fuel mixture or jet adjustment nut settings

[jalexquijano]

i have watched the ztherapy´s  how to tune su carburetor video several time plus Dylan´s 544 setting SU CARBS

 

Anyway, even though i could adjutst the idle speed and balance between both of the 3 screws roundtop carbs i can´t still understand clearly how to get a precise air / fuel mixture dialing the jet adjustment nuts. I started at 2.5 turns clockwise and have raised them both to 3.5 turns clockwise. I am even using the GUNSON Colortune but it doesnt seem to give me a precise Reading. Should i just trust on the color of plugs number 2 and 5 to verify i have the correct mixture?? How do you determine the correct color of the plugs? Do you race the car for 5 minutes and suddenly shut the engine off before taking the spark plugs out to verify the Brown dark color on each plug?

 

[Mark Maras]

  Yes, you can use the plug color to tune the mixture. It's an old school method but still useful for a daily driver.  

 

The plugs should be a light brown (tan) color, not dark brown. What color were the plugs at 2 1/2 turns and why did you go to 3 1/2 turns?

[jalexquijano]

4 hours ago, Mark Maras said:

  Yes, you can use the plug color to tune the mixture. It's an old school method but still useful for a daily driver.  

 

The plugs should be a light brown (tan) color, not dark brown. What color were the plugs at 2 1/2 turns and why did you go to 3 1/2 turns?

3.5 turns for more power. Do you agree?

[Mark Maras]

2 minutes ago, jalexquijano said:

3.5 turns for more power. Do you agree?

 Nope, I don't agree. maximum power is achieved with the proper fuel to air ratio. Richening the mixture will only result in more power if the mixture was too lean. There's many causes for that. Vacuum leak, float level too low, etc. Here's a shade tree mechanic's tip for determining if the mixture is too lean with SU's. At normal operating temperature, try gradually adding choke to the engine while going up a slight grade. If the mixture is too lean, you'll feel the burst of power.

 I can't give you an opinion on the plug in the picture. It looks, to me, like an old carboned up plug that was kinda cleaned. The black uncleaned part looks like a rich mixture. The top white section and electrodes look extremely lean. What is the history of that plug? The porcelain should be a light brown (tan) color if the mixture is close.

[jalexquijano]

any pictures of a correctly burned spark plug? This is a NGK BP6ES gapped at .031.

[Mark Maras]

 www.ngksparkplugs.com has a good chart. You'll want to install a new set of BP6ES's to get an accurate reading.

[jalexquijano]

i have dialed both carbs to 3.75 turns each! Timing is at 14 btdc. New set of spark plugs? these ones are new! can i just simply clean them with brass wire brush and race the car again for 10 minutes, shut the engine off suddenly and pull spark plugs number 2 and 5?? Anyone has a picture of a correctly burned spark plug?

[Mark Maras]

 You can use the old plugs IF you can get the porcelain around the center electrode white. Good luck with that.

[jalexquijano]

I richened the mixture to 4 turns clockwise and lowered the timing to 12 btdc. Good power but still getting deceleration backfire when releasing the gas pedal on second and third gear. Ill guess ill need to check on the float valve level as per manufacturers. Ztherapy sheet refers to .055 mm

[Mark Maras]

 The richer the mixture, the more it will backfire in the exhaust.

[jalexquijano]

deceleration backfire not normal acceleration backfire! Totally different!

[Stanley]

Jake Brake. Illegal in Oregon.