Setting up a carbed bike on a dyno - what do they do?

[D O G]

Following on from this thread, I was wondering what the mechanics actually do when setting up a carb equipped bike on a dyno.

I can understand FI setup, i.e. the map can be changed via computer, but for a carbed bike I don't really know, so I was hoping someone can shed some light on it!

I take it that it is changing jets? Messing about with needles? Not that I know what a needle does!

But having stripped my carbs in the past, I know (I think!) that you have to strip them to change these bits. Seems like a bloody long process. Does it follow the following procedure:

- Dyno bike;
- Take off carbs, disassemble to change jets/needle settings;
- Refit carbs;
- Dyno again, see if better;
- Repeat above steps again.

Is that right, or can you change settings without any dissassembly?

Given that I had my bike setup for about 120squid, it does seem a lot of work involved?

Thanks!

[TUG]

Yep thats right mate, thats pretty much how they do it.
____________________
Haz ER-5, innit!

[NSR Mick]

[Whosthedaddy]

From the dyno graph and fuelling map they can sort of predict what size (if standard) needle would be best suited to the changes in the bikes setup. If the needle has been changed or altered in the past with a kit then it may be a little more investigative work when the carbs are off.

When the 7 was on the dyno it ran a little rich at the bottom and a little lean at the top (or the other way around?) so no real need to play with needle and jet sizes. If the bike was running like a dog then it would have been a good idea to splash some cash to get it set up right.

Price wise, I think its between £2-300 if I remember correctly (and includes parts / kits).

The smile on my face when the bike was on the dyno and spitting flames out of the zorst on the over run is well worth the £30-40 for a plain bog standard test run.

What bhp you reckon on the FZR?
____________________
Current : MSX 125 Past : CBR 900RR Monkeybike : c50 LAC : ZXR750 H2 : FZR600 : ZX7R P3 : YW100 : TRX850: Trophy 900 T309 : GSXR 600 L0: Monkeybike : XJ6S Whosthedaddy

[D O G]

[Kickstart]

Hi

For a start, with a CV carb the fueling is controlled by the idle mixture (pretty irrelevant once moving), main jet (the ultimate limit) and through most throttle positions the needles position relative to the fuel nozzle. The needle is attached to the slide and the slide moves depending on the air flow through the carb.

A half decent operator will know which bits to adjust to change the fueling at any point.

For examples if you use a strong spring above the slide then it will not move as much for the same airflow through the carb. If you drill a larger hole in the slide then it will react more quickly to changes in air pressure through the carb, hence the slide might open more quickly. If you lift the needle up then you richen the mixture in the range controlled by the needle. If you use a different profile needle then you can richen the mixture up in one area more than another.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing