What do they actually tell you and how do you use them?
So folk use them for carb balancing but if one carb is out of balance, what do you do?
If somebody wants to write a quick workshop article on it, I'll stick it in the articles section. :p
Full Version: Vacuum gauges
As I understand it........
For a multi-cylinder engine to run correctly you want all the throttles opening at the same time and from the same place. You don't want one cylinder ticking over at 1000rpm and the other at 1200 rpm.
In the good old days when the most you got were two cylinders (we'll ignore the Ariel Square Four as it had only one carb) it was easy to 'balance' the carbs. Put a matchstick under each slide down the intake trumpet, then adjust the seperate cables so they were pulling together.
With a four carb'd bike it's a bit trickier, but fortunately you can measure the vacuum created in the inlet tract by the engine sucking. So if all the inlets are sucking at the same rate then the slides must be open by the same amount.
So if you stick a vacuum gauge on each inlet you can measure what the engine's doing and adjust the carbs so they're all working the same. The four carb bodies are connected by a rod which has adjusters to get them working together. Usually carbs 1 and 2 are connected together, as are carbs 3 and 4. So you read the gauges with the engine running - warm and at about 1500 rpm - and twiddle the screws.
Set carbs 1 and 2 so they're reading the same on the gauges, then carbs 3 and 4. Then adjust the screw in the middle of the bank and this'll pull 1 & 2 and 3 & 4 together. It doesn't matter what actual reading is shown on the gauge, as long as they're all running the same.
The main problem is rigging up a fuel supply as you normally need the tank off to get at the adjusters. I put the tank on a workmate next to the bike, with a longer piece of petrol pipe to supply the juice.
The result is a smoother and more effieciently running engine. Repeat every 5000 miles or so. A mate of mine threw his GSX1100 over the wall at Guthries during the Manx GP a few years ago - it landed about 20 yards up the field. When we got it back home and ripped the remains of the bodywork/tank/clocks etc off and fired it up it sounded like a bag of spanners in a tumble drier. We thought it must have bent a few valves as it revved it's nuts off flying through the air. In desperation we stuck the gauges on it and they were miles out. A quick twiddle on the adjusters and it was running as sweet as nut again.
For a multi-cylinder engine to run correctly you want all the throttles opening at the same time and from the same place. You don't want one cylinder ticking over at 1000rpm and the other at 1200 rpm.
In the good old days when the most you got were two cylinders (we'll ignore the Ariel Square Four as it had only one carb) it was easy to 'balance' the carbs. Put a matchstick under each slide down the intake trumpet, then adjust the seperate cables so they were pulling together.
With a four carb'd bike it's a bit trickier, but fortunately you can measure the vacuum created in the inlet tract by the engine sucking. So if all the inlets are sucking at the same rate then the slides must be open by the same amount.
So if you stick a vacuum gauge on each inlet you can measure what the engine's doing and adjust the carbs so they're all working the same. The four carb bodies are connected by a rod which has adjusters to get them working together. Usually carbs 1 and 2 are connected together, as are carbs 3 and 4. So you read the gauges with the engine running - warm and at about 1500 rpm - and twiddle the screws.
Set carbs 1 and 2 so they're reading the same on the gauges, then carbs 3 and 4. Then adjust the screw in the middle of the bank and this'll pull 1 & 2 and 3 & 4 together. It doesn't matter what actual reading is shown on the gauge, as long as they're all running the same.
The main problem is rigging up a fuel supply as you normally need the tank off to get at the adjusters. I put the tank on a workmate next to the bike, with a longer piece of petrol pipe to supply the juice.
The result is a smoother and more effieciently running engine. Repeat every 5000 miles or so. A mate of mine threw his GSX1100 over the wall at Guthries during the Manx GP a few years ago - it landed about 20 yards up the field. When we got it back home and ripped the remains of the bodywork/tank/clocks etc off and fired it up it sounded like a bag of spanners in a tumble drier. We thought it must have bent a few valves as it revved it's nuts off flying through the air. In desperation we stuck the gauges on it and they were miles out. A quick twiddle on the adjusters and it was running as sweet as nut again.
QUOTE(fastfitter @ June 25 2003,06:54)
I put the tank on a workmate next to the bike, with a longer piece of petrol pipe to supply the juice.
Doesn't he mind? :laughcont:
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.