Left Cylinder not firing properly

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

Hey Guys I got an 81 xs 650 sh and my left cylinder is not firing so far I have check the gaps at exhaust and intake valves, Checked to be sure I was getting spark, check gap on plug. This later model has only 1 coil and both sides are getting spark, also I don't think it has points I think it is electronic ignition. I am going to try a new plug next.
Thanks for your help

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

If you have vaccuum carbs I'd check that first if not make sure your getting gas to that side

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

I pulled the plug on that side and it seems like I'm getting gas because that plug is wet, But exhaust is cold. I like your bobber thats tight

xsjohn

May have to check compression........and check that side's valve settings......book says 2 thousands or so on intake but that is a bit close for me a loose 3 is better.....6 on the exhaust.........

xsjohn

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

I checked the valve clearances and they seem to be okay, put a new spark plug in and it's getting gas. I don't know what exactly is going on, seem air spark and fuel. There also seems to be a kind of ping on that side I starting to suspect the rings, I'll do a compression check and see.
Does anyone think that this could be the problem or could it be a timing issue?
Thanks

xsjohn

Not timing if the other side is pecking along........check the compression.....throttle wide open.........too much gas and it won't fire either.......but it seems the carb would be overflowing if that was the problem........bad valve wil drop compression too.....wet and dry test.....

xsjohn

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Don't forget to also check the easy stuff - I had the same problem - and it turned out to be a bad spark plug - (Brand New - Bad out of the Box!).

Also check plug wires and ends. Resistance in Plug Caps.

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

hey guys just did a compression test and the cylinder thats not firing is 120 psi and the one that is firing is at 90 psi before oil after oil it went up to about 120 psi. Does this make sense that the cylinder that is firing is lower in psi then the one that isn't. New Rings or new valves that is the question?

Also when I did the ole screw driver in the coil caps to see if there was spark it seemed to be real strong. Nice and bright. And also when I switched the plug wires nothing changed. Maybe I am getting to much gas, I'll check the floats tomorrow, maybe thats it. Anyways it would be sweet if it was always the easy fix

xsjohn

Maybe the ole scrounge out the carb thing is in your future.......I hate to recommend cleaning them cause it such a pain......especially when it doesn't help.....worth a try though......

have you tried taking the plugs out and turning it over a while with the E start ..should ground at least one plug to metal so it doesn't hurt the electronoc ignition .....then shoot a bit of starting fluid in the left and put the plugs baack in........if it has spark it should do something......if it does something then scrounge the carbs out......

xsjohn

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

will try that tomorrow thanks John Hopefully I won't have to do the rings but I think I might go with xs mikes big bore, if I have to anyway. It seems that is the way to go as it doesn't cost much more than stock parts.

Tim

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Thanks for the complement.

I'm having somewhat the same problem and it's a jetting problem with my carbs my left is getting too wet and fouling out plugs.

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

Yeah I finally got the carb all cleaned up it looked good. I put it back together and put them on the bike only to have the same thing going on the left cylinder is not firing at all. Runs just fine on the one but nothing out of the second, What is my next course of action? Don't know weather to take the top end down and inspect the rings or if I should try new needles in the carbs. It could be the same problem as the yamabob but I'm not sure. The plug is definitely getting wet and it's got spark, valves seem to be correct. What else could it be?
Thanks in advance.
Peace

royfisk

dreadtim are you useing new plugs? How do you know it has spark under compression? What is the resistance of the resistor caps? if there not both 5000 ohms replace them. If the left is bad and the right is good, your probably not fireing under compression. yes it will fire with the plug out on the head but when compression comes into the picture she will not fire. If its got fuel like you say. then you have a spark issue. Did you test your coils? If she has fuel and spark it has to fire even if it has low compression, may not run good but it will fire. Other thing when you run it does both pipes get hot? If they do then its fireing and you might still have carb issues with the left carb flooding and fouling the plug. use new plugs after fuel flooding or else you may get the thing fixed but have a bad plug.

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

The left pipe doesn't get hot at all. I will check the ohms in a couple of minutes. How do I check for spark under compression? If the plug fires when it out against the head why would it not fire under compression.
Thanks

royfisk

bad coil, bad resistor cap, or even a bad wire. what year is it? does it have points? If so change your condensor. If its a electronic pull the plugwires and switch them from one side to the other does it fire now. if its points pull your tank, switch the two points wires on your coils and the plug wires, restart the bike does it fire now? If so the left cylinder has either a bad coil, condensor, wire, resistor cap. Obviously i assume the points are good.

xsjohn

Did you ever try drying that cylinder and using a bit of starting fluid to see if would come alive.........

xsjohn

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

How do I dry the cylinder, just wait a bit? I'm going to try the starter fluid now and see if it will come back. I all ready cleaned up the carbs. They really didn't look that bad, I'm on my way to check the ohms and make sure that the coil is good.
Thanks

royfisk

I dont think its a carb issue here. I beleive its one of the above mentioned electrical items. The plug is wet. Use new plugs.

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

I checked the resistance at the primary side and got 2.6 ohms and I can't get a reading at the secondary side of the coil. Red and Black tester wires into the plug wires correct?

xsjohn

Manual says

2.3 ohms primary side
13K ohms on secondary side

looks like bad coil if it reads open......check meter settings....?
I have one in the back room that reads open.....spose it's junk....

xsjohn

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

Meter reads nothing on 20k ohms on secondary test, it wants to stay at, junk? I'll try the starter fluid anyway and see if it makes a difference.
Thanks

royfisk

is that the caps or the coil? the caps are important by themselves.

dreadtim · Full Member Joined: Mar 17, 2008 Posts: 15

That was at the plug caps, should I puncture the wires with my tester to get the reading. Should I take the caps off the wires? I also seem to be having a sort of slap or clink coming from the top of the motor. I don't know what it is.
Also I squirted some starter fluid into the air filter and it was like reving the engine, but the left cylinder still wouldn't fire.
Thanks

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

If it's a newer bike - and you only have one coil - then it's either a spark or no spark situation. Meaning - if you get spark on one side the coil is good - because it is really sending out a signal to both sides. And as weird as this sounds to check the Secondary's on these coils measure between the two spark plug leads (because they both fire at the same time) the primary is from Hot to Ground - the seoncdary is from lead to lead!

Now what that leaves is
1) a bad plug wire -
2) a bad cap (more that 5k resistance)
3) a bad spark plug.

Try swapping the wires right to left and left to right (might have to lift the tank to free up some wire ties) if the no spark moves -
you probably have a bad cap or wire -

If it doesn't you have a bad plug (I had one fail right out of the box before).

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