How I Tuned My XII For Performance

[Merch]

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[SgtSlag]

I used to own a 1979 Honda CB750K, with a CV carb. Many owners on a forum dedicated to the CB750's, tried to use pod air filters on those CV carbs... They threw a lot of time, and money, and jets at them. They always had a flat spot, no matter what.

You are saying that you have overcome this issue, that you have zero flat spots in throttle response? If so, that is quite an achievement. You are the first person to do so, that I've heard of. I've read a lot of posts from guys who were considered to be experts on the subject: they all claimed that there was *always* a flat spot, which could never be overcome without the OEM air box. A few of them changed the exhaust pipes, baffles, etc. None of them were able to overcome the flat spots, though. Interesting.

Thanks for sharing. Cheers!

[Merch]

Redacted

[SgtSlag]

Everybody I've read through, on using pod filters on a CV carb setup, focused pretty exclusively on the jets -- I don't remember anyone ever tuning the exhaust, along with the carbs. Yes, they made exhaust changes, but it was done for the sound they wanted, not for tuning purposes. By doing both, for tuning purposes, it becomes believable, that you could make it work.

I posted in the past, more than once, that if you could make it work, you would be giving up something -- the factory engineers knew what they were doing, they did what they did, for good reason. Your results confirm my speculation: the factory engineers were designing a bike for best performance, balanced with best gas mileage achievable. They adjusted the bike's design for what they felt would please the most people, and sell the most bikes.

Your bike, I am certain, is a screaming machine, no doubt at all. However, you lost gas mileage, to gain speed. You also sacrificed quieter exhaust. The only opinion of your results that matters, is your own. I appreciate your write-up. It shines some light into some long-time darkened corners. I really appreciate that.

I also did some research into exhaust baffles, years ago. My Honda had a factory 4-into-4 exhaust, which I loved. However, the bike was past 30 years young, and the pipes were rusting. It would only be a few years before I had to replace them. My options were extremely limited: parts were hard to find, and while I found a complete OEM exhaust system available, it was $1,400 -- more than the bike was worth! It was no longer available, six months later.

I looked into baffles, fiberglass matting, and such, to learn how I could quiet down some aftermarket mufflers I had scoped out as replacements when the need arrived. It was a fascinating education. I like the look of your baffles -- brings back memories of my research into the topic. Thank you. Cheers!

[SgtSlag]

Just noticed you are running Pirelli MT66 Route tires. Excellent tires, but expect < 10,000 miles from them. They're amazing on the road, ignoring tar snakes, cracks, and grooves; they also give superb traction in the rain. They just don't last long on the Voyager, but since your's is stripped down, they may go further. Cheers!

[Merch]

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[chicagorandy]

Your bike, your choices, you only gotta keep you happy after all. If YOU like 'rat rods'? Giddy-up.

If I think they're kinda dumb? I will decide NOT to have one - lol As to 'speed'? I pretty much drive the speed limit (car or cycle) so it's a non-issue for ME. I added a dandy cup holder to my '86 XII and a pair of LED driving lights, plus an American flag on the trunk rails. MY bike, MY choices. I bought a comfy, quiet bagger cuz I prefer a comfy, quiet bagger.

Happy riding, it's all good.

[HMB Don]

I really liked the article. And the finished bike, a real hot rod. It's a Voyager sport bike. Speed cost money, at 25 miles to the gallon that's not bad for a hot rod. My 68 Road Runner only got 10 miles to the gallon.

[Merch]

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[GrandpaDenny]

even if I’m the odd ball in the bunch

Oh hell no you're not the only odd one around here!

[Jeff Gordon]

I’ll ride my 92 down from Canada to take that for a tear......really enjoyed the article....I often wondered if anyone ever put a big bore kit in one of these bikes....i’ll Never give up my inline 4!,

[SgtSlag]

If you want to fill in those holes in the fake tank: cover them in painter's tape, on the inside; then brush/dab on, with the brush in the cap, some plumber's pipe glue (ABS plastic suspended in a solvent). While it is still wet, you can then scrape it, with a putty knife, to mostly level it with the surrounding surface. Pipe Glue is typically black plastic! If you do not touch the surface, when wet (no scraping, touching, etc.), it will cure with a glossy, smooth surface.

I used painter's tape on a few of the repairs I've made, to keep the viscous ABS Glue from falling through openings I needed to seal. After the Glue dried, I peeled the tape off. It does leave a texture pattern on the side where the glue rests on the surface of the tape...

I made several repairs to two Vetter fairings (SilverWing and a Vindicator, both dating from the late 1970's -- repairs made in the 2009-2012 period), using Plumber's Pipe Glue (ABS Glue). It worked superbly. Used it on a no-name plastic trunk (early 1980's vintage) I had on my Honda, as well: stress cracks formed in the molded top, and bottoms of the clam-shell trunk. I reinforced them with ABS Glue. I've done the same thing with my Voyager's OEM trunk. Works superbly, adheres to the OEM plastic, perfectly, has lasted for 8+ years, so far! Never done "plastic welding", but this is virtually identical, only easier. Cheers!

[tunnelz]

Good article and pics. Thanks for the extensive detail. What does the bike weigh now and what tires do you trust for 120 plus? Where I live you go to jail at 99 and lose your license for six months at 150. But --- faster horses, younger women, older whiskey (Tom T. Hall) tunnelz

[Merch]

Redacted

[GrandpaDenny]

Gene Kap suggested to me using scotch tape with a thin coat of vaseline on the sticky side on the outside of a repair to give it a smooth finish. Don't coat the whole piece of tape, just where the repair is, so the tape will stick

[SgtSlag]

Vaseline on electrical tape. Noted, and filed, for future reference. Cheers!