setting up twin carby toots
Posted: Fri Jun 05, 2015 12:19 am
Stricky speaking to balance the throttle buggerflies a air flow meter is used.
Another way is power balance.
Eg a MGB has a carb for 1 and 2 cylinders and a second for 3 and 4. If no 1 cylinder is shut down by shorting the sparks and thd rev drop noted. Then No 3 the rev drops should be the same. The closer the rev drops the smoother the engine idle.
Mixture.
Fixed jet carbs only the mixture at idle can be adjusted. The overall mixture is adjusted by changing jets.
SU type carbs can be adjusted. To adjust lift piston a 3mm and if engine dies its weak and if the revs rise and stay there its rich. If revs rise then stumble the mixture is about right.
Assuming that the right jets in the fixed jet carb and the correct needle in the SU is fitted.
Adjust both types until correct. Then repeat power balance. Because power balance is effected by mixture as well.
Repeat until the settings are zeroed in.
If after 10 mins the engine is still rough. Then something else is wrong.
Home made flow gauge. The actual amount of air flow is unimportant. The amount in camparision to the other is important.
Rubber bung with a 1" hole in it. Also a small hole with a small bore pipe in it. This small pipe goes to a u tube on a bit of wood --screen wash tube. The open end of the u is plugged. The u tube bit has coloured water in it. The rest is obvious.
Regards
Bob
Another way is power balance.
Eg a MGB has a carb for 1 and 2 cylinders and a second for 3 and 4. If no 1 cylinder is shut down by shorting the sparks and thd rev drop noted. Then No 3 the rev drops should be the same. The closer the rev drops the smoother the engine idle.
Mixture.
Fixed jet carbs only the mixture at idle can be adjusted. The overall mixture is adjusted by changing jets.
SU type carbs can be adjusted. To adjust lift piston a 3mm and if engine dies its weak and if the revs rise and stay there its rich. If revs rise then stumble the mixture is about right.
Assuming that the right jets in the fixed jet carb and the correct needle in the SU is fitted.
Adjust both types until correct. Then repeat power balance. Because power balance is effected by mixture as well.
Repeat until the settings are zeroed in.
If after 10 mins the engine is still rough. Then something else is wrong.
Home made flow gauge. The actual amount of air flow is unimportant. The amount in camparision to the other is important.
Rubber bung with a 1" hole in it. Also a small hole with a small bore pipe in it. This small pipe goes to a u tube on a bit of wood --screen wash tube. The open end of the u is plugged. The u tube bit has coloured water in it. The rest is obvious.
Regards
Bob