Kat'750 - after changing the stock exhaust...

[ivobivo]

Hello, from 2 years I'm riding '01 Katana 750 and last week I have changed the stock exhaust with aftermarket one. It's FUEL Exhaust Slip on, Round Midi 400mm long with removable DB killer. This is the video of the exhaust - http://youtu.be/yN2rnvF4pNc

I'm with the stock Air filter - new Champion Y336 and new spark plugs - NGK CR9EK.

The problem is that after installing the new exhaust with NO DB killer the work of the engine on idle RPM's is not so stable, and between 1000 and 2000 rpm the engine is pulling slow and has less power. After 2000 rpm everything is OK. Sometimes I also have some BOOM's from the exhaust when closing the throttle on higher RPM's.

Please If anyone can help me with some info and explanation for this problems it will be great. Do I need to go for syncing the carbs or I need to do some extra adjustments?

P.S. thank you in advance and please excuse me if I have some inexact explanations, but English is not native for me.

["K"]

Fuel in tank is fresh? Not much power below 2k rpm is normal, but rough idle usually indicate poor fuel quality or flow, check fuel filter or vacuum leak, too.

[ivobivo]

The fuel in tank is fresh and on the video you can hear the engine on idle rpm's with the stock and with the aftermarket exhaust.

I know not to expect much from the bike between 1000 and 2000 rpm, but compared to "with stock exhaust" now in these range the power is 50% less and I definitely feel the "jump" in the power after 2000 rpm. With the stock exhaust there was not such a big "thinking" in accelerating from the start....

[TRPUT]

Generally, a free-flowing exhaust comes into its own at high RPMs, but can actually be a liability at low RPMs when the back pressure and "pulse" provided by the standard exhaust can (theoretically tuned to the bike's carbs, cams, timing etc) maintain smoothness and improve torque. The carbs operate more erratically (not necessarily constantly lean, just not consistently smooth) without some back pressure. Simple solution ... if it runs better with the DB killer, install it. More complex ... fiddle with the carbs (assuming they are clean and functioning properly). The "booms" or pops are an indication you are running too lean at low and closed throttle, so you can firstly try cranking up the mixture screws by 1/2 a turn. A carb synch is never a waste of time. Oh, and there's not a whole lot wrong with your English.

[Kreylyn]

Generally, a free-flowing exhaust comes into its own at high RPMs, but can actually be a liability at low RPMs when the back pressure and "pulse" provided by the standard exhaust can (theoretically tuned to the bike's carbs, cams, timing etc) maintain smoothness and improve torque. The carbs operate more erratically (not necessarily constantly lean, just not consistently smooth) without some back pressure. Simple solution ... if it runs better with the DB killer, install it. More complex ... fiddle with the carbs (assuming they are clean and functioning properly). The "booms" or pops are an indication you are running too lean at low and closed throttle, so you can firstly try cranking up the mixture screws by 1/2 a turn. A carb synch is never a waste of time. Oh, and there's not a whole lot wrong with your English.

+1


To add to this, this is where tuning the a/f screw settings when the bike is running really comes into play. You may already have 1 or 2 that are slightly lean, and the extra flow is exaggerating that further to cause the engine to be missing on one or more cylinders at idle speeds now.


If you adjust the a/f screws out and there is no effect, you may have one or more blocked /partially blocked pilot systems. (that would mean clean the carbs).


Krey

[ivobivo]

TRPUT and Kreylyn, thank you guys for the good advices...first I will do the Carb Synch and if there's no change I will try it with the DB killer ON to see how the power between 1-2k rpm will be.

Because I prefer to ride in city without DB killer, if I leave it that way without adjusting the A/F screw, do you think that I can blow off some of the spark plugs because of rich in fuel mixture while riding, or on higher rpm's everything is OK with the engine?

Sorry if I'm asking stupid questions but I'm not good in carb things...and again thank you all for your efforts to explain everything