my bike, a 1978 cb400n (not a yamy i know but i do own a r6 making my membership of this club legit lol) now runs after ten+ years sat ina garden (not mine). however. when we first got it going a few days ago, after alot of work on the carbs, clutch and bits n bobs, it was runnnig at idle and on both cylinders sweet as a nut.

but now, a few days later, it sounds like its only fireing on one cylinder. it stalls at idle. and when i ride it for a minute or two the left downpipe glows bright red! both spark plugs give a spark. i did clean the carbs thoroughly. my dad recons the silencer is blocked but wouldnt that make both pipes burn?

anyway, im not what you would call an accomplished mechanic and im a bit stuck now.

im trying to avoid taking it to a garage as it was ment to be a winter project for father and son. i do have a bit of money to spend on parts tho.

oh one extra thing i noticed. this is the second day its been like it. and the pipes change, one time its the left that turns into an oblong sun, then its the right.

were both sat down scratching are heads now guys. any help would be welcomed.

thanks

david

Try some new plugs and caps, also give the HT leads and coils a spray with WD40.

Overheating is usually a weak mixture. It could be that it has pulled some dirt or gum (old petrol) down into the carbs and blocked (or partially blocked) a jet. Make sure that the fuel is new (ie drain tank of old fuel) and thoroughly clean and blow through the jets with compressed air to clean (use eye protection).

my bike, a 1978 cb400n (not a yamy i know but i do own a r6 making my membership of this club legit lol) now runs after ten+ years sat ina garden (not mine). however. when we first got it going a few days ago, after alot of work on the carbs, clutch and bits n bobs, it was runnnig at idle and on both cylinders sweet as a nut.

but now, a few days later, it sounds like its only fireing on one cylinder. it stalls at idle. and when i ride it for a minute or two the left downpipe glows bright red! both spark plugs give a spark. i did clean the carbs thoroughly. my dad recons the silencer is blocked but wouldnt that make both pipes burn?

anyway, im not what you would call an accomplished mechanic and im a bit stuck now.

im trying to avoid taking it to a garage as it was ment to be a winter project for father and son. i do have a bit of money to spend on parts tho.

oh one extra thing i noticed. this is the second day its been like it. and the pipes change, one time its the left that turns into an oblong sun, then its the right.

were both sat down scratching are heads now guys. any help would be welcomed.

thanks

david

Does the old worm (rather eat worms than ride a Honda) start from cold ok or is it a chore to start it ? but I cannot understand why the prob jumps from right to left 400n uses wasted spark ignition so the ign timming should be the same cyl 1 & 2 (but if the cdi pick up is rusty the coils could be given false info and run the ign well out). If you feel the silnecers are blocked why not run the bike without them... it might sound like a real bike ! and would discount blocked silencers (unlikley). I take it that the carbs were soaked for days in carb cleaner and then blown with a hi pressure airline and all traces of green grunge was removed... the yellow stuff is ruff too. But I guess you could bury it and forget all about it