Twin webers - Ser Rapier vacuum adv/retard

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Printed on: 15 Nov 2024

Topic:

Topic author: janmarine3
Subject: Twin webers - Ser Rapier vacuum adv/retard
Posted on: 15 Sep 2010 19:44:54
Message:

Hi guys,
I have a pertronix electronic distributor with the vac feature on it and I am not sure what to do about the vacuum adv/retard connection since I installed twin webers.
Can someone pse help me with this.
Sorry if the subject was covered before, I searched and did not see anything on this forum.
Tx
Jan.

Replies:

Reply author: 1922
Replied on: 15 Sep 2010 22:36:47
Message:

The H120/GLS Holbay engines were never fitted with vacuum advance. I think this is because of the strong pulsing in the inlet manifold - it's not going to give a very good vacuum.

On a Lucas distributor that has vacuum advance the base plate beneath the points can move and the vacuum advance unit controls this. On H120 & GLS there is only centrifugal advance and the base plate is fixed, a cover plate is fitted where the vacuum unit is normally fitted.

I think that you will just have to leave the vacuum advance disconnected.

Reply author: janmarine3
Replied on: 16 Sep 2010 11:38:32
Message:

I note what you say and thanks.
I have photo of a Holbay engine setup, with a tapoff from the manifold to the distributor ( I presume ) . My setup is +- identical, except that my engine is stock 1725.
Would it not work for me to do the same or has that engine a different distr setup ?
I am going to try and post the photo from photobucket.

Reply author: janmarine3
Replied on: 20 Sep 2010 21:48:10
Message:

I found this easy to understand article while browsing - for those who might also have questions about adv/retard with DCOE's.

www.racetep.com/webfuelspark.html

Ignition Systems, Spark Output and Spark Advance:
This is a serious topic that seems to get ignored even by professional installers. The essence of a Weber conversion is that you are putting on a Larger carb that flows more fuel and Air to make more HP.

Most older cars that are getting these carbs installed on them had very bad Point and Condensor Igntion systems with very low spark output. These systems were barely adequate for a stock carb let alone a performance upgrade. Adding even a single 32/36 carb to an old BMW, Opel, Etc will overload the stock ignitions systems capabilities.

When you add Dual or Triple carbs you are really causing a problem. You are adding a bunch of extra Fuel and Air but not adding the extra fire needed to burn it properly. This results in jetting problems, rich running conditions, etc. If you are doing a conversion from a later model Fuel Injected car that had a decent Electronic Igntion system on it this will not be as much of a problem although you could have a problem with Spark Advance on these types of vehicles (Read below.)

When doing a Weber conversion on an older Point type Ignition car it is a MUST to at least do an upgrade to Electronic Ignition with a higher output Coil and good wires and plugs. This will allow you to jet and tune the carb to its maximum HP and Fuel Economy potential.

We use the Pertronix Ignition conversion on most vehicles ($89.00- $129.00) with the Bosch Red Coil ($45.00) and good plug wires and NGK SPark plugs. On dual and triple carb conversion we highly recommend the use of the MSD Spark Amplifiers with the Electronic Ignition. We offer these individually or in system packages like the Ultimate Spark Package we do for the BMW 2002. This will insure you have enough spark to burn all that extra fuel you are throwing at it. The difference in HP, Idle Quality, Cold Starts, and Fuel Economy are all very noticeable when doing the Ignition upgrades.

Spark advance is the other problem you are faced with. Most factory carb equipped cars have vacuum advance distributors. This is fine when installing a 32/36 or 38/38 because they have vacuum advance ports int the carb but when installing sidedrafts you do not have this option.

DO NOT hookup the distributor vacuum advance to the intake Manifold. That does not work and is a common mistake we see. If you do that you will pull full advance at idle then as soon as you open the throttle it loose vacuum and the timing will retard quickly causing a big stumble or flat spot and very bad throttle response.

When running Sidedrafts you need to either get a centrifugal advance distributor or leave your vacuum advance disconnected and just run more initial timing. You usually need 12-14 degress advance at 1000 RPM and 36 degrees total by 3000 RPM for the carbs to react properly. These timing numbers are baseline estimates only and can vary from car to car. You have to make sure you do not have a detonation problem from too much advance.

Reply author: argonaut
Replied on: 21 Sep 2010 19:41:44
Message:

I think that with the H120 distributor the inlet manifold doesn't have that vacuum take off, mind you, I haven't looked at one for a while so I'm not 100% sure

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