Spark, But No Fire in Rear Cylinder - Kawasaki Vulcan Forum : Vulcan Forums
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post #1 of 12 (permalink) Old 06-01-2018, 02:50 AM Thread Starter
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Spark, But No Fire in Rear Cylinder

My bike has sat for a long time. It was mostly because of a bad (clogged) carburetor and the cheap new bowl gaskets they sell that don't work. I cleaned it, put it back together and it would leak around the bowl when running. Took the original bowl gasket out, order a new one that looked too thin, put it together and it leaks. Repeat. Finally came up with a solution that works and no leaks so far.

01 Vulcan 800 Classic
Under 5k miles
Carbs were jetted by Kawasaki dealer, Cobra exhaust, EPA equipment still installed.

I meant to drain all the old gas but I accidentally turned the petcock to prime for a second after putting it back together. I drained about a half gallon to look for water or debris in it, I did not see anything. I did add Sta-Bil in it before. I have not added any fresh gas to it yet.

Anyway, tried to fire it up and with the choke open on a cold start, the front cylinder will fire but the rear will not. Figured I would change the spark plugs. Got new ones, gapped the plug, installed them, same problem. Pulled the wire rear boot off the plug and the wire came out of the boot. Stuck it back in, tried the old front plug in the boot and held it to the engine and it sparked. Made sure the wire was in the boot pretty good and put it back in the engine. Tried to start it again and same problem. I even pulled the new plug out and tried the same thing and it sparks. The old plugs aren't really that old because I have changed them before. It will ignite the one cylinder and try to keep running but then dies. After a few tries, one exhaust gets warm, the other does not.

So before I get tired of taking the tank off and letting the bike sit again, I thought I should see if anyone has any ideas. I have the gauge to do a compression test if you think I should. It has less than 5k miles on it and no hard riding so I would think it would be fine. Last oil change was not that long ago as far as mileage goes, but I can do that if you think gas got in the cylinders and made it into the oil. The petcock and float valve have not been a problem that I can recall.

So any ideas or suggestions?

Last edited by Toxarch; 06-01-2018 at 02:52 AM.
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post #2 of 12 (permalink) Old 06-01-2018, 07:15 AM
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So if I reading right you get a spark when you have a plug in the rear wire held to the block, yet you believe in the cylinder it doesnt spark because ts running bad and the rear pipe is not warm?


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post #3 of 12 (permalink) Old 06-01-2018, 08:01 AM
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I don't know owt about the 800 But is the rear plug getting wet ?? IF it were mine I would stick my hand over the carb & crank it over just to make sure that the rear jug was getting fuel

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post #4 of 12 (permalink) Old 06-01-2018, 12:08 PM Thread Starter
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Originally Posted by vulcandoc View Post
So if I reading right you get a spark when you have a plug in the rear wire held to the block, yet you believe in the cylinder it doesnt spark because ts running bad and the rear pipe is not warm?
I think it is sparking in the block. I am trying to figure out why one cylinder is igniting the fuel and the other is not. When cranking, it tries to start up. After a few tries, I can feel both pipes next to the block, one will be warm, the other will be cold.
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post #5 of 12 (permalink) Old 06-01-2018, 12:12 PM Thread Starter
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Originally Posted by magicgrotto View Post
I don't know owt about the 800 But is the rear plug getting wet ?? IF it were mine I would stick my hand over the carb & crank it over [IMG class=inlineimg]/forums/images/smilies/smile.gif[/IMG] just to make sure that the rear jug was getting fuel [IMG class=inlineimg]/forums/images/smilies/smile.gif[/IMG]

Steve
The 800 has a single carb for both cylinders. So if one is getting fuel, then both SHOULD be getting fuel. The valves are pumping air through. I wonder if maybe the Y-pipe between the carb and the cylinders came loose on one side.
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post #6 of 12 (permalink) Old 06-01-2018, 04:59 PM Thread Starter
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Scratch that Y-pipe idea since it is metal and bolted to the engine.
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post #7 of 12 (permalink) Old 06-01-2018, 05:48 PM Thread Starter
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I started draining the rest of the old fuel just to be sure it has fresh fuel in it. I started wondering if the petcock was working right. If it is not working right, then it would not provide enough fuel to the engine, right? I turned it over and only a few drops came out. I think it should be a lot more than a few drops. Bad petcock? Bad vacuum? Is there an easy way to test either of them?

So I turned it to prime and tried to start it, no difference. It would try to start and die. Choke wide open (I changed the choke wire after the plastic nut broke), turned up the idle and started it up. It ran, but it was not like normal. If I gave any throttle at all it dies. Let it run for a couple of minutes and the rear exhaust pipe near the engine would just get warm, not hot. I killed it and got the laser thermometer. The front cylinder near the exhaust showed 250 degrees F. The rear cylinder near the exhaust showed 105 degrees F. I

Once it cools back down, I guess I will try swapping the ignition coils and see if the rear will fire and the front will not. That could tell me if the rear coil is bad.
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post #8 of 12 (permalink) Old 06-02-2018, 12:21 AM
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Fuel/air, spark, and compression. Those are the things you need to get the cylinder to fire. If the front is firing, but the rear isn't then you can rule out fuel/carb issues, as it is a single carb for both cylinders. The ignition coil is timed for each cylinder, so swapping the spark plug wires won't do anything worthwhile. If you can see a definite spark when you crank the engine then it's probably safe to assume it's a compression issue. I would suggest trying a compression test and see what that reveals.
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post #9 of 12 (permalink) Old 06-02-2018, 01:26 AM Thread Starter
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I'm not just swapping the plug wires. I was planning to swap the coils. Then they should still fire properly.
I'll go ahead and check compression as well. Anyone know what compression should be?
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post #10 of 12 (permalink) Old 06-04-2018, 09:57 AM
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The manual I just looked up states 124-191 PSI is the usable range.

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