Not Firing On All Cylinders - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 11-20-2011, 01:05 AM   #1 (permalink)
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Arrow Not Firing On All Cylinders

Shooting Gas Out Tailpipe Exhaust (Not Float Issue?)

Fuel Enrichment (Choke) Cables

Clear Tube Float Check

I need to start a new thread instead of continuing the three above. They were not the problem.

I figured out what my problem is on my 2001 Honda Shadow Spirit VT750DC. The rear cylinder is not always firing.

I had thought I was running too rich. No wonder I could never get the two fuel and air mixture/pilot screws set just right and was shooting a bit of gas out of the tailpipe.

I took the carbs out today and I literally inspected everything on it. There is nothing wrong with them. They are perfectly fine.

I used the clear tube trick in the post linked above. The floats on both carbs come out to the same height which is dead even where the top most part of the float bowl contacts the bottom of the carbs at the screw.

After putting hte motorcycle back together, I took it for a ride tonight as it was good enough to ride in. The bike was really under-powered. I was at full throttle barely going 60 MPH. So I pulled over and checked the rear spark plugs (which I already knew were carboning up) and cleaned them once again. Then I took off and ran the piss out the motorcycle. It was doing fine on the highway but once in town the rear cylinder kept misfiring again and the engine sputtered at idle.

So now I have to figure out why. I will try the obvious fix of replacing the spark plug cable. Hopefully that is all it is. If not, I guess it is the coil?
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Old 11-21-2011, 10:17 AM   #2 (permalink)
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Are you sure you don't have an ignition or electrical issue? How is spark, at ALL 4 plugs? Any difference if you swap coils? What is running voltage? What is compression? Is slide moving freely? No leaks(holes) in diaphram? Test the pulse generators?
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Old 11-21-2011, 10:52 AM   #3 (permalink)
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Quote:
Originally Posted by 93gc40 View Post
Are you sure you don't have an ignition or electrical issue? How is spark, at ALL 4 plugs? Any difference if you swap coils? What is running voltage? What is compression? Is slide moving freely? No leaks(holes) in diaphram? Test the pulse generators?
How do you check to see if all 4 plugs are firing, pull them and see what they look like?
How do you check the pulse generators?
Dan
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Old 11-21-2011, 11:11 AM   #4 (permalink)
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Testing plugs. Run the bike with fuel off until it quits. Pull both plugs on one side, put the wires back on and ground the plug body. In reduced light, crank the bike and you should see the arcs. You'll see sparks for each crank revolution (Hondas are 'wasted spark' bikes) meaning on every piston TDC. If OK, install and do the other side.

Last edited by Nehalem Dave; 11-21-2011 at 11:14 AM.
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Old 11-21-2011, 11:34 AM   #5 (permalink)
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How do you check to see if all 4 plugs are firing, pull them and see what they look like?
How do you check the pulse generators?
Dan
Rest plug firing, if starts, pull plug wires one at a time, if there is no change when you pull the wire. that plug is not firing. Wont start, pull one plug at a time, ground plug against the motor, crank starter. See a spark? No, not firing.
Test electrical items charging and ignition with a VOM. ANY service manual will have the testing proceedures.
Don't over look the safety switches, Run/clutch/nuetral/sidestand!!!!!!

Norvin, don't get target locked on the Carbs. I know people are OCD on them around here. Be sure you eleminate the electrical side as the source of your problem. A little dirt, moisture or corrosion in one of the many connections, can wreak havoc. Once rebuilt a carb 4x, because of a corroded coil wire.
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Old 11-23-2011, 05:20 PM   #6 (permalink)
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I am 95% certain it is not a carb problem. When the rear cylinder finally started working on the highway, the bike ran GREAT! But in town and just idling, it is not firing on the rear. I am going to test the spark plugs later today as tomorrow and Friday are suppose to be fairly warm days in my part of Illinois and I want to get some riding in.
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Old 11-23-2011, 05:36 PM   #7 (permalink)
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Test your compression if you have not already. I drove myself crazy trying to figure out what the hell was wrong with the carbs on my vt500c and turned out to be low compression in both cylinders by a badly scored rear and broken piston in the front.
If compression is low and you tear into the engine, do yourself a favor and take it apart until you find what is broken. When I did this, I first assumed it was the valves and just pulled the heads and lapped the valves, installed new seals, put it all back together, and put the engine back in the frame. No luck, still low compression. Had to take it all back apart again just because I didn't want to take the cylinders off while I was already one step away, if I had, I would have found the problem(s) the first time.
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Old 11-24-2011, 03:32 PM   #8 (permalink)
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Well I walked out to the garage a few moments ago and saw a puddle of gas under the bike. The rear cylinder is now full of gas and I can see the rear insulator is wet.

I am guessing this is a stuck needle, but which one?
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Old 11-24-2011, 04:16 PM   #9 (permalink)
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I am wondering if I should remove the shims from the needles. They make the needles stick out more right?
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Old 11-24-2011, 05:15 PM   #10 (permalink)
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I am wondering if I should remove the shims from the needles. They make the needles stick out more right?
Float needle and vacuum piston needle are different. It is not the shims on the vacuum piston that is stuck. It sounds like the FLOAT needle. It is the pencil shaped thing that is hanging from your float. It is under the float cover on your carb (the same one you remove to change the idle and main jets).
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