UPDATE 21/09/2020 23:20
After threatening to put a 3mm drill through the integral 20cc Pilot jet, I went ahead. Cleaned out the swarf, flushed and blew everything through, then filled the holes with epoxy metal and left to set in a warm place. Rebuilt the carb, a MKI 932 fitted with 220 main, 31/2 slide, needle on No.2 groove from top, 106 needle jet, cast in pilot jet removed and a 25cc Pilot jet in the back of the carb body. The SuperTrapp exhaust, with 16 diffusers fitted and managed to achieve a reasonable tickover of 1,000-1,200 rpm. BUT, would only start if well flooded on the tickler, even when hot! Fitted a new NGK B6HS plug, gapped to 0.035", this improved the tickover, but still black, but not wet after ticking over for 1minute+. Checked the ignition timing again, all appeared satisfactory. I also contacted Boyer Bransden, asking why the condenser needed to remain in circuit across the points, inspite of them acting as a switch and carrying no current. I will post the reply on the forum, in a separate thread, when I have it.
Took the bike for a road test and after 4 miles steady riding up through the gears and held in 4th in a queue of traffic, went into a 30mph built up area, down into 3rd gear and the engine was surging on small throttle openings. After a mile the road is 60mph limit again, so opened the engine up through the gears, clean all the way and pulling strongly up to 60 - 65mph. Had to slow for a bus and shut the throttle, but the revs continued to climb past 6,000rpm (at last glance
), changed down the box and applied brakes but revs refused to stop rising, so cut the ignition and coasted to a halt. Still behind the bus!
It felt as though the throttle was stuck wide open. Yet no sign of icing; the throttle working correctly and snapping shut, with no sign of the slide sticking or slack in the bore either laterally of fore and aft. Almost the same as a diesel engine sucking oil from a blown turbo and on wide open throttle. I would love to know the reason behind the behaviour and suspect an air leak somewhere?
Thought I had started to get the hang of it, and had ordered some bits for the MKI from Burlen to try to tune the bottom end and starting (pilot jets and a choke kit), based on comments posted about needing a proper choke with ethanol fuels and the fact that I was having to repeatedly tickle and kick until I had some heat in the motor before it would idle. Now I'm inclined to junk the MKI carbs and try the MKII again, with a deep float and a No.3 slide. I have been reminded that the MKII is a superior carburettor when compared to the MKI and cleans up the carburation throughout the rev range. Also they are the instrument of choice for competitive Manx bikes. I have tried the 'Stayup' float, but on another thread on Motoscrubs I read that the vibration can cause problems as the float is not sufficiently boyant to seal the float needle on it's seat?
Spec. for the MKII 2932 at present is:
Main Jet: 220 (180 - 280 available)
Needle Jet: 106
Needle: 2A1 (Middle groove)
Pilot Jet: 25cc
Starting Jet: 50cc (assumed, as this is standard fitting and it is siezed in the bottom of the float bowl!)
Throttle Slide: 31/2, but fiddled with by previous owner, cutaway is much taller than that on my MKI 31/2 slides. (Purchase a new No.3 or 31/2 slide?)
Modifications/upgrades:
'Stayup' float, replace with deep float for extra bouyancy.
Float jet appears sound as does the seat, both viewed through a x10 watchmaker's loupe/lens.
Purchase a new rubber adapter, rather than my home made reinforced marine fuel hose.
May need a new 105 needle jet and 27cc and 30cc pilot jets?
Gasket and washer kit (just in case!)
I have read these board threads as well:
Motoscrubs_Amal_Concentric_MKII_R2934/3 and
Motoscrubs_450_which_carb??? but the end never seems to come or a different carb from a MKII 2900 series is eventually chosen.
Maybe it'll have to be a 'Micky Rooney'?
'Nough from me and a wee dram to steady the nerves afore sheet alley!
Good night, Bill