To Drill Or Not To Drill Slide Mods

I already drilled the vacuum slide to 7/64 as instructed in the Harley Performance instructions. After some inquiry, I was told (by several sources) that I should not have increased the diameter or replaced the spring and needle...something about too much response off idle and a variance in metering as the slide acts as a shock absorber and with a lighter spring and larger port, it reacts too quickly and the mixture becomes erratic or unstable. Furthermore, the "constant velocity" is overridden with the lighter and more eratic behavior of the modified slide configuration. It no longer acts in a constant velocity manner. Any truth to this?

I think if you put the stock spring back in you'll be OK, I've seen some that drilled the port and clipped 2 coils off the spring and worked OK, the slide will react quicker with the larger port and lighter spring and could possibly "flutter" at higher speeds but I think that is due to the lighter spring mostly. The needle meters your fuel between 1/4 and 3/4 throttle, so depending whats done to the bike would determine its need for change or not.
What you did will make the stock slide a little like the thunderslide kit for CV's,which IMO is too light.
Try it out as is if you get surging at constant throttle put the stock spring back in and try again. I don't think you wrecked your carb, you may like it.

Thanks...no, I don't think I wrecked it..and fortunately I only drilled to 7/64 and not to 1/8. I did notice surging at constant throttle and low speeds 20-30 MPH and it is annoying! The needle that came with the kit was significantly shorter than the stock needle, so I deduce that the shorter needle will richen the mixture compared to the original needle. I am going to put the original spring back in tomorrow night. I am not sure if I should also put the original needle and the one washer that was in it originally? As far as idle and off idle is concerned, I get no popping off idle and great acceleration at WOT and 80% WOT..and it is very smooth..so that circuit seems to be functioning. It is just the midrange constant throttle that is sketchy with surging etc... I do still get a few pops every now and then on deacceleration-which could be exhaust leaks.

And I thought the mods to the carb were supposed to INCREASE performance... I am going to put the original spring and needle back in and report. The hesitation and surging at low speed and constant throttle is so damn annoying that I don't even want to ride it around town. A guy I know wants to do the carb mods as well since he has SE slip ons and SE air filter..I will definitely advise NOT doing the slide mod! Thanks for the input.

That mod might be good for drag racing when it's instant WOT, but for a street bike, no. Rejet and the '88 Sporty(N65C) needle or either the '94 or '04 Sporty needle, I'm not sure which it is N72 I think, but thats all you need to do for a responsive street bike, no light spring or radius the slide, you gotta take the advice and analyze it for what its worth,what are you gonna gain or loose by doing this. I'm far from an expert, there are a couple on here, but be careful what you read and ask a lot of questions before jumping into something you may not be able to reverse.

Thanks Lucifer... I am doing a whole bunch of work to it today...diamondback throttle cables, clutch cable, chrome belt cover and putting the original spring and needle back. I see the needle is marked..gotta get a magnifying glass to see it, though. I will update after completion.

The needle

I didn't drill mine for the reason cited above.

I just dropped in the '88 Sporty needle. Noticed a difference right off, no more lean condition.

Joe

I had a 05 883 custom. I drilled the slide and put a new spring in that came with the kit. I changed to needle to an adjustable one and it killed my mileage. I went with the stock needle and yellow spring and that worked well. I also had a big bore kit installed and no problems. Have you removed the plug in the carb for adjusting the low speed setting? That might help also.

Kevin

Here is an update:

I decided to go back to the basics..I thought back to the day when I was a Porsche/Audi/VW tech...started from scratch...

1. replaced carb gasket
2. Replaced crossover gaskets and removed washers the previous owner put in the crossover probably to create backpressure, since he removed the baffles from the OEM mufflers (since replaced with CS)
3. Got rid of the EZJust and put stock mixture screw back in. Less burned fingers and knuckles with stock.
4. Put original slide spring and needle back in.
5. cleaned carb (again) and blew air through all holes
6. Checked float level
7. Replaced spark plugs

Also replaced throttle and idle cables with diamondback....to make it pretty, I got a chrome diaphram cover.

It started up and ran smoothly..warmed up and adjusted mixture screw 2.7 turns out from base...idles well and no surging or hesitation with constant throttle and low speed. I don't have all the "punch" I had with the mod slide spring and needle at mid-upper throttle, but it still has snap. I am more concerned with low to midrange throttle...since that is what I use most of the time. Overall, the bike is running very well and I am happy with what was done. There is no pop back on deaccel and it runs smoothly.

I am doing a carb mod to a friend's bike on Wed...definitely not modifying the slide or needle. Jets only...

When I worked for Porsche, guys would come in all the time wanting to put Webers on their 911s and remove the CIS injection..then they would complain about the popping and wheezing when cold as well as the not so great fuel economy....I am not a big fan of carbs.

Guys driving Porsches and complaining about fuel economy??:roflmao:
The Webbers can be a SOB to set up and would need a choke cable or enricher for running while cold.
The CV is a great carb, if you want to try something ,pick up a stock spring and clip 2 coils off of it, I've seen the springs for the kits and I think the guage wire is lighter than stock and they are about 2 coils shorter. Have a stock spring on hand in case it doesn't work and I would still pick up one of the Sporty needles mentioned above instead of shimming the stock needle.
A bud of mine drilled the port 7/64" and clipped 2 coils off the stock spring and it worked well, he also shimmed the stock needle...no surging or flutter, his instructor at the Harley Tech School here in Canada also performed a little "magic" on the heads and that baby really flies.

I have 2 carbs that Ken worked on, they are great. He does a little magic with them. I believe that he sells all the parts to do the same thing. Basicly he polishes and bevels the slide, polishes the bore, changed the needle, I think he cut the stock spring. I tuned the way he explains how to do it. I have had the same carb on 3 different bikes and 6 years later it still works great. I have used it on a stock Evo A built Evo and is now on a TC88. I still get 50 plus miles to the gallon.
The other is pretty much the same thing on a modified TC88. I would rather have a CV anytime over an S&S carb.

I purchased a carb from Ken....Haven't put it on yet (winter project)all I heard is good things about what he does to a CV carb...Will let everyone know how mine turns out next season,I am pulling off a S&S just too big for my bike.

to drill or not to drill that is

Hi! you all, first time posting.I agree with lucifer drilling the slide is a drag racers trick not for the street.i have an 05-883 w/se air cleaner,samson silver bullit slip ons.I thought about drilling the slide but decided to just change the slow jet from #42 to a #45 I left the stock 175 main jet and change the jet needle to the n65c.i adjusted my idle mixture screw out 2.75 turns this combination works good. but to make it better i added a dyna dspt-1 ignition module set at 34a advance curve and 6500 rpm.w/se coil.I,m happy!!!my next upgrade is to change trans pulley from 27 teeth to 29 teeth i do a lot of high way riding. p.s no matter what mods you make budget your money and upgrade your ignition you will notice the difference.