Topic: no fire #2

[Ernest]

I've been using a murcury manometer to sync the carbs on a k4 750.  I bought this bike running but very poorly.  Cleaned the carbs, got it running again but the idle was too high.  I've now had the carbs off 3 times double checking the slow jets, float hieght, then bench sync. 

It starts right up but a fuel/oil mix is getting sucked into the manometer vacuum tube on #2.  Murcury still rises on 2 but only to around mark level 4 while 1,3,4 carbs are synced around mark level 15.  Any attempt to raise #2 doesn't show much result and doesn't seem to effect the others much either.  I pulled the plugs, 1,3 and 4 look carbon fouled,  Plug 2 was clean, no carbon or oil.

I put new plugs in again and get the same reading on the manometer with the #2 hose sucking in fuel/oil.

Is this an electrical/coil problem or is the compression/bad cylinder problem?

any help on what to look into would be appreciated.

[Ernest]

I've been through a number of threads about one or two cylinders not firing but most all answers point to a clogged jet, stuck float or the posts about two cylinders not firing point to the coil or points.

This is only the #2 cylinder.  Only one cylinder is not firing and I have been through the carbs a few times.

the only other thing I have gleaned from searches that I haven't tried is setting the plug on the engine case to physically see if there is a spark.  I'm assuming there isn't but if anyone can tell me other tests I should be doing or if there is no spark on one of the plugs what I would need to do to resolve that.  I thought I was doing great figuring out all the inner working of the carbs but with this I'm at a loss.

[Ernest]

thanks but it would just be too odd that out of two new sets of NGK plugs the bad ones would both be in #2.
I'm going to see if they have a spark on the engine case this weekend.  I hope it's just in the plug cable and not the cylinder.  I don't know If I could rebuild the top end. I just want to ride

[TwoTired]

Run the engine and stop it with full choke applied.
Pull the number two spark plug.  If it is not firing, it will look clean, but be covered with raw gas.
This will tell you fuel is getting to the engine and the carburetor is doing it's job.  If dry, the cylinder can't run without fuel.

Another test is to swap the spark plug with one from a cylinder that is known to work.  Does the problem follow the spark plug?
You can also swap the igntion leads between 2&3, as they both fire at the same time. Does the problem follow?

With the lead connected to the plug, lay the plug body onto the engine and start the motor.
 1.  You should get violent bursts of air pulsing out the spark plug hole at each compression stroke. (an indication of compression)
 2.  You should see spark jumping across the electrodes.

If you have fuel, spark, and compression the cylinder should fire, at least some of the time.

The low vacuum could be an indication of poor compression or valve issues with #2 cylinder.

You can also remove the valve adjuster caps to watch the valve movement compared to other cylinders.  Watch for equal excursion.

Were it me, I'd do a compression check.  But, I have the tool on hand.

Good luck!

[Ernest]

I've run the bike now with the plug lying on the case and I can see a spark.  There also seems to be compression as bursts of air are coming out of the plug hole.  It also seems to be spraying my hand lightly with fuel or a mix of fuel and oil if I place it above the plug hole.  The plug was clean, not dry but it did not smell like fuel too strongly.

I have pulled the carbs off again and went through all the jets and rechecked float height.  I checked all the valves clearance but still there is no fire in #2.

It seems like fuel is gettin in there, the jets are clean, theres fuel in the bowl, what else could possibly be wrong with the carb to prevent enough fuel getting to the cylinder?

The valve clearance are all to spec, could the cylinder not fire if the valves are not seating correctly?

I'm out of ideas and now going to start reading up on rebuilding the top end unless anyone can tell me what I may have overlooked.

[DammitDan]

I'm with Doc on this one...  It's the only reason I can think of why you would be getting gunk spit up INTO the vacuum lines on the carb stix.  When was the last time you adjusted the tappets?  If it was recent, then go with a compression or (better) a leakdown test.

[Ernest]

If this is the case, the intake valve not seating, then would that mean there would be no fire in the cylinder at all or just poor performance?  When running the #2 pipe is cold to the touch which I figure means no fire at all.

If I do have to pull the head then would simply lapping the existing valves and seats fix a leak or would I need to buy all new valves and have the head machined to the new valves?

[grapppa]

I wonder if your carb is flooding.  Early on when my CB550 carbs were getting sorted out my #4 was flooding due to a defective seal on the main jets.  The seal was no good because the carb body material eroded away.  I solved it by replacing the carb (body).  If your air cleaner is off try to start it - observe for a lot of gas coming out the body on the air cleaner side.  Just a thought.

[Ernest]

I picked up a compression gauge.  I ran the bike for awhile to warm it up then pulled the plugs.  Chokes open, full throttle and got up to 150 lbs by the sixth kick on #1.  I hooked it up to #2 and got only 30lbs if anything.  I didn't bother with the rest of the cylinders since I was too bumbed out to go any further.

I'm in too far with this bike to just give up so I guess I've got a bunch of reading ahead of me. 

thanks for your replies