Probably should wait til spring on this, but am thinking of having my CBR600 serviced over the winter to get it running right. After purchasing the bike with 15K miles, I take it apart and find that in addition to the D & D full system it has drilled airbox and jet kit. I don't like how it runs in around town driving and stumbles at 4K rpm badly... I am guessing that the bike is set up to dump maximum fuel in at high RPM with jet kit, etc.. at expense of lower RPM responsiveness? The bike runs way too rich and I want to set it back as close as possilbe to stock. I might be crazy but I think that the base 90 or so HP is quite enough for me ;-)

My question.. what to do first? I am thinking of putting on a stock CBR muffler and keep the D & D header... good idea or bad with this jet kit? Next would be to put a non-drilled airbox cover... then hopefully take it to dealership for stock jetting and tuning. With a stage 1 jet kit do you think I will ever be able to get the bike running well throughout whole RPM range, and will the stage one jet kit need to come out if I go back to stock airbox cover and muffler? Should I have the shop replace the jets and the other parts that have been drilled in the carbs (would it be the sliders?) Or should I just buy a used set of carbs and start over?

THANKS

 

Do it all at once and have it dyno'd... Makes for a great winter project.

 

Leave the exhaust as is. Get a replacement airbox cover or tape over/block the holes.

Get a set of stock jets and install them.

See how it runs then. Hopefully the slides haven't been drilled.

KongBastard

 

The slides have been drilled I think.. pretty much certain. Can these be replaced easily or does this mean new carbs are needed? I suppose if I want to put a quieter muffler on there, I should do it before I change the jets and close up the airbox? The bike seems to run better with the holes open in the airbox lid at the moment, but I guess this will change should I make the exhaust more restrictive and go back to smaller jets.

 

sounds to me like your float height is set wrong, or you have a float needle not seating properly. My recommendation is to take the carbs out and clean them first of all. Second of all check and see what clip the aftermarket fuel needles are on, and 3rd make sure the float height is set correctly, and 4th make sure your mixture screws are set right. Simply reverting back to stock isnt the answer to your problem.

 

Thanks tds....

I was hoping that maybe things just needed adjustment. The dealer I bought the bike from is too far away for me to just bring it back for servicing. My plan is to bring it to a Honda shop and let them sort it out as best they can with what is in there. That would be great if the floats or jet position were the only thing out of whack, and adjusting and re-syncing would fix it. You seem to have a lot of mods on your bike... is it normal to expect a jet kit to create flat spots or poor lower RPM performance? The carbs were just cleaned and serviced last Spring by the guy who sold me the bike, but I have no way of knowing how great of a job he did in there.

 

To be perfectly honest, yes to a slight extent. It depends on the tune. If you have richness or a lean out at a certain rpm range, that will give you a flatspot. That is why you need to go through the proper sequence of tuning your carbs when installing a jet kit. Mistake most people make is simply look at the manufacturers recommended install, throw it in and away they go. Yes that works, and you see performance gains HOWEVER not to the machines full potential. A properly calibrated set of carbs should give you little to no flatspot.

With your particular problem, my first and easiest check would be to pull the plugs out one at a time and check their condition see if any are wet fouled by fuel. If one is and the others are not, you know which carb your problem lies in, and can investigate further. If this were the case, odds are the jet kit install is not the problem. (Would also attribute to your 4k stumble as the bike would only be running on 3 cyl).

 

Thanks again.. I have a set of plugs. Maybe it's time to swap them out to inspect the old ones. It does sort of sound like it is running on less than all 4 cylinders when it stumbles at that RPM range. It is strange because I took the bike out yesterday in cool fall weather and it ran like a champ through the whole rev range... it might be tough to fix this bug but I am hopeful it can be done without swapping out too many pieces. Do you think it is possible to set the aftermarket jet kit to a more "mild" state of tune that will provide better all around performance with maybe a little bit of power loss at top of RPM range?

 

do I think it would be possible to set it to a milder tune? Mild isnt a good word for this, more like Suiting Tune. you say it ran great in the colder air? Was this with the bike cold or warm? Running better in colder temperatures means youre running rich. Youre probably going to find that your plugs are black. Pull those plugs out and see whats up. Odds are you need to lean out a certain rpm range. Hopefully you have enough confidence to pull your own carbs out.

 

Yes.. the bike was warmed up and ran really well in the coldest weather it has seen since I have owned it, and the flat spot and stumbling were almost completely gone during that ride... lots of power. I will try to get the plugs out soon and have a look, but I don't think I am going to do anything to the carbs on my own. If it is as simple as tuning the carbs to run leaner it shouldn't cost me TOO much at the shop. I did speak to the guy who sold me the bike to try to find out how it is set up. He said something along the lines that the jets are at the "highest" setting or position, and that I might want to move them "down" if that makes sense. He was speaking as if I knew as much about carbs as he did... so I didn't really follow the whole explanation.

I have my heart set on getting an F2 OEM muffler onto this bike and am going to try to do that over the winter... then take it to get the carbs set up.... any idea on whether the F2 mufflers will line up with the F1 header? It looks like it can be done with a little bit of modding.