honda CBR600 question!!!!!!!!!!!

[450rKid13]

Hey, just wonderin if anyone on here can help me figure out whats up with my older bro's cbr 600??

Its a '98 CBR F3. We bought it a few weeks ago... From what we we're told, its an ex-race bike. Nothing fancy performance wise tho. Just a Two bros slip on, and apparently some head work. (the guy we bought it from didn't know what was done to it, he just bought it cuz it was cheap) anyway, we got it running last week, but it's not running quite right. when you get on the gas, there's almost no throttle response till like mid range, then it takes off.(no braap) But then on the decel, the bike almost sounds like it doesn't want to come back down off the rpm's. It kinda holds around 2k and eventually gets back into idle at 1.2k. There's some backfiring too, with a nice little blue flame that shoots out the tip of the exhaust. (burnt all the hair off my hand once) lol

to me, it sounds like the bike is running really rich and that's causing the low end bog, and mebbe the throttle cable is sticking, and that's what's causing the slow Decel. Its hard for me to say tho cuz i'm real new to the Street bike scene. A noob at best..

Anyway. let me know if you have any ideas of what could be ailing the bike. I'm pretty sure its a carb issue, but i've been wrong before. It could be timing, or maybe even something electrical. IDK. Any help would be awesome. thanks ahead of time, -Doug.

[derekhonda]

Boy that is a tough one, I'll chime in and get you rolling but I am really not sure.

1. I agree with you on it sounding rich and not having the bottom end, have you pulled plugs to verify?

2. Is the airfilter clean or could the lack of air be why it is running rich?

3. That is an 11 year old bike, when's the last time the carbs have been cleaned? The slow back to idle could be either the carbs not being able to close fully, or possibly still the problem from the richness with the extra fuel trapped in the chamber and needing to be burned off (and keeps it still at higher rpms, longer than you are wanting)

Let us know how the plugs look.

[lghickman21]

it sounds like it is sucking air in from somewhere it isn't suppose to. make sure all the vaccum lines are on.

[greenblood01]

It sounds to me like the carbs need to be synchronized.

[extremeblastr]

Originally posted by lghickman21
it sounds like it is sucking air in from somewhere it isn't suppose to. make sure all the vaccum lines are on.

my thoughts also but just check for a vaccum leak in general not just the lines.

[450rKid13]

Well, all the plugs are new. First thing we did when we got it home was tear the carb assembly down and cleaned everything. After that it still wouldn't start, so we pulled the plugs and found that they were pretty much fouled so we pulled the ones outta our spare motor and put 'em in. They were brand new, never even run in the motor, just there to plug the holes. The bike runs with those plugs.

Now that i think of it, i remember seeing quite a bit of carbon build-up on the intake valves when we had the intake/carbs off of it. Think that could be a sign of anything??


As far as vacuum issues; i have no idea how to check that. We have the lines all hooked up the right way and i'm 100% positive on that. we triple checked it with every diagram we could find.

How would i check for leaks? Should i just look for cracked hoses, fitments, etc?

thx for all the replies.

[Old Head]

race bikes, if it is one, are set up to run at the high rpm range only.

[tri5ron]

Originally posted by 450rKid13

As far as vacuum issues; i have no idea how to check that. We have the lines all hooked up the right way and i'm 100% positive on that. we triple checked it with every diagram we could find.

How would i check for leaks? Should i just look for cracked hoses, fitments, etc?

thx for all the replies.

with the bike COLD,
start the engine, and spray some starting fluid around the intake manifold, and vacuum lines.
Being careful not to let any fluid get into the airbox/airfilter.
ALSO being careful to NOT spray it on a hot header.

If the idle speed raises when you spray the starting fluid, you know you have a leak.

BE VERY CAREFUL DOING THIS !
Use short, well directed, shots of spray.
Do not continueosly hold a long stream of spray, and dont have any open flame or other source of ignition in the area. NO SMOKING, NO SPARKS, ETC.

[450rKid13]

Originally posted by Old Head
race bikes, if it is one, are set up to run at the high rpm range only.

You know, i said that same thing to my brother initially, but he's still intent on proving that it has a problem. I kinda figured it made sense: racing - high rpm's - no bottom end.
It really seems like that's what it is, just bc of the way it takes off at about 4-5K.
Any ideas what would have be done to it to in order to make it run like that? Or what i can do to return it to normal?
Maybe jetting? valve timing?
thx.

tri5ron: thx for the idea, i'll give it a shot someday this week when my brother is home from college. (and when i can go get a fresh can of starting fluid...we burnt up the last of ours getting the darn thing running.)

[Old Head]

I'm pretty sure there was one year honda made a 600 modeled after the race bike. It lacked power until about 8000 rpm because that is how they are ran on the track.