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From 'Ducati Tuning' by Stephen Eke: 900ss 40mm and Conti silencers: 8ccs fuel discharge x 20 strokes; 900SS 40mm and Silentium silencers: 5cc fuel discharge x 20 strokes.
 
I don't think that that information exists! AFAIK, all Darmahs with 32mm carbs were fitted with Silentium or Lafranconi silencers, so you will have to work up fron the standard setting. 1978 Darmah is quoted as 5ccs discharge and 1980 Darmah and 900SS with 32mm and Lafranconis is listed at 4ccs discharge, as is the 860GT. So I'd guess that you should be aiming for either 5ccs or 6ccs.
 
AFAIK, all Darmahs with 32mm carbs were fitted with Silentium or Lafranconi silencers <snip>
Correct. Officially, Contis were available as part of the tuning kit which included a host of other things including cams, valves and seats, and 40mm PHM carbs.

Of course that didn't stop people fitting just the Contis. Which certainly makes the bikes a lot noisier, but IME doesn't seem to do much else.

(P.s. Not politically correct in the world of Beveldrives ... But I got to really hate the Contis on my MHR)
 
Discussion starter · #26 ·
I reckon you're on to something bulldog. I've had a few bikes, this is the only one that has compelled me to wear noise cancelling headphones in the shop when I've had it running. The backfires are tremendous...and no, not in a good way...but like I've said I've not ridden it yet and all may be forgiven once I hear them in the Great Wide Open.

After watching Rob rebuild his vapor blasted carbs I had to dismantle mine, get them blasted too, and then rebuilt them again. It's not night and day by any means but I love the finish now and they won't bug me every time I look at them.

990770


Just waiting for a new banjo filter, (somehow tore the new one) and a 40º angle cable guide for the rear (or left) carb to try and make the pull a little smoother.

Here's one of the causes that makes it a little notchy. Cable nipple get's a little wayward in it's position on the throttle sleeve and has been grinding on the inside of the switchgear- it could cause the throttle to stick. Not good.
990772


I think I might be able to fix by putting a rubber sleeve around the nipple (bit of quality fuel line perhaps) and fill that gap, but it seems too much like a bodge to me, in a place where the artless bodger may pay too high a price.
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990773
 

Attachments

The twisting of the nipples in the drum is a common problem, caused I suppose by the drum being plastic and the holes too large. Let us know if you fix it.

Those Contis are a lovely sound in the right place, but when cruising are horrible. The last time that I rode my bevel 900 any distance was a ride up to Leicester a few years ago where I had to use motorway for about fifty miles, and the roar from the Contis just about knackered me, they are just so loud. I normally stick to back roads where they are not so bad.
 
Discussion starter · #29 ·
Filled the gap in the throttle drum with a small piece of thin walled fuel line expoxy'd in there. I think a responsible fix and feels better already even though cables are not adjusted yet.

990841


Got a nice exhaust nut wrench with the deep grooves for better grip. Idea is to dismantle the exhaust system, put in new gaskets and make sure all the other joins are well sealed with red RTV and so eliminate that possible reason for backfire. Thanks Rob for that tip.
990842


I like these fasteners...
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Waiting for some new fluid to fix my carb sync tool. Not quite sure what I did wrong here during the calibration process because I actually DID read the instructions first....didn't rev it like hell...was simply ticking over :) killed the motor just before the blue stuff went off the scale to places it should not be...
990845


Sign of the times.....3 bikes in the build bay...73 Triumph Tiger for new fork seals and steering head bearings....the Darmah we know about....a 72 H2 for frame up resto..(not pictured a 998 needs it's chain adjusted- been putting off buying one of those pitbull stands).
990846
 
Discussion starter · #30 ·
Reasonably confident I found some issues contributing to the right hand backfiring:
1- Exhaust nut hand tight, header very loose. (Left hand was tight and solid) Funny/mildly concerning that it was lockwired.
2- Existing exhaust gasket extremely sooty.


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990896


more later
 
I have the same MotionPro gauges. I set mine using the rear carb and the little vac pipe tree so that the blue liquid only reached around the 8th or 9th notch from the bottom with the engine ticking over at around 1800rpm so by the time I'd connected both carbs and dropped it to 1000-1100rpm, the fluid level was a little lower. The instructions state "move or raise the gas tank" and to use the MotionPro "deluxe auxiliary tank" but don't say why. I did not do this; I just left the MHR gas tank in place.

Why not use the outer two gauges for the job if the inner two have been emptied? Do they draw from the same reservoir?
 
Discussion starter · #32 ·
that's a good idea Rick....they are all independent so should be ok....I think I need a little more fluid. This one came from Amazon and according to MP they can sit forever and some of the liquid can evaporate but I should be able to balance a couple of carbs with what I got.

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990925
 
Discussion starter · #33 · (Edited)
Note extra spacer (metal ring) on the right hand header that doesn't appear on the parts catalogue nor is it on the left hand header....wonder if it's a proprietary Conti part, necessary and/or partial cause of the backfire.
I think I have 2 choices: don't reassemble it or find one for the left hand header too.

990926


#4 is the Guarnizione tubo scario- or 'gasket' to you...but besides the nut...nothing else.
990927
 
Problems.... The washer that you refer to is part of the exhaust pipe and it should be welded to the flare at the top of the pipe, but has come adrift. You can either get it brazed on again or get a new exhaust pipe, but if you go this route make sure that pipe is NOS or from Old Racing Spare Parts, as pattern ones are a poor fit, or get a complete set of stainless pipes from Keihan Systems.

No wonder the cylinder was backfiring. The exhaust rings are wired by the factory from new, to prevent the nuts vibrating loose and ruining the thread in the head.
 
Discussion starter · #35 · (Edited)
Thanks Duccout. I don't know what possessed me NOT to compare the headers and notice exactly what you are talking about- you are clearly right. I know a good welder who should be able help me keep this system.

Looking at the left hand (non backfiring) header (top of 2nd pic) notice how the small bar on the ring causes the face of the header that connects with the face within the cylinder head to protrude outwards. To me I would think that's an aspect you would not want- wouldn't a more uniform and consistent mating face be the ideal?- but Ducati characteristics surprise me on a daily basis- perhaps that protrusion is supposed to embed itself into the exhaust gasket to stop the gasket moving/spinning? I'm pretty sure I can get the welder to replicate that protrusion while re-brazing the ring on the right hand header if need be OR flatten the face on the left hand header.

Also noticed while cleaning the mating face in the left (non-backfiring) cylinder head...lo and behold there was another gasket in there....the left header was enjoying two exhaust gaskets- is this by chance a common practice amongst Darmah owners or was someone just not paying attention.

990961


990962


a clean cylinder head mating face...
990964
 
Discussion starter · #36 ·
Also, and I truly appreciate all the feedback I have been getting....note where someone (factory?) drilled a hole in a fin in order to lockwire the right hand (front) ring but I cannot find a corresponding one on the left hand (rear) cylinder head nor was it lockwired. Wondering would I/should I drill a hole in the right hand cylinder head to allow me to lockwire the exhaust nut? Anyone have any pics of what you've done on yours?

A hole drilled in right hand (front) cylinder.
990965


no such holes on the left (rear) cylinder head tho...

990966


I note the nuts are lockwire ready with no less than four holes available...
990967
 
Ducati oddities! Yes the front head fin has a lockwire hole but not the rear from the factory. I also found one of my heads had two exhaust gaskets but assume that this was because an earlier owner simply forgot to pull an old one out; they can jam in and look like part of the head. I'm enjoying your pics.
 
2x gaskets is most likely someone being careless, as Rick says. (I s'pose in the extreme, it could be an attempt to rectify the fit of a poorly bent exhaust pipe. But it wouldn't have worked ....)

For a lockwire hole on the back pot, just drill one thru the closest head fin. Photo attached.

Remember the lockwire is most useful as an early warning that the exhaust clamp is coming loose. Don't rely on it to hold the clamp. Even with the wire double twisted, it won't stop the clamp spinning off.

991009
 
Hmmm, I don't recall seeing exhaust pipes made so poorly as yours, if it wasn't for the stamped part numbers I would have said that they were pattern ones. Maybe they were made very late in Ducati's production run and were made that way to cut costs.That protrusion needs to be ground off flush, but if you do, it appears that the ring behind will come away with the weld. If you are getting them welded I would be inclined to braze around the rings and then grind a nice flush surface on the front to get a good seal. The problem with fitting two gaskets is that they take up thread depth and those threads need looking after!
 
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