Topic: CB650 1981 - cylinders 1,4 not producing combustion

[hawk7890]

I have hit a road block on my engine repair project.

My engine had a valve strike against the piston, I replaced the valves and did the timing as per the manual, and I even rotated the engine manually looking at the pistons and valves to ensure no strike would occur, I have also adjusted the valve clearances as per the manual.

When attempting to start the bike it runs only on cylinders 2,3, also it sounds like something is loose in the engine but I am guessing it is due to cylinders 1,4 not working.

I checked cylinders 1,4 for compression and spark and both are fine, the spark plugs are wet which tells me there is fuel, it backfires and there is the smell of gas, probably the unspent fuel coming out of the engine. I swapped the ignition coil for 1,4 with another spare I had, swapped the spark units between each other and swapped the spark generator with another I had kicking around and no difference. .

At this point I have no idea what else to check. Any suggestions of things to look at would be appreciated.

Marc

[hawk7890]

Thank you, I will check again just to be sure, when I adjusted the valves, I checked in piston 1 with a flash light and turned until I saw it at the top and just start to go back down, then reversed it to make sure it was on the highest point, I then aligned the mark to 1.4 T which was a very tiny turn to align it.

I believe on this model of bike the cylinders fire both on the compression and the exhaust stroke.

Marc

[magnum56]

Number 1 and 4 share the same TDC postion.

Make sure you turn the crank while watching the intake valve for number 1.  It will depress / open during the intake stroke, then begin closing for the compression stroke.

As you see the number one intake closing, continue with your clockwise crank rotation to the T index for 1/4.
 
Adjust the valves as indicated for cylinder 1 at TDC.
Next turn the crank 360 degrees (one full turn) to adjust the remaining valves for number 4 at TDC.   

[scottly]

If the valve adjustment were off, the compression test should have shown it.
Marc, the pulse generator coils are polarity sensitive; one of the blue and yellow wires have a white band at the plug end. If the blue wire with the band is reversed with the blue wire without the band, you will still have spark, but at the wrong time. 

[magnum56]

If the valve adjustment were off, the compression test should have shown it.
Marc, the pulse generator coils are polarity sensitive; one of the blue and yellow wires have a white band at the plug end. If the blue wire with the band is reversed with the blue wire without the band, you will still have spark, but at the wrong time. 

Sorry .. that is not true.  Valve "timing" does not alter the cylinder compression value.

 

[robvangulik]

If the valve adjustment were off, the compression test should have shown it.
Marc, the pulse generator coils are polarity sensitive; one of the blue and yellow wires have a white band at the plug end. If the blue wire with the band is reversed with the blue wire without the band, you will still have spark, but at the wrong time. 

Sorry .. that is not true.  Valve "timing" does not alter the cylinder compression value.

 

Valve timing is something completely different as valve gap clearance adjustment!
Oh, and a hot cam with different timing will yield lower numbers at a compression test, so........

[scottly]

If the valve adjustment were off, the compression test should have shown it.
Marc, the pulse generator coils are polarity sensitive; one of the blue and yellow wires have a white band at the plug end. If the blue wire with the band is reversed with the blue wire without the band, you will still have spark, but at the wrong time. 

Sorry .. that is not true.  Valve "timing" does not alter the cylinder compression value.

 

The OP states that cylinders 2 and 3 are firing, so it's obviously not not a cam timing problem, as that would affect all four cylinders. If tappets were too tight, the valves would never close, which would show up on the compression test. 

[scunny]

+ 1 on the compression test. open valves, no compression.
As for the noise, did you seat the cam chain tensioner properly in it's wee slot at the bottom, easy to get that wrong.

[magnum56]

If the valve adjustment were off, the compression test should have shown it.
Marc, the pulse generator coils are polarity sensitive; one of the blue and yellow wires have a white band at the plug end. If the blue wire with the band is reversed with the blue wire without the band, you will still have spark, but at the wrong time. 

Sorry .. that is not true.  Valve "timing" does not alter the cylinder compression value.

 

The OP states that cylinders 2 and 3 are firing, so it's obviously not not a cam timing problem, as that would affect all four cylinders. If tappets were too tight, the valves would never close, which would show up on the compression test. 

If the valve adjustment were off, the compression test should have shown it.
Marc, the pulse generator coils are polarity sensitive; one of the blue and yellow wires have a white band at the plug end. If the blue wire with the band is reversed with the blue wire without the band, you will still have spark, but at the wrong time. 

Sorry .. that is not true.  Valve "timing" does not alter the cylinder compression value.

 

The OP states that cylinders 2 and 3 are firing, so it's obviously not not a cam timing problem, as that would affect all four cylinders. If tappets were too tight, the valves would never close, which would show up on the compression test. 

I apologize ... I misunderstood your comment.