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/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Loss of top speed with Dyna Muff??? /cgi-bin/YaBB.pl?num=1160983031 Message started by Rockin_John on 10/16/06 at 00:17:11 |
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Title: Loss of top speed with Dyna Muff??? Post by Rockin_John on 10/16/06 at 00:17:11 Hey folks, Put a Dyna muffler on the other day with shop made adapter which mated the slide bolt at its farthest forward position with the back hole in the stock bracket. That translates to a pipe about 6" between header and muffler. The Dyna muff is the longer 19" version, so the whole thing ends back about even with the rear brake hub lever. http://www.catoosatrading.com/images/vehicles/cycles/my_ls650/dyna_muff/PA160002.JPG http://www.catoosatrading.com/images/vehicles/cycles/my_ls650/dyna_muff/PA160003.JPG The sound isn't too bad, not as loud nor deep as I predicted, but better than stock. Fine for not waking the neighbors, but just a tad more tame than I had in mind. Don't misunderstand, I've had a glass packed megaphone on an SR500 before that was downright embarassing, and I don't want to go there again, but there has to be a happy "in between." Just out of curiousity I decided to test the bike without any re-jetting. I was certain the idle circuit was a bit rich from the small puffs of black on short throttle blips, but I haven't run it long enough, or swapped and read plugs enough to really read other throttle positions. One thing that really surprised me was an obvious lesser pull above 75mph and my top speed had dropped from a bit over 85 with the stock can, to a shade over 80 with the Dyna. Even with a possibly lean (most likely) main jet, it would seem that reduced restriction would have allowed at least equal top speed. Frankly, I'm puzzled... I've now ordered a similar length large can "turn-out" style with less baffling. http://www.catoosatrading.com/images/vehicles/cycles/my_ls650/dyna_muff/longtout2.jpg I predict it WILL absolutly demand jetting, where I think the Dyna might have been ok as it was, since it ran well except the top speed, and had very little backfire, or notable hotter header pipe. (I've been around hot exhaust and turbo systems enough to be a fair judge of the temp by just feeling the heat from a few inches away.) I've also been reading the thread discussing the difference in throttle response between the direct pull Amal and vacuum pull stock carb. It has me re-thinking my consideration of a "dial-a-jet" and popping for an Amal, but I remember how we used to hate the old leaky ones on our Nortons. Hope the newer ones aren't as unfriendly :-/ Comments, or guideance of more experienced Savage tuners greatly appreciated! ;D |
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Title: Re: Loss of top speed with Dyna Muff??? Post by lancer on 10/16/06 at 04:20:02 My first muffler swap was done without any jetting changes on the stock carb. It made more noise of course (harsh sound), the top speed did not change, it backfired even more than before, and the midrange seemed to pull a little better. Eventually, rejetting/tuning the pilot circuit got rid of the backfire, adding a notch to the needle improved the midrange more, and a larger main jet (#155 ?) made a significant difference on top end. Stock bike = 78 mph, rejetted (several trial& errors) = ~90mph. The bike ran better overall, noticeably stronger acceleration. The dial-a-jet was added later (got it used from ebay) and made a noticeable difference. Top end did not increase much, maybe a couple mph, but the midrange did improve a good bit ... more responsive. The dial-a-jet does not affect the very low range, it is not designed to, that is the job of the pilot jet circuit. The Ultimate Flow Optimizer (UFO) will improve the pilot circuit on a performance carb, but is not designed to fit a CV carb. I think your loss or power on the top end was due to a lean condition getting even leaner with the muffler swap. Your stock carb NEEDS rejetting/tuning. If the bike is several years old, or more, I would disassemble the carb and clean everything, blow out the passages, check for wear/damage/esp the diaphram, etc, so when you start the jetting process you will get the results expected from those changes. A lot of folks start jetting and get frustrated when the carb starts doing strange things. Then they have to go back, disassemble, clean and jet again. |
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Title: Re: Loss of top speed with Dyna Muff??? Post by Rockin_John on 10/16/06 at 10:25:27 I suspect you're right on it with the need for the #155 main jet. However, the tank was cleaned and sealed, and carb rebuilt by the old man I bought the bike from a couple of months ago. I think he must have done it well, as the bike has run well and done very little backfiring while I've had it. Even with the muffler change. I'm not going to tinker with jetting just yet though. I want to try the other pipe I have on the way for loudness, and make a decision between it and the Dyna before committing to carb tuning. |
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Title: Re: Loss of top speed with Dyna Muff??? Post by barry68v10 on 10/16/06 at 15:13:57 Agree with lancer, sounds like a lean condition at high rpms getting leaner and causing a loss of power... |
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Title: Re: Loss of top speed with Dyna Muff??? Post by SavageDude on 10/16/06 at 17:06:42 Lancer is dead on. Without rejetting, your engine is starving for fuel at the top end speed. I put on 155 main and the beast cruise nicely at 70mph and when there is a need to accelerate, 70-80mph in about 1 sec. Unlike stock muff+ stock carb, it takes forever to acomplish that :o |
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Title: Re: Loss of top speed with Dyna Muff??? Post by Dynobob on 10/18/06 at 06:15:39 Rockin_John wrote:
The less backpressure (more loud) you have, the worse your bike will run without changing the jetting. Don't expect a freer flowing muffler to make it any better. |
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Title: Re: Loss of top speed with Dyna Muff??? Post by Rockin_John on 10/18/06 at 07:25:35 Dynobob wrote:
Not at all my intent. Just want to sound test each pipe before I committ to carb tuning for the "keeper" pipe. A bit of explanation: I am very particular about some things, loudness and tone of exhaust from car or motorcycle being one of them. My taste in guitars and/or amplifiers being another. It seems the only way I can arrive at a satisfactory solution on some things, is to try many things. Trial and error is expensive sometimes, but the resulting satifaction is often worth the expense. On my motorcycle parts, as with guitars, I'll eventually sell some of the discards to recoup some of my costs. |
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Title: Re: Loss of top speed with Dyna Muff??? Post by Jim_R on 10/18/06 at 08:23:48 John if you knew how easy it was to replace your jetting on your carb you would at least try it. Even if you change pipes without the carb changes its gonna sound different after you do the changes (might sound a tad deeper, and less backfiring). Anyway while your at it, change your air filter to a k&n or a pod filter. You would be surprised at how much of a difference you will get after you rejet. |
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Title: Re: Loss of top speed with Dyna Muff??? Post by lancer on 10/18/06 at 08:36:55 Good points. I have changed filters, carbs, and pipes/mufflers several dozen times, and rejetted for most of them. There are indeed differences in sound for every change. I now have the muffler I like most on my bike, but of course I will continue to try others. IT IS A LIFESTYLE ;D |
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