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jalexquijano

3 Screws Roundtop Su Carburetor Jet Adjustment Screw Tuning

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Have watched the Ztherapy´s SU CARBURETOR TUNING video several times. Even though i have adjusted the idle speed on both su carbs and balanced them, i still cannot get a precise Air Fuel Mixture as the video does not explain how many turns clockwise should you turn after the initial setting of 2.5 turns clockwise. I am at 3. 5 turns on both carbs. Any other more precise method than the gunson colortune? Should i race the car for 10 mins and suddenly shut the engine down before taking the plugs number 2 and 5 to verify if they are both burning dark Brown??

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 the video does not explain how many turns clockwise should you turn after the initial setting of 2.5 turns clockwise

 

There is no "setting" as such that will suit all cars / engines. You start at 2.5 turns and then adjust to suit. There are plenty of ways to tune SU's,  Colourtune is good, dyno is better, but you can do it simply by lifting the pin on the side of the carb and noting how the engine revs change.

 

If revs increase and stay up, its rich so screw the adjuster in (less turns),

If revs drop, its lean, so lower the adjuster (more turns).

 

You need to let it settle, if revs go up a little then drop back to normal, mixture is OK.

 

The actual final setting will depend on a few other factors. Make sure you have set the float level properly, I prefer to set it by measuring the height of the fuel in the jet as I find that more accurate than the more normal "gap between float chamber lid and float" method. You'll have to google for the exact measurements for  Datsun / Hitachi SU's, I run "genuine" british SU's which may be different.

Edited by 1600dave

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Forget what the literature says, it is only a STARTING POINT

 

Many of your posts have the same theme that "X said Y therefore I should do Z" which just isn't right. Use the tools at your disposal to tune the engine as well as it will run and be happy. Your mixtures are probably never going to be 100% perfect because no two cars are exactly the same and because of the modifications your car apparently has.

Edited by Agno

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Any picture of a correctly burned spark plug? I have dialed both fuel mixture / jet adjustment knobs to 4 turns clockwise and set timing to 12 BTDC

 

Should i also  race the car for 10 mins and suddenly shut the engine down before taking the plugs number 2 and 5 to verify if they are both burning dark Brown

Edited by jalexquijano

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