Hi everyone,

My name is Mladen and i'm coming from Serbia, i hope that you guys can help me to solve problems with my bike because i can not find really good mechanic in my environment.

Last year i bought Honda CBR600F3 from 1996 and i have problems because from 4k rpm up to 6k rpm i have big lag, something happens and engine does not have proper combustion i think. I took bike to best mechanic i can find, he dissasembled them, took carburetors in ultrasonic bath, assemble it again and adjust with vacuum instruments. It was little better because lag was smaller but it was not completely solved. Another thing, when i start cold engine, idle speed is about 800rpms and when it warms up idle speed goes up to 1700rpms.

Can you give me some advices how to try to solve this?

Thanks in advance.

 

Welcome!! I would look at the condition of the rubber bits on the intake system. Have the carb insulators been replaced? They usually good for 10 years and then get rock hard afterwards. I would look at all the o-rings and the rubber hoses between the carbs, and all air hoses into the carbs. What is the condition of the plugs? What jet sizes are installed? If it’s not factory, I would go back to factory jet sizes.I would also check the timing marks to make sure everything is still lined up.Just a few things I would start with.

 

----Moved this thread into the f3 forum---

Greetings. There are quite a few things that could be happening. My initial thought is that the carbs still need to be cleaned. Your symptom is very common.
When it comes to these carbs, they must be cleaned very thoroughly. It's not uncommon for people who have never done this to have to have 3-4 attempts to get it correct.
Here's a list of things that need to be considered.
Every passage has to be spotless. Good enough isn't a correct term in this conversation.

All O-rings must be in good shape and properly lubricated.

As stated by @marc0011 , make sure the proper jets are in place. As a side note, is the air intake original or has it been removed or modified. This directly affects carb functionality.

Are the main jets in the proper carbs? In a stock environment, carbs 1 and 4 should have a #135 main jet, carbs 2 and 3 should have a #138.

Also, as stated, the air intake boots need to be in good shape. An easy way to check this is to spray some sort of propellant near each one with the bike running. If your RPM's increase, the boots are leaking. I usually use Propane, Butane or Mapp Gas. It has the same effect with no mess or residue.

Assuming the carbs are spot on correct, were they sync'd? This is an absolute must if they have been broken apart.

Are your valves within specs? A lot of people don't consider this, but these are vacuum carbs. The engine valves are what produce the vacuum. If they aren't right, nothing you do will correct your issue.

Finally, if you wish to pinpoint where in the carb bank you have an issue, don't use RPMs your diagnosis point. In other words, RPMs are an indicator for a healthy engine, which yours isn't. It's a common thing people look at but doesn't really help when troubleshooting.
Instead, throttle position is the indicator that should be used when troubleshooting, (IMO).
Here's what I do. With the engine off, at completely closed throttle, take a piece of tape and place it towards the top of the throttle grip. Take another piece of tape and place it along side the 1st piece, placing it on the bars. Next go to wide open throttle. Note the location of the tape on the grip. Place another piece of tape on the bars adjacent to piece on the throttle. On the bars, you should have two pieces of tape, one towards the top and one towards the bottom. Now divide the distance between the two and place another piece of tape dead center. Now, measure between the 1st and 2nd piece of tape, placing tape in the center of that gap. Finally do the same thing for the midway point and the wide-open throttle piece of tape.
What you now have is a visual representation of closed, 1/4, 1/2, 3/4 and, and full throttle positions. This is important as at each of these positions, different circuits with the carb are engaged. Using the chart below, you can now see the correlation between throttle position and each fuel circuit.


This should help you somewhat. I do believe that your carbs should be looked at again.

Also, your idle RPM should be 1,200. +/- 100. You should be able to adjust this with the idle stop screw, which is the **** on the left side of the engine by the fuel cut off switch.

Lastly, there is a .pdf shop manual in this forum available for download if you need it.