No 3 & No 6 cylinder not working

[Littleeagle28]

Again, check your valve clearances. You need to know what they are anyway. Then try all new plugs again. Wet - fouled plugs don't work in CBXs.

Dave

Thanks, will do.

[piit]

If said earlier then forget this...
I have had couple of plugs that give spark outside of cylinder but not when screwed in.
Try to swap plug with one of the working cyl or replace by new plug...might be easier to try before opening the valve cover.

-piit-

[cross]

I still don't get why this compression is so low, did you try using an alternate compression gauge?
When I did my compression check, I rented it from local auto part store and compression was scary low, 110/120 but then I used my neighbors snap-on gauge and got average 145.
But then again, they are not from each other which is in a way ok so they should either all fire up or none.
Does the plug smell like oil or fuel?
Dave's suggestion is about right, check valve clearances.
It is very straight forward, check the manual, check online, you tube video etc.
You will need a chart for writing down the measurements (if you don't have one, i can scan and email you)
You will also need calculator to make sure your calculations are good to figure out which shims you need.
Depending on sizes that you need, you may get away with existing ones, swapping them between valves.

[Littleeagle28]

If said earlier then forget this...
I have had couple of plugs that give spark outside of cylinder but not when screwed in.
Try to swap plug with one of the working cyl or replace by new plug...might be easier to try before opening the valve cover.

-piit-

Hi have done this. Swapped other plugs and ht leads also, no difference and the other cylinders still worked.

[Littleeagle28]

I still don't get why this compression is so low, did you try using an alternate compression gauge?
When I did my compression check, I rented it from local auto part store and compression was scary low, 110/120 but then I used my neighbors snap-on gauge and got average 145.
But then again, they are not from each other which is in a way ok so they should either all fire up or none.
Does the plug smell like oil or fuel?
Dave's suggestion is about right, check valve clearances.
It is very straight forward, check the manual, check online, you tube video etc.
You will need a chart for writing down the measurements (if you don't have one, i can scan and email you)
You will also need calculator to make sure your calculations are good to figure out which shims you need.
Depending on sizes that you need, you may get away with existing ones, swapping them between valves.

You could be right about the gauge, however I tried putting my thumb over the spark plug hole and couldn't,t keep it there.
Also Plug is wet.

It has been suggested it may be a sticky valve, and to try to insert rope into plug hole and slowly hand crank engine until rope pushes valve in order to loosen it.
Has anybody done this, and was it successful.
Arnie

[cross]

I never heard of such a thing.
If valve got stuck it could be because it got too tight from not being adjusted properly or not being adjusted at all.
During use, valves get tighter and tighter not looser as many people think.
And this would explain too tight or stuck valve.
At this point since you've tried absolutely everything, swapping the coils, carbs rechecked and made sure they are clean, file mixture left out at 1.25-2 turns out, etc. I would just got with Dave's advice and tilt the engine, take the valve cover off and check valve adjustment.
All you need is a feeler gauge which you can get at any part store just make sure it has correct size feelers.
I don't know what else to say, also try an alternate compression gauge but I don't think it really matters at this point.
And maybe, try finding local club that may have enthusiast that can help you out.

[EMS]

I am not sure, if the geometry of the piston and the combustion chamber will allow a valve to be stuck open.
Then again - that brings up a point. Could it be that you have a bent valve, which doesn't close completely?

[daves79x]

A slightly bent valve would not build any compression. My theory of a valve with zero or negative clearance will build a bit of compression when testing, but not effectively when running enough to fire a plug.

Dave

[cross]

Very true and same if valve is burned!
Maybe he should do leak down test