Carbs adjusting

Hello,

i had to rebuild my carbs on my XJ 650 4k0 after one of the four is only scrap metal. I always had a problem with my 4 in 1 aftermarket exhaust. About 5.000 rmp the bike will stall a little bit, after 5.5000 to 6.000 rpm it runs again like hell. Some guys told me this is the fault of the 4 in 1 exhaust and it can be only solved, when i install a original exhaust. As usual, people use the comfortable way to solve problems. But it is nearly impossible to get an exhaust payable and in a good condition.
Is it possible to solve the problem with adjusting the carbs. At the moment it is running with a 112 main jet and Y-15 Jet needles. I think this are the 2 main parts which mostly influence the RPM between 5K and 6K.
I could not exactly figure out if the bike is running too lean or too rich in this rev band. I tried to take the choke in as soon as it begins to stall. But this would make it even worser. So i guess it is to rich in this rev band.
I want to try a 110 main jet with the Y-15 jet needles. I also have some Y-11 jet needles and 105, 110 and 116 main jets to try in combination.
Are there any experiences in the community which could help me solving this problem??

THX in advance

Michael

 

You should be able to find a decent compromise, but also the pipe you have can be poorly designed regarding helping the engine make even power throughout the range. I fitted a Marving to my KZ650, and it made more power from idle to redline compared to the stock system, without any jetting changes. Just as an example that 4-1 does not need to be bad. MOTAD exhaust 4-1s will perform close to stock in every way.

The best way to get the jetting sorted for your current system would be on a dyno where they can read the exhaust emissions to understand if it is running lean or rich.

 

I have a Motad 4 into 1 on my 900f which runs fine.

 

The SCHEIBEL 4 in 1 is known to be the better one for the XJ650 4k0. Some reviews said... But still the problem with the 5K to 6K RPM.
I think i will play and test with some configurations. Which one will work the best.
I guess with the Y-15 Jet needles (which i have already installed) it will run leaner than with the Y-11 Needles. But still too rich with the 112 Main Jets.
I will try the Y-15 in combination with the 110 Jets at first.

 

Personally, I would have shimmed the needles first, no other change. Two changes at the time can make it difficult to know what worked and not, although sometimes you may have to make several changes at the same time. By shimming under the needle, you will effectively richen the mixture, since the pistons will not go all the way to the top even at WOT at 5000 rpm. So if it runs worse with the needles raised a mm or two, you will know you need to go leaner. And vice verse.

 

airbox or pods?

 

Good question!

 

My 650 on airbox with a dirty old filter runs sweet on a Vance and Hines 4 into 1.
Stick pods on it and who knows, you might need a lot of tweaking to make it work well.

 

Original airbox with original filter. half a year old maybe.

 

You've cocked something up. A 4 into 1 won't have that much of an effect. Go through your carbs again, revert to stock needles and jets. If it was rich you'd have clouds of smoke out the back.