38mm RS jetting

[buff]

Ive just picked up a new set of 38's running on a bog standard 1200 bandit engine, bike pulls well up until 4,500 revs then kind of bogs down a bit. If i pull the choke out its starts pulling again. Standard jets are 135, worth raising the needles or just stick in the 140 mains ?

[george 1100]

Check plug colour after a few hard runs

Try the jets first. Only do one adjustment at a time. Did you check float bowl heights? Is petcock ok?

[buff]

No I didn’t check float height  as they’re new out of the box. Standard vacuum tap.

Edited March 24, 2022 by buff
spelling

[dago]

They're quite well known for float heights to be wrong out the box should be 17 mm

[Joseph]

Fwiw i have the out of the box RS38 jetting on a 1216+cams and plugs have always been the proverbial milk coffee coloured

Float heights were also off on mine out of the box and needed adjusting

Edited March 26, 2022 by Joseph

[buff]

I'll give them another check tomorrow, Ive put 140's in today. Its pulling better over 4,500 revs picking up nicely. But still a little rough just below this. Ive raised the needles a notch this evening. Next time carbs come off I'll check the float height

[Joseph]

Could an air leak a culprit in view of the symptoms ? What state are your inlet boots in ?

[Jaydee]

1 hour ago, buff said:

Its pulling better over 4,500 revs picking up nicely. But still a little rough just below this

I'd play around with the mixture screws. Open then up a quarter turn and check if low down is better or worse. Nothing to lose.

[buff]

1 hour ago, Joseph said:

Could an air leak a culprit in view of the symptoms ? What state are your inlet boots in ?

Boots are all good, tick over etc is steady.

[buff]

Gave it a run earlier, if anything raising the needles has made it worse higher up the rev range. Still a bit hesitant low down, but if I pull the choke out slightly it smooths out. Checking the floats heights in a while and give the mixture screws a tweak

[dago]

Revs have nothing to do with throttle position, you should mark the the twist grip and housing work out where ¼, ½ ¾ throttle are then you can work out which jets are coming into play

[Oilyspanner]

As sago has said - you need to work out at what throttle.  Here's what I did to know which percent of opening I was using, I rubbed some of the markings off while testing, but you get the idea.

 

[buff]

Float heights were all spot on, mixture screws were only 3/4 turn out. So Ive set them at 1 turn. I'm sure way back when I was running 36's it was 1.5 turns out, but that was with an 1170/1260.  Not tinkering with this stuff for ten years means Ive forgotten a little

[george 1100]

Don't forget the accelerator pump also. Start with the default setting and go from there

[buff]

Pump is set to come on at 1/4 to 3/4 throttle. Ive got the switch/throttle marked up ready for a run tomorrow.

[buff]

This evening ride was a different experience. Pulled all the way cleanly from low down, maybe I’ll drop the needles a notch looking a bit rich 

[dago]

Let us know what settings you ended up with please. Looking good though

[buff]

At the moment 140 main jet, needles on middle clip. Pilots on 1.1/4 turns out . GSX  1100 airbox bellmouths with ramair socks. Standard 12 engine with titanium muzzy pipe. 

Edited March 29, 2022 by buff

[buff]

Dropped the needles a notch this evening, not so smooth and missing a bit. So back to the middle clip again.

[fab]

On 3/29/2022 at 7:00 AM, buff said:

This evening ride was a different experience. Pulled all the way cleanly from low down, maybe I’ll drop the needles a notch looking a bit rich 

that plug looks good ,you are better off on the rich side of a tune than lean. 

[Jaydee]

2 hours ago, buff said:

Dropped the needles a notch this evening, not so smooth and missing a bit. So back to the middle clip again.

Do you have a shim washer for going under the E-clip so you can get half settings between notches? Helps with the fine tuning when you're almost there.

[george 1100]

4 hours ago, buff said:

Dropped the needles a notch this evening, not so smooth and missing a bit. So back to the middle clip again.

After you dropped the needles maybe you should've brought your acc pump in earlier then maybe quarter turn increments of the pilot to see if that affect sub 4500rpm. Either or, or a combination of both