Timing Dual Carbs, 27 deg vs 35 deg vs ??? Options

[jr91472]

I am sorry if this has been covered already, but my search revealed nothing.

I am wondering about the timing for carbs on 1.7 / 2.0 motors. I have read that some use 27 other use 35. What kind of difference should I expect and which is the correct setting for different applications.

For me, I have a 1.7 with and an unknown (carb friendly) cam.

thanks
(IMG:style_emoticons/default/popcorn[1].gif)

[euro911]

Right on, flyboy.

[last337]

I was just rereading the timing procedure and I'm wondering if im even doin it right. I have an adjustable timing light and I just set it to 27 and revved warm engine to 3k and turned distributor until painted mark lined up with notch. However, I am wondering if the painted mark indicates tdc (0 degrees) or if it was put there to indicate 27 degrees in which case I should set light to zero and rotate distributor until it lines up with notch. How can I tell what painted mark indicates easiest?

There is a mark on mine at 0 tdc and another one for 27. There is another mark. You have to get under the car and look through the hole where the trans mates to the engine (I think). When you can see that mark, look at the indicator on the top of the fan and whatever mark is showing at that time is 0 tdc. The mark not far from it is 27. Clear as mudd??

When say mark do you mean a notch or a painted mark?

[SLITS]

If you are lucky, TDC was painted white (notch, groove, 0 stamped into fan rim) and 27 degrees would be painted red.

If you find TDC, 27 degrees is 55.5 mm to the right of TDC on the circumference of the fan with the fan facing you or about 4 fan blades to the right and near one of the large bosses for the thru bolts that hold the fan assembly together.

Using your adjustable timing light, your procedure is correct. You have already set the timing so turn the light back to zero and see if a red mark shows in the timing window @ 3000 rpm.

[last337]

If you are lucky, TDC was painted white (notch, groove, 0 stamped into fan rim) and 27 degrees would be painted red.

If you find TDC, 27 degrees is 55.5 mm to the right of TDC on the circumference of the fan with the fan facing you or about 4 fan blades to the right and near one of the large bosses for the thru bolts that hold the fan assembly together.

Using your adjustable timing light, your procedure is correct. You have already set the timing so turn the light back to zero and see if a red mark shows in the timing window @ 3000 rpm.

Well I did this tonight and although there was no red paint on TDC, I was able to find the groove. When the groove was lined up the rotor was pointing almost right at the grove in the dizzy so it looks good. I turned engine a bit more and sure enough there was the white painted mark at what I am assuming is 27 degrees. It seems to be just like I have seen in this pic http://www.thesamba.com/vw/forum/album_pag...p?pic_id=985064

My question is this, I thought that 27 degrees was BTDC. If that is the case, why does the painted mark at 27 show up after the rotor has passed the groove in the dizzy where the number one spark plug would be? It seems like it would be before spark plug number one. Can someone explain this?

[euro911]

In the Samba fan pic, you see the BTDC advance mark OR slit (no association to SLITS) off to the left of TDC (0) mark. From this angle, the crankshaft rotates toward the left so the 'red' mark will show up in the inspection hole X number of degrees before the '0' (TDC) mark does.

Note, not all fans are marked and not all are marked at 27 degrees. They should have a mark for TDC though. After close to 40 years since the original date of manufacture, many engines don't have the original parts on them. There is a possibility that your fan may not be the original one (IMG:style_emoticons/default/confused24.gif)

You should verify and mark your fan for the advance that your particular engine requires. For example, the full advance on a 039 905 205 dizzy is 20~24 degrees BTDC @3000 RPM ... the full advance on a 039 905 205A dizzy is only 22 degrees BTDC @3000 RPM.

The correct BTDC mark on the fan and the slit in the body (under the cap) of the dizzy should line up at specified full advance if everything is correct. Of course, unless you have a clear dizzy cap and very fast eyes, you'll never see the rotor pass over the slit at the precise time it fires anyway. That's why we have timing lights (IMG:style_emoticons/default/biggrin.gif)

What year is your engine?

[last337]

In the Samba fan pic, you see the BTDC advance mark OR slit (no association to SLITS) off to the left of TDC (0) mark. From this angle, the crankshaft rotates toward the left so the 'red' mark will show up in the inspection hole X number of degrees before the '0' (TDC) mark does.

Note, not all fans are marked and not all are marked at 27 degrees. They should have a mark for TDC though. After close to 40 years since the original date of manufacture, many engines don't have the original parts on them. There is a possibility that your fan may not be the original one (IMG:style_emoticons/default/confused24.gif)

You should verify and mark your fan for the advance that your particular engine requires. For example, the full advance on a 039 905 205 dizzy is 20~24 degrees BTDC @3000 RPM ... the full advance on a 039 905 205A dizzy is only 22 degrees BTDC @3000 RPM.

The correct BTDC mark on the fan and the slit in the body (under the cap) of the dizzy should line up at specified full advance if everything is correct. Of course, unless you have a clear dizzy cap and very fast eyes, you'll never see the rotor pass over the slit at the precise time it fires anyway. That's why we have timing lights (IMG:style_emoticons/default/biggrin.gif)

What year is your engine?

My engine is a '73 2.0. I have some pics of what I found below. The white paint mark is 4 fan blades from the slit just as in the image from samba. So are u saying the slit is TDC and the white Mark is 27 degrees or is it the other way around? It would make sense that the slit (which apparently should be painted red) Since that comes before the mark painted white but it runs well with white mark set at 27 degrees so i'm confused.

[cgnj]

Hi,

I believe you have timed your car correctly. Pic number one is the 27 btdc mark. It looks red to me.
Pic 2 is in the tdc neighborhood.

Your adjustable timing light delays the stobe by the setting on the dial. If you set it to zero you would see the red mark @ 3000 rpm.

Carlos

[last337]

Hi,

I believe you have timed your car correctly. Pic number one is the 27 btdc mark. It looks red to me.
Pic 2 is in the tdc neighborhood.

Your adjustable timing light delays the stobe by the setting on the dial. If you set it to zero you would see the red mark @ 3000 rpm.

Carlos

Thanks for the reply I guess I just dont understand why the red mark comes before the white mark though. It seems like the white mark (being 27 degrees BTDC) would be before TDC.

[cgnj]

Thanks for the reply I guess I just dont understand why the red mark comes before the white mark though. It seems like the white mark (being 27 degrees BTDC) would be before TDC.

The red mark is supposed to come first. It is 27 BTDC. The white mark is TDC. If you did not have n adjustable timing light, you would be seeing the red mark in the notch @ 3k rpm. Since you dialed 27 on your timing light, the stobe is delayed 27 degrees, therefore you see the white TDC mark. If you set the timing light to zero, you would be seeing the red mark. Try it tonight

Carlos

[last337]

Thanks for the reply I guess I just dont understand why the red mark comes before the white mark though. It seems like the white mark (being 27 degrees BTDC) would be before TDC.

The red mark is supposed to come first. It is 27 btdc. The white mark is tdc. Better get help before you adjust the valves.

Carlos

Okay, I got it. So since I have set my timing light to 27 and adjusted for white mark (which indicates TDC) at 3000rpm I have in essence set the engine to 27 degrees. If I didnt have an adjustable timing light I would use the red mark (indicating 27 degrees BTDC). Am I right?

[Cevan]

Thanks for the reply I guess I just dont understand why the red mark comes before the white mark though. It seems like the white mark (being 27 degrees BTDC) would be before TDC.

The red mark is supposed to come first. It is 27 btdc. The white mark is tdc. Better get help before you adjust the valves.

Carlos

Okay, I got it. So since I have set my timing light to 27 and adjusted for white mark (which indicates TDC) at 3000rpm I have in essence set the engine to 27 degrees. If I didnt have an adjustable timing light I would use the red mark (indicating 27 degrees BTDC). Am I right?

Yes.