450 desmo carb

[graeme]

Hello Bill,

Here in Australia we have unleaded 91, 95, and 98 octane
98 is ok for higher compression and fuel injection
95 works best for my 450 s
91 for the mowers only.

98 seems to be too dense and tends to deliver too much fuel ???

Also I thought you said you had not fitted valve guide seals ???
Why ?
Is this the cause of the oil?
Or did I misunderstand?

Graeme

[themoudie]

Aye Graeme,

Thank you for your thoughts. We have the unleaded 95 and 98 octane ratings only, over here, unless you start adding a touch of AVGAS. I have been using 95 with Castrol valvemaster until the last 5 litres, when I used the 98 and Castrol valvemaster. Nigel Lacey had mentioned different plug colours when using the Castrol valvemaster additive. We are also going to be using 10% ethanol in both octanes as from 1st September 2021. We have 5% ethanol in both at present.

As for the valve guide seals, I have new 'Viton' seals sitting in a drawer, but there was some scuffing wear on the valve stems when I took the head off to change the '173A' cam for a 'White' cam. The clearance between the phosphor bronze guides that are lined with bronze 'K liners' and the valve stem was between 0.00125" and 0.0015" that was considered "tight" by Nigel and the engineer who I had entrusted the job to. Also the oil seals had prevented any oil from lubricating the bronze 'K liners' and bronze performs best when lubricated. Hence the decision to ease the clearance in both guides to the valve stems to 0.002" and run without the valve seals to lubricate the guides. Even though this produces a haze of grey on the overun and this wet oil deposit on the earth electrode and around the rim of the plug body. It doesn't appear to be causing the misfire/hesitancy and is not fouling the electrodes of the NGK B6HS that is in the engine at present. Apparently, I could fit a "hotter" plug, but if the fuel mix is at all weak, I would be more likely to put a hole in the piston!

I hope this clarifies my "thinking" My problem is that I am not an engineer, but happy to have a crack at most things and too fertile a brain!

Good health, Bill

[themoudie]

FINAL UPDATE 13/5/2021 from me

...swapped the 25 pilot for the 27 cold start jet and left everything else alone. Again good colour on the plug and with the air screw three quarters of a turn out off the seat the hesitancy is less but still there in 3rd and higher gears at the transition from pilot jet to slide. The cold start now works, with the 25 jet in place, it has not worked correctly with any of the larger jets, from the 50 jet supplied as 'standard', down to the 27 jet.

So, swapped the 26" long 'Gold Star' pattern exhaust, with a single plate baffle and a 30mm dia hole in it for the short SuperTrapp 317-1500 Universal 3M Steel Dirtbike Muffler Body - 1.500in ID Inlet, with 12 baffle discs fitted. Still get the hesitancy, but this has now moved at the transition from pilot jet to slide to the transition between the slide and the needle nearer to half throttle and in all the gears.

So, as I suspected, the AMAL MKII 2932 appears sensitive to exhaust back pressure dynamics.

Having dropped the needle clip by one notch to the 3rd from top/middle notch (raised the needle, allowing more fuel through the jet), the hesitancy has now gone from the half throttle position, with the SuperTrapp, set up as above.

The AMAL MKII 2932 32mm carb, on a Triumph TSS inlet rubber, without air filter and the 'standard' short bellmouth in place, is as follows:-

Main Jet 210, Slide 3½ anodised, Needle Jet 106, Needle 2A1, with the clip in the 3rd land/notch from the top of the needle, Pilot Jet 27, Cold start jet 25, Air Jet 3.5, Air screw between 1 and ¾ turn off the seat and the slide/idle screw ~1½ turns in after lifting the slide off the venturi seat.

A 'standard' OME length exhaust pipe, with a SuperTrapp 317-1500 Universal 3M Steel Dirtbike Muffler Body - 1.500in ID Inlet, with 12 baffle discs fitted.

With the baffle discs directly beneath the righthand footrest and my ear directly above it, ear plugs are required if you want to keep some sembalance of hearing! I intend to construct another exhaust, based upon measurements/proportions published by Royce Creasey, in Classic Mechanics, #15 Oct-Nov 1985 and #16 Dec-Jan 1986 after his visit to and conversation with Alan Baker at Motad, during the development of the Hightechati FF machine (001).

Thank you to everyone who has offered advice, beer, whisky, a sympathetic shoulder since page 4 of this thread. I apologies for hijacking it.

Keep using these singles.

Good health, Bill

[Duccout]

Well done Bill, you have kept us entertained during lockdown.


Cheers,

Colin

[blethermaskite]

Hi Bill, sounds like (no pun intended ) you have it sorted, well done, its been a long old slog for you, however determination will always win in the end. Re exhaust back pressure I have found over the years with the 350 MK3 using a variety of exhaust systems from full race open megaphone to my own design of manual Yamaha inspired 'exup' adjustable baffle megaphone, conti, dunstal decibel, and many other pattern 'silencers' that just about every change of system has required some sort of carb jet, slide, or needle adjustment on the Amal mk1 concentric, at one time I used a Gardner flat slide race carb which was adjustable like an SU with simple jet tube and needle combination, this made exhaust swaps easy to tune for, on one level I was sorry that I removed it, but it was a bit of a pig at low throttle on a road bike. However once you have settled on a pipe and got it tuned to suit hopefully that will be that.
Cheers,
George

[themoudie]

Aye George and Colin,

Thank you for the compliments.

Now have over 300 miles on the setup and going well. However, urban traffic and traffic lights can prove problematic and can result in a cough and splutter! Dismount, fold up footrest and brake lever, kickstart, unfold controls and then "make progress", before the sodding lights change back to red!

Have already acquired some second-hand oil filters for butchery, along with perforated sheet and will see if I can get the gutted 'Gold Star' exhaust to work better. I was tempted by a stainless steel replica Conti from 'Feked', but I thought that I should try the experiment first. Royce' final Motad type system gave readings of 84db, quieter than the clutch cover side of the engine and an increase of 10 BHP after setting the carburation up for the exhaust that apparently was leaner through the full range. I will see!

The Gardner flat slide was used by quite a few on the race bikes over here, to good effect, but it was agreed that on a road machine it could be cantankerous!

Good health, Bill

[Dan C]

Hi Bill,

I've been offline for a while and just caught up. Congratulations on your progress, persistence pays off!
And with summer coming on I hope you get out and enjoy it!

Cheers
Dan

[themoudie]

G'day Dan,

Thank you and for the PM, will reply when not galavanting on the old bird! At present it wakens the dead, runs on the rich side and leaves a haze behind on the overrun, with nearing a 1,000 miles on the clock.

Awaiting the blacksmith to weld up a home made exhaust that I will fit and then re-jet the carb, if necessary. If it doesn't work then another exhaust will be necessary, but it is cheaper than a genuine Conti, which are now £476-28 + 20% VAT or £571-54 + P&P! Or AU $1051-28! How many gimmers is that?

Now, where did that Velocette fishtail exhaust go?

Good health and stop doing the face plants, Bill

[themoudie]

The old chestnut raises it's ugly head again!

So, after managing to destroy the AMAL MKII 2932 needle circlip and grooves on the needle a couple of weeks ago, requiring the flatbed of shame to uplift and carry the '74 450 MKIII home after ~2,500 miles of use, I had another "incident" today!

Out for a quiet run round some backroads when the engine became hesitant and started popping and banging on the overun. Managed to cajole, nurse the bike into Creiff and stopped at the entrance to the caravan site. The vapours that occasionaly come from the carb where also coming from behind the front circlip holding the Triumph TSS cranked inlet rubber to the inlet spigot! And, as you correctly surmised the rubber had split after ~2,700 miles! This without a whiff of E10 passing along it. Just E5 and Castrol Valvemaster. Two touring motorcyclists (in campervans), with their motorcycles on the back of each van, expressed an interest and after much banter a large roll of electrical insulation tape was produced. After two failed attempts to get the inlet rubber to stay on the stub and remain in one piece, I managed to make my escape and managed to run the 14 miles home at a steady 50mph, without further incident. PHEW! Parked the bike outside the workshop, turned the engine off, switched the fuel taps off and the carb fell off the inlet stub, pouring the float bowl contents over the hot crankcases and the exhaust! It vapourised, without igniting!

So, I shall be reverting to my marine fuel hose, that is reinforced with a steel wire and canvas, in a bid to prevent the splitting and hope that this doesn't "upset" the carb settings. It shouldn't, but who knows with an AMAL MKII.

George may yet have a disciple in a return to bolting the carb, in the form of an AMAL MKI 932 directly to the head, rather than extending the inlet tract length, with aluminium stubs and inlet rubbers that fail with regularity!

Keep wearing them out, Bill

P.S. OH! By the way the oil filter/Royce Creasey/Motad/silencer element welded into the gutted Gold Star exhaust works a treat.

[Duccout]

God Bill, you live an exciting life! I used aluminium manifolds joined by car radiator hose for many thousands of miles on my 350, but that was before ethanol, but I find it hard to believe that ethanol would rot radiator hose as it is so tough. Keep us informed.

Colin