Dunstall Silencers?

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OK, just sent the seller $50 to cover his $25 asking price plus $25 to ship. I'm lucking out with all the exhaust bits I've ordered recently...got some pretty nice headers for $20...came with a dual carb hamcan complete with screen, good rubbers and old filter for another $20. And I'm about to finalize a deal on a K&N filter for the hamcan....$50 including another hamcan front plate with brand new rubber (he wanted $75 for just the bare filter ?!?!). New K&N's got around $120, so this seems like a good deal.
 
850cmndo said:
That's a new one. I've run these off and on for 40 plus years and have never heard mention of that.
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I like the burble coming out of the Decibel silencers. However, in the above video clip there are signs of high-frequency pressure pulses coming out of the left silencer, although unrelated to the particular silencer I think. Is this kind of the chirping sound mentioned by Interbak?
I would take a closer look at the particular exhaust valve and the camshaft, also the L/H carb setting.

-Knut
 
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mdt-son said:
I like the burble coming out of the Decibel silencers.

-Knut
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Like he said. I always thought they sounded like fart in the bathtub. (Reminiscent of the Suzuki “L” series cruisers of late 70’s/early 80’s)
Sorry guys. JMWO
 
Had a set on my 72 Yamaha XS2 650. Those didn't come with the retaining flanges so I had to cut the stock ones off and use those. Sure changed how the engine breathed and where the power really kicked in. Got 2 tickets and decided to go back to stock and had to buy a set of new pipes!

I did get a set of Dunstall pipes with a project bike I picked up. Has a cross over where the ones on the 850's are but the pipes are necked down just past the first bend and a sleeve is welded at the end where the muffler mounts. Haven't decided what to do with them.

John in Texas
 
I would be interested to hear how you get on with them, my old man has a pair on his bonnie, they sound pretty nice although nowhere near as loud as my straight through peashooters.
 
I'll try to make some recordings...existing muted peashooter with balanced headers, then dunstalls, then with unbalanced headers.
 
Seems the postman has a item for me....but can't collect until tomorrow >:-(
 
When you change mufflers, you change the back pressure in the exhaust system which affects the jetting, it also affects the revs at which power band works. You can adjust the jetting and also the valve timing to get better power, however that also usually adversely affects the noise level. Some guys manage to have very powerful bikes which are also acceptably quiet. I have never managed to achieve that with any of my racing bikes. They have always been too loud.
I think the Yamaha Exup system is more about noise than it is about torque. It probably allows more dramatic valve timing to be used while defeating the noise meters.
 
Understood. I'm sure my current setup, single 32 mm Amal with balanced headers and mutes peashooters is already far off optimal jetting.
Will be interesting to see affect dunstalls have, then add a k&n hamcan filter, then migrate to unbalanced pipes, then one day two carbs ...need a bigger tank though...getting 40-45 mpg on single these days...makes 2 gallon HiRider tank useable, barely.
 
I have dunstall mufflers and a K&N filter on my commando. The stock carb settings work perfectly on my bike.
 
These pipes came with a parts bike I picked up some time ago. Dunstall I think. The exhaust nuts are made with the pipes before the flange was attached.

John in Texas Dunstall Silencers? Dunstall Silencers? Dunstall Silencers? Dunstall Silencers?
 
Got the Dunstalls. Pretty rough but should be serviceable. Need to sort a few bits of hanger strap and a reducer fitting to go 1-1/2 to 1-3/8 (or whatever the headers are).
The internal perforated sections seem intact, not rattling. Can't tell if any deadening packing present, should there be?
 
o0norton0o said:
I have dunstall mufflers and a K&N filter on my commando. The stock carb settings work perfectly on my bike.
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Working perfectly can be very deceptive. Often you don't know you have improve the torque output of your motor, until you raise the overall gearing of the bike. Also If the mufflers cause your motor to run slightly rich, the motor can be more sluggish, but the difference is often not detected. You might find that changing the mufflers and slightly leaning off on the needles and needle jets gives much better acceleration. If you fit a megaphone to a well tuned bike which usually has mufflers without re-jetting, you can easily burn a piston.
 
acotrel said:
Working perfectly can be very deceptive. Often you don't know you have improve the torque output of your motor, until you raise the overall gearing of the bike. Also If the mufflers cause your motor to run slightly rich, the motor can be more sluggish, but the difference is often not detected. You might find that changing the mufflers and slightly leaning off on the needles and needle jets gives much better acceleration. If you fit a megaphone to a well tuned bike which usually has mufflers without re-jetting, you can easily burn a piston.
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No Alan, YOU don't know! I actually have the exact combination of modifications that "tornado" is asking about. I've posted my findings based on my actual experience, not based on your speculative proclamations of voodoo.

The last norton rider who swapped his 850 for my 750 on a ride, asked me afterwards if my bike was a "combat" because how powerfully it runs with a 21 tooth sprocket up front too... Stop lecturing everyone here, like we're all idiots.

Tornado wants to switch to dunstall mufflers and a K&N air filter, which is exactly the set up that my bike has. Who is more experienced with that set up?? You or me?... So shut up...
 
FYI I have a rather old Dunstall Decibel of a Commando, which has 3 bolts holding the baffle on at the rear, some were pop rivets, this internal baffle has some sound dreading material wrapped round and held on by wire.

It was common in time for this soft material to get blasted out of the muffer.
 
N0rt0nelectr@ said:
These pipes came with a parts bike I picked up some time ago. Dunstall I think. The exhaust nuts are made with the pipes before the flange was attached.

John in TexasView attachment 9952 View attachment 9951 View attachment 9950 View attachment 9949
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Yep, those look to be original Dunstalls. Pre Blair 2-1-2. They had an accordion flex pipe balance tube. I think Comnoz commented that they are an ideal design for exhaust flow from a 2 pipe system.

I've had Dunstall silencers since 1973 on my 750 and later on 850 that came with them. Balance tube headers sound slightly different, but both have a nice tone and sound even better at higher rpm's. Once I shaved the 750's head to 10:1 and added 32mm carbs, it had an even nicer bark at WOT. Re-jetting was necessary on the Amals. Recommended was to go up 2 steps, I think I ended up at 240.

I really don't buy that other riders find them obnoxious. My friend on a Guzzi Griso loved being behind me going up a long hill. 90 % of Harley's sound worse and make no power.
HD, the most efficient means of turning gasoline into noise.

It's a '70 motorcycle, not a Prius!
 
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Talking about Dunstalls that is my Bonneville over 30 years kitted out with a
2 - 1 - 2. I can't really remember how it sounded but it was terrible trying to fit the thing. After a time I went back to the original which had the better lines.
 

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I had the dunstall 2 1 2 on my 850 commando , the fit was good but it made no difference to the power that I could notice, it did run nice though
But the rear Y piece just rotted away I replaced the rear section with a single short reverse cone megga
Again this made no difference to the power that I could notice
It just got louder
I still have the down pipes, maybe I'll remake the system and try it again 40 odd years later , although this time I'm not doing battle with gs750s and zed 9s etc
 
When you change the exhaust system you usually change the power characteristics of the motor. You don't necessarily get more top end power, you often just get a change of power in different places in the usable rev range. In the end, your setup is a balance between jetting, ignition timing, valve timing and the exhaust system, as well as the gearing. Discovering whether you have actually achieved an improvement is often quite difficult. In my own case, I usually only ride on one race circuit, so for me it is a bit easier. I know when I am getting around certain parts of the circuit better. Even then, if I get an improvement in mid-range power, I don't seem to recognise it until I raise the overall gearing. The Commando engine pulls hard but it does not spin-up very quickly. If you improve the midrange, you don't seem to get better acceleration until you raise the overall gearing. With the wide ratio box, it is hopeless. You need to keep the crank spinning high and race-change up through the gears.
 
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On our local race circuit, there is a tight hairpin right hander followed by a straight of about 300 metres, then a left hander which turns more than 90 degrees. I use that to calibrate my bike. If you cannot get around there super-fast, you are usually too slow everywhere else. Whenever I change anything, I always take careful notice of what my bike does on that section of track. If you ride on public roads, you rarely have the situation where you can make reasonable before and after comparisons. I rode motorcycles on public roads until I was 29, then I went racing. I am certain my road bikes were never tuned anything like near the optimum.
 
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