450 desmo carb

[themoudie]

Thank you Graeme, duccout and Nigel for taking the time to consider the problem and offer data and suggestions. Also, my thanks to Nigel for your generous offer of the loan of your 350's carb. For the time being I'm going to persevere with my own MKII 2932, with altered settings, very different from those that I have used so far. And also set up the ignition timing using a different method from my previous attempts.

I have also had a conversation with Andy from SCR Classic Motorcycles, Soham, whom I have spoken with and watched race for many years, 250, 350 and 450 Ducati singles in various states of tune and a Royal Enfield Constellation outfit! The Ducatis have all run MKII 2900 series carbs, and won races including the Ducati Club races at Assen, but with essentially weaker settings than those when the carb is despatched by AMAL as "standard"! The "standard" settings are a good starting point for the size of carburettor, but as you can see from Nigel's experience, I'm intending to run a 'small' diameter carb on a 450, when compared to the more common sizes chosen for 450 machines.

I'll also revert to the gutted Gold Star exhaust.

I will post further settings and their outcomes as I continue. I'll try not to overtighten the clips on the carb rubber inlet, but I don't want the carb dropping off! As for ".... run like tractors and pull hard from 3,500rpm", I assume that they are Lamborghini tractors! That orange and blue colour scheme on a Duke might be quite fetching!

Good health, Bill

[LaceyDucati]

Keep at it Bill!

I saw this old pic on my computer this morning, I've been around MK2's for awhile, this was 30 years ago on John Carpenters Dyno at Mistral Engineering. Quite where the time went......

47a.jpg

The Ducati club races were the best Ducati meeting ever (hopefully still are) and Assen is a brilliant circuit to ride. I rode there for 7 or 8 years in a row at the Club races, indispersed with a couple of Dutch TT's in the 90's.

Regards Nigel

[themoudie]

Good morning Nigel and other followers,

Time always seems to whizz by when your having fun!

Further to my last post and conversation with Andy at SCR, he suggested that I should read the following article "AMAL a comprehensive look" from the vintagebikemagazine. You will need a clear head and time to absorb the information.

Here is the link to the article: 'AMAL a comprehensive look'

Thank you for your help.

Good health, Bill

[George]

Excellent article Bill. I have printed for my files.
I have been following your trials and tribulations with great interest. For what it is worth I am not convinced that carburation is your problem. I am no expert but sometimes you need to step back and then rethink cause and effect. You know the effect but not the cause yet.
Good luck, sure you will get it running eventually.

[Duccout]

Bill, could the problem lie with the Escort points/cam set-up? Although I Don't see how.....A spark is a spark. It just seems that you have exhausted all the carburration possibilities. What about an air leak, as Nigel suggested? The fact that the tick-over won't come down could be a clue to that.

[themoudie]

Aye Colin,

The Escort cam/points set up was a temporary 'fix', so that I would have transport when I started my new job in the IoM back in 1976. At that time obtaining the necessary points, AAU, backplate, etc, was not a problem, apart from my stretched funds and once the funds improved I fitted the genuine Ducati parts and these still remain in place. The brass pivot on the backplate did slacken from it's swaging and so this has been brazed in position, again many miles ago.

Further to the current saga, I retimed the ignition with the AAU jammed in the full advance position and the spark occuring at 28°BTDC. Then checked were the spark would occur, with the AAU in it's static position, 3°ATDC, not the 0°BTDC that I had assumed. So, leave it, or re-adjust to Tassie graeme's preferred 0.5°ATDC and then give it a kick?

Air leak? This "reving" is not an initial startup phenomenon. It is only after the engine has been warmed through at ~2,000rpm for ~4 minutes that the engine starts to "hunt" as though the fuel has been turned 'OFF'. If the air gap beneath the slide is temporarily blocked, the revs drop to an idle and it is only when the throttle is blipped that the revs rise and stay raised, or the carb gets blown off! I still think that it is a carb issue having changed the cam and havered ("haver") with my ignition timing. THIS IS NOT CRITISM OF THE CAM, BUT A PHYSICAL FACT. With oddball porting, a lowish compression piston (I don't have squish figures, sorry! ), a non-standard exhaust, they all have an effect upon the harmonics of the gas flows through the induction, engine and exhaust system. I appear to have made a dogs breakfast of it, with my "suck it and see" approach rather than the calculated approach. So, now to make it run!

Good health, Bill

[Celes]

Bill earlier in the discussion, you asked if forum members had experience of a 32mm Mk 2 Concentric on a 450 Desmo.
I have just joined the forum and offer this contribution..
I have a 450 Desmo fitted with a twin plug head off an RT, a domed 900SS piston, Lucas Rita ignition running 2 X 6 volt coils and a 32mm Mk 2 concentric. I have a small cone type air filter and a Conti type silencer.
These settings seem to work for me. Main jet 240, needle position 2 cutaway 3 pilot jet 25 and 1.75 turns on the air jet. This is my 6th carburettor setting iteration for a bike that was difficult to start, keep to a consistent idle and pickup smoothly. The breakthrough for me was to replace the 106 needle jet with brand new. I had not realised that the old one was worn. Slight wear here wrecks the idle and pickup on low throttle openings and is not visible to the eye. This carburettor had not done much work but vibration, a hardish needle and soft brass jet material does its worst.
A further consideration is your flywheel weight. I have fitted an Electrex 12V 120W system and remember that the flywheel weight is quite a bit less than the original 1.98 kilos. Electrex list one part number for the whole Ducati single range with a 1.42 kilo flywheel for all models. Although the reduction in weight will aid acceleration, in theory, it does require a higher idle speed, makes the bike slightly more difficult to start, prone to stalling and increases the engine braking effect. In consequence, the lighter flywheel has made the bike more sensitive to compression ratio, carburation and ignition setup.

[LaceyDucati]

I would second the wear on the Amal needle jets on both on Mk1's and Mk2's, I always replace the needle jet every other year on race bikes as they do wear rather alarmingly over time. They don't wear in the two years of racing noticeably, but it heads off the gremlins before they get the chance to rear their heads.

Regards Nigel

[themoudie]

Aye Celes and Nigel,

Thank you for taking the time to share your AMAL MKII 2932 settings. My ramblings on this thread are because my '74 450 MKIII is not that different from a 450 Desmo. After all when the two models came out of the factory both models had a 29mm Dellorto in place.

Yesterday, re-adjusted the ignition timing to Tassie graeme's 0.5°ATDC, then connected up the Boyer ID unit and checked the spark was good and healthy.

Fired up the engine with the new 2932 installed (less than 200 miles 5 hours running), with the following settings:

Main jet: 220
Needle jet: 106
Needle: 2A1 with the clip in the 3rd groove from the top (middle)
Slide: 3
Pilot jet: 20
Air screw: 11/2 turns out, off the seat
Cold start jet: 35

Starting was nice and easy, but the pick up was definitely weak, with spitting back and cutting out. Turned the air screw in until only 1/2 turn out from seating, still a bit weak. Installed the Gunson Colourtune plug, which confirmed a weak mixture at that setting. After 4 minutes continuous running the revs climbed, without prompting, to sit up at ~4,000rpm. Blipping the throttle to reduce the revs made no difference at all and I tried to find an air leak in the intake tract. No luck. But, I am very suspicious of the joint between the bolt on alloy inlet stub and the cylinder head inlet face, as both the MKI and MKII carbs have shown this revving behavior. So, that joint will be remade before I try Celes' 2932 settings. The pilot jet was going to go up to a 25 anyway after my test.

I'll post an update.

Good health, Bill

[graeme]

Hello Bill,

To be clear about the half degree ATDC,
My Yellow Desmo and Scrambler both use the original Ducati electronic red box ignition.
They are both set by slight pinking under load at 4000 plus revs, then retarded a small amount.
The RT has a Sachse ignition that tended the kick back when statically set to 0 degrees TDC, so I set it to the half degree ATDC.
Start easy and runs well.

Re your possible manifold leak,
You could spray a small amount of petrol around the joint in question, if the revs change you have found a leak.
I have done this and it works.

NOTE !!!! I accept no responsibility for your bike or shed catching on fire !!

Good luck

Graeme