Exhaust!!

[dsmmrm]

Or how about "Loud pipes risk rights". Whatever. To each his own. We all have our preferences and no one has the right to tell anyone else how to live their lives,as long as they stay within the law. With regard to loud pipes, the law is fairly ambiguous and enforcement is inconsistent at best so a sensible approach is just tend your own garden. Live and let live. I am a musician, I choose to protect my hearing. I always wear earplugs while riding. I don't judge people who choose not to.

That being said, I am in the process of buying the cobra pipes posted by draxxis. It is my understanding that they are not all that much louder than stock and do away with the George Jetson whistle. I really hate that whistle, at the right rpm and steady state I can make entire neighborhoods bust out laughing.

As far as performance, any change in the fuel delivery that would give you a noticeable performance boost would require a rejet. Most people have said the cobra pipes do not so I don't expect a performance increase. I have a K&N filter on the intake side so I am actually hoping I get a lean state and have to rejet. Then I likely would see a performance increase. rejetting a carb is not difficult once you get them out. it's the R&R that is a PITA. Plenty of folks here have done that job, some several times, but I still see a lot of people reticent to rejet. Not sure why that is. Those universal individual filters someone posted a while ago looked pretty sweet but the consensus was the bike runs like crap after the switch. I think an intense carb tuning/rejetting day might fix that.

And yes, I know a zillion smart guys designed it in the first place and you can't do better than they did. Maybe so, maybe not. They had EPA standards to met, we don't.

[SgtSlag]

Actually, the issue with the individual pod filters is that the carbs are designed for Constant Velocity air flow (CV). To achieve this CV condition, all four carbs need to draw their air from the OEM filter housing which was designed to provide the optimum air flow for the CV carbs... Pod filters do not give the proper air flow/vacuum.

I had this on my 1979 Honda CB750K: same CV carb type, same issue. People tried, and tried, and tried... Rejetting became second nature to them. The situation always remained the same: "I got it perfect... Except for this one flat spot in the throttle." They spent untold hours, and money, rejetting their four carbs, adjusting them, ad nauseum. They never got rid of, "that one flat spot", in the throttle response. What was truly frustrating, is that the CV carbs didn't start until either 1978, or 1979. From 1969-1977/8, you could install pod filters, and get a performance boost... Then Honda came out with the CV carbs, and the door to pod filters closed.

The worst part was that many of the CV owners either garbaged, or sold, their OEM air box -- no going back after that, unless they sourced an OEM replacement! I hate to see anybody go down that road, again. I installed a K&N Air Filter on my CB750: altered the sound slightly, but nothing I could "feel", in my oh-so-accurate, butt dyno. Only cleaned that air filter once, after four years (didn't need cleaning, just felt like I should, so I could learn how to do it).

Ask yourself: How much performance increase will I be able to get? Is it worthwhile, for the return on my investment of time, money, and effort? Is it worth the risk of ruining my bike's engine? Installing a K&N air filter, or a foam filter, with oil, may improve performance, slightly. No matter what, chances are a dyno won't show anything. The CB750 owners went far down that road, as well. They swore by their butt dyno's, but the few who put their bikes on a real dyno, found... Nothing. No measurable improvement.


My recommendation is that if you want better performance, buy a bigger bike, with more displacement. That is the only certain way to gain performance.

You can, and should, research CV carbs and pod filters. Google is your friend. Cheers!

[cranky]

... congrats on yer 6th star!!!!

[Nails]

I have a K&N filter on the intake side so I am actually hoping I get a lean state and have to rejet.

Personally, I think K&N filters don't really do anything. Heaven knows I've bought my share. I think it's a charming concept that rarely pans out in the Real World. I could see it with pricey tuned exhaust at 15K RPM, maybe.

rejetting a carb is not difficult once you get them out.

Yes, changing jets is easy (once off the bike). But changing to the right jet, not so much. This requires performance testing (color tunes can get close), like repeat stopwatch or max-speed runs on a selected hill. And that's just to get the main jet and skinny part of the needle right -- repeat for the other carb circuits. This means changing jets or whatever multiple times over a short time period like one morning (same tank of gas, same weather, &etc). Which means pulling the carbs multiple times in a morning, for a few mornings. I'm not really willing to do that with this bike. I did take a Hail Mary based on my elevation (8K ft): 6% less air in the air, therefore a jet/needle that delivered about 6% less fuel across the needle's range. But that's really just another charming concept, based on the jetting being right (for sea level) in the first place. (Often a pretty safe bet.)

Pod filters do not give the proper air flow/vacuum.

I notice that large volume airboxes can greatly improve the torque and power band. I think having two large airboxes is a primary reason why our bikes have good torque. In dirt bikes, when they offer two similar models, the "better" one usually has a larger airbox. One example is Yamaha XT and TT. They seem almost identical in passing, but the larger airbox on the TT apparently led to a gob of small differences all over the frame &etc. Given that hardly anyone notices the airbox, I reckon they had a good reason for that.

the few who put their bikes on a real dyno, found... Nothing

When I'm serious about performance testing, I always start with stock. I often end up there, with a minor change that makes sense for the elevation issue. You can spend lots of time and money without really bumping the needle. Maybe better to spend that money on a good mechanic and tuneup.

And remember, the engineers also call our carb design "constant depression". Some days, I can totally relate.

[dsmmrm]

It is a "process" to be sure. As I said, I am really just trying to get rid of the jetsons effect and maybe get a bit better overall tone. If it's too loud they will be going back up for sale again.

If it leans out any I'd just bump the jet size the next increment available and see if it's enough. I doubt I'd need more than 1 or 2 iterations of that process to get it back to where it needs to be. I am not looking to actually go with the pod filters at this point, just tossing it out for discussion. Yep, CV carbs can be a PITA. I have never really understood why the direct cable to slide attachment my older bikes had was abandoned, but I don't pretend to be an engineer.

I put in the K&N last fall due to not being able to find the OEM filter and the thought that if I have to mod whatever I'm using to fit the bike I only have to do it once if I use a K&N. I've used them for years in various bikes and already have the oil and cleaning stuff in my garage. It did not make a difference in any way, and that was fine with me.

[Nails]

I hear you. That's basically the reverse of what I did for the elevation.

the jetsons effect

I'm not entirely sure what you're talking about, the whir of the straight-cut gears? (I don't really mind that, even if it reminds me of farm tractors.)

I have never really understood why the direct cable to slide attachment my older bikes had was abandoned, but I don't pretend to be an engineer.

Tons of info on the web, but https://gadgetsfixitpage.com/article.ph ... carburetor is the best resource I've found (even if it is 20 yrs old). Even includes chatter about slide vs CV.

This animation is kool: https://www.youtube.com/watch?v=wyspAHrMbb8

I also liked: https://www.youtube.com/watch?v=y836ZPjvoMI

[Danger4u2]

As you advance the throttle cable that's connected to the butterfly valve, the butterfly opens to allow more air through the venturi. This increases the vacuum effect that is transferred up through the vacuum drilling (the hole you bored out for the Dynojet kit), on the diaphragm valve (slide), that leads to the TOP diaphragm chamber
I copied this from your gadgets fix it page.
Has anyone drilled the diaphragm valves (slide) on the Voyager XII like they do on the KLR. I drilled the slide on my KLR and it helped.

[dsmmrm]

Interesting read on the CV stuff. Thanks for the links.

As for the jetsons effect, apparently it only effects some bikes. It's not the gears, it is the exhaust. At the right rpm it get this syncopated whistle that sounds just like George jetson's space car on the old cartoon. I don't think I have ever seen a recording or video of it. I can't get it to do it in neutral or on the center stand, it seems to require a load and it's tough to record the exhaust while riding. It is very different from the gear whine, which is actually not too bad on my bike. I only get a lot of that in 1st gear, which I can easily tolerate. That also appears to vary quite a bit from bike to bike.

[dsmmrm]

Danger4u2. I had a KLR and put a K&N and a pipe on it and had to rejet. With just 1 carb it's pretty simple, like everything on a KLR. Due to the commonality of these mods the best jet size, needle clip settings, etc. are pretty well established for most elevations and aftermarket farkles. I held off on drilling the slide at first and the bike ran ine. It had better throttle response and maybe a wee bit more overall power than stock. The smaller countershaft sprocket i put on it made a much bigger difference, as you would expect. It was a wheelie monster, but I digress yet again.

My point is that eventually I tried the slide drill mod and it ran worse. Throttle response was abrupt at first them bogged down. I ended up buying a new oem slide. It seems it is really hard to undrill something. Who knew?

[VoyKimmer]

You want performance. Have Carl Leo rebuild your carbs. OMG mine now runs like a bat out of hell. Performance greatly increased but MPG suffers a lot now.

[Danger4u2]

On my KLR I drilled the slide, added the 2 small washers under the needle and drilled out the plug so I could adjust the air screw.
It ran great with quicker throttle response. All the KLR stuff I've read says don't try for more horse power, make it more dependable, make it more comfortable. dsmmrm, you probably could have JB Welded the hole and drilled a new, same as stock hole next to it.

[dsmmrm]

Yep, in hindsight that likely would have worked just fine. Where were you 10 years ago when I needed that advice?

[dsmmrm]

So, Scott, aka Draxxis, rode out to the halfway point between our respective dwellings aka Erie PA to meet me and deliver the Cobra pipes I bought from him. Thanks Scott, great way to go the extra mile(s).

I just thought I'd offer an opinion of the pipes. I can confirm you do not need to make any adjustments to the carbs, which also means there won't be any significant performance impact. That's fine with me. I can also confirm that the jetsons effect has been banished. Yay. At first I thought those of you who said they are only a little louder than stock were off your respective rockers. On the center stand it seems quite a bit louder but once I got the helmet and earplugs on and rode to work this morning I can agree with you. Under normal acceleration it's only a bit louder than stock with a much better tonal range although with a pretty distinctive timbre.

Under hard acceleration and high rpm it sounds like a mid 60s British sports car, like a Lotus Super 7 or summat. I am ok with that. All in all a worthwhile upgrade that won't peeve off the neighbors unless you want to. Thanks again to draxxis (Scott).

[Danger4u2]

That's great that both of you are happy with getting rid of and acquiring the exhaust pipes. The meet half way brings thoughts of my half way meet for my parts bike. He wanted $500 for the bike. It was a little more than an 8 hour drive from my house to his. I asked if he would take $400 because it was such a long drive for me. He countered with $450 and he would meet me half way. I acted reluctant and accepted his offer. I drove 8 hours less for $50 bucks.
Man was that a no brainer for me.

[dsmmrm]

No Doubt. Maybe you should have offered him another $50 to bring it to your house.

[Draxxis]

You are very welcome David. I am happy you like them. And no they won't irritate your neighbors. Now mine will lol. But honestly I fire mine up every morning to come to work, and when I get home, I haven't had anyone complain. Even when it's nights where windows are left open. Probably because I don't let it sit idle for 5 mins before heading out lol.