40dcoe_18 Weber Tuning

[steveww]

BTW: Where did you attach the O2/Lamda sensor?

[type26owner]

Hi Steve,
Welded on a threaded bung a few inches below the expansion chamber of the stock exhaust system a few years back for a regular unheated sensor type so it would get hot enough to work at idle. It did but that type sensor proved to be of little help for tuning purposes. The Wide Band O2 type sensor is heated though and can be mounted virtually anywhere. In fact, it can be overheated so mouning it aways downstream from the engine is advised. For $50 dollars Innovate sells a bracket to mount the sensor temporarily into the exhaust system tailpipe. I bought one but it's a bit on the bigside to use in the Elan's tailpipe without seriously obstructing the flow of exhaust.
Regards,
Keith

[type26owner]

Geez! Turns out the idle jets I possibly need are no longer available to fill the gap between a 45F8 and the fattest 40 series. They are available in the 40 F-numbers sizes (F2, F11 & F13) with identical sized well and air bleed hole diameters. Luckily a set of reamers and pin gauges are modestly priced and I can modify those to get the desired sizes as 45's.

If these leaner idle jets don't affect the mains mixture too much my selection of main jets to get best fuel economy is 95's. Can tell already it's helping by the reduced rate of comsumption the fuel gauge is indicating.

Measured the pressure output of the mechanical fuel pump the other day at 5.5 psi. Weber recommends 3.5 psi as the maximum. Installed an Italian brand combination fuel pressure regulator and filter called a Filter King which I purchased from Pierce Manifolds and set it at 2.5 psi. Don't know if this is really necessary. Haven't ever had a filter installed though and don't want to continue to push my luck.
Keith
p.s. Here's a link to the only authentic appearing Weber document I've been able to find which gives a value of 3.5 psi for the maximum fuel pressure. See Section 2G.
<a href='http://www.francisscott.com/~bmw2002/webertrouble.pdf' target='_blank'>http://www.francisscott.com/~bmw2002/webertrouble.pdf</a>

[rgh0]

Keith

With regards your discovery of the need to close up the progression hole to get the light load mixture right. I was looking back through the notes from the guy who set up the carbs on the dyno on my Elan engine many years ago and he had noted after he had set the idle and main jets to get the mixtures right at the extremes of idle and full load. "Peened over progression hole in each carb throat to correct cruise mixture".

Sounds like its a well understood need by those who do it properly. Your piece of wire trick sounds a lot better than peening the hole closed a little, at least it is more easily reversible.

Rohan

[type26owner]

Rohan,
The need to reduce the fuel mixture flow from the third hole was not detectable by me from just driving the car. Without the AFM I'd never have known there was a problem. The fellow that tuned your engine has my highest respect if he did the diagnostics by other means.

Bending up the wires is a bit of fuss and bother intially until you've determined the correct shape and size. Took about six attempts to get it right the first time. After that I could clone them in about sixty seconds apiece.

Opened up the package of reamers last night and was aghast at how small and delicate they are. This could be a very painful experience. Anyone used these type reamers before? Might have to resort to try phoning down any supplies of old stock idle jets afterall.
Regards,
Keith

[DrEntropy]

Opened up the package of reamers last night and was aghast at how small and delicate they are. This could be a very painful experience.

Need a good pin vise (my choice: Snap-On YA-806), a set of steady hands and a ton of patience. Short-shank the ream so only the length you need to do the job protrudes, and do it in ~tiny~ increments. A small soft jaw vise is your friend (I like the PanaVise with the vacuum base)!

Micro Tools, or Ed Romney should have 'em: Google camera repair tools.

That assembly of lovely stainless you showed me leads me to believe you will study it well before you start cutting. It's watchmakers' scale stuff, but still: the metallurgy is all the same.

Good luck(!) and report back?

[type26owner]

Dr E-
Here's a link to what this reamer looks like but they call it Broaches, English Pattern. It's pictured at the top of the page. Compared to the depicted one, mine is 1/3 the overall length and 10 times smaller in diameter. The pin vise was included. Trouble is when I spin this reamer the sharp end runs out by a couple of millimeters. :angry:
<a href='http://shorinternational.com/broaches.htm' target='_blank'>http://shorinternational.com/broaches.htm</a>

Luckily a #77 drill is only 7 microns bigger in diameter the desired size. So instead of enlarging the hole by the ideal 50 microns it might have to actually be 57. Hey, Webers are a solution set of compromises anyway.
Regards,
Keith

[DrEntropy]

a couple millimeters?!? Yikes... Can you send it back?

Hey, Webers are a solution set of compromises anyway.

Amen, brother.

[type26owner]

Dr E-

a couple millimeters?!? Yikes... Can you send it back?

Yep but I'm not really concerned about the cost. Just the precision of the finished holes. Webers are a design solution of compromises but the required precision to be held so they respond well to tuning is very high. Fudging in the holes with an oversize drill might work okay but it's going to bug me to no end. Ordered from Drill Technology some carbide stubby drills which are 0.450mm +0.000/-0.007 in diameter at $5 apiece. I'll have them for the following weekend.

Hopefully my rollbar hoops are bent up today so I've got a Lotus related assembly task to keep me busy this weekend.
Regards,
Keith

[steveww]

If you really want the engine to run sweet at all rpm and all loads etc. then why not just fit throttle bodies and an engine management system, say DTA?

Just think of the fun you could have endlessly tweeking the map

I guess it boils down to why you are doing this? Do you want a perfectly running engine or do you just enjoy tinkering with carbs?

[type26owner]

If you really want the engine to run sweet at all rpm and all loads etc. then why not just fit throttle bodies and an engine management system, say DTA?

Why would I bother doing that now? I've already achieved the same result by correcting the faults of the Weber carbies.
Regards,
Keith

[DrEntropy]

And additionally passed on the knowledge/experience/equipment to allow the rest of us to duplicate the task, as well.

BTW Keith: did you bother to affix a TPS (throttle position sensor) of some description? I've been giving that some thought of late. The set of Vebbers on th' Alfa are a mis-matched 40DCOE pair I had lyin' about, and that O2 sensor is burnin' a hole in the back of me pea brane... with that and emperical data abput th' physical bits, I know it'd pe possible to "dial in" even those into fair compliance.

[type26owner]

Dr E-
Weber brand Throttle Position Sensor p/n 99902.660 $93.34
Still awaiting the electrical cable connector to arrive from Pierce Manifolds. This fits all Weber DCOE types and the Dellorto. Installation takes about two minutes flat. I bought the anti-clockwise version which fits on the #1 cylinder end. The clockwise direction version is available too but I don't have a part number for that one.

Still investigating buying and installing a rpm sensor to mount onto the Elan's driveshaft which can output a 0-5v signal to one of the recording channels of the AFM. Going to have to invent my own sensor system to indicate the gear selection on the Hewland Mk5 on the 41.

Keep in mind the general tuning limitation of the AFM. Since it has only one sensor it measures the averaged values from four separate cylinders. If one cylinder or throat of a carb is seriously out of kilter from the rest it can be useless as a diagnostic tool. You'll then need something like an array of thermocouples with an EGT meter to have single cylinder diagnostic capability.

Don't think I've left out an necessary details so others can't replicate the process. If I have just ask. Just don't wait to long though cause I'm at that age my brain is full all the time and there's no more room.
Regards,
Keith
p.s Picked up my rollbar bits today! Yeah!

[type26owner]

Found recently that properly tuned Webers are a good way to identify having purchased sour gasoline. Can now tell within the first mile when it's a problem by the quite familiar bog, popping out the exhaust and the induction coughing. This has happened to me twice in the last month. First time it happened it caused me to take a different direction in my tuning procedure which left me totally mystified when it could not be repeated. It happened again to me last week while I was not making any changes this time. My local Chevron dealer has now really peeved me off. :angry: Only way I could have identified this problem before the Weber tweaks was maybe by the much more foul smelling exhaust fumes. Would-be tuners be wary.
Keith