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Sparkz
7th April 2006, 06:02
I need help from somebody who has been through this pain before.

I am fitting a full Yoshi zorst and OEM replacement K&N ait filter to my '87 FZR1000. My original plan was to fit a Dynojet jet kit to sort out tuning, but I have heard so many bad stories about them that I will probably no. I fitted the same parts to my '87 FZR750 (free-flowing zorst, K&N and Dynojet kit) and I could never get it to run properly under 4k.

I have the carbs off as one had a leaky float bowl gasket, so now would be a good time to change main jets.

Anybody know how much, if at all, to increase main jet sizes by? I can tune the low end with the needles and mixture screw, but I need a starting point for main jet size.

SARGE
7th April 2006, 06:45
got this article off an FJ1200 site.. should be the same carbs....

Jetting Recommendations


Here is a simple set of jetting guidelines that have worked for me. For those considering jet changes, this might help select a starting point.

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

2 jet sizes for both single K&N and drilled airbox

2 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size)

Under a mismatch condition, like individual filters and stock exhaust or 4 into 1 header with stock filter and air box, subtract an additional 1 jet size.

Check plug color often, sync carbs after each jet change, make sure the floats are set correctly, and seriously consider purchasing a Color Tune.

Make sure your carbs are in perfect working order before making jet changes.

Example from my '79 XS1100 F:
Stock main jets: 137.5

Stock pilot jets: 42.5

2 sizes for 4:1 exhaust (Jardine)

1 size for single K&N

1 size for drilled air box

4 (main sizes) - 1 = 3 or 137.5 + (2.5 * 3) = 145.0
1 (pilot jet size) or 42.5 + (2.5 * 1) = 45.0

With this jet configuration I get 32-38 mpg on the open road, Smooth idle, very strong acceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 65K mile on it, of which I have put 33K with this jet configuration.

Happy Jetting
Additional info: Decrease main jet size one step per 2000' above sea level. Decrease pilot jet every 6000' above sea level



i have also attached a word doco to help tune it once you get it close...did this to the Mighty FJ and she pulls like a freight train

limbimtimwim
7th April 2006, 08:58
In my extremly limited experience, I found factorypro ( http://www.factorypro.com ) easy to deal with. I will fit one of their kits once I get the $$ and the pipe.

They have a kit for your bike, way down near the bottom of the page:

http://www.factorypro.com/Prod_Pages/indexmake.html

Mind you, it's USD$130 + shipping :-/

F5 Dave
7th April 2006, 16:10
Factorypro are the go & will give you a good baseline, but only trial & ideally dyno will get things spot on. However it is very common that the emulsion tubes wear oval & fueling will progressively go to crap after say 20,000k & up.

Factorypro do replacement tubes for FZRs. Just done mine on the RF, but common on FZRs see http://exupbrotherhood1.com & you will read many others having done the same. Helps mileage as well.

R1madness
11th April 2006, 18:24
Try lifting the needles right up and run 145main jets. Use the STD airbox with filter but run it without the filter retainer lid. Just use a self tapper to hold in the filter.
I used to run mine with a magnum 4into1 system. It works best with a whole heap of other mods but that will give you a really good baseline ot begin with. Then run it on a dyno with a gas analiser and a very good operator that knows how to interprite the results. A little fiddle and you will be away.