TheSamba.com :: View topic - ignition timing, how to adjust? idle L Jetronic

Sat May 10, 2025 10:32 am

What is the timing at idle when warmed up?

Sun May 11, 2025 12:00 am

you mean when i rode? because it usually comes back to 7.5 btdc. when do you want me to take the measurement? the timing goes up then sometimes stays at 10 btdc i'm getting my new timing light this week because it died on me yesterday

Sat May 31, 2025 2:39 pm

I still don't understand why my engine speed is 1200 rpm at idle.
However, I checked the following:
- Compression is at 90 psi on all 4 cylinders.
- I adjusted the rocker arms and everything is fine.
- Cylinder head temperature sensor I is new and ok.
- Sensor II on the air flow meter is measured at 2230 ohms (normal between 2.3 and 2.7 kOhms) if I test between 6 and 27.
- I have no air leaks in the air circuit (I performed a smoke tester and found no leaks).
- My additional air valve is checked OK: it closes when the engine is warm (and 30 ohms are OK on the tester).
- My fuel pressure regulator is checked OK: 2 bars if I reconnect the air distributor hose to the pressure regulator.
-My ignition system is good, the plate inside the distributor moves well.

When I set my advance to 7.5 BTDC, I'm at 1200 rpm.
If I set it to 5 ATDC, I'm at 900 rpm.

My engine has the number: GD 021625 (September 1976). It's a 2-liter L Jetronic injection engine.

The vacuum distributor is 022 905 205 S / 0231170093.

When I refuel, I smell gasoline when I go around roundabouts. Maybe the vent hoses are porous, but no leaks were detected by the smoke tester.

I have a fuel consumption of 9.6 liters per 100 km.
I have an ultra-long gearbox with a differential.

I don't understand why I'm always idling too high. Do you have any ideas?

(I'm going to check my cold start valve tomorrow to make sure it's not leaking...) and i must check the decel valve.

Sat May 31, 2025 4:30 pm

With the engine idling remove one hose at a time from the intake air plenum and plug its nipple with your finger. If one makes a noticeable difference in your idle speed you may have found your culpret. The engine may stall when you remove some of the large hoses so have a stopper or other way to block those nipples off if you don't have a helper to start the engine while you plug the nipple with your finger.

How well do your power brake work?

Sun Jun 01, 2025 4:04 am

I plugged the hole in the large hose that attaches to the intake pipe with a cap.
I started it and revved to 3000 rpm.
When I suddenly closed the throttle body, I felt a suction with my finger,
but it seemed weak...

So I'm wondering if that's the problem.

I don't know where to find a deceleration valve?
I saw two for sale on the samba.

You're talking about testing the deceleration valve, right?

Sun Jun 01, 2025 7:59 am

Is that your throttle body in the picture? It doesn't look quite the same as mine, and I have a similar setup to what you have.

Also, Robbie's advice was solid...turning the idle screw clockwise (to the right) will decrease idle. If it doesn't then you have a leak in the S-boot somewhere.

S-boots crack in the peaks and valleys of the molding and leak, and the other two connections can also leak. Did you do the smoke test, and what did you find?

If you can post a few more pictures of what you have setup, that may be helpful.

Sun Jun 01, 2025 9:55 am

Pepite73 wrote: I plugged the hole in the large hose that attaches to the intake pipe with a cap.
I started it and revved to 3000 rpm.
When I suddenly closed the throttle body, I felt a suction with my finger,
but it seemed weak...

So I'm wondering if that's the problem.

I don't know where to find a deceleration valve?
I saw two for sale on the samba.

You're talking about testing the deceleration valve, right?

I am wanting to test each hose and whatever it hooks to for leaking, this would include the booster for the brakes which wouldn't show up in a smoke test. If you have an EGR valve you need to block off the flange where it attaches to the intake plenum as well, a piece of sheet metal, heavy paper, or a coin with some silicon on it will do the job.

Sun Jun 01, 2025 11:33 am

I have no leaks on the smoke tester. When I drive at 100 km/h the engine does not go down, it remains at 1650 rpm and -15 degrees btdc at idle while I had set it to -7.5 at 1080 rpm. Even after a few minutes it does not return to 1000 rpm. So I wonder if it is not the vacuum igniter? To test the brake lever I do not know what the procedure is.

Sun Jun 01, 2025 12:17 pm

did you put four or five drops of oil on the wick under the rotor to be sure the mechanical advance has adequate lubrication? It needs a couple drops of oil once in awhile when servicing it.

Quote: you mean when i rode? because it usually comes back to 7.5 btdc. when do you want me to take the measurement? the timing goes up then sometimes stays at 10 btdc

Quote: When I drive at 100 km/h the engine does not go down, it remains at 1650 rpm and -15 degrees btdc at idle while I had set it to -7.5 at 1080 rpm. Even after a few minutes it does not return to 1000 rpm.

Quote: I still don't understand why my engine speed is 1200 rpm at idle.

Sun Jun 01, 2025 2:21 pm

SGKent wrote: did you put four or five drops of oil on the wick under the rotor to be sure the mechanical advance has adequate lubrication? It needs a couple drops of oil once in awhile when servicing it.

Quote: you mean when i rode? because it usually comes back to 7.5 btdc. when do you want me to take the measurement? the timing goes up then sometimes stays at 10 btdc

Quote: When I drive at 100 km/h the engine does not go down, it remains at 1650 rpm and -15 degrees btdc at idle while I had set it to -7.5 at 1080 rpm. Even after a few minutes it does not return to 1000 rpm.

Quote: I still don't understand why my engine speed is 1200 rpm at idle.

For the first lube after years of negligence maybe use ATF as it will soak into the felt better, followed by lightly wiggling the rotor back and forth a dozen or more times to get the rotor moving freely.

Sun Jun 01, 2025 2:37 pm

Thanks SgKent and wildthings. That's a good idea. Do you have a picture of what I need to remove (the electronic ignition) to lubricate properly and know where to put the oil drops?

Sun Jun 01, 2025 5:39 pm

Pepite73 wrote: Thanks SgKent and wildthings. That's a good idea. Do you have a picture of what I need to remove (the electronic ignition) to lubricate properly and know where to put the oil drops?

No. But you take the cap off. Lift the rotor up and there will be a felt pad under the rotor in the center of the shaft. Using ATF or MMO, or 10-30 will work the first time but use a few drops of engine oil every year. If the center can't rotate or sticks then the timing will advance and hang up which causes the timing not to fall back to idle, and the RPM to stay high.

Sun Jun 01, 2025 8:33 pm

Pepite73 wrote: Thanks SgKent and wildthings. That's a good idea. Do you have a picture of what I need to remove (the electronic ignition) to lubricate properly and know where to put the oil drops?

If you haven't done so get a copy of John Muir's VW idiot book and do some reading. It primarily covers a Type 1 but much of it applies to Busses with Type 1 or Type 4 engines as well. The book is written to help people in their early years of their VW aircoolded ownership.

Sun Jun 01, 2025 11:21 pm

Wildthings wrote: Pepite73 wrote: Thanks SgKent and wildthings. That's a good idea. Do you have a picture of what I need to remove (the electronic ignition) to lubricate properly and know where to put the oil drops?

If you haven't done so get a copy of John Muir's VW idiot book and do some reading. It primarily covers a Type 1 but much of it applies to Busses with Type 1 or Type 4 engines as well. The book is written to help people in their early years of their VW aircoolded ownership.

I have it, I will read it. Thanks