AJ's guide to Transfer Port Synchronization

[AJ/FormS]

Transfer-Port sync; 1)Make sure the fuel level is on the money.2)With the Curb-idle screw,set the t-port exposure under the butterflies,to about square to rectangular,or .025/.030 high. 3)Set the idle-speed with bypass-air,and idle-timing.4)Limit your power-timing to eliminate detonation 5)Bring in the mechanical advance at a rate that the engine accepts and likes.(don't force it too fast).6)Vacuum advance;Try to bring it in as fast and hard as she will accept it.If it pings under light acceleration,you may have; too much idle-timing,too fast a mechanical curve,or too fast a V-can rate.Cans are adjustable 7)Typical street-cammed SBMs may run 12to18*initial,and 32to36*power, and up to60* cruise. 8)You may have to re-index(phase)your rotor to ensure the spark goes to the intended cylinder. 9)Fresh 87E10 is clear,or very nearly so.

 

[AJ/FormS]

i did not invent this procedure, nor copy it. it is just a recap of what works.

 

[AJ/FormS]

i did not invent this procedure, nor copy it. it is just a recap of what works.

In #3 above, I said to set the idle speed with timing and or idle air bypass.
But it seems Ineglected to mention vacuum leaks.
Idle air bypass is introducing a controlled air leak.Big cams want more air to achieve a decent idle speed, and the common fix is to increase the curb idle speed. But of course this upsets the sync you so carefully just set. So what to do? Well firstly;the PCV system needs to be functioning as it is the primary idle air bypass, as the carb is continuously pulling air thru that little valve. Then if the idle speed is not fast enough, you have to add air elsewhere until your engine is happy. The usual places are secondary cracking, or holes drilled thru the primary throttle valves. In my experience, introducing dry air past the secondary throttle valves, introduces its own problems, in that the rearmost cylinders run lean and the engine runs rough.
So I much prefer to introduce the bypass air near to where the low-speed circuit gets it's air.
If you've ever worked on small engines, and especially outboard engines, you may have seen small holes drilled thru the throttle valve(s). These set the minimum idle speed when the engine is fully idled down and fully retarded.Often there is no curb-idle screw.
Well the same thing can work for us hot-rodders. I drill my holes on the the T-port side, about half way between the shaft and the bore-wall. I usually figure out how much air the engine wants by introducing a leak into the PCV system first. Then recalculate that orifice size to the equivalent of two holes; one for each valve. I usually drill a little smaller than the equivalency, in case things change. On some bigger cammed engines, I drill two small holes in each valve cuz the smaller holes are easier to fine-tune.

Now, the above assumes that air is not getting into the engine from any other source besides the PCV and the primary throttle valves! It assumes that you have previously proved that there are no vacuum leaks of any kind, anywhere; including the power-brake booster,any vacuum device, and the various gaskets.
When the engine gets air from somewhere else, one of two things can happen; 1) the idle speed cannot be slowed down enough, or 2) it runs rough no matter what you do.
If the air leak is variable in nature, it can drive you crazy.
The brake booster is a special case. It may have just a tiny leak at idle when manifold vacuum might be 10 or 11 inches, and so you can easily compensate for it. But as the rpm increases, and manifold vacuum begins to increase to say 21 at 2100, at cruising speed, now the leak may be passing a lot more air, and so the engine goes lean, and you get a big problem.
Or ,again with the booster; perhaps the diaphragm is ok, but the differential valve leaks whenever you step on the brake. So now, say you are stopped, in N/P, and you step on the brake,and again since you are only pulling 10/11 inches, you notice the slight rpm drop, but maybe it doesn't raise a flag for you. So then, you put it into gear, the TC puts a load on the engine, and maybe the engine runs rough which you expect cuz well it has a cam. But maybe the engine stalls.So now the reaction is to crank up the curb idle until it stays running. Suddenly your idle speed is 800 in N/P, and 550 in gear and and it is idling very rough, you can't figure out what's going on. But you take your foot off the brake and motor away, with no further problems. Until you come to a stop again
For me, testing the booster has become routine, so I missed mentioning this in line #3.

 

[PinkGT]

In #3 above, I said to set the idle speed with timing and or idle air bypass.
But it seems Ineglected to mention vacuum leaks.
Idle air bypass is introducing a controlled air leak.Big cams want more air to achieve a decent idle speed, and the common fix is to increase the curb idle speed. But of course this upsets the sync you so carefully just set. So what to do? Well firstly;the PCV system needs to be functioning as it is the primary idle air bypass, as the carb is continuously pulling air thru that little valve. Then if the idle speed is not fast enough, you have to add air elsewhere until your engine is happy. The usual places are secondary cracking, or holes drilled thru the primary throttle valves. In my experience, introducing dry air past the secondary throttle valves, introduces its own problems, in that the rearmost cylinders run lean and the engine runs rough.
So I much prefer to introduce the bypass air near to where the low-speed circuit gets it's air.
If you've ever worked on small engines, and especially outboard engines, you may have seen small holes drilled thru the throttle valve(s). These set the minimum idle speed when the engine is fully idled down and fully retarded.Often there is no curb-idle screw.
Well the same thing can work for us hot-rodders. I drill my holes on the the T-port side, about half way between the shaft and the bore-wall. I usually figure out how much air the engine wants by introducing a leak into the PCV system first. Then recalculate that orifice size to the equivalent of two holes; one for each valve. I usually drill a little smaller than the equivalency, in case things change. On some bigger cammed engines, I drill two small holes in each valve cuz the smaller holes are easier to fine-tune.

Now, the above assumes that air is not getting into the engine from any other source besides the PCV and the primary throttle valves! It assumes that you have previously proved that there are no vacuum leaks of any kind, anywhere; including the power-brake booster,any vacuum device, and the various gaskets.
When the engine gets air from somewhere else, one of two things can happen; 1) the idle speed cannot be slowed down enough, or 2) it runs rough no matter what you do.
If the air leak is variable in nature, it can drive you crazy.
The brake booster is a special case. It may have just a tiny leak at idle when manifold vacuum might be 10 or 11 inches, and so you can easily compensate for it. But as the rpm increases, and manifold vacuum begins to increase to say 21 at 2100, at cruising speed, now the leak may be passing a lot more air, and so the engine goes lean, and you get a big problem.
Or ,again with the booster; perhaps the diaphragm is ok, but the differential valve leaks whenever you step on the brake. So now, say you are stopped, in N/P, and you step on the brake,and again since you are only pulling 10/11 inches, you notice the slight rpm drop, but maybe it doesn't raise a flag for you. So then, you put it into gear, the TC puts a load on the engine, and maybe the engine runs rough which you expect cuz well it has a cam. But maybe the engine stalls.So now the reaction is to crank up the curb idle until it stays running. Suddenly your idle speed is 800 in N/P, and 550 in gear and and it is idling very rough, you can't figure out what's going on. But you take your foot off the brake and motor away, with no further problems. Until you come to a stop again
For me, testing the booster has become routine, so I missed mentioning this in line #3.

How do I test the brake booster for a vacuum leak? I'm suspicious of mine in general. Thanks

 

[AJ/FormS]

The booster chamber is supposed to be sealed, except where the big vacuum line enters it. Here the line is attached to a fitting with a check valve in it.
So,you could remove the valve and then Tee into that line, and install a vacuum gauge.Next,start her up, rev her up a bit to say 15 inches of vacuum, and then clamp the line completely shut. Let the engine return to idle and shut her off. Ideally, the vacuum in the reservoir should remain there forever. Practically, I would guess, a 7 minute test with little to no pressure loss would be fine.
Now, go step on the brake with moderate pressure, and hold it there. The vacuum should fall to a slightly lower level, but then remain steady;as steady as your foot remains steady.

Alternatively'
put a tach on the the engine.If you have a lumpy cam, rev it up until the idle speed is reasonably steady, say 15 inches of vacuum.Then, clamp the booster line completely shut.The engine rpm should not change at all. Then release the clamp, and again the rpm should not vary at all.Well, you might get a tiny dip and then back to where it was.
Next remove the clamp, wait for the vacuum to stabilize and step on the brake, and hold. The engine might drop up to 30 rpm or so and then jump right back up.Release the pedal, same result.
And finally
Charge the booster;( start the engine,bring the vacuum up to 15 inches), clamp the line completely shut, and shut off the engine. Now begin pumping the brake pedal.Notice on the first pump, you can feel the assist. By the third pump, the pedal is getting harder, and not traveling as far. By about the fifth pump the assist is probably gone, you have exhausted the vacuum chamber.
And one more. Put everything back to normal. With the booster exhausted, depress the pedal with moderate pressure and start up the engine. As the vacuum comes up, you should feel the pedal fall away under your foot; that is normal.

 

[PinkGT]

The booster chamber is supposed to be sealed, except where the big vacuum line enters it. Here the line is attached to a fitting with a check valve in it.
So,you could remove the valve and then Tee into that line, and install a vacuum gauge.Next,start her up, rev her up a bit to say 15 inches of vacuum, and then clamp the line completely shut. Let the engine return to idle and shut her off. Ideally, the vacuum in the reservoir should remain there forever. Practically, I would guess, a 7 minute test with little to no pressure loss would be fine.
Now, go step on the brake with moderate pressure, and hold it there. The vacuum should fall to a slightly lower level, but then remain steady;as steady as your foot remains steady.

Alternatively'
put a tach on the the engine.If you have a lumpy cam, rev it up until the idle speed is reasonably steady, say 15 inches of vacuum.Then, clamp the booster line completely shut.The engine rpm should not change at all. Then release the clamp, and again the rpm should not vary at all.Well, you might get a tiny dip and then back to where it was.
Next remove the clamp, wait for the vacuum to stabilize and step on the brake, and hold. The engine might drop up to 30 rpm or so and then jump right back up.Release the pedal, same result.
And finally
Charge the booster;( start the engine,bring the vacuum up to 15 inches), clamp the line completely shut, and shut off the engine. Now begin pumping the brake pedal.Notice on the first pump, you can feel the assist. By the third pump, the pedal is getting harder, and not traveling as far. By about the fifth pump the assist is probably gone, you have exhausted the vacuum chamber.
And one more. Put everything back to normal. With the booster exhausted, depress the pedal with moderate pressure and start up the engine. As the vacuum comes up, you should feel the pedal fall away under your foot; that is normal.

What does it mean if I get a small idle drop when I step on the brakes at idle? There's a corresponding drop in voltage showing on the ammeter. I might also be having a minor electrical issue, I'm noticing some slooooow flasher blinking and weird behaviour with the ammeter and the stereo together.

 

[AJ/FormS]

Please start a new thread on it, being sure to include what you're working on.

 

[AJ/FormS]

Correction;
In post one I said the T-port exposure might be .025 to .030 when the slot is square to rectangular. It may actually be as much as .040 on the rectangular.

 

[Tooljunkie]

Had this problem with my neighbour’s holley. He’s very picky to how things are done.
Drove car over and it was running horrible. Kept trying to get idle up by adjusting idle stop screw and
Mixture screws. I tried to get him to pull carb but he refused. I mean flat out refused. So i was no help to him.

Until that day, i had nothing to do with holleys.

He loaded car and hauled it 80 miles to a speed shop that dialed it in.

As the story goes,the transfer ports can and will pull a ridiculous amount of fuel.
No amount of timing or idle mixture adjustment will work unless you get the transfer ports set to establish a baseline.

I am thankful for this site and threads just like this for the education im getting.