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CB500/550 / Ongoing PD46 carburettor woes (possibly)
« on: June 01, 2020, 09:10:57 PM »
Sorry - quite a long post!!
As per earlier posts, following major fuel seepages from around the carb bowls and (as it turned out) the fuel tubes between the carbs and also sporadically from the overflow tubes, I undertook to rebuild them.
With help from comments on this forum and Brainj who miraculously managed to supply me with four springs used on the throttle slider link arms, which had been lost during cleaning, the carbs have now all been re-assembled, bench balanced and refitted to the bike - re-fitting them was a nightmare!
During the rebuild the carbs have been vapour blasted and cleaned in an ultrasonic cleaner as well as having all the replaceable jets etc have been replaced along with the seals and O-rings etc. Taking note from others comments I have tried very carefully to make sure that all the internal passage ways were clear and clean.
The good news is that they look good and all of the fuel leakages have been cured.
To complete the exercise I have just finished carefully making sure the timing is spot on (at least statically), the points are good and the tappets are all correctly set up. (Both the timing and some of the tappets clearances were a little bit off).
The bad news is that the bike will not run smoothly at all!
Actually no-1 cylinder is hardly firing - its exhaust pipe is still cool after a couple of minutes whilst the other three cylinders are all hot. just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.
To explore a bit further I did remove the screw where you would attach a vacuum gauge and spray some carb cleaner in and immediately the revs picked and No1 cylinder fired up, perhaps suggesting an issue with the fuel delivery to that cylinder. I have also checked that there is fuel in the cab (by opening the drain screw) and confirmed there is a regular flow of fuel.
Its worth saying at this point that No1 cylinder has always been a bit of a problem in this regard, causing the engine to 'chug' at tickover until the engine has warmed up which makes me wonder if there is possible a more deep seated problem?
I am loathed to remove the carbs again and have another go at clearing them as there seems to be no clear way of knowing if the clearing is successful.
Does anyone have any suggestions - is there anything else which could cause this type of symptom other than the carbs? If I do take them off again what can I do to make 100% sure that all the passageways are clear and there is nothing else causing the problem? Any guidance would be appreciated!
As per earlier posts, following major fuel seepages from around the carb bowls and (as it turned out) the fuel tubes between the carbs and also sporadically from the overflow tubes, I undertook to rebuild them.
With help from comments on this forum and Brainj who miraculously managed to supply me with four springs used on the throttle slider link arms, which had been lost during cleaning, the carbs have now all been re-assembled, bench balanced and refitted to the bike - re-fitting them was a nightmare!
During the rebuild the carbs have been vapour blasted and cleaned in an ultrasonic cleaner as well as having all the replaceable jets etc have been replaced along with the seals and O-rings etc. Taking note from others comments I have tried very carefully to make sure that all the internal passage ways were clear and clean.
The good news is that they look good and all of the fuel leakages have been cured.
To complete the exercise I have just finished carefully making sure the timing is spot on (at least statically), the points are good and the tappets are all correctly set up. (Both the timing and some of the tappets clearances were a little bit off).
The bad news is that the bike will not run smoothly at all!
Actually no-1 cylinder is hardly firing - its exhaust pipe is still cool after a couple of minutes whilst the other three cylinders are all hot. just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.
To explore a bit further I did remove the screw where you would attach a vacuum gauge and spray some carb cleaner in and immediately the revs picked and No1 cylinder fired up, perhaps suggesting an issue with the fuel delivery to that cylinder. I have also checked that there is fuel in the cab (by opening the drain screw) and confirmed there is a regular flow of fuel.
Its worth saying at this point that No1 cylinder has always been a bit of a problem in this regard, causing the engine to 'chug' at tickover until the engine has warmed up which makes me wonder if there is possible a more deep seated problem?
I am loathed to remove the carbs again and have another go at clearing them as there seems to be no clear way of knowing if the clearing is successful.
Does anyone have any suggestions - is there anything else which could cause this type of symptom other than the carbs? If I do take them off again what can I do to make 100% sure that all the passageways are clear and there is nothing else causing the problem? Any guidance would be appreciated!
