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Let's Talk Carbs & Tuning

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etemplet

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Louisiana
Water Crafts
1996 SPI, 1996 GTX, 1997 GTX
#1
OK... I spent a lot time on Seadoo carb over the last few months and I know I need to have a greater understanding of exactly how these carbs work. Some answers may be simple. I've rebuilt carburetors throughout my life. I've never had issues with fuel, carbs and tuning like I have with these skis. I am as meticulous as they come... I clean, inspect and check everything.

1. Pop-off - My carbs are all in the low range of this setting. What are the effects, benefits of the pop-off being at the top or bottom of the range

2. Diaphram - Lever-Spring- Needle valve - How they work together. Does the diaphram and lever actually "lift" the needle off the seat or, does the diaphram just remove/lessen the spring tension so the fuel pressure can push the fuel into the chamber? I have weighed the needles and found some heavier than others... what effect would this have on fuel flow. (some kits the needle is noticeably lighter) Too me, higher in the range (above 50%) is better because the higher the pressure the more likely it is to shut fuel flow and prevent unwanted leakage into the carbs (I may be wrong :) That said my carbs are all at the bottom of the range. I have never replaced springs so this is a growth area for me. I need springs.

3. My high speed adjusters are closed (set at Zero turns out) on 2 GTXs. I am one turn out on the low speed. The skis idle fine in the water and do not load up. They don't feel lean. They do not smoothly accelerate from idle to 4K RPM, the engines sound kinda hoarse and power is not linear. The Carbs are CLEAN done that twice meticulously. Mikuni kits but not sure about the springs being correct. Pop-Offs are in range. (No leaks in the fuel system)

4. When the high speed adjuster is opened is it letting in more fuel or more air ? I assume fuel which is why I leave it closed.

5. It says the low speed adjuster is for idle only. One turn out seems to work fine. Skis idle well.

Plugs are a little black but no fouling lately.

The problem with all this is the only way to adjust is to get in the water and adjust which may well be what I am going to do. :)

Help/insight is appreciated no matter how small or great the input. Discussion is good.
 


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