throttle body question
throttle body question
I have noticed that there is a small black adjustable wheel right below the throttle body housing (actually connected to it). What is this for? The help is appreciated. Happy new year!
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LaRy
Hi,
You are not mentioned what kind of car you have, but I assume that you have an "old fachion" throttle, a Pierburg or Senith-Stromberg in a 240 or 740. You are not mentionening why you are interested in this adjustment. Normally it is just adjusted if the CO value is to high.
In the bottom of the throttle house you have a round plastic cover. If you take it away, you will find an adjusting screw for the air/gas mixture. It is actually the adjustable seat for the needle. If you turn it clockwise, the mixture will be more lean. Pro workshops adjust it while checking the value for the CO.
Amateurs can do it like this:
Drive the car so it is really warm. Let it idle and loosen the big long rubber hose going from the air intake to the pulsair system. Now the engine is making more noice, and the noice will help you make the adjustment easier.
Turn the adjustable needle seat anti clockwise one turn, and hopefully the engine is running nice, not vibrating. If it is not running good, change spark plugs. Use NGK, Volvo 240 and 740 just loves them, it is running much better than with origin spark plugs.
Now turn the adjustable needle seat clockwise slowly,and the sound from the hose opening will be just a little bit smother, continue slowly until you can hear some single missfiring. When you hear some single missfiring stop the adjusting. Put the rubber hose back.
You are not mentioned what kind of car you have, but I assume that you have an "old fachion" throttle, a Pierburg or Senith-Stromberg in a 240 or 740. You are not mentionening why you are interested in this adjustment. Normally it is just adjusted if the CO value is to high.
In the bottom of the throttle house you have a round plastic cover. If you take it away, you will find an adjusting screw for the air/gas mixture. It is actually the adjustable seat for the needle. If you turn it clockwise, the mixture will be more lean. Pro workshops adjust it while checking the value for the CO.
Amateurs can do it like this:
Drive the car so it is really warm. Let it idle and loosen the big long rubber hose going from the air intake to the pulsair system. Now the engine is making more noice, and the noice will help you make the adjustment easier.
Turn the adjustable needle seat anti clockwise one turn, and hopefully the engine is running nice, not vibrating. If it is not running good, change spark plugs. Use NGK, Volvo 240 and 740 just loves them, it is running much better than with origin spark plugs.
Now turn the adjustable needle seat clockwise slowly,and the sound from the hose opening will be just a little bit smother, continue slowly until you can hear some single missfiring. When you hear some single missfiring stop the adjusting. Put the rubber hose back.
The knob you describe is the idle speed adjustment.
The mixture setting on the SU constant velocity carb is critical for good running. The correct SU recommended procedure to set mixture without a CO meter (I even prefer this method with a CO meter).LaRy wrote:Hi,
You are not mentioned what kind of car you have, but I assume that you have an "old fachion" throttle, a Pierburg or Senith-Stromberg in a 240 or 740. You are not mentionening why you are interested in this adjustment. Normally it is just adjusted if the CO value is to high.
In the bottom of the throttle house you have a round plastic cover. If you take it away, you will find an adjusting screw for the air/gas mixture. It is actually the adjustable seat for the needle. If you turn it clockwise, the mixture will be more lean. Pro workshops adjust it while checking the value for the CO.
Amateurs can do it like this:
Drive the car so it is really warm. Let it idle and loosen the big long rubber hose going from the air intake to the pulsair system. Now the engine is making more noice, and the noice will help you make the adjustment easier.
Turn the adjustable needle seat anti clockwise one turn, and hopefully the engine is running nice, not vibrating. If it is not running good, change spark plugs. Use NGK, Volvo 240 and 740 just loves them, it is running much better than with origin spark plugs.
Now turn the adjustable needle seat clockwise slowly,and the sound from the hose opening will be just a little bit smother, continue slowly until you can hear some single missfiring. When you hear some single missfiring stop the adjusting. Put the rubber hose back.
Disable the high idle solinoid on the intake and set the idle speed on the carb for 750 rpm. The mixture adjustment screw is located on the front side of the SU, clockwise rotation richens mixture, CCW leans mixture.
Remove the air intake hose connected to the carb and with the engine at operating temperature use a small screwdriver and lift the "venturie damper" (the piston in the carb that rises as airflow increases) about 1/8".
Listen carefully to the engine, if the mixture is correct the rpm's will rise slightly and then fall off. If the mixture is too rich the rpm's will rise and remain higher, too lean and the rpm's will fall as soon as the piston is lifted even slightly.
I have uses this method for many, many years on single and multiple SU equipped engines and it never fails.
As a side I definitly agree that it is hard to beat the quality of NGK spark plugs, they are a great product.
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