PDSIT Idle

[Amskeptic]

Colin, I have a Gregory's manual from Australia which mentions that you should have no throttle gap if the thottle plate has a relief drilling in it ( ie a small hole). The PDSIT's I have have this small hole in the throttle plate. This seems to fit with your process for setting throttle gap?. Have you come across this before??

One of the benefits of the stop screw is to prevent the throttle plate from sticking in the bore as the bushings wear. Another benefit is tweaking the position of the plate edge against the little pilot holes. Having the edge of the throttle plate just above the lower hole helps get a start on drawing fuel/air through the transition holes as you accelerate. The holes in the throttle plates I believe are for the greater displacement engines 1800 and 2000. Bottom line is 500-700 rpm on the dual carbs only with correct timing and mixtures. When you kick in the central idling circuit, you should get 950-1,000.
ColinAin'tThisFun?

[Dave105]

Guys: as mentioned in my last post do I set my throttle plates to get no signal on the vac advance at idle? How do I set the other carb as I assume that both throttles have to be the the same position at idle? Do I take the airflow reading from the master carb as the datum and adjust the slave to match?

looking at my carbs they do indeed have a hole in the throttle plate but as far as im aware they came from a 1700 engine?.

so I guess the hole allows the air through so the position isnt too critical for airflow just for vac signals?

At the moment my bus wont start as I think ive done somthing stupid (again)! In my last post I had trouble with the timing not returning to the correct position after reving. thought it might be a sticking dizzy removed it checked ok put it back now it wont start!! so keep with me while I get it started then Ill let you know how I get on.

Jaffa: any chance of a copy of 'Gregory's manual from Australia ' as any more info is always welcome and interesting to add to by already vast collection about PDSIT tuning.

Once again thanks to allthe helpful people out there!

[Amskeptic]

Guys: as mentioned in my last post do I set my throttle plates to get no signal on the vac advance at idle?

That cannot be answered. There is no such thing as setting the throttle plates "to get no signal on the vacuum advance at idle." You set the throttle plates as written here or as instructed in the Bentley. IF you have vacuum advance at idle after setting the throttle plates, THEN you have a problem, as written here as well.

How do I set the other carb as I assume that both throttles have to be the the same position at idle? Do I take the airflow reading from the master carb as the datum and adjust the slave to match?

Sure. But if you find that you cannot get the slave to match the master, then what? Go back and just do the 1/4" from contact. Your one side of the engine may have airflow issues that you cannot compensate for, such as a worn valve guide or a flat lifter. You just do the best you can without pivoting and imploding on yourself.

looking at my carbs they do indeed have a hole in the throttle plate but as far as im aware they came from a 1700 engine?.

As mentioned, who cares as long as you can land 500-700 rpm at idle on the dual carbs, and get another 2-300 as necessary when you kick in the central idling circuit.

so I guess the hole allows the air through so the position isnt too critical for airflow just for vac signals?

Actually, airflow around the perimeter is very important as it determines the fuel draw through the pilot circuit.

At the moment my bus wont start
removed distributor put it back now it wont start!!

Put timing mark at "0" and rock engine back and forth. IF #3 rockers both move, the you know the engine itself is at #1 TDC. If they don't, see if #1 rockers are moving as you move engine. If so, rotate the crankshaft a full 360* and get the mark on the fan pulley lined up with "0" again, and double-check that now #3's rockers both move. Now double-check distributor rotor position (if all stock it should be facing somewhat rearward towards latch of decklid actually, and the vaccum can should be very near the bale for the breather and the notch on the perimeter of the distributor body should be under the rotor.
Colin

[Dave105]

Happy New Year to all the folks over the pond. Been tinkering with the bus over the Christmass break and found a few interesting things, and re-reading Colins post about setting the fast idle

My problem is that the choke on the master carb does not open as far as the slave carb choke. Checking the temperature the master carb choke is about 35C while the slave carb choke runs at 45C. Checking current draw the master carb choke draws 0.5mA and the slave carb choke draws 0.8mA, so I guess this accounts for the difference in temperatures. If I let the engine warm up (10 mins or so) the slave carb choke comes off nicely while the master carb choke stays on, therby keeping the throttle off the stops letting vac remain on the advance side of the dizzy-result 2500rpm that wont come down. If i stick my finger in and flick the choke plate fully open then the throttle stop screw seats and everything settles down, no addvance and a nice dollop of retard vac on dizzy. Blip the throttle and the choke catches and stays on again

My questions:
Can I simple adjust the rotation of the choke element to compensate for the lower temp? will this force the choke plate open

Re-reading Colins how to: do you use the throttle linkage to balance air flow at 2500RPM and the throttle stops to set airflow at idle?

One last but not least question, My bus will not start when warm, no matter what I try to do It simply will not start, it turns ovner but does not even try to catch, while it starts first time when cold, Any ideas will be very welcome

[Amskeptic]

A) My problem is that the choke on the master carb does not open as far as the slave carb choke. Can I simple adjust the rotation of the choke element to compensate for the lower temp? will this force the choke plate open

B) Re-reading Colins how to: do you use the throttle linkage to balance air flow at 2500RPM and the throttle stops to set airflow at idle?

C) One last but not least question, My bus will not start when warm, no matter what I try to do It simply will not start, it turns over but does not even try to catch, while it starts first time when cold, Any ideas will be very welcome

CHOKE OPENING SYNCHRONIZATION
A) There is no "master carb". There is a left carb and a right carb. The central idling circuit has taken up residence on the left carb, but nobody is a master and nobody is a slave in the democratic world of Solex.
To adjust the chokes, you want to find the index marks on the covers and align them with the notch in the upper carburetor boss. THEN you see who opens all the way first. THEN you decide if the late carb is the one to back down or if the early carb needs to brought up. Usually these engines are racing-when-warm, so you want to adjust the late carb to open earlier. Please note, we are talking ONLY about the plates reaching full open at roughly the same time.

FAST IDLE SYNCHRONIZATION
Bentley says adjust the fast idle LINKS with carbs off manifolds, but we can do OK with them on. Cold engine off. Close the chokes with the throttle crossbar slightly pressed open (so you don't bend fast idle cam hardware), then release the crossbar so the throttles are "sitting on" the fast idle cams. Look at the gap between the throttle lever stop screws and the carburetor bodies. The gaps should be similar and generous.
Start engine with air horns and all hoses reinstalled, do not jar the throttle crossbar. You should get immediate light-off and an idle above 2,000 rpm until you blip the accelerator. Then the idle should drop somewhat (this proves that the vacuum break diaphragms are operational).
NOW we can talk about synchronizing fast idle airflow with the fast idle LINKS. If, with a properly cold engine just started, you get a nice 1,800-2,200 idle that kicks down below 2,000 when you blip the accelerator, the overall adjustment is OK. You can tweak the fast idle LINKS with less than a 1/4 turn on those 9/32" nuts or whatever they are.
But if you want smooth "fuel-injection worthy" cold engine performance, you can synchronize the fast idle links. With a warm engine, take off the air horns and press the cross bar lightly as you close the choke plate only halfway, this will engage the fast idle link. Doing both carbs simultaneously will test your patience, but we want both carbs on the middle step of the fast idle cams. Now use your UniSyn to see which carb is drawing more air. That carb you want to shorten the fast idle link just barely until both are synchronized.

Did you say it will not run when warm, or it just wont start when warm? Can you start it cold and keep it runing as it warms up and it will idle when warm as long as it wasn't shut off?
Colin

[Dave105]

Hi Colin thanks for the prompt and very useful reply. Had a look at my chokes and neither are alinged with the marks on the housings, so will note down there relative positions and have a go at following your advice.

My van runs fine when hot, if I knock the choke off with my finger, idles nice and smoothly. If I turn it off and try to restart it once its warm it just will not start. Tried all sorts of acellerator positions; to the floor, none, pumping, but none seem to work. Not a sign of life just turns over nice and quick but wont fire.

There seems to be fuel in the filters but after a couple of minuets the whole back end smells of petrol, not the leaky kind just the out of the exaust kind, is this a symtom of flooding? Not pulled a plug to see if they are wet.

The whole ignition system is new, tappets set ok (not fitted the pertronix as yet as i thought Id get it running first)

One last kinda unrelated question: does anyone know of a good technical book that details how these carbs work? had a look on amazon and cant see a relevent one.

Thanks again for all the dvice, hopefully I will be able to return the service somtime.

Dave

[satchmo]

Here is a schematic of the left hand side carb (PDSIT-2). It may help you a little. Maybe your German is better than mine? Solex has some tuning guides, but nothing specific to the carbs on your bus as far as I know.

Good luck, Tim

[albumimg]2355[/albumimg]

[Amskeptic]

If I turn it off and try to restart it once its warm it just will not start.
back end smells of petrol, not the leaky kind just the out of the exaust kind, is this a symtom of flooding?

Yep. Flooding. Obtain portable mirror and flashlight. Next time it is hot, upon shutoff, run to the back and pull the air cleaner horns off. Shine some light down down the throats and see if you can observe dripping out the discharge nozzle just above the throttle plates. These carbs can empty the gas tank into the crankcase. If you have dripping, pull the carbs, and replace the needle valves and reset the fuel level to 13mm below the carburetor body.

Do you have the original fuel pump with the "anti-percolator valve" built in? If you have an aftermarket fuel pump, many do not know what to do with fuel expansion during hot-soak. This will drive the needle valves open and flood the engine. You can re-route your fuel lines away from hot engine surfaces to help reduce this.
Colin
(to start a flooded engine, place accelerator to the floor, leave it there. Crank engine. Allow 15 full seconds of cranking to see if it will catch. If not. Let the starter rest for a minute *all the while keeping your foot on the accelerator do not move it*, and repeat up to three times. I have never had a flooded engine not start with this technique. Do not let the engine rev up once it catches! your piston rings will hate you for that)

[Dave105]

Evening all, had a twiddle with the left had choke and now I get no vac signal on the dist advance at idle, so looks like its come off the fast idle cam. I found a privious post on samba I think it was between Colin and Ratwell describing the choke/fast idle link set up will give it a go, hopefully over the weekend

looking at the fast idle cam it has 4 distinct levels with the highest step being the first and I assume the fastest idle position, is it in this cam position that the fast idle links are balenced?


Looks like I still have the origional fuel pump with no visible petrol dripping into the carb, looks like both chokes may be 'too hard on' would this caues the flooding as it looks like the chokes are fairly well closed even with a warm engine.

Why are there 3 further steps and what kind of RPM are associated with them?

Thanks for the pic satchmo, found another useful document, but also in German...any one have the English version?

http://vwbus2.dyndns.org/bulli/michaelk ... 2-34PDSIT/

[Amskeptic]

now I get no vac signal on the dist advance at idle, so looks like its come off the fast idle cam.

There will be no idle retard vacuum if the choke is on. If the choke is fully open, and the throttle levers are sitting on the stop screws, then you better have retard vacuum. This will confuse you unless you properly separate these components in your mind. The retard vacuum is NOT RELATED to the fast idle links/adjustment/chokes. It is only related to throttle stop screw position, and you'd be grossly out of spec if the stop screws were adjusted that poorly. If you get no vacuum retard AND the chokes are stuck on, well, there you go. Fix the choke adjustments. They should be fully open in less than five minutes, fast idle links should be rattle loose.

looking at the fast idle cam it has 4 distinct levels with the highest step being the first and I assume the fastest idle position, is it in this cam position that the fast idle links are balanced?

Only if you are doing the Bentley procedure, which says to close the choke plate fully and adjust the fast idle links to yield a throttle plate gap of .060" or whatever.

The choke plate is never never fully closed when the engine is running. The vacuum break diaphragms pull the chokes open a bit the instant the engine starts. I like a mellow engine rpm when twiddling with the fast idle lik synchronization so I do just the first step (i.e. the lowest step). It is easier on the engine and your ears. You just slowly move the open choke plate towards closed until it stops against the edge of the cam. By barely nursing the throttle lever open, you can feel it glide onto the first step. Now you cannot touch the throttle lever or the spring will throw it off the fast idle cam step. Do this for both carbs and then synchronize for equal airflow. I checked my cold engine rpm this morning. At 37*F, my engine lit off instantly and held 1,700 rpm until I tapped the accelerator pedal where it settled down to 1,300 rpm.

Looks like I still have the origional fuel pump with no visible petrol dripping into the carb, looks like both chokes may be 'too hard on' would this caues the flooding as it looks like the chokes are fairly well closed even with a warm engine.

Good lord yes.

Why are there 3 further steps and what kind of RPM are associated with them?

These steps are to cover Very Cold Engine, Pretty Cold Engine, Sort Of Cold Engine. If you are adjusted correctly, they will all yield a nice 1,500-1,700 RPM initial start that settles down to 1,200-1,300, then finally your normal idle.

You understand that the choke fast idle is normally hidden somewhat by thick oil when the engine is cold. When I am synchronizing my fast idle links, it is on a warm engine. I expect the rpm to be higher when I am fooling around with choke sets on a warm engine. But when it is cold, my warm adjustments-that-were-too-fast-rpm, will yield a nice mellow smooth start/drive-off. Get there.
Colin

[Dave105]

Hi All, well just about got my carbs set up and running ok now. Had to screw in the throttle stops to finally get the revs down to about 800 (with idle out) dropped to about 5 to 600 when each carb was 'dissconected'. Sounds nice and smooth when warm, and now idles at about 900 to 1000. Drives nice no hesitation and no flat spots.
Only thing I've now noticed is that when comming off choke, it starts to complain just before its truly fully warm. If I keep blipping the throttle it keeps it from stalling, takes about 1 min to settle down to a nice idle. Thought it was the chokes comming off a bit early so gave them both a tweak, but to no avail. My question is: has altering the throttle stop screws changed the fast idle cam position? That is, does it now come off the fast idle cam quicker because the throttle gap has been reduced? (does new throttle stop positions transfer to the choke fully on throttle plate gap?)
Will give them a tweak next time I get the chance for a play but just thought I'd ask before hand.

[Amskeptic]

when comming off choke, it starts to complain just before its truly fully warm. If I keep blipping the throttle it keeps it from stalling, takes about 1 min to settle down to a nice idle. Thought it was the chokes comming off a bit early so gave them both a tweak, but to no avail. My question is: has altering the throttle stop screws changed the fast idle cam position?

No. VW knew about this. The two solutions were to have preheated air for the air filter (with a thermostat to shut it off located in the right air horn), and a little baby enrichment box for the central idling circuit located on the left carb with a 12 volt wire going to it. This little enrichment device covered the hole. You can best cover this transitional leanness thusly:
Jack up the idle speed to no less than 950 preferably 1,000. Enrich the central idling circuit by about a 1/4 turn. Reduce the left and right mixtures by barely an eighth turn in each. Test over the next couple of days. If transition stall spot is still there and you have other driveability issues, reverse this procedure and let me know.
Colin