If you want to not mod the airbox, my friend got great results with a slipon and mid-pipe, a radio shack shim, and a 102.5 mainjet(1 up from stock) and a mixture screw adjustment and no Airbox modding. But if you would like an extra 15 horsepower for an hours work and clean the jetting up a lot. Drill an extra 1.5" hole in the airbox lid, keep the stock air filter, don't buy a K&N, pop in 110 mains(or 112.5's if a little weak) and turn the mixture screws out to 3.75 to 4 turns out and a couple of radio shack shims under the needles.
Radio shack shim part number: 64-3022A
Or you can go to a hobby store and get some shims to fit underneath the needle to raise them which will kill that dead spot and give you a bit more power especially with the 1 up on the mainjet.
I have a Holeshot kit where the shims are .5mm, the radio shack ones are 1mm. So two .5's or 1 1mm should be fine. You are actually LOSING power with the factory lean jetting getting even worse with an aftermarket exhaust and no jetting. Does the D&D can have an aftermarket mid-pipe? Are the mixture screw plugs drilled out?
I had the same bike as you but up here in Canada we got the nice Full fairing version the GS750EF's Here is a pic of my last bike same colours, Jetted with a Yosh can, fun as hell:
1984 GS750EF, actually sold it at a profit after fixing it up. My Bandit 1200 reminds me alot of this bike, same riding position and sounds as its the same mill just a 750.
We didn't have the stupid "Bail Harley out strange CC" law up here. So it was a real 750, not a 700. Why didn't Harley just get their shit together and start building better bikes instead of asking for a bailout from Regan? I though Republicans were all for free trade, open markets, etc, etc. It was actually bad for HD as instead of being forced to innovate it turned them into a fashion house instead of a Motorcycle company. Sad, just sad. Although the writing was on the wall back in the late 60's when they pussied out and got out of road racing, instead of trying to compete with the new fangled Japanese bikes coming on the market.
At the minimum, you could shim the needle and adjust the mixture screws, you'll like the extra power trust me. You're running super lean right now if you have the stock jets in there.
This is what I'm running now.....check sig. I might go to 115's or 117.5's and the K&N filter I have that's getting lonely in it's box, as it was just a bit too lean even with 112.5's, went back to the stock filter for now. Need at least 115's or 117.5's for the K&N. I tried the suggested 110 mains but it was just a little too lean up top even with the stock filter. I think it's my Muzzy slip on and Mid-pipe which is very free flowing and I'm fairly close to sea level so it probably needs the extra juice. I'll see how lazy I am in the spring. I'm working with a guy in Australia because its summer there now to jet the stage 1 with a K&N instead of the stock filter which will probably push the horsepower up a few ponies and close in on 118 or so instead of 113-115 and breathe alot better and have a cleanable, instead of a throwaway, air filter.
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