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Old 09-12-2012, 05:49 AM   #1
sailah OP
Lampin' it
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Joined: Aug 2005
Location: Turning expensive metal into scrap
Oddometer: 5,815
Noob 4 cyl carb tuning help

So I have built 2 frankenbikes at this point, first one is a 2004 Yamaha FZ1. Running stock motor with Ivans Performance pod filters and the jetting kit for these pods. It has the stock headers with EXUP valve intact and then a Sailah Customz midpipe to a Arrow exhaust can.

The second bike is a 1997 CBR. I kept the stock airbox, stock filter. I built the headers out of slightly smaller OD tubing, same length pretty much, into a midpipe and then out a carbon Arrow exhaust.

The FZ1 I have been riding for 2 years now. I always felt it had a flat spot off idle but honestly it had so much power that I never really bothered to change anything. A buddy who also had an FZ1 mentioned he thought the bike was down on power so it got me thinking. I set up Ivans kit exactly how he described it, settings and all.

The CBR went on her maiden voyage last night and I couldn't believe how much snappier it was than the FZ1. Yes it is a lot lighter but the motor was much more peppy and just seemed much more willing to pull harder at all throttle settings. More eager if you will. Maybe that's a function of the motor vs jetting but regardless I am interested to learn more about carb tuning.

I can take carbs apart, I can clean them, I know where the various components are located and what their names are. But I still have a very fuzzy understanding of how they interact, and also how to interpret their behavior. Like that bog on the FZ1. I know that's not a main jet problem, but how do I know if I need to go up or down or change the mixture, slow speed jet?? See what I mean? Noob here.

Since I have two bikes and can weld, I thought it might be interesting to use a wideband o2 sensor like the innovate LC-1 setup. That way I can use one gauge to tune both bikes.

Maybe I'm just looking for the easy way out but any reason not to go this way? Or do you have any other suggestions? Bear in mind both bikes are not factory and rather involved in removing components, especially the carbs. I have precious shop time and would prefer to spend it smart than just randomly throwing parts at the bikes.

Here's the setup I am considering with a gauge so I can mount it on the bikes

Thoughts and constructive criticism other than to stop build wacky bikes and buy a stocker? Ha, I did that this winter and bought a new Husky 449. Bike still doesn't work and no warranty and that has fuel injection
We're not out here to rough it. We're here to smooth it. Things are rough enough in town.


sailah screwed with this post 09-12-2012 at 05:58 AM
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