My 72 (l28) has a bit of a problem running when cold. Its got 72 SU's with no smog equipment other than pcv system. When i pull up the choke, the engine revs, but it dies easy with a small amount of load. Sometimes even when its warm, it will bog off the line a little bit. Ive got the carbs balanced and mixture set correctly. Whats up with this? SM needles wouldnt help as they only richen up at 2k or so right?
ben240z
- Status
Two things to check-
One: the choke interconnect to the throttle. It's that little dogleg shaped link on the side of the carb. It controls how much the throttle plate opens when you pull on the chokes. When the nozzles drop the throttle plate needs to open just a bit to increase the choked idle speed. The only way to adjust is to bend the doglegged link. When the choke is full 'on' the space between the throttle plate and throttle body inside should be only .59-.69 mm (.023-.027"). At this setting you will get in the neighborhood of about 2k rpm at full choke. That should help the bog with choke on.
Second: try using 20wt oil in the carb dampers, or make sure that whatever oil you are using is at least up to the top mark on the damper rod. A lack of oil or too thin of oil can cause a bog or stumble or 'lean pop' from the carbs. Here is an easy way to get the right level in the dampers. Fill both damper reservoirs to just below the top. Slowly push the dampers back into position. Now start the engine and run it to complete warm up. Just take it for a drive. The excess damper oil will have overflown into the carb piston and will burn off. The damper fluid level will in a fairly short time seek the proper level. I know some people won't agree with this procedure but I've used it for almost 30 years without any problem and it reduces the 'arrrrrggghhhh' frustration level. Over the years I when helping people set up their, carbs only about 1 in 5 would have enough oil in the dampers. It is something that should be checked on a regular basis, frequency depending on how hard you drive the car. Also if you are using a lighter weight oil it should be checked more frequently. Using light oil or no oil may arguably help on high end performance, but it may also hurt off idle performance and driveablility.
One: the choke interconnect to the throttle. It's that little dogleg shaped link on the side of the carb. It controls how much the throttle plate opens when you pull on the chokes. When the nozzles drop the throttle plate needs to open just a bit to increase the choked idle speed. The only way to adjust is to bend the doglegged link. When the choke is full 'on' the space between the throttle plate and throttle body inside should be only .59-.69 mm (.023-.027"). At this setting you will get in the neighborhood of about 2k rpm at full choke. That should help the bog with choke on.
Second: try using 20wt oil in the carb dampers, or make sure that whatever oil you are using is at least up to the top mark on the damper rod. A lack of oil or too thin of oil can cause a bog or stumble or 'lean pop' from the carbs. Here is an easy way to get the right level in the dampers. Fill both damper reservoirs to just below the top. Slowly push the dampers back into position. Now start the engine and run it to complete warm up. Just take it for a drive. The excess damper oil will have overflown into the carb piston and will burn off. The damper fluid level will in a fairly short time seek the proper level. I know some people won't agree with this procedure but I've used it for almost 30 years without any problem and it reduces the 'arrrrrggghhhh' frustration level. Over the years I when helping people set up their, carbs only about 1 in 5 would have enough oil in the dampers. It is something that should be checked on a regular basis, frequency depending on how hard you drive the car. Also if you are using a lighter weight oil it should be checked more frequently. Using light oil or no oil may arguably help on high end performance, but it may also hurt off idle performance and driveablility.
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