Maximum Vacuum at Idle Engine Tuning

[CBDZ]

I am trying to improve my idle. I have been using this article as a guide...

http://classicinlines.com/vacuum.asp

I seem to be getting only 5" -6" hg. of vacuum. So, I am trying to determine if this a true measure of vacuum, or am I missing something.

First question: How much vacuum should I expect?

Second question: The cam is a Engel 110. Is the over lap of this cam such that I won't ever get a high vacuum.

Third question: Where should i be referancing the vacuum signal? I am running German FI plenum. Currently I pull signal from the side of the plenum. Should I change the referance location to just below the throttle plate?

Another demon that i am chasing at idle is a stinky exhaust. I previusly had a fairly good idle, but it seemed very rich and stinky. I really want to clean up the stink.

[Marc]

Setting ignition timing for peak manifold vacuum will nearly always result in excessive advance, which wreaks havoc on your rings and piston ring lands. In addition it typically causes excess HC emissions (why they started running idle-retard back in the `70s, before modern engine management systems existed to handle that issue - perhaps that's why your eyes are watering).
It's a technique that may be fine for tuning a Massey-Ferguson back on the farm, but IMO shouldn't be used elsewhere. Backing the timing down enough to reduce the vacuum reading by ~1 inch or so MAY get it in the right ballpark, but it's no substitute for knowing what the actual setting is.

The vacuum reading should be essentially the same anywhere downstream of the throttle plate.

Note that valve lash will affect your effective duration - looser adjustment reduces overlap which may be enough to squeak by an emissions test.

Are you certain that the cam timing is correct? The W-110's not that radical of a cam, I would suspect with readings that low (assuming vacuum leaks have been ruled out) that the cam may be installed a tooth off. This can be checked through the oil pump hole (if it's off, of course, it'll take a full teardown to remedy unless there's an adjustable cam gear with sufficient range to remedy it - unlikely). You can't see the timing marks on the gears but the oil pump drive slot points right at one of them on the cam gear (assuming the gear's bolted on correctly - but if it weren't it'd be a full 120° off and the engine wouldn't run at all). And on the crank gear the timing marks are 180° across from the Woodruff key slot.
When the crank's positioned at TDC #1/3, the Woodruff keys are at 9:00; rotate the crank 90° clockwise from there, to where the keys are at 12:00 - this puts the crankshaft gear's timing marks at 6:00 and the slot in the cam should be exactly vertical.

[Piledriver]

Set your idle timing to some sane value around 10 BTDC and use the idle VE feature to essentially adjust for best lean idle as you would on a carb. (OK, you have MS1, and have to set it in the VE table, or AFR table (can't be much help there have never run MS1)

Set it for fixed timing and idle controls off (or set all the cells in the idle area for same value with MS1) while doing this, you'll be able to easily adjust for peak RPM.
Not sure what you have for idle speed control, you will want your IAC or stepper set to some fixed value.

If your eyes are watering you are doing it wrong, most motors idle best around 13:1ish, some need a little more fuel, some less.

If you have really low dynamic compression or no squish it is likely to need more fuel to idle.
Injector timing matters greatly at idle too,
( if you had MS2e/MS3 you'd want to make sure you enable semi-sequential at least so the timing is at least consistent)

[CBDZ]

Thanks for the tips.

I had a really nice idle, but it just seemed to be really rich, even though the AFR was on the lean side (Per O2 Sensor). Should I ignore O2 at idle?

I am starting to question the O2 reading. The sensor is placed in the collector of a Tri-Mill Buggy Header.

[Max Welton]

What is your AFR reading at idle? You only said "on the lean side". At one point I was advised by a carb guy that 12.5 would give me a nice idle but I found 13.5 to be more stable and actually cooler (CHT-wise) than 12.5. Of course, your engine may tell you otherwise.

Max

[Piledriver]

Thanks for the tips.

I had a really nice idle, but it just seemed to be really rich, even though the AFR was on the lean side (Per O2 Sensor). Should I ignore O2 at idle?

I am starting to question the O2 reading. The sensor is placed in the collector of a Tri-Mill Buggy Header.

yes, see where best lean idle ends up...

If it idles best at 17:1 i'd look hard at the wbo2 calibration.