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The subject has come up several times about momentary hesitation when the accelerator is pressed down. I haven't really had the time to address it until now.

There can be several reasons for it. internal carb issues, disassemble, clean, and rebuild may be needed. Vacuum leaks, trace down, and correct the leak. If you are sure none of these issues are in play and if you have built your carb, etc and still have hesitation, the most likely issue is your manifold heat butterfly setting. This problem is more prevalent in cold weather. It will also happen in warmer weather, but may clear up as the engine has time to warm. Depending on your climate, it may be imperative that you change the butterfly setting as the seasons change. If you live in an area that doesn't get really cold, the summer setting likely will work fine for you year round.

Here's what you need to be aware of, then you will have a better understanding in order to make an informed decision as to the setting you need where you are. As liquid enters the intake manifold from the carb, vacuum vaporizes the gas. This chills the manifold walls sort of like spraying an aerosol on you skin does. With the now cold manifold from the sudden chill, in the winter it will stay cold, in some conditions frost will form. In these conditions, as you accelerate and vacuum drops, gas no longer will vaporize. Instead it condenses on the cold manifold walls until they are totally saturated with wet gas, this takes a few seconds to occur during which time no fuel is going to the engine, thus the hesitation. After the manifold walls are completely saturated with raw gas, the air flow will finally pick up the extremely rich fuel mixture and cause minor flooding. Liquid gas does not distribute equally to all cylinders, as it does when vaporized, thus the appearance of a rich fuel mixture on the plugs, some will appear worse than others because of the poor fuel distribution. Using this practical information, taking into consideration your climate conditions, and playing with the butterfly settings will cure the hesitation when the butterfly is correctly set so that exhaust flow heats up the intake manifold to the proper temp to prevent the chill and keep the gas vaprorizing if everything else is functioning correctly.

Hope this info is helpful to those who are having this problem, you simply do not have to put up with annoying hesitation.

MSeriesRebuild wrote:The subject has come up several times about momentary hesitation when the accelerator is pressed down. I haven't really had the time to address it until now.

There can be several reasons for it. internal carb issues, disassemble, clean, and rebuild may be needed. Vacuum leaks, trace down, and correct the leak. If you are sure none of these issues are in play and if you have built your carb, etc and still have hesitation, the most likely issue is your manifold heat butterfly setting. This problem is more prevalent in cold weather. It will also happen in warmer weather, but may clear up as the engine has time to warm. Depending on your climate, it may be imperative that you change the butterfly setting as the seasons change. If you live in an area that doesn't get really cold, the summer setting likely will work fine for you year round.

Here's what you need to be aware of, then you will have a better understanding in order to make an informed decision as to the setting you need where you are. As liquid enters the intake manifold from the carb, vacuum vaporizes the gas. This chills the manifold walls sort of like spraying an aerosol on you skin does. With the now cold manifold from the sudden chill, in the winter it will stay cold, in some conditions frost will form. In these conditions, as you accelerate and vacuum drops, gas no longer will vaporize. Instead it condenses on the cold manifold walls until they are totally saturated with wet gas, this takes a few seconds to occur during which time no fuel is going to the engine, thus the hesitation. After the manifold walls are completely saturated with raw gas, the air flow will finally pick up the extremely rich fuel mixture and cause minor flooding. Liquid gas does not distribute equally to all cylinders, as it does when vaporized, thus the appearance of a rich fuel mixture on the plugs, some will appear worse than others because of the poor fuel distribution. Using this practical information, taking into consideration your climate conditions, and playing with the butterfly settings will cure the hesitation when the butterfly is correctly set so that exhaust flow heats up the intake manifold to the proper temp to prevent the chill and keep the gas vaprorizing if everything else is functioning correctly.

Hope this info is helpful to those who are having this problem, you simply do not have to put up with annoying hesitation.

I brought this thread back up after reading the post concerning carb iceing. This is the most common cause for that issue.