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Discussion Starter #1
I need help before i take it to the dreaded dealer. Its a 2005 4k miles on it missing badly. I changed both coils NGK wires NGK plugs are new. I checked the fuel seems fine. The only problem I'm having is the right rear plug is missing. I'm a car guy and not good with motorcycle terms so don't shot me to hard on it. I'm going to get the battery charged up today and going to check the vacuum lines to make sure there connected properly. Other then that I'm at a lose. I have a friend that use to build custom bikes and he told me to check the vaccum lines on it that might be the problem but he's unable to look at it due to health reason. need help havent riden this bike in 2 years for this problem and due to my own injuries from Iraq and I'm in the riding shape again.
 

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Linkmeister Supreme
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I need help before i take it to the dreaded dealer. Its a 2005 4k miles on it missing badly. I changed both coils NGK wires NGK plugs are new. I checked the fuel seems fine. The only problem I'm having is the right rear plug is missing. I'm a car guy and not good with motorcycle terms so don't shot me to hard on it. I'm going to get the battery charged up today and going to check the vacuum lines to make sure there connected properly. Other then that I'm at a lose. I have a friend that use to build custom bikes and he told me to check the vaccum lines on it that might be the problem but he's unable to look at it due to health reason. need help havent riden this bike in 2 years for this problem and due to my own injuries from Iraq and I'm in the riding shape again.
This is a 2 cylinder engine and has 2 plugs in each cylinder. The second plug is to start another burn from the other side of the cylinder and contribute to more complete combustion and lower emissions.

So even with the right rear plug not firing, the rear cylinder should still be producing a large percentage of its potential power.

If the rear coil is failing, both rear plugs would not fire, - and you would have a definite misfire situation.

You say you have 2 (new?) ignition coils, new ngk plugs, and new ngk plug wires.

After charging your battery and checking the vacuum lines do these checks.

Try pulling all 4 plugs again and check to see if any are wet. What color is the ceramic insulation around the center electrode.
Are all 4 the same color, or are the rear ones lighter colored (indicating a leaner fuel mixture).

After these checks, ground the plugs against the engine.
Crank the starter over and double check which plugs are actually giving you a fat blue spark.
(Have a fire extinuisher handy as you are dealing with gas and sparks.)

What did you do when you "checked the fuel"?
ie. is there fuel in both carb bowl drains?

Post back and let us know what you find. :)
 

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Linkmeister Supreme
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Is this still the same problem you posted about 2 years ago, or did you ever take the bike in to a mechanic for repair?
http://www.vn750.com/forum/showthread.php?t=11178

Edited opening post from above thread.
Hello all. I have a 2005 VN750 with only 3500 miles. Ok I have had this problem for a while now and since my cars are now fixed it's time to get the bike ready to go. I have a misfire only on the 3rd cylinder. When the bike runs I can pull all of the spark plug wires and it drops rpm way down and when I do the 3rd cylinder (EDIT: RIGHT REAR PLUG WIRE) it barely even goes down. I have replaced all sparks plugs, NGK wires new, front and rear coils new, battery new. I had 2 wires touch just before winter and ever since then it's been misfiring. The 2 wires were going from the strator to the voltage regulator. I know the strator and regulator is the charging system but I have no problems with them. I'm leaning towards the pulsing coils or ICD. Please someone help me.
You only have 500 miles more on the bike now than in the previous thread, and the right rear plug still seems to be the problem, so it seems nothing has been done.

In post #23 of this thread you say you already checked the ignition pick-up coils located by the rotor and they are ok. (A bad pick-up coil would account for the rear ignition coil failing to fire both plugs and give the mis-fire you are experiencing.)

niteriders suggestion in post #22.
Disconnect the vaccuum hose that comes off of the intake on the rear carb, now plug the nipple at the intake. Start up the bike see if the miss goes away.
I`m not sure where that vacuum hose goes, or why plugging the carb vacuum port would help?
Can anyone else explain this for me?

Do you still have the old ignition coils that you replaced 2 years ago?
Did you ever do a resistance test on both primary and secondary circuits to confirm they were the problem?

Can you do a compression test too?
Specs call for between 129-199 psi with no more than 10 psi difference between cylinders.

I`m no expert, but it seems we are missing something pretty basic here. :(
 

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Discussion Starter #4
yea unfortunately I started to go through a lot of hell with all my injuries and wasn't able to do any work on the bike so I stored it then moved to a new house 800 miles away and now it's been stored in another building for the last 2 years so it never made it to the shop back then. Now my health issues are a lot better now and and since I'm settled in my new house just needing a garage built is all time for the bike again.
I'll make it back to the building in a few days to check everything you guys posted and check it out and post back. I'm hoping it's something simple. The bike ran great before this. The coils I still have the old ones just in case they were good for spare parts. the left side cylinder seems to be running fine thats kinda why I'm confused. I'm thinking it might be internal also on the right side.

The fuel I checked the lines and drained the bowls but will do it again since it's been sitting.
 

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mine was missing bad and read on here to make sure the vent tube is connected to the backside if the right air box. when i did runs so smooth. hard to believe a vent tube can have such a affect.
 

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If you think the carbs might be gummed up, drain the fuel from both and refill with straight Sea Foam. Leave it in there two days or longer. Just did this on another bike and was amazed at how much crud came out when I drained the Sea Foam.
 
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