Problem with Dragstar 650

Balarama108 · L Plate Warrior Joined: 07 Apr 2016 Karma :

Hi there, 3 month ago I bought a 2002 Dragstar 650 Custom with only 12.5k miles on the clock. Sofar she has been running great but yesterday something strange happend.
I was on the motorway and she was running fine but when I got her up to 60mph I noticed a strange "thumping". It's hard to describe... It felt like something isn't running smooth, somewhat like a tumble dryer with an uneven load. I didn't hear anything with the wind noise but could feel that "thumping/rattling" through the footpegs.
When I let off the gas it stopped. Putting it back on and the "thumping" seemd less. The same thing happend today only I had to let off the gas two or three times.
Does somebody have an idea what could cause this?
Both engine and crank oil levels are fine and it only happens when I hit 60mph

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

Sounds like it`s running on one cyl at this speed, could be tight valve clearances on one cyl or a carb running dry.

Balarama108 · L Plate Warrior Joined: 07 Apr 2016 Karma :

Thanks man!
I guess I'll have to bring her back to the shop not being overly mechanically gifted myself but it helps if I can give them some idea where to look instead of just a vague "thumping" something....

doggone · World Chat Champion Joined: 20 May 2004 Karma :

There will probably be some kind of balancer mechanism driven by chain (I guess) - could need attention.
Make sure engine mounting bolts all present and correct.

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Service it before you go looking for a problem.

There are many things that can cause a thumping noise - from one cylinder not working due to lack or fuel/air/spark, through valves being massively out of adjustment and on to more terminal things. It could also be a frame/wheels problem rather than an engine problem.

The cheapest possible problem is duff spark plug or HT lead, or even just a loose spark plug. On many V-twins the front spark plug and HT lead get a hard time because they get wetter, both from being at the front of the engine and from crap thrown up that way from the wheel. SV650s were notorious for it.

Give it a proper service - oil, filters, plugs. Drain the carbs into a cup and look for water in the fuel while you're at it. Don't get into any diagnosis work until the service is done, you'll just be pissing money up the wall.

talkToTheHat · World Chat Champion Joined: 21 Feb 2012 Karma :

See above. Do service before clutching at straws.
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