Jetting Database

[Tom R]

Has anyone ever put together a database of bikes and how they're jetted. It seems every other week or so there's a question that goes something like: I just put a 4-1 header on my bike and added a blower, do I need to re-jet?
It'd be helpful if you could just point them to the database and hopefully they could find a starting point for their own bikes. Or maybe just a sticky thread for each model of bike where the year/model, miles, mods, jetting, and assessment of how it runs
For instance mine would read -
- '80 GS1100L
- 31,000 mi - Stock carbs, K&N pods, V&H Supersport 4-1 pipe, '83 cams, Factory Pro stage 3 needles fourth slot from top.
- 142.5 Mikuni main, 47.5 pilot jets, idle screws 4 turns out
- Starts and idles nicely, pulls smooth to redline, has flat-ish spot at cruise between 3100 - 3900, plugs look good.

Of course every bike is different, so its would just be a guide, but it could help people get close to the right setup.

 

[Steve]

There have been several suggestions over the years, but like you said, there are SO many variables, it would be hard to say "do this and you will be good".

One of the best approximations that I have seen is to add 2-4 sizes for a pipe and 3-5 sizes for pods (assuming they are good ones).
Deviations like straight pipes or cheap pods will, of course, have to be taken into account.

Then again, there are differences in the carbs themselves. The earlier VM carbs had adjustable needles, the later BS carbs did not, at least in the USA. For the BS carbs, the "old standard" is to go with a DynoJet kit that not only gives the larger jets, but a re-shaped needle that is also adjustable.

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