Bike seemed to be running ok. Synced carbs and now its running lean? 1987
 

1987 CBR600f.

To preface - All of this has been done with the airbox OFF.

I rebuilt (using stock size jets - in illinois) and cleaned the carbs really well recently and the bike fired right up. I adjusted the idle and synced all 4 carbs without a whole lot of issue. At first the bike seemed to be doing fine, but had a slight bit of hesitation when I would first get on the throttle at low rpms, but as soon as it overcame that hurdle the revs would pick up effortlessly. I test rode the bike and it seemed to do well the entire time.

Now, seemingly for no reason, the bike seems to be running lean. I can't start it with full choke. If I give it full choke while its running it dies. I replaced the spark plugs for good measure and it didn't help anything. Now the bike seems to struggle to warm up and it takes an excessive amount of time to reach full operating temperature. I have to monitor it and sometimes even adjust the idle up and down until its fully warm to set the idle properly.

I do have some rattle from what I'm assuming is the cam chain tensioner. My manual one should arrive Monday.

I did try putting the airbox on, but it didn't really seem to make a whole lot of difference. I do know on another bike I have that I had some sputter down low with the airbox on, but putting it on completely changed the dynamics of the bike. The air filter for the CBR is a red, foam air filter almost like an extremely thin sponge. Is this a high flow air filter and should I swap to a normal one?

For the lean condition - I am going to take the carbs off again tomorrow and take a look at things. I did adjust my float heights to manufacturer specs, but maybe I'm not measuring them well. These floats seem somewhat difficult to get them to "lightly seat." The new needles also did not come with any clips for shims.

Should I only adjust the float height if needed or should I try turning the air fuel screws in on each carb slightly to see if it richens the mixture up at idle?

Ok I think I fixed it.

I am apparently retarded. I swear I turned the A/F screws out 2 1/4 turns.

I added an additional half turn, with no results, then an additional full turn and then the bike wouldn't start (duh lol.) So - when I turned them back in I counted ~2 3/4 turns? I double checked all and set them to 2 1/4 turns. I also found that my carbs weren't 100% seated in the boots so I'm sure I had at best an intermittent vacuum leak and at worst a full on one. I seated them properly and adjusted the idle to 1200/1300 and now the bike seems to do fine!



Revs fall happily, bike seems to warm up quickly, and overall it just "Feels" better.

The date stamps on the tires are 375 so I'm pretty sure these were made in 85 or 95 - holy ****. Of course the original owner had the money for a custom paint job, but not for new tires.