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jalexquijano

fuel mixture or jet adjustment nut settings

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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?

 

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  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?

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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?

20170618_101621.jpg

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2 minutes ago, jalexquijano said:

3.5 turns for more power. Do you agree?

20170618_101621.jpg

 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.

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

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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?

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

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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

20170621_085754.jpg

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1 hour ago, jalexquijano said:

deceleration backfire not normal acceleration backfire! Totally different!

 I realize the exhaust popping is driving you nuts but achieving a light tan spark plug color should be your goal. When the plug color is right then worry about what the exhaust sounds like. Whatever is causing the problem, be it, rich mixture or back pressure you want the mixture to be right.

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2 hours ago, sweatybetty said:

i wish

No ? I saw an official-looking "no Jake Brake" sign on a big downgrade there in 2001 but maybe it was a concerned resident that put it up and not D.O.T.

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19 hours ago, Mark Maras said:

 I realize the exhaust popping is driving you nuts but achieving a light tan spark plug color should be your goal. When the plug color is right then worry about what the exhaust sounds like. Whatever is causing the problem, be it, rich mixture or back pressure you want the mixture to be right.

Of course its driving me nuts! Some people like that popping at the exhaust when releasing the gas pedal while  others as me do not as with the stock pipe, resonator and dynomax muffler i had previously installed it was not presentIMG_00002477.jpg. Anyway do you have a picture of a correctly tanned ngk bp6es spark plug?

THis is a picture of the former exhaust which caused no popping on deceleration.

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 Google "spark plug color chart". Almost every spark plug manufacturer has one on their website. The shade of tan you're shooting for is anywhere from an Ivory color to the color of your spare tire well, to the left of the tank, in the pic above. As i stated before, the important thing is to get the mixture right first and then assess the exhaust noise. Some of the backfire may go away with the right mixture. It's also possible that the new exhaust is causing most or all of the problem with noise but you won't know until the mixture is right.

 To any and all Hitachi SU freaks out there, does anyone out there have experience running SM needles? They seem to be a common replacement but not really satisfactory, at least from what I've read.

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im tired of troubleshooting the car and not getting the deceleration popping over! I called MSA and the seller says he also has a 1972 240z and has no deceleration popping at the exhaust with the same exhaust:

http://www.thezstore.com/page/TZS/PROD/15-6302

How much shall i richen the mixture so the popping goes away? im at 4 turns clockwise. Car has good power and response but still popping!

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1 hour ago, jalexquijano said:

im tired of troubleshooting the car and not getting the deceleration popping over! I called MSA and the seller says he also has a 1972 240z and has no deceleration popping at the exhaust with the same exhaust:

http://www.thezstore.com/page/TZS/PROD/15-6302

How much shall i richen the mixture so the popping goes away? im at 4 turns clockwise. Car has good power and response but still popping!

  You seem to believe that richening the mixture will make it stop popping. Where did that idea come from?

 Did the seller with the 72 and the same exhaust tell you if he had a hot cam in his engine? The cam may be contributing to the popping.

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2 hours ago, jalexquijano said:

How much shall i richen the mixture so the popping goes away?

I heard the opposite: that rich mix causes popping in exhaust and lean mix causes popping through carb. But the cam might have something to do with it. Race cars always seem to be popping on deceleration.

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1 hour ago, Stanley said:

I heard the opposite: that rich mix causes popping in exhaust and lean mix causes popping through carb. But the cam might have something to do with it. Race cars always seem to be popping on deceleration.

 Thanks for the confirmation.

@jalexquijano Start leaning the carbs out. If you think the floats are close to the right setting, set the nozzles at 3 turns down, drive it for a while and check the plug color. You'll need clean plugs to get a good reading.

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damn it! now im buying a 12 NGK BP6ES Spark plugs gap them at .032, install them and race the car again following the QUICK SU DIRTY TUNING

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4 hours ago, Mark Maras said:

  You seem to believe that richening the mixture will make it stop popping. Where did that idea come from?

 Did the seller with the 72 and the same exhaust tell you if he had a hot cam in his engine? The cam may be contributing to the popping.

No. I will ask my cam is a Schneider 274F and im not changing it!! Its weird it did not pop on deceleration with the former exhaust system:

http://schneidercams.com/274FL6.aspx

 

 

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32 minutes ago, jalexquijano said:

 

 

 

 Did you change, adjust, or do ANYTHING else (screw with the carbs, change the timing, adjust valves, etc.) at the same time you upgraded the exhaust?

 What do you mean by race the engine before checking the plugs? You're looking for a tan color plug in normal driving.

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