I went the wrong way several times.
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VM Tuning Re-visited
- Thread starter atom4488
- Start date
Sometimes down dead ends.
Useful and interesting... clearly the engine likes the free-flowing Cone Engineering mufflers with a little richer jetting to suit. Are you using EPO's in addition to the TPO's? I'm quite convince that my setup is not far off, so the thought first put forward by @Jim that there are some negative effects from reversion seems more and more plausible. haven't had the time to do any tuning lately, but hope to do so before the season ends.
I am using the EPOs and TPOs as I have 1.75" headers. The TPOs are 1 3/8" (1.25" ID). If you use the 1.5" headers you should not need either. Some say that EPOs help, but it is debatable. I would open up the mufflers and then see. Over the winter, you may want to consider adding wide-band oxygen sensor ports (bungs) to the headers to tune your jetting. that is what I ended up doing: https://www.xs650.com/threads/wideband-sensors.66143/post-844888
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I agree that the 1.5" headers shouldn't be too big. I have a MAC 2-into-1 pipe on a stock 650 which has 1.75" primaries. It doesn't exhibit any of the mid-range symptoms that I'm getting on the VM-equipped bike. I like the thought of the wide-band sensor. More stuff to consider...
what does the quiet core Cone Engineering megaphone look like on the inside? does the baffle block the flow and forces it around, or is it see through?
It has a baffle that obstructs the core about 8" in from the tail end of the mufflers. At first glance, it does not appear to be removable, certainly not from the outlet end. I could well imagine that exhaust gases hitting that blockage would bounce back up the pipe towards the exhaust port. I'm now thinking open-core mufflers before fooling with EPOs.
The baffle is probably similar to that in the crossection schematic from S&S below. You can likely just cut away around the perimeter from inside the inner tube to remove the baffle. The question is what the perforated core looks like. If it a simple perforated tube, or is it louvered. You should be able to see that if you take the mufflers off and look from the inlet end. The simple perforated tube will be louder than louvered, and may generate stronger reflections from the muffler end than the louvered core, but will generate more horsepower. The open/straight core mufflers from Cone Engineering have a louvered core made from perforated tube: a nice balance of sound and horsepower.
here is the core on the straight/open core Cones from Cone Engineering. The lovered pattern is quite intricate. Other lovered core mufflers have simpler patterns but are loud.
Also note, that the commonly sold reverse cone emgo mufflers and others actually have a perforated plate down the middle (it may be pssible to punch it out)
here is the core on the straight/open core Cones from Cone Engineering. The lovered pattern is quite intricate. Other lovered core mufflers have simpler patterns but are loud.
Also note, that the commonly sold reverse cone emgo mufflers and others actually have a perforated plate down the middle (it may be pssible to punch it out)
Well, I had an interesting phone call this afternoon. I called Cone Engineering to talk to their tech-line folks to ask whether the baffle in the Quieter Core muffler was removable. The lady answering the phone says sorry, tech guy has stepped away from his desk, but let me see if I can get you someone else. Guy answers and was very helpful and knowledgeable.
We have a very long conversation about all things exhaust and intake too. Turns out that he has had extensive experience working with a reputed Triumph tuner (the Triumph being another parallel twin, of course). Through this experience they found that one of the greatest positive effects on tractability and tuneability, after having the same midrange issues as I am having, was to incorporate a balance pipe between the head pipes at a distance of at least 19" from the exhaust port. The balance pipe diameter needed to be no more than 75% or so of the head pipes. Another comment was that extending the length of the air inlet tract had a similar positive effect on tractability. He spoke extensively of large airboxes/large filter elements to ensure sufficient airflow accelerating through the mid-range. He was not aware of anyone having exhaust reversion issues with the Quieter Core mufflers and suggested that the first step would be the balance pipe, followed by inlet tract length. I asked specifically whether he had ever played with intake manifold length with his Triumph guy; he said no. Lots of food for thought and things to try.
While signing off and thanking him for his time and insight, I asked him a last question; what's your name? He's says "Craig". So who was the guy on the phone? Craig Stenberg, owner and president of Cone Engineering, a company founded by his father Ed in 1970.
A big tip-of-the-hat to Craig and Cone Engineering for their support of enthusiasts like us!
The balance pipe made a huge difference in power with my SG. Of course, I was runnin' the shitty EMGO cheapies... and to be honest, I thought she performed pretty good, but reinstalling the stock exhaust with the crossover was like night and day. Mid range grunt felt like it doubled. Yeah... I know it didn't, but seat of the pants said it did. Oh.. and someone drilled extra holes in the end cap, so that prolly helped too?
Any chance you have the stock exhaust you can just throw back on for testing?
From back in May...
https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-841639
So Yamaha had half an idea what was up whilst us idiots went two into two systems. I am glad I am not racing for $ and going heads up against factories. I can't say " I suspect they are right" because they have the engineering and research to develop the consumer product. How do I get one of those systems with lovely Commando Mufflers? 
@Jim, between the original Yamaha engineers, Craig's (Cone Eng.) experience tuning Triumphs and your observations, I tend to think there must be something to it (the balance pipe). Go look at an exhaust system on a Nascar V-8; they have had X-pipes and other forms of balance pipes for a long time. These days, any half-decent system for a V-8 has one too; either an H-pipe, X-pipe or other merge of the two cylinder banks.
Looks like that's the next move... not easy to do as a mock-up on otherwise good/new head pipes, needs to be done properly or not at all. I do have a set of stock head pipes w/o a balance pipe that could serve as proof-of-concept test articles. Still quite an effort but hopefully worthwhile?
a balance pipe is a higher order enhancement. You should be able to get your bike running well without it. Give Michael Morse a call at 650Central. He can help your VM tuning issues. Gary Hoos is good too for the VM questions, but he is a maximalist. Gary's thinking is not for the street...
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The carbs initially came from MM at 650Central. The present jetting setup is as supplied/ as recommended by 650Central. I will make that call to get another opinion on possible issues and solutions.
Haven't had the time to do any more fiddling as other priorities have ruled the days. Hope to get in a few more tests before it really gets too cold to ride up here. I did ride today (my XT)... it was 10*C / 50*F and windy. Got pretty cold faster than I thought it would. Going to be in the low to mid 40's next couple of days. Call me a fair-weather rider, but that's too cold for my bones. A little warmer later in the week... we'll see.
The crossover pipe on the stock exhaust was not on the headers but rather at the beginning of the mufflers. So, I suppose one could make a small "H" pipe to fit between the headpipes and mufflers.
That's exactly the arrangement my Guzzi had.
Though I imagine the pipe should connect the mufflers near the inlets before the perforated core and packing start
Also the header diameter needs to be taken into account for where to place the pipe if one were to match specific engine rpm for improvement in scavaging. The exhaust pulses will travel slower with the ladger header ID.
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looking forward to what you hear from MM. Another thought that crossed my mind, and I don;t think this is the root of your problem, but have you upgraded your clutch? in my experience, as soon as I installed the 700cc kit, my clutch started to slip. Changing to Vesrah springs and fresh friction plates fixed the issue. First I changed the springs only, but the clutch would still slip once in awhile on a dyno. MM can sell you the springs and the plates.
Looks like this thread will go dormant for a while, at least from my end; I won't be able to get at it until the first week of November. November being what it is up here means that it is looking less and less likely that there will be any more rides this season 
. That said, there was a lot of input in the "Perseverance Pays Off" initiated by @Mannyroad that seems relevant. looking forward to further trials!
. That said, there was a lot of input in the "Perseverance Pays Off" initiated by @Mannyroad that seems relevant. looking forward to further trials!
Jim, your big improvement with the stock exhaust may be due to replacing those crap EMGO Commando copies?
