these small brass tubes. I talked to a co-worker and he though they may be used when the engine is built, to do the initial vacuum setup on each carb. So I took the tank and filter off and stuck a toothpick in each one and took it for a drive.

WOW! Not only did it run better than when I first bought it, it ran exellant through all gears at all rpm's. So I bought a pack of 4 peg-board hooks that had little rubber covers on the ends and covered all 4 tubes as shown in the photographs. I forgot to take a picture prior to putting the caps on and they were very hard to get on (very tight fit) Go figure.....

Thanks for all the input. There still is a slight hesitation at around 6k but not at all of concern. I just might pull the K&N and use a stock to see if that fix's that. Thanks again.

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Old 01-10-2008, 1:15 AM   #7
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Re: Running too lean?

Those are spots are where some carbs main jets run from. You can adjust idle mixture screws from the other end where the float bowl is(they're usually capped). Carbs are fun to play with once you get the hang of them.
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