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I have a pretty old Varadero. It's a 125cc twin-carb v-twin.

I open the choke to start it, it starts first time, warms up slowly (10-15 mins), then when I push the choke in, the idling doesn't really settle, it fluctuates.

I ride it for about half an hour, and the idling still fluctuates at ~2000rpm by about +/- 200rpm. If I then don't rev it and I leave it idle, after about 20 seconds, the idle will slowly drop and it will cut out. When it's cold, it doesn't seem to cut out and it seems to idle better.

What could be causing this behaviour? Is there anything in the carbs that may need to be replaced? Is it a mixture problem? Do the carbs need to be balanced?

Are there any simple tests I can do to narrow down the possible causes?

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  • What year is your Honda?
    – DucatiKiller
    Commented Sep 22, 2016 at 20:23
  • Have you tried removing, disassembling, and cleaning the carb? Most issues like this are resolved this way.
    – cory
    Commented Sep 22, 2016 at 20:25
  • @DucatiKiller It's a v2 from 2001 or 2002. (No injection)
    – n00dles
    Commented Sep 22, 2016 at 22:58
  • @cory Yeah, that's my next step. I just wanted to get some advice to be sure I need to and also to see if there's anything I need to look out for or replace. They're the only things I haven't had to take apart and fix on the bike in the years I've had it.
    – n00dles
    Commented Sep 23, 2016 at 0:00

2 Answers 2

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Yes, there are some tests

It sounds like you are describing an air leak between your carburetor and cylinder head. This is called unmetered air. When you have air going into the combustion chamber that is not metered through a carburetor or throttle body your air fuel mixture becomes leaner and you get strange behavior such as misfires and rough idling.

Check your rubber intake manifolds or O-rings between the carburetor and the cylinder head for cracking or leaks. Also check to see if you have any vacuum lines that are cracked or have bad connections.

Here are some helpful links to some tests you can perform to validate this theory.

The second link has other links that could be helpful for you in identifying the root cause of your problem. What you are describing sounds like a classic air leak problem.

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  • Thanks for the info. This will help me a lot. I'm having work done on my property atm so frustratingly, I can't get the bike out to work on it. But I will definately check this out as soon as I can. Thanks for your time.
    – n00dles
    Commented Oct 6, 2016 at 13:54
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It sounds like you have an air leak between your carburetor(s) and the head. This will cause lean running and the engine to be slow to return to idle.

You can spray carburetor cleaner, WD40, etc. to find the air leak. When you spray on the leak the idle will change, it will probably go up, but it will change.

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  • What did you find out?
    – Eric
    Commented Oct 10, 2016 at 20:07

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