Weber Conversion vacuum

[husky drvr]

Where was the vacuum advance originally connected on these engines?

Mike, all Alpines, sI through sV, were originally equipped with "ported vacuum" from a carb connection. If you check, all original Alpine intake manifolds lack any vacuum ports, except for PCV and brake booster ports.

Hope this helps,

 

[Bill Blue]

Jim, I've always believed the way you describe "total advance". Recently read that total advance should NOT include vacuum advance because there is minimum vacuum while producing power, when total advance is needed. Sounds good to me.
Bill

 

[260Alpine]

Bill, you never count vacuum advance, consider it after you do initial, mechanical and total. I know of two V8 guys recently that had cooling issues while stuck in traffic and switched to manifold vacuum and haven't had that issue again.

 

[Shannon Boal]

Alpines do not seem to stay cool in creep n crawl conditions w/ high ambient temps. Jim N. mentioned manifold vacuum advance as a possible solution for this. (I figured the issue was airflow across the radiator, but maybe this can help....) One way to find the timing sweet spot, is a vacuum gauge. I do not have a test port to hook up a gauge, so all I got is the idea. If the timing at idle can help keep it cool, maybe it can be part of a perfect timing advance scheme.

 

[Mike O'D]

Don - I am running a Weber and haven't messed with original carbs. Is the tap above the throttle plate = "porteed", or below the throttle plate which is effectively "manifold"?

 

[Shannon Boal]

I know of two V8 guys recently that had cooling issues while stuck in traffic and switched to manifold vacuum and haven't had that issue again.[/QUOTE]
Do you happen to know if they were running automatic transmissions?

 

[260Alpine]

Yep, one was 700R4 auto other was Muncie 4 speed.

 

[260Alpine]

This thread is the one with the 4 speed manual. The auto wasn't on a message board.
Just Checking In (Page 50) : MG Engine Swaps Forum : MG Experience Forums : The MG Experience

 

[husky drvr]

Don - I am running a Weber and haven't messed with original carbs. Is the tap above the throttle plate = "ported", or below the throttle plate which is effectively "manifold"?

Mike,

The tap on a DGV 32/36 is ported vacuum. I don't think I've ever seen a true manifold vacuum port on a DGV.

If the throttle plate in the primary side is properly adjusted, then the edge of the blade should be just below the edge, to partially eclipsing the lower edge of the vacuum port. If a vacuum gauge is attached to the port, there should not be any measurable vacuum noted at idle.

If your throttle plate is adjusted too far open at idle, then you would already be uncovering the port and applying some vacuum to the distributor vacuum can.

An improperly adjusted throttle blade (too open) would cause a couple of problems. First, any vacuum through the ported port will be erratic due to the low, pulsed airflow at idle. The erratic vacuum will cause the ignition timing to hunt which will make idle speeds fluctuate. Second, it requires only a small throttle blade movement to begin flowing fuel through the progression ports. If fuel is being pulled through the progression ports at idle, then the fuel to be used for transitional acceleration is depleted and not available when needed - engine stumbles on initial acceleration. Also, the fuel drawn from the progression ports can not be adjusted with the idle mixture screw. That is, it makes the idle mixture seem rich and nonadjustable. The fuel for idle mixture screw is from the same well that feeds the progression holes, and both the progression holes and idle mixture screw fuel supply are metered by the idle fuel jet.

I've a feeling that's more than you wanted, but I hope it helps.

 

[beamdream]

Alpines do not seem to stay cool in creep n crawl conditions w/ high ambient temps. Jim N. mentioned manifold vacuum advance as a possible solution for this. (I figured the issue was airflow across the radiator, but maybe this can help....) One way to find the timing sweet spot, is a vacuum gauge. I do not have a test port to hook up a gauge, so all I got is the idea. If the timing at idle can help keep it cool, maybe it can be part of a perfect timing advance scheme.

I've used the manifold drain port as a source for measuring vacuum

 

[beamdream]

Mike,

The tap on a DGV 32/36 is ported vacuum. I don't think I've ever seen a true manifold vacuum port on a DGV.

If the throttle plate in the primary side is properly adjusted, then the edge of the blade should be just below the edge, to partially eclipsing the lower edge of the vacuum port. If a vacuum gauge is attached to the port, there should not be any measurable vacuum noted at idle.

If your throttle plate is adjusted too far open at idle, then you would already be uncovering the port and applying some vacuum to the distributor vacuum can.

An improperly adjusted throttle blade (too open) would cause a couple of problems. First, any vacuum through the ported port will be erratic due to the low, pulsed airflow at idle. The erratic vacuum will cause the ignition timing to hunt which will made idle speeds fluctuate. Second, it requires only a small throttle blade movement to begin flowing fuel through the progression ports. If fuel is being pulled through the progression ports at idle, then the fuel to be used for transitional acceleration is depleted and not available when needed - engine stumbles on initial acceleration. Also, the fuel drawn from the progression ports can not be adjusted with the idle mixture screw. That is, it makes the idle mixture seem rich and nonadjustable. The fuel for idle mixture screw is from the same well that feeds the progression holes, and both the progression holes and idle mixture screw fuel supply are metered by the idle fuel jet.

I've a feeling that's more than you wanted, but I hope it helps.

Spot on

 

[Mike O'D]

Don - I appreciate the response - no such thing as too much information. I was aware that the Weber has a ported tap - I was actually asking about the tap on the original carbs.

 

[husky drvr]

Don - I appreciate the response - no such thing as too much information. I was aware that the Weber has a ported tap - I was actually asking about the tap on the original carbs.

The OE carbs all used ported vacuum - series 1 through 5.

 

[Shannon Boal]

If the throttle plate in the primary side is properly adjusted, then the edge of the blade should be just below the edge, to partially eclipsing the lower edge of the vacuum port. If a vacuum gauge is attached to the port, there should not be any measurable vacuum noted at idle.

If your throttle plate is adjusted too far open at idle, then you would already be uncovering the port and applying some vacuum to the distributor vacuum can.

An improperly adjusted throttle blade (too open) would cause a couple of problems. First, any vacuum through the ported port will be erratic due to the low, pulsed airflow at idle. The erratic vacuum will cause the ignition timing to hunt which will made idle speeds fluctuate. Second, it requires only a small throttle blade movement to begin flowing fuel through the progression ports. If fuel is being pulled through the progression ports at idle, then the fuel to be used for transitional acceleration is depleted and not available when needed - engine stumbles on initial acceleration. Also, the fuel drawn from the progression ports can not be adjusted with the idle mixture screw. That is, it makes the idle mixture seem rich and nonadjustable. The fuel for idle mixture screw is from the same well that feeds the progression holes, and both the progression holes and idle mixture screw fuel supply are metered by the idle fuel jet.

That is perfect..... better than I have seen in textbooks

 

[Mike O'D]

Thanks for the information guys. Everything is a clear as mud now. If manifold vacuum was the right way to go, why wouldn't the factory have used it?

 

[Shannon Boal]

Thanks for the information guys. Everything is a clear as mud now. If manifold vacuum was the right way to go, why wouldn't the factory have used it?

Good question. Some first class design engineering went into these cars. Most car stuff is better than it was,but not the gas. It used to be, that engines ran better with a little more than stock timing. Aggressively recurved distributors (heavy weights, light springs) worked wonders. If we still had super premium leaded fuel, they still would. Now, the only question I have is if the timing controls can help with idle/creeping traffic high coolant temps. Overall, IMHO, ported vacuum runs better.

 

[260Alpine]

View attachment 25348 GM and Ford during emission days used a coolant vacuum switch that changed from manifold to ported. They used manifold for when the engine was cold and switched to ported when warmed up. Seems backwards to me but helped with emissions .

 

[Mike O'D]

Good information, thanks guys.

 

[Mike O'D]

Finally got a chance to try manifold vacuum - Weber carb with Pertronix distributor. Much better idle and less/no lag on acceleration after downshift.

 

[puff4]

Finally got a chance to try manifold vacuum - Weber carb with Pertronix distributor. Much better idle and less/no lag on acceleration after downshift.

Great news! How did you plumb it?