Mystery about ignition timing. Engine big troubles. Help !

[twinfalls]

I found the ignition timing set wrong at 10° advance.....The 1800cc 1974 AW engine should be timed at 10° retard.
I thought I had found why my engine was prone to heating, then got disapointed when setting at 10° retard where idling turned out, terribly bad.
I do not understand this 20° discripency.
My strobe light has no adjustment to offset it's own timing.
I changed this AW egine some 30 years ago. I bought it from VW, quite sure it is as the original. Is there an engine ID I could check ?
I did the work myself, I see no way I could have offset the pulley versus the crankshaft.
The pulley has a faint white paint mark, I did find a tiny notch behind.
The timing scale does show a red dod at 10° retard, a tag on the fan housing indicates it is an AW engine to time at 10° retard at 900 rpm.
BUT. This engine is happy at 8° advance.....refuses the 10° retard.

I recently had the dreadfull brake booster vaccum elbow go unpluged, made the mistake to check the right one and did not see the left one got out. Drove back overheating badly with a lot of backfirings, little power.
When the elbow bug was finally found, I saw this condition made advance all wrong and way too much, hence overheating and backfirings.

Back in business with elbows on and potential air leaks checked. New points new condenser new coil.
Bus is running, but poorly at max speed 60 Mph. ( It was that way just before the recent overheating and may be before it stayed unused for 6 years ).
Here are my findings.
Dwell 52 ( drifted from 50 at recent install )
Rpm 950
Timing 8° advance ( with 10° retard as it should...... engine is not happy ).
Distributor is the original 0 231 181 005 VW 021 905 205 N
I do see centrifugal advance working ok when revving the engine.
Retard and Advance vaccum hoses. They are in good shape, no leak.
Unplugging the advance hose.....Timing goes strongly retarding, rpm drops and it wants to die. I do feel vaccum from the carb at the hose.
Unplugging the retard hose.....Nothing happens at any speed. I do not feel vaccum from the carb at the hose.


Another thing.
The hose from the oil breather to the air filter was popped out.
The oil breather blows a lot of air out. I never checked this about engines, How much blowing out is too much ?

[satchmo]

Check to see if your retard function on the distributor vacuum can is functioning properly. Either use a vacuum gauge on the vacuum can nipple or remove the retard hose from the carb and put a little suction on it with your mouth ("Tastes Great!"). Put your tongue on the hose and see if the vacuum is maintained. Or, if you have the distributor cap off, look to see if the plate moves when you apply the vacuum.

If the retard function isn't working, you get a higher speed at idle, and when you try to set it back to the 10 degree ATDC (retarded) spec, the whole advance curve is way retarded and it doesn't accelerate or idle well. To make up for this, mechanics typically set the timing to 6-8 degrees BTDC (advanced) and run the distributor as if it were a dual advance, SINGLE vacuum distributor. This pretty much eliminates the functioning of the central idling system, so then it is more difficult to tune your dual carbs, but you can run this way for a while. Just don't try to tune the carbs using the central idle speed and air screws; they won't do much.

Also, to get a good idle at 8 degrees advance, it is likely the throttle plates are open a bit to get better air flow. Why? Because the central idle system isn't functioning. And when the throttle plates are open even a bit at idle, your vacuum signal goes away. That's why you don't detect a vacuum in the hose for the retard function.

My advice: Find a fully functioning dual vacuum can.

The leaking elbow issue is separate, and I hope you haven't done any damage to the valves. Check your valve gaps and the compression.

Tim

[twinfalls]

The retard function on the distributor vacuum can is functioning.
I disconected the hose from the carb, sucked with my mouth and saw the distributor governor plate moving.
However, I had to suck strongly to get it moving and twice to move it all the way.
Tongue on the hose, It does hold vaccum.

What next ? Checking about closed throttle plate ?

So far I do not dare touching carbs adjustements.
The engine is running ( Bad until warm, then idle is good, the air screw of the central idling does adjust rpm, on the road, power is low, max speed is 60 mph ).

There is no hope about help from the local mecanic. He says, there is no such a thing as an engine timed at 10° retard. For him all engines are timed with advance at idle.

I' ll see a VW agent and check what he knows about the 1800cc AW engine.

[satchmo]

Check to see if the throttle plate on the left carb is actually touching the stop screw at idle. Sometimes the dual carb linkage holds it open too much and that takes away the vacuum in the retard hose. If the throttle plate is touching the stop screw at idle, back the screw out a little and see if that re-establishes the vacuum signal. If no luck, you might need to remove the carbs and reset the throttle plate position.

If the linkage is holding your throttle plate open, you will have to readjust the linkage and rebalance the carbs. Check Colin's write up on dual carb tuning for the full story. http://itinerant-air-cooled.com/viewtop ... =50&t=7767

[Amskeptic]

The retard function on the distributor vacuum can is functioning.

What next ? Checking about closed throttle plate ?

There is no hope about help from the local mecanic. He says, there is no such a thing as an engine timed at 10° retard. For him all engines are timed with advance at idle.

Satchmo is right on. You'd think that he has owned a dual carb bus . . .

The default timing adjustment must be performed, 28* @ 3,200 rpm, no hoses attached to the distributor.
Adjust the timing here, then leave it alone. This is where your engine performs its work out on the highway.
Whatever issues you have after this adjustment must be addressed on their own terms.
If you have low power, adjust the valves correctly, then do a compression test to see if the engine has sustained damage.
Colin