another carb question

[Sam-Jaffa]

im running mk1 bandit 1200 carbs on a powerscreen motor using pod filters.

im running 130 jets and after 3k it pulls like a train but power it seems a bit boggy and tickover is lumpy.

the mixtures are currently 3.5 turns out IIRC and i doubt adjusting them more will make much difference, so, pilots...

with the mains being increased my 27% would my pilots benefit from a similar increase?

they're currently stock (37.5) im thinking if i go upto 45's (20% increase) then the rest should be able to be adjusted by the mixture screws.

anyone able to tell me if my logic is right or am i talking a load of bollocks?

[Oilyspanner]

Main jet doesn't have much affect at pilot jet type level. Normally 1 size increase on the pilot should do the trick with pods, so 37.5 to 40, I've heard of some needing 2 sizes up, but it's rare I think. FactoryPro go up just one size in their stage 3 kit, that's good enough for me !

If the pilot jets were a long way out, the bike would kangaroo a bit a lower revs/slow cruise/small throttle opening and revs would be slow to drop to tick-over.

Fuel level will affect all circuits of the carb, top and bottom the most though.

[Sam-Jaffa]

Sounds like i need to go up one on the pilot then, i do get a bit of kangaroo-ing sub 3k so I'll get some pilots 

Edited March 19, 2017 by Sam-Jaffa

[suzook12]

Could be an idea to invest in a 12mm colourtune kit, will help you nail the mixture cock on

 

[Sam-Jaffa]

Got one in my watch list ready

[nlovien]

use the mikuni HS40 manual as yir guide - bloomin good doc. - ref: the bit about fine tuning the idle / primary circuit - bigger fuel jet or smaller air jet maybe of interest 

http://www.mikuni.com/pdf/hs40_manual.pdf

 

[Gixer1460]

On 3/20/2017 at 0:41 PM, suzook12 said:

Could be an idea to invest in a 12mm colourtune kit, will help you nail the mixture cock on

 

But they are really only any use for idle mixture! Bit tricky riding at WOT and peering down a Colourtune at the same time LOL! 

[Solcambs]

5 hours ago, Gixer1460 said:

But they are really only any use for idle mixture! Bit tricky riding at WOT and peering down a Colourtune at the same time LOL! 

They work OK on a dyno I'd imagine - but that kinda defeats the object of them doesn't it!

Edited March 21, 2017 by Solcambs

[Sam-Jaffa]

Cheers for the input guys, I'm assuming the manual there will work the same for he bst36's then?

[nlovien]

9 hours ago, Sam-Jaffa said:

Cheers for the input guys, I'm assuming the manual there will work the same for he bst36's then?

the principles are the same - key difference is in appreciating the difference between direct lift and CV  with respect to how you imply the relative jet circuit operating range

on direct lift - the 1/4 - 1/2 - 3/4 - full is directly related to throttle lift position = so you can mark the throttle lift in quarters to gauge this

on CV - its more related to engine demand  - I think of it as idle / light / medium / full on = so you got to be more focussed on how the engine actually responds to load demand during acceleration - marking the throttle isn't accurate

another area ref: Cv not covered is in playing with how the CV throttle slide lifts - ref: the return spring and pressure balance holes but with the bst 36 - i've not found a reason to mess with this - std seems to work fine  

[suzook12]

On 21/03/2017 at 4:49 PM, Gixer1460 said:

But they are really only any use for idle mixture! Bit tricky riding at WOT and peering down a Colourtune at the same time LOL! 

Pilot jet mixture screw IS set at idle, the op is asking about pilot jet, not mains

[Gixer1460]

3 hours ago, suzook12 said:

Pilot jet mixture screw IS set at idle, the op is asking about pilot jet, not mains

Agreed - but Pilot jets don't just affect idle - they are from idle up to and onto the needle and need to be checked under load ie dyno or out on the road - WOT or not you can't look at it while riding.

[suzook12]

3 hours ago, Gixer1460 said:

Agreed - but Pilot jets don't just affect idle - they are from idle up to and onto the needle and need to be checked under load ie dyno or out on the road - WOT or not you can't look at it while riding.

True enough, but have found in the past, if you can get a good mix at idle at sesible turns out, then its a good indicator the pilot jet is right size as well, not every time granted, certainly 75% of the time.....

Back on topic, had a similar setup to this and 2 1/2 turns out was sufficient, but every bike is different