81 xs650 BS34's 160 main jet hesitation mid range

[francocali]

I have a 1981 XS650 with BS34 carbs , been working on build about 2 months, had a problem with stock bs34 carbs (i did good carb cleaning), had loads of black fluffy carbon dry on plugs, i am running wide open, pod filters, chopped pipes loud...

spoke to my friend and he said i need to run 160 main jets bacause needed more fuel which i did, that worked great but noticed the mid range of acceleration was flat, sounds like not enough fuel...here are the facts :

1) 1981 xs650 bs 34 carbs changed main jet from 132.5 up to 160
did not change any other jets did not touch anything else just did good carb cleaning with carb cleaner and compressed air cars.

2) running open with air pods chopped pipes loud, installed pamco ignition (love it).

3) runs good but when i accelerate the engine boggs down in the middle section of power band... like as i roll on gas runs good then as i hit the middle range of power band sounds like not enough gas (maybe 160 sucks the gas from the float bowl too fast .should i raise float bowl level..?

4) also the left plug look perfect the right plug tiny bit of carbon, but not too bad...do i need to adjust air screw on the right carb?

would like to know if i need to change the pilot and idle jets.

what about swapping in mikuni vm 34 or vm 36 after market carbs?

 

[swbill]

Read my post "weak cylinder". Sounds similiar to your problem. We found the cheap pod filters were the problem. I am sure your going to need a larger pilot jet also.

 

[Lunatic]

That's a massive main jet. I would say way too big. I'm running pods and was running straight pipes up until a few weeks ago with totally stock jetted BS34s (with Canadian needles/needle jets) with no problems at all.

I would say you are going in the wrong direction, go back down to a stock or near stock main and then start tuning from there. Look up the carb tuning guide here and go through it carefully step by step. You may want to look at the Canadian needles and needle jets from MikesXS as they are adjustable and seem to sort out many of the issues with the BS34s.

 

[Sundie]

had loads of black fluffy carbon dry on plugs,
spoke to my friend and he said i need to run 160 main jets bacause needed more fuel

Your friend was incorrect. Stop listening to him.

1) 1981 xs650 bs 34 carbs changed main jet from 132.5 up to 160
did not change any other jets did not touch anything else

Do you run a lot at 5k+ at WOT? And by a lot, i mean all the time.

That's a massive main jet. I would say way too big. I'm running pods and was running straight pipes up until a few weeks ago with totally stock jetted BS34s (with Canadian needles/needle jets) with no problems at all.

You falter a tiny bit at 6k+. But you hardly ever run up there, so it's not exactly an issue.

You may want to look at the Canadian needles and needle jets from MikesXS as they are adjustable and seem to sort out many of the issues with the BS34s.

I firmly believe that swapping the needles/needle jets to the CDN type fix all the issues with the BS34's.

 

[650Skull]

Way to big, will wash the bores in 2 seconds flat = rebuild

 

[dqnjuan]

Mine bogged down with the 145 mains went back to 135 with 47 pilots and pulls cleanly with good color on both plugs. Im running pods' open gordon scott drag pipes' and xsjohn(rip) needles.