450 desmo carb

[Harvey]

Giday Bill hope your are holding up well, and are sufficiently fortified.

I too am finding it difficult to resolve how, when the valves are both shut, the engine is able to create an explosion in the inlet tract! Pre-ignition on steroids!

Yes that is an interesting statement that got me thinking, as it can happen, if the engine rotates backwards.

Consider this situation, you are kick starting it, the engine does not fire, so it keeps rotating till the piston comes up to compression again but does not go over, so it spins backwards the piston goes back down, the Inlet valve opens, and the points cam rotates backwards till the heal of the points meets the back side of the lobe to fire the plug.

As you have changed the points plate and the modified cam lobe it may just depend on how long the lobe holds the points open, compared to the original cam, that would allow this to happen.
It would be worth rotating the engine backwards till the points start to break just see where the valves are positioned.
What do you reckon.?

[graeme]

Hello Harvey,

That makes sense,,,
Edit, but that would happen to a lot more 450s other than just Bill’s ?

[Bevel bob]

If you do perfect the art of running the motor backwards ,please tell all as I have got myself in a few situations where it might have been a help !!.

[themoudie]

Good morning and G'day,

Thank you for all your sugestions and encouragement.

Both Celes' and Harvey's comments need to be investigated. But, I have bitten the "electronic" bullet and all being well, will be stepping away from the analogue ignition. I will continue this thread even though it may now be very inappropriately titled!

Off to deal with a Morini and watch the swallows and sand martins that have arrived in a sunny, and now rained on, but chilly Perthshire.

Good health, Bill

[themoudie]

UPDATE 01/05/2021

A small parcel arrived earlier this week and it took until today to fit the contents and then gird up the loins to give it a try!

The AAU, points, coil, condenser and Boyer IDU have all been stripped off the 1974 450 MKIII and the installation of the Hall Effect CDI unit, pulser ring and pulser trigger proved painless. OK! Me being me, found the pulser ring a wee bit tight to slide into the timing cover and the right hand fuel tank mount needed easing with a pair of padded stilson to enable the coil part of the CDI unit to fit behind the headstock. The wiring was a simple, if steady wee number. I used additional heat shrink to seal the upper end of the glass fibre cable cover supplied and found the 3pin plug for the pulser ring wires a bit stubborn. Ensuring that there was clearance around the CDI and that the wires were all tucked out of harms way, was the longest part of the job.

This morning, Kat came and helped check that I had the timing set up correctly. I then put the now battered and chipped MKII 2932 on the Triumph TSS rubber inlet onto the inlet. Set up the remote fuel supply and we were ready to give it a go. Prime, with the cold start open and not a lot happened. After three kicks there was a cough, so knocked the cold start off and tried again and away it went. I didn't touch the throttle and just allowed the revs to build and the engine to warm through. Set the tickover at a steady 1,300rpm on the slide screw and left evrything else alone.

Next, gave the throttle a couple of blips and the engined settled back to a steady 1,300rpm, with a little popping and banging on the overun. There was also a wee touch of richness (reek) on opening the throttle, but a clean pick up from the engine and a hint of grey reek on shutting the throttle. Valve guides running in and without oil seals fitted, so I am not worried about that, it just shows that the guides are now getting lubricated and the plug could be a bit sooty.

Turned the engine 'OFF' and fitted up the timing gun. Set the advance on the gun to zero and aimed at the easy to see marks on the pulser ring and trigger (no messing about with pointers and oil seals on the opposite side of the engine! ). Nice steady advance movement across the full 28° range and a return to a steady 1,300rpm tickover.

Yet to go for a wee shakedown canter, but I think the carb blowing off has been rectified.

This link is to a very short YouTube video of the tickover after my fitting of the Electrex Ducati Singles Hall Effect CDI Ignition System - STK-169D: 1974 450 MKIII_Electrex_Hall_Effect_ignition_fitted_tickover

So, my humble apologies for hijacking a carb thread with an AAU/timing fault that has lead us around the houses to find a cure (I hope! ) My sincere thanks for all your thoughts and encouragement over the past 20 months, yes, it was September 2019 when this started!

Good health to you all, Bang Bill

[Duccout]

Well done Bill! Fingers crossed that now your carb launching days are over. The pulsar ring was a bit tight in the housing on my Spanish 250 as well. Keep us posted.

Colin

[graeme]

Are you “ordinary Bill” yet ? (Ex bang Bill)

How did it go ?

Graeme

[George]

Hi Bill we are all waiting for results of next test run and hoping for success. Enjoy the summer on your 450.

[themoudie]

Good morning Gentlemen,

I think that we can say that I am now ex BANG! But the MKII continues to be a phaff! Bit on the lean side and the plug colour is screwed up, as the guides without oil seals and a 0.002" working clearance are colouring up the plug from burnt oil! A little white haze on the overun.

You can hear the difference in the two wee videos that I have posted links to in previous posts, with the engine ticking over.

So, before this next Atlantic low pressure sytem floods and blows us away, I am off to the workshop.

Good health, Bill

[LaceyDucati]

Bill
I will look into the fit of the ring, It hasn't been an issue that has been brought to my attention and we have sold a lot as those parts which are the same as the STK161 and STK164. The ones I tried in covers here were okay, but I will give it another look at and flag it at Electrex if needed. The issue could well be Ducati's variable tolerancing and as always establishing specs is difficult from patterns without the original manufactures drawings. That said even with original specs, from my experience you still wouldn't cover all eventualities.....Ducati didn't always manufacture to their own drawing specs! The trouble is we engineers like to make things a nice fit, rather than on size fits all, which invariably ends up in some cases like a p**** in a shirt sleeve

There was an issue with the rotor for awhile with excess plating in the hole, but that was resolved and with the new anodized aluminium rotor should not reoccur.

Hopefully it's down to Carb tweaking now.... Lets see how the ignition goes and hopefully that has solved the main issue....I have some interesting enlightening regards the ignition in due course.

Regards Nigel