SOHC.co.uk Forums > CB500/550

MISFIRE ON NO4 CYLINDER

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blade918:
THANKS FOR INPUT NO BITS CHANGED IN CARB, CARBS WERE SONICALLY CLEANED , SWAPPED PLUGS STILL SAME , FLOAT HEIGHTS ALL SET TO MANUAL AND DOUBLE CHECKED, O RING LOOKS OK ,CARB ASSEMBLED OK STILL DOES NOT RUN PROPERLY AFTER CLEANING PLUG IM OPEN TO ANY OTHER IDEAS AS IM AT A LOSS WITH THIS ONE MANY THANKS FOR HELP SO FAR KG

K2-K6:
Compression check to see what you've got  ?

Sesman:
Swap the leads over on cylinders 4 and 1, This will eliminate the coil if the misfire stays on cylinder 4. If it moves to one you can focus on cap, lead and coil in that order.

Compression check…make sure the tappet clearances are set correctly. Then check for compression relative to other cylinders.

You have already swapped the plugs eliminating a failing plug issue.

Failing that, it’s definitely a carb/fuel issue.

blade918:
THANKS FOR INFO SWAPPED PLUGS AND COILS COMPRESSION OK IM LEANING TOWARDS CARB ISSUE ILL REMOVE TANK CARBS STRIP NO4 DOWN DOUBLE CHECK FLOATS ETC AT WEEK END THANKS ALL KG

K2-K6:
If there's nothing fallen out in the carb (main jet, emulsion tube etc) then it's worthwhile with very close examination of idle circuit to be absolutely certain there's no impairment.

If the air passage into the carburettor for that circuit is blocked, then effectively it'll run full bleed on that idle jet as soon as you start it. Start will be OK as it's "choked" by this effect and won't be seen at initial running.

You could try turning the idle screw adjustment on that #4 to assess if it's doing anything. No response indicates it's blocked for air supply.

If so, you can remove the screw itself, spray carb cleaner down into there, then blow out with compressed air to see if it'll clear without dismantling.

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