To drill or not to drill......

[Racer-unk]

Firstly it is good to see some activity here on the forum with some new members that contribute and share their pics.

Getting to the point: I received my 6-Sigma jet kit.

1) I assume.....regardless of whether you have a flowed head or have bigger pistons, etc..... drilling an auxiliary hole in the slide and shortening the spring is all about throttle response and nothing else?
2) I am aware that it affects your low down running of the motor, in terms of operation in traffic etc.....but I am only using the bike on a track and currently it runs rubbish low down anyway so I am used to it.

Has anyone still active on this forum, done this mod on standard carbs? Please elaborate and advise.

Serious want to do the mod, but not doing it blindly.

[dicky]

I have done similar mods on big single cylinder enduro bikes running BST-38 carbs.
Cut a couple of turns off the spring, drill a couple of holes in the bottom of the slide.
The intention is to reduce the pressure of spring and the 'air spring' effect inside the slide to allow it to lift with lower venturi pressure (ie vacuum), thus helping improve throttle response. It only works up to a point as it is still a CV card and relies on the inlet vacuum to lift the slide, so when you crack open the throttle you still have to wait for the vacuum to build before it can move the slide. Best results are in the mid-range.
For my KTM I cut 4 turns off the spring as it was being used on-road as a super motard. For off road the general consensus is to only cut two turns.
The reason is that if it reacts too fast it basically shakes up and down, which at low revs causes the engine to bog down.
I'm not sure what your kit recommends for the holes, on my bike I drilled out the two side holes in the bottom of the slide to 1/8"
After all this I could barely tell the difference. It's still a CV carb.

[cobbadiggabuddyblooo]

I have a pair of Japanese import CV carbies in the garage that have an ACC pump fitted and was thinking down similar lines that they may already be set up like this from the factory????
I'll get around to pulling them apart 1 day and looking to see if any difference between the slide and Spring on a Std trx carby.

[Racer-unk]

Basically I sent them my bike's info and they sent Pilot and main jets. 145 Main and 47.5 pilot.
(K&N Filter, standard air-box and Really open 2-to-1 pipe) ridden at the coast.
I have to drill 1 small hole next to existing hole. not much larger than 1 mm. Reason being you can seal auxiliary hole and then standard hole remains as is.
recommendation is to remove one coil at a time. still don't know how I will put the one coil back after I realized i went too far...

There is a lot of criticism about this practice, but I am sure the chaps went ape without having proper advice and it did not work for them.

[dandywarhol]

I did a similar conversion on my SZR single with a kit from offroad.de. The kit has a larger air jet for the slide and a 2mm spacer fitted under the carb top to allow the piston to lift further

[Racer-unk]

Pulled Carbs last night....CV carbs dont have space to drill an extra hole...can only enlarge existing holes. will just leave the matter for now........begs a question about how well these jetting experts do the job when they send you a kit......none the less I am going with the jets they send to me