Topic: #3 cylinder not running on '78 CB550

[SCutchins]

I bought a CB550 a couple of weeks ago.  Cleaned the carbs, charged the battery, and she fired right up.  Didn't run great, but it ran.  Only has about 8300 miles but it was left outside.

I checked the pipes to make sure all were hot and the #3 is barely warm whereas the others are scalding hot.

The cylinder has spark, good compression (I checked #3 and #4 and both are at 147), and I assume its getting fuel since the carb bowl is filling with gas.

I haven't checked the valves yet.  Previous owner removed the stock airbox (threw it away dammit!!) and put on no-name pod filters.  For some reason the previous owner also put on a new rack of carbs, and told me that they weren't sync'd.

So, any thoughts?

[TwoTired]

Assuming that the carb's jet are clear because the bowls fill is very risky.

Didi you pull out the slow jets to see light through them?  They have the smallest orifice and are the first to clog.

A weak cylinder can be created with a poor carb vacuum sync.  All the carbs have to give each cylinder equal marching orders for them to pull together.  Otherwise, some loaf while others work and make heat.

If you are totally confident the slow jets/pilot circuits are clear, then it's time for vacuum synchronization.

Cheers,

[bryanj]

I'm with TT I will lay odds that the pressed in pilot jet is blocked

[Lars]

Typical problem when out of synch, I would try to synch them before opening the carb.