Update** running better. Slow jets and bystarter jets were completely clogged. R/R and stator being replaced currently.


After spending weeks on the forum before I picked up this bike from a friend for 300$ I became very familiar with potential issues and was ready to dive in when I got it a couple of days ago.

Last year he had the carbs cleaned because it wouldn’t start, and the battery would always die on him so he ended up getting a new bike.

the bike has I believe just a slip on and a jet kit 138 1/4 and 140 2/3. #40 slows which we’re completely clogged. Main jets looked ok but I cleaned and blew compressed air through each, and through each orifice in the carb itself. I was impatient and fixed the leaking float bowl gaskets with motoseal because my gaskets won’t come for another week. Also have new insulators coming but these aren’t super hard and seem to be ok.

when I pulled the carbs off I noticed the top insulator screws weren’t even there and the float bowls were mixed up because the drains weren’t facing the right direction. So at that point I’m walking into, what did the last mechanic do 😅

I replaced the R/R due to the old one failing the ohm test as I didn’t get a reading across anything, following the clymer manual. Also put in a new battery.

After the cleaning, crank and crank, choke engaged or not engaged WOT, not a single fire. Sprayed alittle carb cleaner in the intake of the carbs and it fires right up for a couple seconds, sounds healthy and then stops. She will not start without carb cleaner!

The exterior of the bike is in great condition, everything looks solid. Has a switch installed on the rear to release or engage pins for the seat which is nice. The bike only has 14k miles. He said it ran great last year and his dad tried to get it running.

i also noted the pilot screws were around 2-1/8 to 2-1/2 turns out.

Any suggestions on next step? Pull the carbs and do a complete cleaning? I only did the jets and orifices, no fuel in the floats and they seemed to be ok, rubber on the stem that sits in the float we’re in perfect condition. Also, I didn’t reconnect the evap lines or solenoid when attempting to start after the clean, does that matter when just trying to start? As I’ve seen a lot of people did the mod to delete all those extra hoses.

Also, I jumped the fuel pump and it pumps pretty fast and when opening the float bowl drains fuel comes out so it seems like at least the carbs are filling up with fuel. Choke rail slides both ways pretty smoothly. Also just tried to adjust the idle **** so not sure where that was in the beginning and can’t find a factory turn spec on that 🤦‍♂️ Hopefully not missing anything!

Any help is greatly appreciated!!!

 

Hey there and congrats on the new to you bike. I would absolutely completely disassemble the carbs thoroughly clean them, then clean them again. They are great things but do insist on being spotless.
A good sync of the carbs will be in order also.

as to the idle adjustment screw, there isn’t a spec or requirement just use it to keep the warm idle RPMat 1,200. Be very careful so not to completely unscrew it while it’s on the bike. There’s no stop on it and it will come out completely and you’ll have a fun time looking for
the spring.

 

will definitely give it a shot again, obviously this time removing everything just before separating the rack because the orings in between don’t leak and the butterfly’s are all in good shape 😅 also ordered spark plugs, when I pulled 1 and 4 they were wet and looked worn with a slight brownish tint. I’ll keep this post updated! Parts are supposed to be here Thursday 🤞

 

Visually, the butterflies in the throat seem to be open different amounts. That could be just an illusion, but doing a balance is a good idea. Keep in mind that opening the throttle while starting does not help. It also reduces the effectiveness of the enrichment circuits (choke). If the engine is cold, then using the choke lever is all you should need if everything is working properly in the carburetors. Maybe even consider checking valve clearances since the engine is pretty close to the time, and you've got it this far apart anyway.

 

Funny thing is I have the valve adjustment thread in the forum bookmarked and open in another window. I might as well at least check the clearances and replace the gasket since I had slight oil on the threads on #4. I would love to do a balance once the bike runs, should I do a bench sync first, or just focus on getting it started? And if so, any recommendations on doing a proper bench sync?

 

Like @IDoDirt said a check of the valve clearances is a good idea. It’s actually the very first step in insuring a good set of carbs.

the bench sync is very simple. All you are doing is placing an object in the carb throat and adjusting the butterfly valves until each one touches the object with the same amount of pressure. That leaves the basic same amount of space for all the butterfly valves. The amount of space really isn’t as important as all of them being the same.
the object used can be anything. Some people use feelers gauges, use use a guitar string. I use a sewing needle. Don’t ask me why that instead of anything else as I don’t really know. I suppose the first time I did it, a needle was the first thing I found.

A bench is a great starting point but if you really want to dial it in a vacuum sync will get everything humming the same tune.

 

The engine is a big air pump. The valves have the most control over how much air gets into the cylinders. The cylinder bore and piston stroke are fixed, so no control. Depending on how much the intake/exhaust valves open determines the airflow into the engine and as a direct result, how much vacuum the carburetors are exposed to. That vacuum and flow of air through the carburetor body determines how much fuel gets added into that air. If it's not right at the beginning, then it will never be right at the end. Hopefully you'll be lucky and all your valves will be within spec and you don't have to go any further.

 

that’s a good idea! Never saw any videos or people saying they’ve used this method but definitely a good starting point! Ordered a set of feeler gauges anyway for the valve clearance so I’ll see how far each butterfly is from each with them 👌🏻 I hate waiting for parts, my anxiousness is killing me because I think I have all the info to get her started once it’s back together. Will have an update Saturday as this will be my Saturday project. Thanks so much guys!

 

Sorry I can't help on the mechanical side but as an aside yours is the first CBR600 that I have seen in the plain yellow colour aside from mine. I have had mine for about 15 years and it was resprayed years before that by a previous owner

. Is yours a respray at some point? I'm UK so wondered if US bikes were supplied in this paint scheme?

 

The US did not receive that color scheme. You've even got the factory exhaust. What year is your bike, 97 or 98? Here are the US colors for that year.