Club 80-90 Forums

can someone give me a quick run down of how it works and what pipes should go where and which ones should have strong suction on a warm engine.

i think my racing tickover is vac advance related as it drops to normal if i disconnect it at the dizzy.

thanks

As far as I can remember from my old DG there is only one vacuum line that feeds straight from the carb via a white plastic pipe with a fabric covered rubber tube on each end.

When you put your foot down the pressure drops inside the engine pulling more fuel and air mix into the cylinder heads, this vacuum also goes to your ignition advance unit on the dizzy to advance the timing for better performance. Advancing the timing gives better response, power and economy. At tick over the vacuum isnt strong enough to advance the timing, but as a fail-safe you set up the timing with that rubber tube disconnected and blocked off ( so that the engine doesnt suck in more air than it should through this tube.) You can then attach a timing light, and with the vacuum pipe attached, when you rev the engine, you should see the timing marks move ( from where they were set) as the vacuum advance works.

If your tickover is set too high, then there will be sufficient vacuum to advance the timing. These flat four engines tick over quite slowly, and even a bit too high will advance the timing and upset the apple cart.

To tune up the engine you need correct tickover, correct timing, and then correct carb settings.

It's worth checking the non return valve on the vacuum line which goes to your power assisted brakes.

When the engine is ticking over there will be the slightest little bit of suction if you put your finger over the end of the tube at the vac advance end.
Simon.

syncrosimon wrote: When the engine is ticking over there will be the slightest little bit of suction if you put your finger over the end of the tube at the vac advance end.
Simon.

im getting a strong suction at tickover, any idea what could be causing that?

the advance on the dizzy seems to be working fine as i can increase the tickover by sucking on the pipe.

So long as the tick over is at the right speed, then the suction on the pipe will be correct. There is no way ( i believe ) that you could hook it up wrong to get more suction. Maybe your vac advance is weak, and give full advance too quickly. If you can swap it for a mates one thats good, then you could illiminate it that way.

simon.