YD100

[Chainlube]

Not to say ya did something wrong
WOW your brave sanding the taper on the needle and drilling the slide
I figure you thought it needed more air in one place and more fuel in the other
Now your stuck with what you've created. IDK if your carb can ever be tuned correctly now.

Have you sanded the needle and drilled the slide on other carbs before to have them run better.
I'm always interested in suggestions for new ways to improve carb performance.
I know some of these China Carbs can be off with their clearances or spec tolerances

Could you explain your reasoning of why you did these Modifications?

I know some of the needles for my SU carbs will have a little different taper, and there will be a slight bog in one spot. The cure for the bog is to sand the needle in that spot, it takes a lot of careful tuning and measuring to know exactly where to sand the needle. A 5 second burst with 400 grit sandpaper and the drill press set at 730rpm will take off .001". That would most likely be enough to get rid of the bog.

 

[Mugsy13077]

Hi Chainlube...I couldn't make heads or tails of what he meant when he said

I don't know if he meant adjusting the "C" clip up a notch, thereby "lowering the needle" more so into the float, thereby leaning out the mixture, or if he meant lowering the "C" clip, making the needle itself higher, thus making it run more rich ???
For that matter, which of the notches of the four or five available is it at right now...lol.

As far as

I haven't a clue what is meant by that statement...lol...DAMIEN

as far as

I know that usually that shouldn't even be necessary unless there are burrs etc., but changing out the jet to another size maybe what is needed ???...i know...I was born confused...lol...DAMIE

That was kinda why im asking what carb, as i have seen NT carbies referred to as NT speed carbs by various vendors...When he mentioned "middle" position, it made me think NT...DAM

 

[Mugsy13077]

Okay, so ive opened up the main jet with torch tip cleaner, and set e clip to the top notch. Sanded needle at the middle. Probably too much adjustment at once. Carb is a 19mm speed carb I'm working with. Putting it back on in the am and see how it runs.

 

[Mugsy13077]

I know some of the needles for my SU carbs will have a little different taper, and there will be a slight bog in one spot. The cure for the bog is to sand the needle in that spot, it takes a lot of careful tuning and measuring to know exactly where to sand the needle. A 5 second burst with 400 grit sandpaper and the drill press set at 730rpm will take off .001". That would most likely be enough to get rid of the bog.

Yes I've done this before. It's a bush fix to the cheeper speed carbs that only have so much tuning capabilities. Cordless drill and 800grit.and a drill bit does a lot. Oh ya and torch cleaning files

 

[Mugsy13077]

Just a 19mm speed carb, clamp on

 

[Wrench]

I know some of the needles for my SU carbs will have a little different taper, and there will be a slight bog in one spot. The cure for the bog is to sand the needle in that spot, it takes a lot of careful tuning and measuring to know exactly where to sand the needle. A 5 second burst with 400 grit sandpaper and the drill press set at 730rpm will take off .001". That would most likely be enough to get rid of the bog.

Yes I've done this before. It's a bush fix to the cheeper speed carbs that only have so much tuning capabilities. Cordless drill and 800grit.and a drill bit does a lot. Oh ya and torch cleaning files

Thanks guys that's explains alot,
I was thinking ya sanded the length of the taper and that didn't make sense to me.
If I mess up, Needles can be replaced IDK why I thought it was a big risk, I guess because sometime I forget to think
If I ever run into the bog issue that I can't fix with normal tuning I'll remember this needle sanding trick.
To sand about .001" with 800grt at the spot on the needle when the bog accrues.

 

[Karl Snarl]

ditch the jetted carbs and go pumper carb. Just make a simple spacer and isolator if not using a reed block. a higher end saw carb will have a hi and low and some will have an idle enrichment circuit for a choke ( or RUNNING NOS!!! WOOT WOOT!!!!). while yes they are simple carbs, NT'S, they suck to tune. take it apart, put it back together, take it apart, on and on and on till it's dialed in. saw carb, just turn the screw while the bike is moving and in a second or two you feel the difference.

addition:::: an if you are low on funds or just a cheap mother lover like me when I build a kids bike for free, use a pumper pocket bike carb, only has one fuel circuit, but they work well on a budget. They are slightly smaller a venturi than the nt, so it will reduce top end slightly, but its cheap version of a saw carb. a good saw carb will cost ya $30, a cheap pocket bike diaphragm carb will cost about $15

 

[Chop-chop]

Sanding the needle is an old carb tuning trick that dates back to the SU carbs that were used in the old Datsuns & Jaguars. The SU carbs ran a similar needle setup where the needle is elevated by a vacuum operated piston inside the chamber containing the venturi. I remember seeing a display poster in a workshop many years ago that had illustrations of the different needle shapes that would give you different torque characteristics at different rpm ranges etc.
For example, if the needle has a constant taper thru its entire length, then the rate at which the fuel is added is constant, however, if the angle of the taper, or the rate at which diameter changes at various stages along the needle's length, you can effectively change the rate at which fuel is added into the carb...
Having said that, one must KNOW what they're doing when 'shaping' the needle at the various stages/heights... in this day and age, providing you know what you're doing AND it would be superb if you had access to a precision lathe or better- a CNC machine to create the perfect needle.... it can be done... but only if you know what you're doing. To be honest, it would be easier just to set up a cheap efi running a single injector lol