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Discussion Starter #1
Ok I put seafoam in my gas and the back cylinder fires no problem but if I dont have seafoam in the gas the back cylinder will not fire at low rpms just at high rpms. I have done the mod where the ignition coil is wired directly to the battery and it did make the spark stronger because I was only seeing 11.5 volts at the coil now i am seeing 12.5. I just want to make sure it is the coil before I replace it or if the carbs need to be rebuilt and synced. I have two of these bikes and both my 2002 and my 1993 are both acting the same way.
 

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Since the problem goes away when you're running Sea Foam in the gas, I'd think it would be carb related. Have you tried running 1/2 a can per tank for a tank or two? Might get rid of whatever is gunking things up.
 

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Welcome to the Vulcan madness. Here is a link to a free service manual if you need it.
http://www.tocmanufacturing.com/Files for Download/VN750 Manual and Parts.pdf

Have you done an impedance/resistance test on both circuits in the ignition coil?
Check both coils on both bikes to get a good base line for what is normal.
Swap one of the front coils to the rear of the other bike to see if that works, before buying new coils.

The primary coils specs are 1.8-2.2 ohms. Specs are not as important as the fact there is continuity between the two terminals.

The secondary resistance between the two spark plug leads should be 19K-29K ohms.

The coil needs to be warmed to a minimum of 68*F for accurate readings.

Have you checked the condition and gap on all the plugs, or replaced them with new ones yet?
 

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Discussion Starter #4
Ok I moved the front coil to the back and the back coil to the front and it is doing a little bit better. I have replaced and regapped the plugs all the way around. I did not switch them from one bike to the other. I think it was just that the rear coil is getting weak seeing as it is in the worst spot of the two now with the two reversed it seems to be running ok. Are the rear coils a big problem on these bikes? On my 93 it was flooding the plugs but not so much on my 02 maybe because my 02s coils havent gotten that weak yet. This really didnt start happening till I got some bad gas but when that happened I drained the tanks and the fuel bowls on both bikes and I replaced the plugs and it ran fine for a few days then started acting up. So I am wondering if it was the coils all along and not bad gas.
 

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Ok I put seafoam in my gas and the back cylinder fires no problem but if I dont have seafoam in the gas the back cylinder will not fire at low rpms just at high rpms. I have done the mod where the ignition coil is wired directly to the battery and it did make the spark stronger because I was only seeing 11.5 volts at the coil now i am seeing 12.5. I just want to make sure it is the coil before I replace it or if the carbs need to be rebuilt and synced. I have two of these bikes and both my 2002 and my 1993 are both acting the same way.
you seem to have answered your own question here .it seems to be fuel related since just adding Seafoam causes the problem to go away.Although I would ,if you haven't already, install Iridium plugs.I had the same problem on my 750 and the Iridium Plugs cured it.I don't know what it is, but mine had a much bluer ,fatter spark with them than regular NGK plugs,may be the thin center electrode and maybe they will fire hotter with marginal voltage.Also look at regapping your ignitors to.018,there is a thread on here about how to do it.
 

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you seem to have answered your own question here .it seems to be fuel related since just adding Seafoam causes the problem to go away.Although I would ,if you haven't already, install Iridium plugs.I had the same problem on my 750 and the Iridium Plugs cured it.I don't know what it is, but mine had a much bluer ,fatter spark with them than regular NGK plugs,may be the thin center electrode and maybe they will fire hotter with marginal voltage.Also look at regapping your ignitors to.018,there is a thread on here about how to do it.
I think denny means regapping the ignition pick-up coils, located down behind the alternator cover.

Link to procedure:
http://www.scribd.com/mobile/documents/34298778
 

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Discussion Starter #8
Ok on the 93 the back cylinder is flooding the plugs. On the 02 the back cylinder isn't getting enough gas or isn't getting any at all. I am wondering if the carbs are out of tune but what I don't understand is why the front carb on both bikes is acting right while the back carb is messing up. Is it a normal problem on these bikes for the carbs to mess up?
 

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Discussion Starter #9
Oh and I have already reduced the gap on the pickups as well as direct wired the coils so I know it is nothing to do with the spark.
 

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Ok on the 93 the back cylinder is flooding the plugs. On the 02 the back cylinder isn't getting enough gas or isn't getting any at all. I am wondering if the carbs are out of tune but what I don't understand is why the front carb on both bikes is acting right while the back carb is messing up. Is it a normal problem on these bikes for the carbs to mess up?
The flooding carb sounds like trash holding the float needle open, or the float level adjustment too high. Sounds like it`s time for a carb cleaning and refurbishing. I suggest doing one bike at a time.
 
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