Carb Tuning, Why it's so hard for me?

[tderida]

Ok Fellas, I don't care who thinks that  me as a dumbass but I could not get the idea and make the mixture well.. maybe tried times I tried.

First of all , I have to mention that  I make some changes on '90 FJ1200 as a custom cafe. She has big pod filters and hayabusa mufflers on it. Carbs are syncronised.

The problem is, I can't get a stable idle. I mean it strumbles on 1/8 throttle and some popping on exhaust (is that too lean?) while warming but on road after 100 celcius the rev comes down slowly after full throttle.(is that too rich?)

I try to set  idle mixture screws. First all 3 turns out. But did I get something wrong? Or maybe I need a rejetting, huh? Please give some tip.


https://goo.gl/photos/5hgE1KnUZTdJYRSJ8

[FJmonkey]

Have a look through these posts, full of good info on carbs. http://www.fjowners.com/index.php?board=21.0

[4everFJ]

If you have changed both airfilter and exhaust to more open types, you will need to re-jet your carbs. You can't make the necesarry adjustment with the mixture screws alone.

Re-jetting needs to be done on a Dyno to get it right.

[tderida]

If you have changed both airfilter and exhaust to more open types, you will need to re-jet your carbs. You can't make the necesarry adjustment with the mixture screws alone.

Re-jetting needs to be done on a Dyno to get it right.

Dyno is not availible in our location.  I hope  some dirty old school tricks from the masters  
Should I change both pilot and main? I remember some guy changed jets  to 115 main 40 pilot for a likely situation ?

[FJmonkey]

Your pilot jets are most likely #40, here in the USA they were smaller for emissions compliance. The main jets and needle position are your next possible change. The needle position is easy if you have after market needles with slots for different positions. They can be adjusted without removing the carbs.

[fj1289]

If you have changed both airfilter and exhaust to more open types, you will need to re-jet your carbs. You can't make the necesarry adjustment with the mixture screws alone.

Re-jetting needs to be done on a Dyno to get it right.

Dyno is not availible in our location.  I hope  some dirty old school tricks from the masters  
Should I change both pilot and main? I remember some guy changed jets  to 115 main 40 pilot for a likely situation ?

I scanned your previous posts - I may have missed it, but I don't see anything about THOROUGHLY CLEANING the carbs.  If any of the carb passages - especially the small idle circuits are not very clean, then you will always have troubles with carb tuning!

And YES, carb tuning CAN be done without a dyno.  And without an O2 sensor.  It is a case of setting up a good starting point.  ONLY change ONE thing at a time and write it down - write what change you made, how you tested it, and what you think of the changes.  THEN, try another change, and repeat until you get a nice tune on the carbs. 

A few things to remember - if you are new to tuning carbs, it will take time, and you will have to go into the carbs a lot of times.  Don't make a large change at once - make small changes.  If you can't tell a difference, make another change in the same direction.  Keep going until you know for sure it is getting better or worse.  Then go the other direction and keep going until you know if it is better or worse.  If you find something that gets better - keep going until it stops getting better and go back to what was best. 

Don't change the wrong things.  If you have a problem starting or at idle, don't be messing with the main jet or needle.  Likewise, if you have a stumble up higher, don't mess with an idle adjustment you've already tuned in. 

There is a big difference between a carb tune that runs, versus one that runs right!  It's something you won't fully understand until you feel it.

Good luck!  And be willing to ask questions and post about your progress   

[bigbore2]

sounds like the same kind of problems I was having trying to tune my 84.   I noticed one spark plug was darker than the other 3.. Which means too much fuel, not a lean condition. I was thinking lean too.

I looked at everything with my magnifying glass, just to be sure I did not miss anything. Everything was clean in the carbs. the problem ended up being a bent float pin.  It was not letting the needle seat and extra fuel was getting thru on carb #3.