Itinerant Air-Cooled

The bus has dual Solex PDSIT carbs.

Timing set to 28deg BTDC at about 3,300 rpm with advance and retard hoses detached.
Hoses replaced, idle set to about 1,000 rpm via central idling speed screw.
Now timing at idle hovers around 15deg ATDC.
Disconnecting central idling circuit solenoid wire does not drop idle.
Blocking central idling air intake kills engine.
Releasing reference hose drops idle instead of raising it.
So I don't know how to get the idle below 1,000 rpm in order to get the timing to 0-7deg ATDC at idle.

Drove the central mixture screw all the way in (full rich), then out one turn to where it idled well at about 1,000 rpm. Releasing reference hose still drops idle.

Idles well, drives well, has good power...but am I killing the engine with this very retarded timing at idle? It was a little hot sitting there running and a lot hot after shutdown: like so hot I couldn't keep my hand on the fan shrouding or dipstick. Ambient air temp was ~70F.

whc03grady wrote: ↑

Fri Jul 20, 2018 12:44 am

Timing set to 28deg BTDC at about 3,300 rpm with advance and retard hoses detached.
Hoses replaced, idle set to about 1,000 rpm via central idling speed screw.
Now timing at idle hovers around 15deg ATDC.

Where does the timing fall at idle with hoses off after timing at maximum advance?

By using the max advance as a reference point and then checking for vacuum retard behavior at idle you'e kinda mixing apples and oranges.

Also, from the OldVolks Home Ignition page:

Old Volks Home wrote: Bus & Pickup 1974 * 1700 Manual Trans, Dual Carbs

Distributor: VW 021-905-205N, Bosch 0231 181 005
Can Use: VW 021-905-205J, Bosch 0231 173 009 or 010
Points: 01 011
Condensor: 02 074
Rotor: 04 033
Note: Originally equipped with Speed Limiting Rotor 04 016 (5400rpm)
Cap: 03 010
Coil: 00 015 (Blue Coil 00 012)
Vacuum Can: 07 115
Ignition Wires: 09 171
Spark Plug: W8CC
Timing Set At: 10deg ATDC @ 800-950rpm w/strobe, vacuum hose(s) connected
Advance/Retard Range: Vacuum: 7-12deg Adv, 16-18deg Ret; Centrifugal: 9-14deg @ 1600rpm, 21-25deg @ 3400 rpm

So if Ludwig is a manual transmission bus, then 15deg ATDC isn't too far off from the specified 10deg ATDC.

In fact, if the total mechanical advance in your distributor is at the high end of the range at 25 deg (and given its age, it could very well be more), then setting your maximum advance to 28 degrees will put the base idle timing at only 3 deg BTDC. If your vacuum can gives you the full 18 degrees of retard, then that puts you at 15 deg ATDC with a distributor that is fully within spec.

Sometimes an engine on the retarded end of the timing spectrum will “feel” hotter to our human meat-flesh skeletons. When the spark is fired so much later, the combustion flame front continues out the exhaust and heats up everything around the exhaust system. Our bodies perceive this heat as “engine is running hot” all while the cylinder heads and pistons are enjoying their vacation that comes with retarded engine timing lessening the workload.

If you have confirmed that your central idle circuitry is participating effectively while the solenoid does not click, I would like to join you in being confused.

If the reference hose drops the idle, do you think you’re on the lean end of the mixture spectrum?

Robbie

whc03grady wrote: ↑

Fri Jul 20, 2018 12:44 am

Timing set to 28deg BTDC at about 3,300 rpm with advance and retard hoses detached.
Hoses replaced, idle set to about 1,000 rpm via central idling speed screw.
Now timing at idle hovers around 15deg ATDC.

A) Disconnecting central idling circuit solenoid wire does not drop idle.

B) Releasing reference hose drops idle instead of raising it.

C) So I don't know how to get the idle below 1,000 rpm in order to get the timing to 0-7deg ATDC at idle.

D) Drove the central mixture screw all the way in (full rich),

am I killing the engine with this very retarded timing at idle?

a) make sure chokes are fully open on a warm engine (and make sure the mixture screw is OUT at least 2 turns for this experiment). With ignition on, engine off, check that the central idling plunger is giving you a good click. Start engine with everything plugged in. Remove only the air intake hose to the central idling circuit. It should be a noisy hiss. Pull central idling circuit solenoid wire. Hiss should drop out and engine should slow considerably. Reconnect wire. Blip throttle smartly. Hiss should return. Report back.

b) lean. Central idling circuit changes its own mixture based on air speed, so mixture needs to be adjusted after you have established the hiss at a suitable idle rpm

c) I do not understand your goal here. Timing at idle is determined by distributor mechanicals and vacuum signal from retard port. There is nothing you can do for idle timing once everything is plugged in and you have established your base timing at 3,400 rpm. Well, there is, but we're not going there (limiting the retard movement by bending the stop)

d) Driving the mixture screw in clockwise leans it! Counterclockwise opens the fuel passage as you move the screw pintle out. Did you inadvertently lean out the central idling circuit, and that is why there is no difference when you pull the wire?

You are not killing the engine at retarded idle.
Colin