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Join Date: Nov 2007
Location: Chandler, Arizona
The Vulcan 750 has always been hard to start, even when new. My '02 has done what you are describing (other than a whirring noise) once in a while since new. I have used huge booster batteries with tons of amps, and the starter still turned over slowly (at least a lot more slowly than I am used to on any other bike other than a Harley) I believe the ignition system is weak, and that cranking that slow does not produce a good spark.
Also, these bikes do not like to sit very long. I always keep a battery tender on mine, and still have trouble starting it after it has sat for a few days. Sometimes it will backfire, then start up on one cylinder, then the other cylinder kicks in a few seconds later. I am pretty sure this is a carb issue. I recently rebuilt my carbs, and the problem was still there. These are weird carbs, they are actually a one piece unit bolted together. The jets are way down on the bottom, not in the float chamber where they usually are.
If it did run fine, then hopefully your carbs don't need cleaning. It's almost as easy to pull the engine in this bike than remove the carbs.
I would drain the carbs, then fill them up with Seafoam through the fuel lines. Let soak a couple of days. Check the battery, if it is good, make sure it is fully charged. And check the plugs. Bad plugs combined with a weak ignition system can cause your problem.
I tried the iridium plugs, they didn't do anything for me, other than cost a lot of money. Others claim they help. Worth a shot if the problem still exists after trying everything else.
I am a motorcyclist, NOT a biker.
1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike