Video: Manifold and Advance Vacuum

[randy]

3phase,

Have you given any thought as to why the advance vacuum has that occaisional flutter?

[3Phase]

All these differences in advance curves and vacuum units leads me to another thought; all the parts swapping that sometimes goes on could cause subtle changes in timing that may be some of the tuning issues that crop up.

[...]

But with the 'frankenbike' history that many of these have, that will be tough to do...

That was what I was thinking.

It's not difficult to test and verify the advance. In theory you can set up a vacuum pot straight off of eBay to match a specific year/model. Advance is supposed to be checked when the timing is set but now you can fix it without buying another vacuum pot if something is worng.

3phase,

Have you given any thought as to why the advance vacuum has that occaisional flutter?

Manifold vacuum remained low while the advance signal went high, began to flutter, then dropped closer to manifold pressure at the Off -> Neutral -> Accelerate throttle transition: part-throttle lean -> open-throttle normal.

The edge cutout on the throttle plate is over/just past the vacuum advance port, amplifying the advance signal while manifold vacuum is low. Apparently the restrictor in the #2 carburetor nipple isn't all that restrictive and the gauge fluttered because I was slightly lugging the engine instead of downshifting.

The manifold gauge didn't flutter because the line to the gauge was over-damped.

The line to the vacuum gauge was not damped at all except for the built-in restrictor in the carburetor so that is what the advance pot was 'seeing'.

[b.walker5]

JAT. When you get sick of risking life and limb, and video camera to film the vac advance, consider ditching it completely (and eliminate the dodgy pick up wires) and fit one of these http://www.elektronik-sachse.de/ZDG3/frset_zdg_en.htm

click on Model Selection on the left

Kinda reminiscent of the old Boyer Bransden system often fitted to old brit bikes, and fairly pricey too, but not a bad looking thing for all that. Read the fitting instructions for more info.

[3Phase]

Thanks, Brian, but after all the years of more and more solid-state devices, digital computers, controllers and equipment I find that I prefer the simple, old-fashioned, analog parts.

They make better videos, too. Focus a camera on the XJ's TCI then go for a ride and nothing would appear to be happening.

Boring!

[WMarshy]

JAT. When you get sick of risking life and limb, and video camera to film the vac advance, consider ditching it completely (and eliminate the dodgy pick up wires) and fit one of these http://www.elektronik-sachse.de/ZDG3/frset_zdg_en.htm

click on Model Selection on the left

Kinda reminiscent of the old Boyer Bransden system often fitted to old brit bikes, and fairly pricey too, but not a bad looking thing for all that. Read the fitting instructions for more info.

Are you familiar with the Fuel Injection Mod that is on the site? Do you have any idea if this digital ignition is compatible with the Mega/Micro Squirt controller? I guess me real question would be, would it make sense to use the above digital ignition control you listed with an ECU like the mega squirt? This technology peaks my interest and Im still learning about it all...

IIRC the MS controller is responsible for controling spark and timing advance. Ultimately, you have to use a GM style OBD II sensor and make a timing sensor wheel for timing pickup. Im just wondering if the pickup from the digital controller would be an easier/more accurate solution to the OBD sensor and home made pickup wheel.
My guess would be the you cant use them both and it would create a discrepintcy between the two controllers as MS controller is for ignition and fuel but, the elektronik digital ignition control only...

[randy]

Looks to be a bit short on advance for the XS. My charts show 52 degrees total @ 5400 rpm. This one max's out at 39 degrees. Also, eliminating the vacuum canister will affect driveability and steady-cruise economy.

Fitting instructions digital ignition ZDG3H for Yamaha XS1100
1. Function - 2. Fitting - 3. Electrical connection - 4. Adjustment - 5. General
The digital ignition ZDG3 replaces the magnetic pickups and the vacuum advance unit.Function: per revolution of the crankshaft starting from TDC, the momentary peripheral speed is determined and by this means, the time up to ignition is calculated. Because the peripheral speed varies substantially during acceleration, this long measurement is selected in order to determine a relatively exact measurement.
The following computation of ignition timing is divided into 4 ranges 1. 0-400 rpm Starting range, ignition always at TDC
2. 400-1000 rpm Idling range, 2-8° advanced ignition, depending upon curve selection
3. 1000-6200 rpm Partial load range, the spark advance adjustment occurs here.
4. 6200-10000 rpm Maximum load range, constant 32°-39° advanced ignition, depending on curve selection.

[crazy steve]

...In theory you can set up a vacuum pot straight off of eBay to match a specific year/model. Advance is supposed to be checked when the timing is set but now you can fix it without buying another vacuum pot if something is wrong....

Well.... maybe. If Yamaha used the same spring in all the advance units, yes, you could recalibrate any unit to any bike. But if you ran into a different spring rate, then it may be a bit tougher.

The thing I'm still wondering about is why the factory used that 'hybrid' vacuum source. I understand that they wanted no vacuum advance at idle, but why? It would be interesting to try a straight manifold vacuum source if the idle speed could be got down with the vacuum advance working. But maybe there's an issue with velocity through the carb or an inconsistant vacuum signal with the probably-needed more 'closed' throttle plates. Just thinking out loud...

The main thing I see is with the lag in vacuum advance falling off during the transition between 'closed' and 'open' throttle positions, you can have too much timing (if only momentarily) at certain points. I know my bike would knock for an instant at some rpms if I wacked the throttle open, so this would seem to explain that.

But every ignition system (unless it's fully electronic with knock sensors, etc), is a mess of compromises, so it is what it is I guess...

'78E original owner

[b.walker5]

Looks to be a bit short on advance for the XS. My charts show 52 degrees total @ 5400 rpm. This one max's out at 39 degrees. Also, eliminating the vacuum canister will affect driveability and steady-cruise economy.

Fitting instructions digital ignition ZDG3H for Yamaha XS1100
1. Function - 2. Fitting - 3. Electrical connection - 4. Adjustment - 5. General
The digital ignition ZDG3 replaces the magnetic pickups and the vacuum advance unit.Function: per revolution of the crankshaft starting from TDC, the momentary peripheral speed is determined and by this means, the time up to ignition is calculated. Because the peripheral speed varies substantially during acceleration, this long measurement is selected in order to determine a relatively exact measurement.
The following computation of ignition timing is divided into 4 ranges 1. 0-400 rpm Starting range, ignition always at TDC
2. 400-1000 rpm Idling range, 2-8° advanced ignition, depending upon curve selection
3. 1000-6200 rpm Partial load range, the spark advance adjustment occurs here.
4. 6200-10000 rpm Maximum load range, constant 32°-39° advanced ignition, depending on curve selection.

I dont pretend to know much about these units but I would think that a lot of research has gone into it, the Germans tend to be pretty thorough, and they're obvioulsy comfortable with the results. It's a pity theyre so expensive as it would almost be worth buying one to compare results with. Personally I dont think that eliminating the vac advance would be such a bad thing, if the digital advance is programmed properly to compensate for it. One less thing to go wrong.

[3Phase]

Well.... maybe. If Yamaha used the same spring in all the advance units, yes, you could recalibrate any unit to any bike. But if you ran into a different spring rate, then it may be a bit tougher.

That's why you'd have to check the vacuum pot. If you have X advance at Y vacuum then Robert is your father's brother.

The thing I'm still wondering about is why the factory used that 'hybrid' vacuum source.

I still don't know where you're getting 'hybrid' from. Aside from the restrictor orifice that eliminates most of the one-cylinder pulsing in the vacuum signal the XS11 vacuum advance circuit looks like the vacuum advance circuits on my Edelbrocks, Rochesters, Carters and, except the ones used with Ford Load-O-Matic distributors, assorted flavors of Holleys.

I understand that they wanted no vacuum advance at idle, but why?

You don't work for Toyota, do you? There is no advance vacuum at idle and very little during overrun (deceleration) because no one needs to make power when the throttle is closed.

It would be interesting to try a straight manifold vacuum source ...

That's been done. Stick a restrictor like an old idle jet in the vacuum advance line and run the advance line off the manifold boot. It works but it works backwards at some critical times: there is ignition advance at idle, full advance on overrun, no advance at part-throttle lean.

The main thing I see is with the lag in vacuum advance falling off during the transition between 'closed' and 'open' throttle positions,

There's a slight lag in the advance vacuum signal drop during the open -> close throttle transition but not close -> open.

Watch the video.

Advance vacuum did not fall off at the close -> open transition because there was little or no advance vacuum at closed throttle. The vacuum advance signal rose and fluttered as the throttle plate opened and swept the advance port then, more or less, equalized with manifold vacuum.

When I backed off/closed the throttle, manifold vacuum rose and advance vacuum dropped.

you can have too much timing (if only momentarily) at certain points. I know my bike would knock for an instant at some rpms if I wacked the throttle open, so this would seem to explain that.

It shouldn't knock unless you lug the engine. You may have something else going on like a lean fuel/air mixture, the static ignition timing is off or the mechanical advance is sticking and not returning.

Again from the video:

From about 35 to 38 seconds, advance vacuum started to climb/flutter and manifold vacuum dropped as I pulled away part-throttle from a stop sign.

When I rolled the throttle WFO (~12 to 18 seconds into the video and again at ~39 to 45 seconds as I left the stop sign), advance vacuum was about in the middle of the advance range and it dropped when manifold vacuum dropped. There was very little vacuum at WFO until both advance and manifold vacuum began to climb back up as the engine picked up speed.

Personally I dont think that eliminating the vac advance would be such a bad thing, if the digital advance is programmed properly to compensate for it. One less thing to go wrong.

A preset RPM/timing curve can only emulate a mechanical advance but it wouldn't be too bad. Adding throttle position and vacuum sensors along with multiple ignition timing maps could help emulate a vacuum advance. Then you just have to trust the six-year-old boy making microchips in China instead of the eighteen-year-old girl in Japan making vacuum advance pots.

I think the XJ uses a vacuum sensor and two ignition timing maps but no throttle position sensor so it's no fun making a video of the XJ, either. I guess you could watch the engine spin but nothing else would happen that you could see unless you hooked up a timing light.

[petejw]

Hey Scott,

you nailed that.

[crazy steve]

I call it a 'hybrid' design because of the odd port location that cuts off vacuum at closed throttle/idle conditions. Now admittedly, when I got into ignition systems the deepest was 'back in the day', and it was usually with points or later a MSD 6A add-on. These were hopped-up street V-8s, so with an eye to fuel economy I ran vacuum advance units; I learned my lesson about mileage and straight mechanical advance fairly early. But virtually all of those ignitions had some vacuum advance at idle; that's why you needed to disconnect the vacuum to set 'base' timing. Connecting the vacuum would add about 4-5 degrees more timing at idle. It was all about getting as much timing in as fast as you could without having pre-ignition, while accounting for load. But these were all non-emission motors; I know that when emission controls came in big, a lot of the 'conventional' knowledge went out the window.

As far as not 'needing' advance at idle, it's really not about power; it's more about efficiency. More advance = longer burn time before TDC, so as long as peak combustion pressure doesn't arrive before TDC, more fuel gets burned. I know one car I had (the one that finally cured me of no vacuum advance on a street car; single digit mileage numbers even at the 39.9 for Chevron white pump got expensive) loaded up at idle less after the conversion. As far as 'overrunning', I don't see why timing would make any difference here; there's very little fuel present and no load, so knocking won't be an issue. I suspect this may be more of an emissions thing (trying to reduce NOX).

I did re-watch the video (several times); I didn't see what I thought I saw.... so basically, the vacuum advance is operating as a 'manifold' type.

As to my bike's occasional knocking, it's done it since new; I took it back to the dealer and was assured it was 'normal'. I checked the timing myself (not trusting the dealer), and it was spot-on. I'll look at that closer when I get it running again...

As to 'fully electronic' ignitions, I'm not a huge fan of the 'simplified' ones. They can work extremely well if you have enough data inputs, but on a bike that would be a pretty big amount of 'stuff'. Harley uses a system very similar to the XJ; it has two curves, and a vacuum switch toggles back and forth between them depending on manifold vacuum. Works fairly good on a stock motor, but start altering things and it struggles. There's aftermarket units that elaborate on this (up to fully programmable units; big $$), but a big-power motor can still be a bear to get right.

'78E original owner

[3Phase]

I put the vacuum advance from my '79F on my 80G and rode to Santa Cruz and back, a little over six-hundred miles.

The bike runs better and it has more power with the '79F vacuum advance. It gets better gas mileage too when I'm not going uphill pushing the barn door/fairing into a 35/40mph headwind.