my cousin has a ds and he took the spark arrester and then he noticed when he went at full throttle for just a couple seconds it would start to backfire. well i figured it was because he was running lean so i went and got him a jet and put that in, raised the needle one notch, and i turned the mixture screw all the way in and turned it out like 3-4 turnes, and then we took off the air box lid, and it was firing less but still doing it.
does it just need to be jetted richer or is it hitting the limeter or what?
should i have him run full throttle and turn it off and then check the spark plug?

thanks

 

Removing the baffling on the end cap increased air flow, so it was lean.
Putting in a larger main jet would help counteract this on the top end - what jet did you put in??? The one you need will depend on your elevation.
Raising the needle will richen from 1/4 to 3/4 throttle - are you sure you actually raised the needle, because to raise the needle you would lower the clip?
Removing the lid increased flow again, making it even more lean than it was, creating the need for even more fuel and bigger jet again.
The idle mixture screw controls mixture at idle only, but if its set wrong it can cause the bike to backfire when the throttle is let of - to set it, turn it in until the bike begins to bog, then start turning it out counting each 1/2 turn until the bike bogs again, then position the screw exactly halfway between the two points of bogging.

Tell us what main jet is in it now, and exactly what was done to the muffler, and we can get you very close to where you need to be on the jetting, and then put in a new white plug, ride, and check for color.

 

the elevation is less than 2500 feet, not sure exactly what elevation is thoe.
all he did is take out the spark arrester.
i put a 185 main jet in, and yes i did raise the needle by lowering the c-clip.

does the ds have 2 spark plugs and if so do you have to check both or just one?

thanks

 

Jetting sounds close to right, within one size probably, every bike is a little different.
Yeah it has two plugs, but they will both look the same so you only have to pay attention the easy one to get to.
They burn really clean, if jetting is right it'll take a couple hours to get good tan color like you'd expect from other bikes in 1/4 that time.

 

so i should check the spark plug and see what it looks like?