BS34SS pilot screw effective adjustment range?

[dweller]

Wondering what the effective pilot screw adjustment range is on the BS34SS carbs on my GS11E? Obviously from seated out to some point. At what number of turns out is the passage fully unobscured? I've got a slightly lean idle (based on plug readings and decel lean popping with throttle closed). Going out further on the screws does not seem to be solving it so I guess the pilot jets will need to go one step bigger. Just curious if there is a known range of effectiveness for turns out on the pilot screws? Thanks

 

[Steve]

Have the carbs been cleaned in recent memory? If the passages inside the carb body are not clean, no amount of screw twiddling will make any difference at all.

Now to answer your question: When the carb was made at the factory and the screw was pre-set and sealed, it was likely out about 1.5 to 1.75 turns from lightly-seated. Over the years, it has been found that the rather lean setting might have been OK for emission control, but was absolutely lousy for general running. The addition of Ethanol in the gas also requires just a bit more liquid flowing through the jets, so most carbs will require 2.25 to 2.5 turns out. I have seen changes up through about 4 turns out. After that, I would suggest going up one size, which is 2.5 numbers.

.

 

[dweller]

Carbs are in perfect shape, completely rebuilt two years ago and only non-ethanol run in bike year round since. Right now I've progressed in a couple steps from 3 to 4 turns out and am seeing no difference in idle plug readings. About to do a road test at 4 turns out now, but I suspect I'll have to go up one size on the pilots. Thanks for the response. I'm also slightly lean at just-cracked throttle setting and will likely be raising the needle one more step to address this. But I want to get pilot circuit adjusted first since these two do have a slight overlap. Bike runs perfectly except for this slight lean condition at idle and just opening from idle.

 

[chuck hahn]

Look at the STICKIES at the top of carb section. There's a good. Guide called CV CARB TUNING.

 

[dweller]

Look at the STICKIES at the top of carb section. There's a good. Guide called CV CARB TUNING.

Thanks, I have read that guide. It's a little misleading because he talks about rpm range instead of throttle opening position. I understand How CV carbs work, but jetting is still also a function of the throttle setting, not just rpm. Mains are good I think. Plugs look good chopping ignition at wide open throttle in the 6000 rpm range. Have already raised the Dynojet needles two positions from their recommended initial setting and it's almost perfect now as far as response and seat of the pants hp. Floats set at Dynojet's recommended height. Idle and just off-idle throttle openings are slightly lean and with mixture screws out 4 turns, I'm thinking I need to go up one size on the pilots. I want to try this first rather than raise the needle another position which I feel will make mid to wide open throttle settings too rich. I think ceramic coating the Kerker header may be what's causing the difference between this bike and Dynojet's baseline. Otherwise stock with APE pods.

 

[Steve]

... Have already raised the Dynojet needles two positions from their recommended initial setting and it's almost perfect now as far as response and seat of the pants hp. Floats set at Dynojet's recommended height. Idle and just off-idle throttle openings are slightly lean and with mixture screws out 4 turns, I'm thinking I need to go up one size on the pilots. I want to try this first rather than raise the needle another position which I feel will make mid to wide open throttle settings too rich. I think ceramic coating the Kerker header may be what's causing the difference between this bike and Dynojet's baseline. Otherwise stock with APE pods.

Not sure what jetting differences would be caused by ceramic coating, but it's sure nice to know NOW that the carbs are not stock. :-\\\

.

 

[Gorminrider]

I haven't much expertise with all the stuff you are doing but I've never noticed much difference at the idle-mix screws outside of half a turn either way from a central setting...

 

[dweller]

Not sure what jetting differences would be caused by ceramic coating, but it's sure nice to know NOW that the carbs are not stock. :-\\\

.

I didn't think the mentioned changes would affect the adjustment range of the mixture screws, that's why I didn't mention it initially. It sounds like the effective range of adjustment is basically seated to 4 turns out max. And possibly not even that.

Thanks for the responses everyone.