450 desmo carb

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themoudie
Posts: 649
Joined: Sat Jun 14, 2014 12:44 am
Location: Scotland

Re: 450 desmo carb

Postby themoudie » Thu Apr 22, 2021 9:56 pm

UPDATE 22/4/2021

The 450 head went to my local engineer for a check of tolerances, with a new stainless steel exhaust valve and the stainless inlet valve. The head was cleaned in a ultra-sonic bath and the guides were both measured having a clearance of 0.0015" (0.038mm) so both phosphor bronze guides that have already had 'K-liner' fitted were eased to give 0.002" (0.05mm) clearance. The valves were checked for concentricity and the valve seats lightly "kissed" to give a good seal and the ports were then vacuum tested, with excellent results.

Washed the head in hot soapy water, thoroughly rinsed and dried. Then assembled 'White' cam and checked rocker pad contact, 90% area contact. Installed valves, with plenty of red liquid chainsaw grease, then the cam and rockers and set up the inlet with 0.003" (0.076mm) and the exhaust with 0.004" (0.10mm) clearance. New 'O' ring on oil feed spigot on top of barrel. Torqued head bolts to 25ft/lbs, checked the mesh of the upper bevels across the ground flat, again, with the timing chest cover removed, checked the timing marks to ensure that valve timing and the ignition timing were all correct and then re-assembled. Checked cam valve timing and all readings appear to be within 3° of the Clymer manual figures. Whilst the timing chest was open, ensured that the AAU was in good condition and free to move, with no corrosion or slack springs. Gapped the points at 0.013" (0.33mm) and then using a bulb in series with the battery, direct to the points timed up the spark at 0°BTDC. Installed a clean NGK BH6S plug, with a electrode gapped at 0.025" (0.63mm). Exhaust is OME pipe and a single plate baffled 27" long "Gold Star" pattern exhaust.

Installed the new Amal MKII 32mm on the angled Triumph TSS inlet rubber, installed the remote fuel supply. Turned on the fuel, brought the piston over TDC with the de-compressor, put the cold start 'ON' and gave a good swinging kick. A loud explosion, the carb took another chunk out of the frame webbing and more dents in the bellmouth whilst spewing fuel over the floor! :evil: :evil: :evil: :evil: :evil:

Checked the ignition timing, re-installed the MKII carb. Connected everything up, cold start 'ON', swinging kick and the motor fired up and ran for about 5 seconds, then stopped. So, brought piston over TDC and gave another swinging kick and "BANG", the carb was hanging again with more chips and dents and fuel spewing on the floor! :evil: :evil: :evil: :evil: :evil:

Could the height and consequent head of fuel into the carb be causing this by over coming the force on the needle exerted by the 'Stay-up' float? :?: I have the resevoir about 2' (60cm) above the float bowl, with about 400cc of fuel and a 6mm bore hose into the float bowl filter feed.

I am thinking of returning to the 1977 set up, with an Amal MKI 32mm bolted directly to the head, rather than the rubber inlet stub and the MKI or the MKII carbs. Tomorrow will see! :roll:

Good health, Bill

Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: 450 desmo carb

Postby Bevel bob » Fri Apr 23, 2021 4:13 am

Gosh Bill , you are a glutton for punishment !, Sounds like you are in a closed loop . I'm thinking of retracting my generous offer to swap bikes !. You appear to have covered all the fundimentals but sometimes a different approach breaks the circle. I may have a used set of old points that you can try , will look tomorrow.

graeme
Posts: 939
Joined: Sun Mar 25, 2012 12:00 am
Location: Tasmania Australia

Re: 450 desmo carb

Postby graeme » Fri Apr 23, 2021 4:44 am

You need priest Bill,,,,,,,,,

Seriously, second kick after 5 seconds run and die, it must have fuel in there to make it go bang ????
Something wrong with the spark ?

Also what is red chainsaw grease ?

Graeme

Duccout
Posts: 1285
Joined: Wed Feb 05, 2020 1:20 pm
Location: Essex UK

Re: 450 desmo carb

Postby Duccout » Fri Apr 23, 2021 5:17 am

Good Grief! Bill, you DO need an exorcist!

No idea. Baffled. It is akin to an organ transplant, where the patient is rejecting the organ. The idea of going back to the directly-bolted Mk 1 is good, but now you have eliminated the cam as a possibility, then the problem has to be with the ignition system, and my money is on the AAU.

Colin

graeme
Posts: 939
Joined: Sun Mar 25, 2012 12:00 am
Location: Tasmania Australia

Re: 450 desmo carb

Postby graeme » Fri Apr 23, 2021 6:32 am

Bill,
I feel for you,,,
What year is your 450?
I have 3, 2 with the red box late model 1974 and a '71 RT with Sachse ignition. (all going bikes.) If yours is pre '74 I doubt the red box ign will work.

I'm willing to remove a complete ignition (if it is suitable to your bike) and send it to you to try.
And 32PHF with manifold from RT or Scrambler.
You pay for post from Tasmania,,,,,

We have to put this behind us so you don't do something you shouldn't.

Serious offer,,,,,,

Graeme

graeme
Posts: 939
Joined: Sun Mar 25, 2012 12:00 am
Location: Tasmania Australia

Re: 450 desmo carb

Postby graeme » Fri Apr 23, 2021 6:34 am

Oh, I forgot to say, You send it all back when you get your bike going.
Also, I have a few AAU that I will never use. Yours for the post costs. What numbers ?

Duccout
Posts: 1285
Joined: Wed Feb 05, 2020 1:20 pm
Location: Essex UK

Re: 450 desmo carb

Postby Duccout » Fri Apr 23, 2021 7:07 am

Good on you Graeme, that's a generous offer.

If it were me, having eliminated the cam as culprit, I would change the entire ignition system and fit a Sachse or an Electrix World; at least then that part of the equation would be put to bed.

blethermaskite
Posts: 477
Joined: Thu Mar 01, 2018 1:06 am
Location: northern ireland

Re: 450 desmo carb

Postby blethermaskite » Fri Apr 23, 2021 9:29 am

Bloody hell! Bill If ever there was a "ghost in the machine" you certainly have it in this one, I cannot for the life of me see what it is you have missed, unlike the stamina you have to continue with this battle I don't have the stamina to re read all the posts on this issue but if I knew nothing about the trials you have gone through and was hearing about your problem fist time I would simply say " your condesnser is duff" or is shorting out someway. I always mount my condenser on the coil. A quick story to example another "ghost in the machine" a 1970s Suzuki gt380 I was given free many years ago that no one could get to run properly...it would start ok then would slowly go off each cylinder until it was only running on one pot like a pig, I changed everything on that engine and I mean everything to the point where I fitted another entire engine from a running bike...same problem, replaced the carbs replaced the entire ignition system, replaced the entire wiring loom, no good, there was nothing left to change.......sounds familiar......the Suzuki has a little brass plunger choke slide with a rubber button seal on the bottom......it was split :roll: .......keep at it good luck.
Cheers,
George

themoudie
Posts: 649
Joined: Sat Jun 14, 2014 12:44 am
Location: Scotland

Re: 450 desmo carb

Postby themoudie » Fri Apr 23, 2021 10:53 pm

Aye Bob, Graeme, Colin and George,

Thank you for your support and offer of parts etc. it is very much appreciated.

"Red chainsaw grease" is the 'Oregon' liquid red grease used to lubricate the roller bearings in the sprocket nose of a chainsaw guide bar and the needle bearings for the chainsaw clutch. It is quite viscous and stays in place throughout a rebuild, giving good initial lubrication to all bearing surfaces when making the initial start-up. Specific engine assembly fluids are available.

By using a Boyer IDU in the ignition circuit I do not need a condenser in the circuit. However, I have a condenser bolted to the coil clip that in turn is wired direct to the central frame earth. So that I can run the points without the IDU, if necessary.

After posting yesterday, I too was pondering the AAU and the ignition timing in general. So, snap, Colin. ;)

I have always, since the red box ignition failed in 1976, timed the ignition with the AAU at fully retarded, no tension on the bob weight springs. I had read this article on timing Ducati singles ignition, by Vintage Veloce™. There is a link on this Forum's front page that is old and circuitous, so here is a direct link: Vintage_Veloce™_setting-ignition-timing-advance In the 7 sides of A4 instructions Vintage Veloce says that he times the ignition maximum advance, with the AAU bob weights fully extended and the springs at maximum tension. He does not adjust were the ignition spark occurs, with the AAU static and the bob weights and springs in full repose. Andy Hunt from SCR Classic Motorcycles, uses the same principle when timing all his Ducati singles. I was unsure of what might happen, if at repose, the ignition was timed ATDC. Consequently, I kept repeating what might be my error!? :oops:

Today, I jammed the AAU (AA359) fully advanced, the points gap at 0.013" and with the points having been set at 0°BTDC when the AAU was in repose, the points (bulb in series between points and battery) now broke at 34°BTDC! Maybe my "swinging kicks" are advancing the ignition too much when starting? :? I then re-set the points, with the AAU at maximum advance for a 1974 450MKIII engine of 28°BTDC. Then I released the jam on the AAU and in repose measured where the spark occured, this was at 4°ATDC.

Does this make sense? :?: I intend to give this ignition setting a try and hope that it is not too retarded and the engine runs "hot" at tickover.

Thank you for your time and help.

Good health, Bill

Duccout
Posts: 1285
Joined: Wed Feb 05, 2020 1:20 pm
Location: Essex UK

Re: 450 desmo carb

Postby Duccout » Sat Apr 24, 2021 5:55 am

Hi Bill,

I think that this move has to be a good one, as you are setting the timing to what you know is going to be correct at full advance, but, the AAU is still a variable ( pardon the pun). It looks like the timing was running too advanced and maybe causing the explosions? We are waiting for an update!

Good luck,

Colin


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