Slide, to drill or not to drill, that, is the question

My CVP carb parts order has finally arrived! My Friday night carb build can begin. Can anyone tell me why the slide port was recommended to be drilled to 1/8 in the past, then no bigger than 7/64, and now some say leave it as stock? I have a new slide ready to go in to replace my burnt, drilled one. Should I drill it or leave it alone and what does the drilling accomplish? I assume faster throttle response???

Drilling will result in quicker throttle response but is usually accompanied with the installation of a lighter spring.

I would not drill or try to clean up the slide hole, even if it were to make a difference it would be so minimal you would not even notice the difference. Just leave it alone, the drill bit is to drill the filler material out of the air adjustment screw hole.

The bit that came in the kit is for drilling the cap off the idle mix screw...it's the same size as the vacuum port so you could run it in by hand to clean or de-burr the port,but you don't want to enlarge the hole...since it's a new slide I'd leave it alone...the lighter spring in the kit will let the slide raise quicker and you won't get any hunting or surging...

Thanks for all the advice, I'll leave it be. Anyone have any thoughts on mild chamfering of the slide edges facing the airflow and polishing slide with mild steel wool? Oh yeah, is the EZ just screw with the kit usually a bit difficult to thread in? Mine goes in 3-4 turns and seems to fetch up. The stock mixture screw threads fine and the EZ just screw threads look fine, pitch and diameter look same, and it isn't anywhere near bottomed out.

I got the drill bit with my CVP kit. I used it with a new slide and it seemed to enlarge the hole only very slightly. Have had no problems with surging or any other carb related issues.

If the EZ adjust screw is fetching up, get a tap with the same thread pitch as the screw and clean out the threads in the bracket.

I wouldn't do anything to the slide. If it moves up and down smoothly, let well enough alone.

I read the mod on nightrider.com back in 2000. Mine and every carb I've done has been drilled to 1/8". A friend who was the head mechanic at a dealership drilled mine, before I found the mod on nightrider. I felt a tiny bit, could have been a plasibo effect too. I learned how to do my own carb mods in the last 13 years, and drilled them all with no drivability issues I can tell. Now that there is a caution in the wind I don't think I will drill anymore.

Why did you change your slide just for burn marks? News to me to do so.

Saw a video on youtube of a guy with a Harley shop who mentioned in his video or comments that if it gets burned it should be replaced, made sense to me as the rubber of the diaphragm would be brittle at that spot. Wouldn't use a fire damaged condom, would you?

Guess I should mention, reassembled using recommended jets, did not drill slide but used supplied spring from kit, rounded edges of slide with file and polished with fine steel wool, replaced accelerator pump diaphragm and spring with all CVP stuff, HOLY $#@*! This bike is mega smooth and starts before I can release the starter. I AM A VERY SATISFIED CUSTOMER!

Now your making sense to me, I thought you were referring to the black suit on the slide as burn marks. I've not had the unpleasant burn mark issues on any condms yet lol.

You are the first person I've heard mention, burn marks on a diaphragm.

Condom burn marks are more of a high school/university thing. I assume the burn marks on the diaphragm of the slide were due to the preexisting lean condition at off idle, when the bike would sometimes give a carb fart and then stall on occasion, usually downtown in front of the clubs on nice summer nights in front of everyone...

I have drilled every the OEM slide on every CV carbed bike I have worked on and installed the lighter spring; all with no issues and an improvement in throttle response. I consider it SOP when fine tuning the CV carb. The drill does remove some material but little more than cleaning up the bore. JMHO but throttle response is the difference in performance between the CV and the Mikuni.

I use the Yost kits which includes two drill bits; 7/64" and 1/8". The larger bit is to drill out the needle hole in the bottom of the slide and the smaller bit for drilling the vacuum port in the slide, although, depending on application, the larger bit can also be used to drill the slide vacuum port. I particularly like the Yost kit for bigger bore motors and prefer it to the CVP kit. JMHO.

Seems to be as many opinions on slide setup as sands on a beach! I can only speak for my limited experience, but on my 1200 Sportster with a 1/8 drilled slide when I bought it and a Dynojet kit installed shortly after, it seems to work better with the CVP kit and a new undrilled slide I recently installed. That being said, I still have a carb fart but now only once in awhile when I close the throttle as opposed to when opening throttle when I was running the Dynojet kit.

Carb farts and decel popping are both unacceptable for yours truly. :gah: Both generally indicate a lacking state of tune and both can be eliminated; just takes time and patience with a carbed motor.

Open (aftermarket) exhaust are louder and what sometimes is thought of as decell popping is actually just gases be burned in the decell process, even when the throttle is backed off there is still gas being pumped into the cyclinders, Stock mufflers muffle the sound and it is not noticed as much as with open exhaust.
Carb farts on the other hand are unacceptable.

As I stated earlier, Roadsterguy, I used the drill bit that came with my CVP kit. It is a 7/64" I believe. The other kits mentioned above drill out 1/8", which in some cases can be too much.

I drilled my brand new slide with the CVP bit and I have had NO problems with my carb. If you are having the occasional fart and/or decel popping (more a firecracker sound instead of normal detonation), you need to fine tune your carburator. No big deal. Start with the settings recommended by Ken in the instructions that came with your CVP kit. You may have to tweak your mixture screw one way or the other. Experiment with different settings until you find the sweet spot. Worked for me on my 1200 shovel.

My slide has been drilled for around 80,000 miles. I get great milage better then most and the same as the rest. My throttle response is smooth and quick. I have the same spring that comes in the cv 44 mm carb # 27728-99. If I'm getting ill effects from this my butt nor hand can tell. I wouldn't replace my slide if someone gave me a new one. It's sealed up and working great. This is the first site I've read that says don't do it. I've made my mind up sense it's not my carb if I do anymore I will give the caution a warning, and simply won't drill anymore. But as said, you couldn't give me a new slide and tell me to replace it. My throttle is right now!!! No lag no hesitation it's right now! If it flutters from being drilled I can't tell so the time for me to install a free slide would be in my opinion, time spent ridding instead ;^)

If I can get a time when it isn't raining I'm planning on doing some riding/fine tuning of the carb. Hoping some mixture screw fine tuning will eliminate the final carb fart gremlin, but at least now I can safely accelerate from stop signs and not have it stall out randomly. Now it seems to be more of a closed throttle/deceleration issue. Since I rarely close the throttle or decelerate I see this as an improvement!