1985 honda shadow vt500 poor performance and diagnosis

First of all, let me say that you’re doing a great service to a lot of riders.  It is much appreciated.

I bought a 1985 shadow vt500 last summer, and did not receive to much information on the history of the bike.  I got it for a bargain, but it has some performance issues.  The first issue it had was a seemingly spent battery(it was completely dead), which I promptly replaced, as well as new plugs.  It was starting but just seemed to be running poorly overall.  I would need to choke up to start even in perfect conditions, and the bike would hesitate often.  A few weeks in I noticed a hesitation on the throttle, it would often seem to “skip” in the middle of acceleration.  I didn’t do anything about it last summer as I didn’t have a space to work on it, so I just stored it.

I came back two weeks later to put some fuel stabilizer in for the winter, and the bike would not start.  I played around with the electrical, the battery was on a trickle the entire time, but didn’t start with a jump either or a bypass of the solenoid.  I pulled the wire leading to the plug on one cylinder and ground it to the frame to make sure I was getting spark, which I was, but with the first spark to the frame, the bike started!(hesitantly).  I’m assuming I fouled my sparks again, but that seems very odd behavior.

I’m assuming I need a carb clean.  And an additional thing, the specs on my tank say it should hold 3 gallons – I have run the bike until there is no more fuel, and topping off the tank would only fill it to 2 gallons. Is it possible that there is really that much gunk in my tank? Or am I missing something.

Besides a carb/fuel system issue, is there anything else that could be causing this behavior? And for normal maintenance, what else should I look at replacing on the bike?

Thanks, sorry for the lengthy post.


Hi Dave – Thanks for signing up, hopefully I can give you a hand.

The hesitation and poor throttle response you were noticing initially sounds like it is likely carb related. Dirty carbs can definitely cause this symptom. A partially blocked jet, or clogged up emulsion tube or needle can create all kinds of wacky running behavior.

You could also have an air leak around the intake – how do the rubber boots between the head and carbs look? On any older bike I usually start with the carbs because in almost every case of working on an older bike, they have always needed a cleaning. It’s very rare that I work on an older bike running poorly and the carbs aren’t at least partially to blame. Yank them out and give them a proper cleaning.

While you’re doing that carefully inspect the intake manifold boots (rubber boots between the carbs and head) for any cracks or other damage.

A proper valve adjustment certainly won’t hurt you at all either.

Start off by giving the carbs a proper internal inspection and go from there.

Also – make sure your air filter isn’t real dirty or full of mouse nests!


Evan Fell

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