1800: B20E timing and erratic idling

[capt jack]

Hi All,

After all sorts of travails due to rusty fuel tank, seized fuel pump and brakes, knackered pressure regulator etc etc etc, Monica, my 1800ES auto, is now running and nearly ready for her MoT. She's a late 72 with the B20E engine (Bosch D-Jetronic)

Getting the timing right is proving interesting! I've a dwell/tachometer - dwell angle is 62 degrees, which is in the middle of the range specified for the engine (59 to 65 degrees), the points are new and set to .035mm. Using a strobe light, I've attempted to set the timing as per the book to 10 degrees BTDC. This is quite easily achieved with the vacuum line off the dissy and plugged, although when I put the line back on to the dissy the idle becomes very lumpy, and the RPM drop, the timing is then retarded. I've read elsewhere on the forum that the vacuum line is best plugged and left off anyway - if that's the general experience I'll happily live with that.

As I've got things set up now, at idle with the vacuum line off, the RPM fluctuate a bit around the 900 mark, and with the benefit of the strobe, I can also see that the timing marks wander about a bit, although really, not very far. For the RPM I'm watching the dwell/tachometer rather than trust the car's rev counter.

As the engine speed is increased, the revs pick up and everything smooths out.

I've also noticed that pumping the brake pedal with the engine idling will cause the RPM to increase to about 1200 rpm, and that then the lumpiness then goes.

At the moment for the purposes of setting things up I'm using unleaded petrol. The fuel pressure regulator is set to 2 bar; the auxiliary air valve appears to be working OK; the coil, points, plugs, leads are all new; the distributor has been stripped and cleaned, with replacement springs fitted.

Am I expecting too much for the idle to be perfectly smooth? My suspicion is otherwise that there's probably a bit of a vacuum leak. I know that getting an engine to idle smoothly can be something of a black art!

If anyone has any experience of setting up a B20E then I'd be really grateful for any tips you can pass on.

Thanks

Cheers

Jack

[B20F]

If the idle goes up while pressing the brake pedal, that means there's probably a leak in the brakebooster. Could be the one way valve in the vacuumline to the brakebooster that's gone bad. Check if the vacuumlines aren't mixed up. The one going to the brakebooster should be fitted on the manifold plug without restriction, the one from the crankcase ventilation (from the oilfiller cap) should be connected to the plug with a restriction in it.
The B20E/F won't ever idle very smooth, a bit of fluctuation is pretty normal around 50rpm up or down. But when you notice the ignition wandering that could mean that the central ignition shaft is worn. See if there's lateral movement in it. A remedy could be to install an electronic ignition to replace the points. I'm very happy with the Pertronix unit in my B20F, it makes it idle much smoother. Indeed disconnect the vacuum and plug of the manifold, leave the plug on the vacuum pot open. If your timing it with the connection on the manifold open there would also be a small vacuum leak which increases the rpm. This vacuum retarding system is a pain in the %ss, only there for emmission reasons. Your much better of with it disconnected. Also check the timing at 3000+ rpm, maximum advance should be around 35 degrees.

[capt jack]

Thank you very much for that - I'll check all these things out - much appreciated.

Cheers

Jack

[capt jack]

Bingo! The one way valve in the servo/booster line is a bit of a two-way valve!

Will try to source a replacement and see if that solves the problem.

Thanks again

Jack

[B20F]

Your wellcome, hope that it'll sort it!