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Number 2 not firing, not sure where to look next

  • Thread starter Thread starter simonp
  • Start date Start date
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simonp

Guest
1982 GS850GL, 10458 miles.

Compression dead cold first thing this morning:
140-125-135-140
After warmup:
145-140-135-140

PO had the carbs rebuilt, I have gone through cleaning them twice myself since taking over. They were pretty clean when I got into them and the CV diaphragms on top looked like new rubber.

From reading on this forum I knew to change the manifold boot o-rings. I replaced the screws with the hex caps at the same time. Boots were somewhat pliable. Spraying brake cleaner on them while running no longer changes the idle.

Airbox has been cleaned out and re-sealed with weatherstripping. Light oil on the K&N.

After the O-Ring replacement only number 4 was firing. I went through all the carbs again and now all but number 2 are working.

The petcock seems OK, except the primer setting doesn't seem to work. Does it matter which way the white plastic part inside is turned when you reassemble it? If I apply vacuum to the vacuum line gas will gush right out, and it has no problem keeping the carbs filled as it runs. No gas seems to be coming through the vacuum line. (If it was I should have tasted it:)

I have spark on number 2. At least if I connect an old plug to it and ground it I can see the plug sparking.

She starts up right away and will idle.

I have a metric feeler set + sync vacuum gauges + shim tool coming from z1 this week. I plan to check valves next weekend, but since compression is good could the problem on number 2 be valve related?

At this point I don't think cyl 2 is firing, the exhaust pipe is not hot like the others. If I disconnect the spark plug from #2 nothing changes.

I took the carbs off again and disassembled #2. I did notice that the float needle spring seemed weak on #2. (it compressed very slightly when turned upside down) I tried to compensate a bit by increasing the float height.

#2 plug end is black, like it's running rich.

Can any recommend any other avenues to investigate? I not sure where to go from here. What can I do to help track down why it's not firing?

I'm suspicious of the float needle right now. Can anyone recommend a place to get a new OEM one? One symptom is that after cleaning, when I first allow gas into the bowls, I'll get some gas running out of the overflow valve on the left side. This always stops though, and I used to think it was just a needle taking a moment to properly seat. Now I wonder.................

Thanks for all the information on this fantastic forum.

--Chris
 
Have you tried opening the drain screw on #2 to see if you get a reasonable amount of fuel out of the bowl?
 
I did try that, but the shot glass I tried to catch it in wasn't big enough and it overflowed. Maybe I should try again and see if I can get an accurate measurement, and compare it to another working carb?
 
First I would bet the petcock is BAD. The vacuum for the petcock is drawn from the #2 carb so if the petcock daiphram leaks it will flood the #2 cylinder with gas. Sounds like you have the petcock with the screwdriver slot ? if you do replace it.... They are not rebuildable
Don't try to compensate for a bad needle by changing the float level
 
I think all your problems will be solved with the valve shims and carb sync tool. Most likely the #2 cylinder isn't firing because it the carb is not opening the throttle enough on idle for that cylinder. The sync will take care of this.
 
simonp said:
I did try that, but the shot glass I tried to catch it in wasn't big enough and it overflowed. Maybe I should try again and see if I can get an accurate measurement, and compare it to another working carb?
Click to expand...

With the engine running, spray a shot of raw fuel into the #2 carb. If the rpm's rise quickly you still have a dirty/clogged #2 carb. If you hear no change in rpm's then you've ruled out fuel delivery.
 
I swapped the float and needle I was suspicious of with the ones in the #3 carb. The problem stayed with #2.

I still had the run of gasoline out the 1-2 overflow when I reconnected the gas line. It stopped like usual. Is this normal? Is it OK for this to happen as long as it stops quickly?

Next I tried putting gas into #2 while it was running. I couldn't figure out how to get gas in there with the airbox on, so I disconnected the vacuum line to the tank and attempted to "lift" some gas in a straw, and dump it into the hole. It seemed to affect the idle some, but not a lot. When I sprayed brake cleaner into the hole I could get a momentary rise in RPM. One interesting note is that disconnecting the vacuum line didn't cause any change in the idle.

I re-verified that no gas is coming out of the vacuum line.

I keep thinking it's running way to rich from the black crud on the spark plug. Am I off base in thinking that?

--Chris
 
Try switching spark plug caps and making sure you have some good clean wires to screw them back into.
 
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