Topic: backfires through the exhaust on #3

[gto_ron]

the first 15 minutes after starting cold cylinder #3 backfires through the exhaust, the float setting is about 5mm using the clear tube method.  I installed a new needle & seat anyway but it didn`t help. Where should I check next?  The bike is a 750K6

[Jimray23]

Idle plug chop. Its typically lean carb causing that but also check the valve clearances

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Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[TwoTired]

Do the spark plugs show different deposits among the cylinders?

Is there an exhaust leak?

[BobbyR]

Yes check the plugs. If it is on deceleration it is most likely a low float bowl level.

[HondaMan]

If that one carb slide is low (more than 2%) compared to the others, it will pop like that. Do you have vacuum gages available? If not, a visual check of the slides (carefully) will often help. Make sure they are all very close to each other, like maybe slip a drill bit into the back of each one to see which one(s) is higher than the others, etc.

[gto_ron]

thanks for the responses, I'll get out to the shop tomorrow and put your advice to work.  I didn't mention this but the bike runs great after it warm up.

[HondaMan]

thanks for the responses, I'll get out to the shop tomorrow and put your advice to work.  I didn't mention this but the bike runs great after it warm up.

Aha! This can also be caused by a too-tight valve (lash). Check the clearance on the #3 exhaust? Should be 0.003"-0.004" at TDC for 2-3 with that one on compression stroke.

[PeWe]

Bad connection between coil and plug? I have had similar symptom due to Dynatek coils automotive type of wire connection. The wire creeped out from the coil terminal