SOHC.co.uk Forums > CB500/550
PD46a carb problem
hubster123:
--- Quote from: Bryanj on May 18, 2022, 11:00:23 PM ---There are always vents or the carbs cant work, it has to be fuel bypassing the needle seat somehow.
Another reason to hate PD carbs
--- End quote ---
Believe me Bryan, I despise them!!! Someone has mentioned on the 46a’s, the vents are the 2 small tubes on the intake end of the carbs. I can confirm that they are all clear. I agree it can only be fuel getting past the needle but this only seems to happen when I do the clear tube test or run the bike up.
Sent from my iPhone using Tapatalk
deltarider:
--- Quote from: hubster123 on May 18, 2022, 08:17:00 PM ---[...]
Strangely, if I don’t do the clear tube test, let the fuel fill up the bowl and let it sit for however long, then the fuel will not start leaking out of the overflow tubes.[...]
--- End quote ---
Smell if maybe there's petrol in the oil.
--- Quote ---[...] But when I start up the bike, carb 4 clearly isn’t running well (header temperature is less than half of the other 3 on tickover).[...]
--- End quote ---
What does the #4 plug nose look like, at idle and cruising? Have you checked the #4 plugcap is OK and there's no accidental arcing to ground? I know this is not carb related, but all CB500/550s, sooner or later, will suffer from this. And it's easily checked in the dark.
--- Quote ---[...] I have replaced both the float and needle with new ones and it has made no difference.[...]
--- End quote ---
OEM or aftermarket?
IIRC, these carbs join one vent route, where as the oldstype carbs have two tubes, but... I could be wrong. Furthermore from memory: irregularities have been reported, which could be adressed by simply cutting the vent tube where it dangles behind the engine, near the swing arm, by an inch (or two). Make sure tube does not become pinched.
There's been said many negative things about these carbs and I fear we've now reached the stage where everybody echoes the other. There's a risk in this. It's my gut feeling these carbs can be helped to work as they should, by applying a maintenance (10-15ml) dose of fuel system cleaners, like Redex, at every fill up. More won't hurt. The stuff is perfectly safe and has no side effects. Please, do not experiment by adding doses of oil or diesel!
hubster123:
--- Quote from: deltarider on May 19, 2022, 08:40:45 AM ---
--- Quote from: hubster123 on May 18, 2022, 08:17:00 PM ---[...]
Strangely, if I don’t do the clear tube test, let the fuel fill up the bowl and let it sit for however long, then the fuel will not start leaking out of the overflow tubes.[...]
--- End quote ---
Smell if maybe there's petrol in the oil.
--- Quote ---[...] But when I start up the bike, carb 4 clearly isn’t running well (header temperature is less than half of the other 3 on tickover).[...]
--- End quote ---
What does the #4 plug nose look like, at idle and cruising? Have you checked the #4 plugcap is OK and there's no accidental arcing to ground? I know this is not carb related, but all CB500/550s, sooner or later, will suffer from this. And it's easily checked in the dark.
--- Quote ---[...] I have replaced both the float and needle with new ones and it has made no difference.[...]
--- End quote ---
OEM or aftermarket?
IIRC, these carbs join one vent route, where as the oldstype carbs have two tubes, but... I could be wrong. Furthermore from memory: irregularities have been reported, which could be adressed by simply cutting the vent tube where it dangles behind the engine, near the swing arm, by an inch (or two). Make sure tube does not become pinched.
There's been said many negative things about these carbs and I fear we've now reached the stage where everybody echoes the other. There's a risk in this. It's my gut feeling these carbs can be helped to work as they should, by applying a maintenance (10-15ml) dose of fuel system cleaners, like Redex, at every fill up. More won't hurt. The stuff is perfectly safe and has no side effects. Please, do not experiment by adding doses of oil or diesel!
--- End quote ---
The plug gets pretty carboned up but I’m putting that down to the fuel level moving all over the place. The coils and leads were replaced a couple of years ago and I put new plugs in last week.. The spark is fine
Sent from my iPhone using Tapatalk
hubster123:
I’ll stick an update on here when I get the chance but it looks like I’ve sorted it… thanks everyone for all your help
Sent from my iPhone using Tapatalk
Andy1488:
How did you sort it, and what was the problem ..?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version