450 desmo carb

[themoudie]

Aye Nigel,

Thank you for your rapid response and offer to rectify any clearance problems with the pulsar ring. (I would have used email rather than a forum if anything was way out!) This is, as you suggest, the proverbial "p**** in a shirt sleeve"! There is a slight ovality in the mouth of the timing case casting for the points chamber (could even be down to a spectacular "off" I had in 1978. So, once that had been diagnosed, I slid the ring in at an angle and then squared it up inside the chamber, with no further issues.

Since fitting the Hall Effect ignition, there have been no further "explosive events"! Although the bell mouth and frame web appear to have been in the jaws of a Great White shark!

Have now been on a couple of shakedown runs (50 miles) and the MKII is proving fickle, or my technique still requires improvement, probably the latter! I now have a steady tickover, there can be hesitancy or a "cough" just as the slide takes over from the pilot jet eighth to quarter throttle and more toward the eighth. So may try the No.3 in place of the 3.5. I know that this will screw everything else up, but once I have something sorted through the bottom to mid range, I'll move onto the needle. The main jet at present is a 220 and seems about right.

As for the "earworm" comment at the end. "I have some interesting enlightening regards the ignition in due course." I suspect that'll leave me with another on my copy book. Who cares, its all a learning process!

Good health, Bill

[graeme]

Bill,
Happy to hear you have sorted your long term problem.
The rest of the fine tuning will now make sense.

Regards
Graeme

[Harvey]

Giday Bill great to see that you have fixed the problem, and can now just enjoy the 450 on the road, but the sad bit is that this thread that has gone on for 22 pages will end.
Please keep us in mind ,when you decide to have another most interesting problem, I, as others have, really enjoyed your adventure.

[Duccout]

It ain't over until the fat Megga sings.......

[LaceyDucati]

Okay,

Regarding the Elextrex pulsar ring fit into the timing cover recess, I've given it some assessment. The issue relates to damage to the timing cover rather than a manufacturing fault. The ring measures 64.95mm and the covers all measure 65.10mm (8 covers measured). However the ring only fitted in two of the eight covers that I tried. I could see or measure damage, distortion or "nicks" at the outside edge of all the offending covers. Most likely all of this occurs from either accident or storage damage. The points backplate will enter these covers as it is thin (also largely slack as hell!) and can be passed into the cover at an angle avoiding any damage at the edge, unlike the thicker pulsar ring. If anyone experiences fitting issues they will just need to identify what is preventing the ring entering and carefully scrape out the offending incursion into the recess (as Bill did).

Regards Nigel

[Duccout]

Hi Nigel,

Yes, that makes sense, as my timing cover had been in the wars. I gently relieved the high spots until the ring fitted.

Cheers,

Colin

[themoudie]

UPDATE 10/5/2021

Since fitting the Electrex ignition, starting, idling and general running have all improved. And last night I put 60 miles on the clock after an oil change and installing some new rear shocks (Separate thread to follow later).

However, I still cannot get the AMAL MKII 2932 32mm to fuel cleanly!

Main jet 210, Slide 3.5, Needle clip 3rd notch from top, Pilot jet 25, Air screw 1 turn off the seat and cold start jet 30. 'StayUp' float, fuel level 2mm below top of the float bowl and the Triumph TSS angled inlet rubber onto the cylinder head stub. No air leaks.

Tickover, good and stable. Pick up from pilot to slide is clean without any stuttering. But, past there it is rich all the way. Constant yellow flame in Gunson plug from ~2,000rpm upwards and at a constant ~3,000 rpm no difference. Plug outer electrode wet and internal electrode and porcelain nose black but not sooty.

A small amount of oil coming into head down 0.002" clearance valve guides (hint of grey on the overun) but is this screwing up the plug colour?

When looking at the slide after a run, the whole of the outside of the slide appears wet with fuel?

Will raise the needle clip to the 2nd groove from the top of the needle (weakens mixture).

I am not sure about dropping the Main jet to a 200. On the road the engine pulls well from half throttle upwards (60mph+) up a long dual carriage-way incline. But I don't want to test the patience of the local traffic officers!

Any thoughts, please?

Thank you, Bill

[veloduke]

Hi Bill

When looking at the slide after a run, the whole of the outside of the slide appears wet with fuel?

I have had this effect when I was trying to get a MK1 concentric to run properly. I would go for a run, the bike would not feel right at full throttle (although yours seems to be OK). Back home I took the slide out and it had fuel sloshing about in the slide. Cured by reducing the size of the main jet. I was running a 340 jet, reducing to 310 fixed it.

Have to say that this was on a Velocette (hence the main jet sizes), but the principle could be the same.

Best of luck

[themoudie]

Aye Max,

Thank you for the words of experience and re-assurance, I shall continue to try and not goad my local traffic occifer!

As for the Velocette, a good, potentialy cantankerous, idiosyncratic, bit of single cylinder technology that could easily cast a spell over me.

Good health, Bill

[themoudie]

UPDATE 11/5/2021

Three runs today and a further 100 miles under the wheels.

Definitely, getting quite a bit of oil on the spark plug, earth lectrode. However, have checked the main jetting, again, and with a good uphill pull in 4th and the throttle wide, the motor just keeps pulling and I am getting a battleship grey insulator nose and central electrode. Using a 210 main jet and a 3.5 slide in the MKII 2932. Super unleaded fuel and Castrol Valvemaster maybe the reason for the grey colour, but there is no sign of glassy deposits or blistering of the insulator.

The pilot jet was a 25 with the airscrew half a turn out off the seat. with a noticeable hesitancy at the change from pilot jet to slide. In all gears. Remember this is a road bike, not a track bike that will get pinned in every gear! So 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. That by over fuelling, with a large pilot jet, the hesitancy can be masked/cured, I have previously gone as large as a 40 pilot jet, with best results using a 35 jet. But, at the expense of "fuel-wash" in the cylinder bore.

I will move the clip on the needle from the 2nd from the top groove to the 3rd from top groove and see if this takes the hesitancy away from the mid throttle opening in all the gears.

A different exhaust (27" in length, with some better back pressure and designed energy wave disruption) or the AMAL MKI 932 jetted, with a 210 main jet, 3.5 slide, 106 needle jet and needle clip in the middle groove and see what happens.

Even though the carburation is AWOL, the B, C and U roads are a delight. 300lbs weight, with maybe ~30HP on tap and nimble "no-think" handling, I should have rebuilt it straightaway, rather than leaving it for 15 years!

Good health, Bill