Carb Jetting Suggestions - Kawasaki Motorcycle Forums
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post #1 of 11 (permalink) Old 01-30-2017, 02:41 PM Thread Starter
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Carb Jetting Suggestions

Hi everyone! I have a GPZ 900 cafe/street fighter project in which I have swapped in a 1986 GPZ 1000 engine. I've attached some pictures if you're interested!

Anyways, the engine isn't running properly. The exhaust is a custom with duel 2.25 ID glass pack mufflers. The carbs currently have K/N duel pods as show in the attached images.

Due to the modifications to the chassis and battery relocation the stock airbox will not fit. In the spring I may fabricate an aluminum intake manifold that can fit in that space which will flow air "similar" to the stock system.

So here's my 2 questions:

1) What size jets would you suggest for the new exhaust and stock airbox?

2) What size jets would you suggest for the new exhaust and the k/n pod filters?

Thanks in advance!
Attached Images
File Type: jpg kawi pods.JPG (44.1 KB, 4 views)
File Type: jpg cafepic1.jpg (760.9 KB, 8 views)
File Type: jpg cafepic2.jpg (688.6 KB, 7 views)
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post #2 of 11 (permalink) Old 02-01-2017, 04:23 PM Thread Starter
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Anyone have any experiance rejetting their GPZ?
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post #3 of 11 (permalink) Old 02-02-2017, 03:23 PM
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Originally Posted by imaninja View Post
Anyone have any experiance rejetting their GPZ?

There's not real "standard" to jetting, there's so many variables to consider, that each bikes setup will be slightly different. From the altitude, fuel octane, component wear, and of course your modifications. It sounds like you should start from scratch (idle), and work your way up to wide-open-throttle through all gears, to get your ideal fuelling set for each RPM range. You'll know when you've got it right because the bike will be responsive and crisp across the rev range. Here's the technique I use on my MX bikes:

Install new plug/s, set carb float to OEM specs, and have bike at operating temps at all stages of tuning.

1. Close air screw, then open 1.5 turns.

2. Start engine.

3. Turn idle screw in until slightly fast idle occurs (to stay running).

4. Turn air screw in and out until fastest idle is found. (If screw is less than 1 turn from closed, install larger pilot jet. If 2.5+ turns from closed, install a smaller pilot jet).

5. If pilot screw is changed, tune pilot and air screw again for fastest idle (repeat steps 1-4).

6. Reduce idle with air screw to pre-stalling level and ride bike with closed to ⅛- throttle intervals. Adjust air screw for sharpest response.

7. Mark throttle grip at and turns of open. Ride bike in this zone, and I bogging occurs, lower the needle clip 1 position. If pickup is rough, raise needle clip 1 position. Continue adjustments until sharp response occurs.

8. Install fresh plug, and perform full throttle run, through all gears. Once at top speed, engage clutch, kill engine, and coast to stop.

9. Remove plug and inspect insulator closely for condition. White/Grey is Lean, and Brown/Black is Rich. Correct colour is Tan. Adjust main as required to set correct level.

I hope this helps you a little.

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post #4 of 11 (permalink) Old 02-02-2017, 09:21 PM Thread Starter
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Oh yea, this didn't just help a little, this helped a lot! So if I were to get this jet set you think it would be a good start?

https://www.amazon.com/gp/aw/c/ref=mw_dp_buy_crt

In addition, based on your experience can you suggest a starting jet size/number?

Thanks!
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post #5 of 11 (permalink) Old 02-03-2017, 04:56 AM
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Originally Posted by imaninja View Post
Oh yea, this didn't just help a little, this helped a lot! So if I were to get this jet set you think it would be a good start?



https://www.amazon.com/gp/aw/c/ref=mw_dp_buy_crt



In addition, based on your experience can you suggest a starting jet size/number?



Thanks!


The link took me to an empty shopping cart, try editing your post to the item link instead?

As for the jets, you should always start with stock and adjust, then if the adjustments go outside the "range" of stock jets, then you swap for a smaller/larger option - as stated in the setup method I shared.

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post #6 of 11 (permalink) Old 02-03-2017, 08:14 AM Thread Starter
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Sorry, here's the real link:

https://www.amazon.com/gp/aw/d/B006Q...X2KUBO21&psc=1

Most people have said for the pods and exhaust that, aroundstage 3 would be a good start. I shouldnt have to drill into my carbs for this size.
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post #7 of 11 (permalink) Old 02-03-2017, 12:46 PM
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Originally Posted by imaninja View Post
Sorry, here's the real link:



https://www.amazon.com/gp/aw/d/B006Q...X2KUBO21&psc=1



Most people have said for the pods and exhaust that, aroundstage 3 would be a good start. I shouldnt have to drill into my carbs for this size.

Ah, it's an entire kit! It would make sense to go for something like that because it has enough jets to cater to so many different setups. Get that, get dialled in, and ride!

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post #8 of 11 (permalink) Old 03-03-2017, 11:01 PM Thread Starter
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Hey guys! So the jet kit finally came it. The seller advertised as "stage 1-7" So I assumed there would be 7 stages of customization. The kit ended up coming with the #140-k main jets, #145-k main jets, 40-y pilot jets, 8 needle adjusters (metal spacers), 4 nilon spacers, and some drill bits.

So my questions:

1) will the 145 and 140 main jets work with the 40 pilot jet? If so, which should I use.

2) is it the needle adjusters (spacers) that will dictate more or less fuel?

Thanks
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post #9 of 11 (permalink) Old 03-08-2017, 12:13 PM
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What's the general temperatures and altitude above sea level in your area?

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post #10 of 11 (permalink) Old 03-08-2017, 12:17 PM Thread Starter
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I live in Winnipeg Manitoba. So basically sea level (230m elevation) and the summers are around 20-25 degrees Celsius on average
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