Solex H30/31 PICT carb choke and tuning

[eng622]

Having set up the timing, carb and checking the obvious on my new bug I now have a cold starting issue. The carb is new but installed during the previous ownership. First the fast idle cam was never adjusted so read up on how to do it and now done. Car would start from cold and during warming up you could see the cam rotating to the end and the choke butterfly ending up vertical.
But now will not start from cold. It fires, has run for 2 secs at the most but dead after that. It is not electrical all checked out OK.
It is bizzare, I tied up the cam so that the butterfly was fully open (vertical) as if warmed up and it started straight away. Would not idle and a bit sluggish till warmed up as expected. Next day had to use the same trick to start it.
So this one is beyond me. The cam closes the butterfly correct for a cold start, the engine fires but cannot catch it to keep it running. Is it too rich/insufficient air?
Also when fully warmed up adjusting the idle with the bypass screw is opposite to what I have read. I'm have to screw out to reduce the idle rpm. Is this correct?

[ashman40]

For carbs like the 30Pict-3, H30/31 and 34Pict-4 with the large bypass screw on the left side, the warm idle rpms are completely controlled by the bypass screw. Turning this screw CCW allows more air-fuel to bypass the closed throttle plate and increase the idle rpms.

The common mistake is to think the screw at the end of the throttle arm is for fast idle adjustment. That may be the case for most other carbs, but not here.
The screw at the end of the throttle arm should be set so the throttle plate is nearly completely closed. With the screw at the lowest level of the cam, loosen the screw until it is no longer touching the cam; tighten it in until it is just touching; screw it in 1/4-turn more just to keep the throttle plate from resting on the inside of the carb throat. That is it. From here the idle is adjusted with the small volume screw (mixture) and the bypass screw (idle rpms).
The choke coil on the right side of the carb controls how long (time) the engine will run at fast idle with the throttle arm screw resting on the fast idle cam. Close the butterfly more and it takes longer to fully open. You want the choke operational for 5-10min while the engine is stone cold.


One other thing to check is that the float bowl is over flowing. After you have the engine warmed up, shut off the engine and remove the top of the carb to check the level of the fuel in the bowl. Once stabilized it should be 3/4" from the top of the bowl.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[eng622]

Warm idle on most carbs you rotate the screw CCW which reduces the idle as the butterfly closes. This is what mine is doing but the opposite is stated, so do not understand how the bypass screw controls the idle on this carb.

Regarding the fast idle/choke set up as stated. From cold you can see the cam rotate as the engine warms up over 5/10 minutes until it reaches the bottom and the choke butterfly is vertical (this is when I remove the wire holding the cam once started).

This is not solving my problem as the car will not start with the cam in the cold position. As stated will only start with the cam in the hot position (have not tried in between though).
Any thoughts.

[jarmchairpilot]

Hi I have a 72 stock 1200 bug and changed from my original German solex30 pict3 to a new Bocar h30/31 pic that has a manual choke cable attached.
It has taken some time to fine tune correctly because I rebuilt the engine a few months ago but have been using this car as my daily driver for 12 years now.

In my experience it's essential to go through all the checks that a good owners manual would recommend for a major service and don't be tempted to assume anything is correct.
Check and double check before you go onto the next step.
It's not expensive to fix problems like this but....it does take quite some time.
Tuning the carb is the Final step after all the basics are covered with a fine tooth comb.

Points gap set correct. 0.4mm
plug gaps correct take them out to check condition, don't assume they are fine, if in doubt renew and snug them up or torque them correctly.
Change the engine oil...it's not expensive. I use 15/45, 20/50 is more widely available.
Fresh tank of new gasoline, fill it up.
New distributor cap and rotor every few years, I do 10,000 miles a year or less so it's every 2 years for me.
New ignition leads every 5 years.
New fuel filter, I use a cheap Mann brand vw golf/rabbit MK1 or MK2 type with hose clamps and new ethanol resistant fuel pipe/hose over the rear axle, just near the clutch adjusting wingnut.
Carb cleaner spray down the carb throat after the oil bath is off, give it a minute to work then blast it out with airline, a tyre pump will suffice, put the oil bath back on.
Tighten all the manifold to carb nuts and bolts to spec.
Tighten the manifold to cylinder head nuts to spec.
Tighten the exhaust mounting bolts and tailpipe nuts to spec.
Make sure all the fresh air hoses and heat riser from the exhaust to the manifold is in good condition. All engine lid seals and engine bay seals have to be in good condition.
If you park outside , lie down underneath the engine ,look up and you should not be able to see any daylight coming through the engine bay. If you do you have to fix that too.
Valve gaps adjusted to 0.15mm
Ignition timing set correctly it varies for every engine and I have tried static timing, tuning by ear and strobe timing for 28 to 32 degrees at maximum advance.
However this is what I now recommend and that is to set the ignition timing using a vacuum gauge connected with a T piece to the hose that goes from the vacuum advance cannister on a distributor to the carb body. When the engine has warmed up I simply gently rotate the distributor very slowly until I achieve a stable reading, the needle on the guage reaches its highest position and stays there without jumping about across a range of engine speeds and at idle, running sweetly.
There are excellent Vintage VW official videos on u tube that show how to set ipoints,valve and ignition timing and cárb. tuning.

[jarmchairpilot]

I forgot to add the simple but often overlooked check,
take out the rear seat and make certain the battery is in perfect condition.
Clean the battery posts and connectors because the lead can corrode very quick and cause a poor electrical connection, I use a small brass wire brush and also check if your battery needs a top up of water/acid.
Check the earth strap is good as new.
Tighten the connections to spec.
Put a cover over the battery after you have checked that it holds a charge over 12 Volts.

[ashman40]

[balljoint]

On the choke side of the carb there are two jets. Make sure the one facing to the right 3 (o'clock)is the 65 and the one facing slightly to the back (5 o'clock) is 50.
Its common for them to get mixed up or even come in the wrong location from new.
_________________
It's an ongoing journey, never forget where you came from....

65 rhd Beetle
72 rhd kombi

[kpf]

The choke butterfly shouldn't be closed as far as it will go. The correct cold setting is something like 75% closed. I have accidentally set mine too far closed and it would smoke, load up, and die unless I held the choke open partially.
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1971 Super Beetle

[eng622]

Thanks for the pics and link. I think I am now seeing how this carb works. I can see if you turn the bypass screw CW you reduce the air volume and hence lower the idle tickover. I will bottom out the screw and see how many turns out and then set 2.5 out as a starting point (still cannot see why turning ACW reduced the idle, perhaps should check the 'o' ring). I did bottom out the idle mixture screw and adjustment behaves as expected. I will take out the idle jet and blow it out as well.
Regarding the throttle plate I screwed in the cam screw until just touching the cam (at its bottom point) and then in 1/4 turn so think the plate is open about the suggested 4 thou. Running the car hot on idle I checked by turning the screw back/forth a small amount and the idle did not change. So think this indicates that the screw is not being used to adjust the idle.
Now on to the choke. It looks as if the choke butterfly fully closes when I touch the accel pedal and the cam moves up the notches. Agreeing it may be too rich so need to adjust. I read you loosen the choke 3 clamping screws and do you then just rotate the choke to say 3/4 closed and re clamp?

[ashman40]

[eng622]

Choke adjustment - having problems
Got the choke butterfly too much open when cold with the setting below mid step on the cam . Starts fine and runs for half a mile ok then goes too lean as expected until fully warmed up.
Clearly made an adjustment but do not know how I made it. Undid the 3 screws and could rotate the choke CCW but it springs back to original position. Would rotate a very small amount CW. Rotating in either direction the butterfly did not move. So gave up and tightened screws. BUT as said must have done something as the butterfly was fully closed at the start.
What I have noted is although the cam and butterfly rotate with the throttle arm released there is some free rotational movement between them so do not understand what this is. Stumped all round!

[ashman40]

The screw at the end of the throttle arm is pressing down on the fast idle cam which is holding the choke butterfly in place. You need to pull on the throttle arm as you adjust the choke. This allows the choke butterfly + fast idle cam to rotate freely. Once the butterfly is where you want it, tighten down the three screws and release the throttle arm.

The same applies when you first start the car. The throttle arm screw will be resting on the lowest level (engine shut off fully warmed up) preventing the choke from closing. You must press on the accelerator pedal to release the cam+butterfly before you start the engine. This also squirts some fuel from the accelerator pump nozzle to get the engine running. Pressing on the accelerator pedal before starting the engine is a required step to activate the choke.

Once running on the taller steps of the fast idle cam, you need to periodically blip the throttle to release the fast idle cam to rotate as the choke coil heats up and opens the butterfly. VW recommends you immediately drive off after starting. Since you will be on the throttle most of the time as you drive the choke+cam are free to slowly rotate open over time to open the choke. It only becomes a problem when you warm up the car in the driveway without pressing on the throttle pedal. The choke tries to open the butterfly but the throttle arm screw prevents the cam+butterfly from opening.


This is normal for mechanical/electric chokes. It may be uncommon for those who grew up with EFI. EFI adds air using solenoids and valves to raise the cold idle. Over time it closes off this extra air to drop back to normal idle. Chokes do it mechanically by holding the throttle plate open... old school.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}