I would have posted this in the Type 4 room, but since this pertains to 412's and any conversion perversion engines you might run into with your 411/412 I thought I would post it here.
OK here's the scenerio,
ok suppossedly my 412 has a 1800cc Bus engine.
Well doing some maintanence yesterday and today, I came across something that puzzles me.
My shroad has a W engine code number - acording to my "How To Rebuild Your AirCooled Volkswagen Engine" this is for a 1700cc Type 4.
My Engine has an AW code stamped on it.
My question is
When I time the engine should I use the notch in the shroad?
OR
should I pull off the air intake cone and install a Bus timing scale?
Riddle Me this BATMAN!
-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Ray-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Timing is kind of an odd term for these. Technically 2 cylinders are very close...and two are way out. But, VW split the difference close enough that at idle..and proper ignition timing, you should not not have any real issues.
The problem is this. When you move the distributor body tou move the to set ignition timing...you move the trigger points. If everything is stock....its all correct. But when you go with something like pertronix and a new cam like a web 73, the ignition timing is changed in location. So you move the distributor body to set it right. The injection timing moves. What is causes is a slightly lumpy idle because atomization is poorer. It is not really noticable...idle wise. But....it causes a flat spot off the line. That lumpiness alters the vacuum signature. That altered vacuum signature causes spikes to the MPS. Those spikes cause richness at idle because the oscillation in the MPS is rapidly and minutely moving the armature enriching you. So...you get a flat spot. you try to adjust it out at the MPS....you get a nice idle..but a lean midrange.
If Want to see this visually? Strangely enough...you can see it with the fuel gauge. As you move your timing...and especially if you are using a slight bit more timing than stock...say 32 BTDC ( which also slightly alters the vacuum signature because of valve overlap).....the gauge needle starts a rapid oscillation like about 3-4 psi drop back and back to the set point. So fast that its almost a blur. You can watch that STOP...by turning the trigger plate. It moves the timing around a slight amount....about 5-15 degrees...and smooths the idle oscillation to almost "0". You do this by slotting the screw holes in the trigger plate. Use an offset screwdriver to loosen then while running. First set you timing correctly. Then check the fuel gauge...and turn the trigger points until the oscillation is the smoothest. Its a noticable difference. Oh...and mark the triggger plate and the distributor body with a puch mark first...before you slot the plate....so you know where the centerline is...and have an idea of how much you moved. Ray
The problem is this. When you move the distributor body tou move the to set ignition timing...you move the trigger points. If everything is stock....its all correct. But when you go with something like pertronix and a new cam like a web 73, the ignition timing is changed in location. So you move the distributor body to set it right. The injection timing moves. What is causes is a slightly lumpy idle because atomization is poorer. It is not really noticable...idle wise. But....it causes a flat spot off the line. That lumpiness alters the vacuum signature. That altered vacuum signature causes spikes to the MPS. Those spikes cause richness at idle because the oscillation in the MPS is rapidly and minutely moving the armature enriching you. So...you get a flat spot. you try to adjust it out at the MPS....you get a nice idle..but a lean midrange.
If Want to see this visually? Strangely enough...you can see it with the fuel gauge. As you move your timing...and especially if you are using a slight bit more timing than stock...say 32 BTDC ( which also slightly alters the vacuum signature because of valve overlap).....the gauge needle starts a rapid oscillation like about 3-4 psi drop back and back to the set point. So fast that its almost a blur. You can watch that STOP...by turning the trigger plate. It moves the timing around a slight amount....about 5-15 degrees...and smooths the idle oscillation to almost "0". You do this by slotting the screw holes in the trigger plate. Use an offset screwdriver to loosen then while running. First set you timing correctly. Then check the fuel gauge...and turn the trigger points until the oscillation is the smoothest. Its a noticable difference. Oh...and mark the triggger plate and the distributor body with a puch mark first...before you slot the plate....so you know where the centerline is...and have an idea of how much you moved. Ray