When should I optimize the carburetor settings of the motorcycle for better performance, is it immediately after starting or after engine got heated?

Problem which I am facing is:
1. When I change the settings when engine is heated then it will turn off imminently in cold start while switching to first gear.
2. When I change the settings in cold start to avoid turning off on first gear, then the engine idling RPM will increase so much the it will cross 3K and will come down suddenly once I start releasing the clutch. This is affecting the gear shifting as I listen to the noise making by the engine to decide when to make upper shift.

Is this normal for motorcycles? Is there any fix for this?

I was initially using 15W50 engine oil and I changed it to 10W40 because of winter and the engine started to make more noise (higher RPM) because of previously tuned settings. Does engine oil types will affect the RPM?

  • What is meant by "cold weather" ... what temperatures are we talking about? Feb 23, 2018 at 14:16
  • @Pᴀᴜʟsᴛᴇʀ2 Not much cold, nearly 16 to 18 in the morning. Still I feel cold
    – Bharadwaj
    Feb 23, 2018 at 14:17
  • 16-18C really isn't that cold :o) Is 15W50 what TVS calls for in the engine? I cannot really answer the 2nd part of the question, but for the first, your bike should be completely warmed up when you tune it. This will give it the best running characteristics. Feb 23, 2018 at 14:21
  • @Pᴀᴜʟsᴛᴇʀ2 I have elaborated my problem.
    – Bharadwaj
    Feb 23, 2018 at 14:30
  • 1
    The jets are located inside the carburetor. They are little needles that allow a certain amount of fuel through. Get yourself a manual/watch some youtube vids or take it to a mechanic.
    – DamoC
    Feb 26, 2018 at 15:23

1 Answer 1


Carb tuning can be pretty involved. Sounds like from what you are describing that you are "optimizing" by just changing idle or other adjustments that can be done with the bike running, when you may need to actually swap out a jet.

Can't say much without knowing what kind of bike & carb you are dealing with, but if you are seeing bad performance at low or idle rpm, and adjustments that fix that are making it run out of whack at other rpms, you might consider changing the idle jet size.

I will relay an experience with my first bike, a GS 500 that is similar. The problem I had was as follows:

  1. the bike took an overlong time to warm up, even in relatively warm spring and summer mornings.
  2. The bike was a little anemic feeling when pulling off the line or cruising slowly in first gear. This was very subtle, because I didn't realize it was even a problem until I fixed #1. I just thought it didn't have much guts.

I did some searching online and there was a pretty definitive answer, as a lot of people have had the same problem with this bike. The fault was that the idle jet in the carb was too small, and they were sold like that from the factory to comply with emissions standards, even though it affected the performance a little.

As commonly recommended, I replaced the idle jet with another that was one size up from stock, and after that the bike ran near-perfectly. Warm up times changed to just a couple of minutes, and there was also a marked improvement in performance at low speeds/low idle.

  • Where is this jet located?
    – Bharadwaj
    Feb 24, 2018 at 3:09
  • 1
    Jets are inside the carb, so replacing them means you have to pull the carb out, and open it up. After that it's usually a pretty simple matter of just unscrewing the jet and putting in the new one. Taking carbs off is not hard but you may have to disconnect/turn off the gas and potentially drain the carb. I suggest a good repair manual for your bike if you don't have one already. Feb 26, 2018 at 17:22

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