Re: 450 desmo carb
Posted: 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!
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!
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!
Good health, Bill
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!
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!
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!
Good health, Bill