Tuning the webers…. advice/experience requested..

Hi Ollie,

I hadn't heard of fuel density as an issue with this before? Interesting.

Do you have alcohol blended into your gas there?

Have you tried this with your Espada as well yet?

Bob S.

 

Filled the tank yesterday afternoon. Drove 200 miles exactly (322km), filled 75l fuel.

That yields 23l/100km, or 10MPG.

Today I want to adjust the float level first, taking into account two factors.

1. If fuel is less dense, that would call for a lower float level to take into account the lesser buoyancy, meaning a *larger* float level measurement (putting the float lower in the bowl when it closes the needle valve and the fuel level lower). I.e. from 50 to 51.5.

2. If Tony "lowered the float levels 1.5mm (0.060") and got such profoundly better drivability", that would indicate the same, if I understood him correctly ("lowered" meaning the floats are further from the carb cover, further down in the fuel bowl, as 1. above), which also gives 50 + 1.5 = 51.5mm.

Both are opposite from what DRW46 suggested, but I supposed if it runs worse I'll have to do it all over anyway and can try 48mm float level instead. At least I will have learned something.

Roberto - the idle on my car is smooth and even, as is acceleration, even without the vacuum retard. We didn't go over the whole advance curve on the dizzy, just checked at a few points in the RPM range to make sure it was actually advancing. Looking in the service manual, the US/EU specs are almost identical, with only 1degree difference (and even the specs there are given as "roughly"). Not sure how much difference that would make, when mostly cruising around at < 3000 rpms...

 

I don't know how your distributor is currently setup but mine was less aggressive than the european configuration which can be found for a Bora here:

http://www.thecarnut.com/Manuals/MUM_BoraAm117.pdf page 64

If you watch that vacuum retard in operation with the timing light as you just come off idle you can see how long it takes to unwind it's effect.

Of course my driving desires in the Bora may have been a bit different than yours in the QPIII? Ten mpg sounds bloody awful though. Was Jarle able to shed any light on that?

Bob S.

 

Page 79 here: http://www.thecarnut.com/Manuals/MUM_Quattroporte_0124-2000K-G63.pdf

shows max 15 degree advance @ 3000 rpms. Added to the 7 degree static advance at idle gives 22 degrees BTDC total at higher RPMs. (Vacuum retard disabled)

My mechanic measured 21 degrees BTDC @ 4200rpms, which fits pretty well with what the manual specifies.

I didn't get a chance this evening to reset the float levels unfortunately, hopefully sometime this week.

My driving desires are cruising, rolling hills, open highways, windy mountain roads.

Jarle was planning on measuring his timing and checking his tuning and let me know, but a blown head gasket kind of offset his plans...

The timing light I ordered came today, so I'll see what I can do sometime during the week.

 

You can go at least another 5 degrees with the curve used by the Bora engine.
I imagine the Ghibli SS motors are similar?

I'm not aware of any thing that's all that different on the 4.9 QPIII motor? But I've never owned one either.

I don't think that explains your abysmal mileage numbers though.

Are you a lead foot?

 

Something about the data listed by Quattroporte3 does not make sense. He states the manual shows 15 degrees @ 3,000 rpm, for a total of 22 degrees. I wonder if the 15 is actually "distributor' degrees (30 crankshaft degrees). If his car is only showing 21 crankshaft degrees of total timing, it is way retarded.

On our Ghibli SS #2386, the engine calls for 40 degrees (crankshaft) total timing. The Euro timing starts with 10 degrees static on the crankshaft and the US distributor starts with 0 degrees static on the crank. However, the US distributor catches up with the Euro unit by 1800 engine rpm and they are identical from that point on up to 6,000 rpm. I was able to recurve my US distributor to start at 0 crankshaft degrees static, and catch the Euro timing by 1,200 rpm (just above idle), so I now have the European timing for all driving conditions.

 

Look at the manual yourself, it's available on Ivan's website for download.

The curve shows an increase from 7 deg. BTDC @ 950rpms to 12 deg @ 1500rpms and maxes out at 15 deg @ 2200rpm, as far as I can tell. Page 2-12. It shows an approx 2-3 deg. acceptable variation at max advance.

Whether it's right or not, or even if I'm reading it right, is up for discussion. It doesn't seem like a lot of advance, I would think 30-36 deg BTDC would be more in line with a performance V8 @ 4000 rpms, but who knows. Perhaps the 15 degrees is as you say distributor degrees, spinning half the speed of the crank, meaning 30 in actuality. I can't say, maybe someone else here can.

I had a mechanic set it to 7 deg static (i.e. at idle, before any centrifugal advance sets in), he double checked it and says it's correct. A timing light won't help me here because there are no marks on the torque converter (note to anyone refurbishing their transmission - if you send in your TC for rebuilding, make sure that the timing marks are left on!). The mechanic is the go-to guy for all the classic Ferrari and other exotic owners in this area, I feel he's competent to know that the timing is set according to what the manual states. Whether the manual is right is another matter altogether.

We haven't touched the engine or pulled the dizzy off the drive shaft, and are assuming that the engine internals and timing between the crank, valves and dizzy are correct as set. The heads and valves were done about 6-7 years ago by the PO, I have no reason to doubt that they are correct, but I suppose that's always a possibility.

The long and short of it is that there aren't any other mechanics who can work on a car like this anywhere near me (try finding one who's even seen a carburetor these days), so I'm on my own, with whatever help I can get from the Ferrari guy.

By the way, any comments on float height settings in light of the other posters' comments above? Just wondering what your experience is, and basis for recommending 48mm. That would mean a higher fuel level in the float bowl, as far as I can tell.

Cheers!

 

You should time the engine and put your own marks on it otherwise you're open to error.

 

Quattroporte3: I had trouble downloading the Quattroporte manual on the website. However, I did look at the Bora manual. It plainly says that the distributor has 14 degrees of 'distributor" advance on page 61 and there is a chart showing the distributor curve in crankshaft degrees (28) on page 63.

As for the 48 mm float height, that is the factory setting for a Euro Ghibli with 42 DCNL carbs.

I think you should take everything said here into consideration, as most people are actually trying to help you solve your problems. Get a really good mechanic, remove the distributor and test it on a Sun Machine to verify the total advance and the shape of the curve. Only then will you actually know what you have. Find somebody who has experience with a Quattroporte, (I do not), and see what total timing they are running. I have worked professionally on Italian cars for 50 years and was just trying to share some of my experiences. Good luck.

 

He's got to physically time the engine and mark it first. Finding TDC should be no issue but accurately putting degree marks on with the engine assembled and in the car is more challenging. Finding out the number of teeth on that torque converter is the best place to start.

Yes those newer timing lights ARE quite useful. I used one to verify the proper operation of the distributor on my Espada after conversion to a different style rotor and installation of a pair of Pertronix units. The factory timing mark was almost impossible to see on that car as well. Some people have claimed that theirs have none. It's usually just very hard to see under all the grime and corrosion.

 

Hi DWR,

not discounting your advice, simply trying to make sense of (at times) conflicting information.

The V8 in the QP3 should be more or less identical with the one in the 5000GT (except the first two), QP1, Mexico, Indy, Bora and Khamsin. AFAIK only the Ghibli had a somewhat different engine configuration with a dry sump.

I'll definitely have a look in the Bora manual and compare specs. There's also a document floating around comparing the timing curves between US and Euro cars that's pretty useful, it's been posted here before.

Like I said before, out here on the edge of the known universe - "get a really good mechanic" isn't a simple matter! Finding one with a Sun machine is even less likely. But I'm doing what I can, and asking about things here as well to learn. (Considering the problems both Mitchell and William have both had - both in major metropolis' on both sides of the pond - in finding someone, anyone who can do proper work on a QP3, it's not hard to understand how difficult it is here. Especially when there's no culture of preservation here, everyone dumps last years model and moves on to the newest thing, it's rare to find someone who can do something other than operate a computer to read the OBD II codes and replace whatever the computer tells them is at fault).

With over 50 years working on Italian cars, you're more than welcome to come up here and work on my car, if you'd like . (jk)

On a more serious note, I know a QP3 owner who's car runs very well, and was going to check his timing and report back, but he blew a head gasket before he could check. Maybe I can find someone in the LA area when I'm back there soon who can give me a few pointers, or even knows the car, I dunno. There aren't a whole lot of these cars left anymore.

Bob, I did in fact buy a timing light recently, and I'm pretty sure it has the "reverse" function where you dial in the advance desired and it changes when the light flashes while you just keep everything at 0, instead of the opposite. I'll have to double check that. The mechanic punched a line on the pulley and a small matching mark on the engine block to allow checking from under the hood, without having to put the car up on a lift (and using two people to check and set the timing). It also displays RPM, which should be handy when doing my next round of carb/airflow tuning.

Thanks!

 

DWR46 is right, your timing is to retarded. As a rule of thumb, most hemi head engines like 42 degrees of total advance. You apprear to be running distributor degrees on the crankshaft which is giving you exactly half the timing you should have. When you set it at 42 degrees (instead of the 21 you have now) at 4200 RPM you are going to be in for a suprise in how strong it runs. It will also help drivablity by improving the just off idle throttle response (ie eliminates flat spots)

Cheers Jim

 

I mean to lower the fuel level.
So, if 50mm is the distance from say, bottom of float to underside of carb top, when the float tab is touching the needle.
Then I'd make it 51.5mm.
Not trying to lower the fuel level over original spec, but to return the fuel level to its original spec. The fuel level has effectively got higher because it is lighter, and more of it is needed to raise the floats.
The Espada using the DCOE carbs has responded exactly the same. Most important characteristic for me is the reduced fouling of plugs in stop start town driving (the stuff we all hate). I never check fuel economy in these cars as it seems a futile exercise, clean and reliable driving being my goal, but cleaner plugs indicates less fuel use.

Good luck buddy.
Let us know how you get on.
Tony

 

Reviving an old thread, I'm curious to know what other people are running as far as jetting goes.

I.e. if you have a Maserati V8 car, with 42DCNF carburetors, what are your:

1. Main jet:
2. Air jet:
3. Emulsion tube:
4. Idle jet:

To answer my own question:

1. Main jet: 135
2. Air jet: 185
3. Emulsion tube: F25
4. Idle jet: 70

The reason I'm asking is because two Maserati mechanics have independently suggested that I move to a smaller idle and main jet (60/130), and consider moving up a notch on the air jet (200). This will make the engine run leaner overall, but possibly improve power and mileage compared to current figures.

ColorTune tuning and idle appear correct at present, the engine runs smoothly throughout the rev range, but emissions measurements show that the engine is still running rich, and it's using more fuel than what others report as "normal".

Looking at the QP3 service manual, I see that Maserati specified:

1. Main jet: 135 (130 also ok for Euro spec)
2. Air jet: 155 (Euro) 180 (US)
3. Emulsion tube: F25 (Euro) F125 (US, which I believe to be a typo, Weber doesn't have an F125 emulsion tube)
4. Idle jet: 60 (Euro) 70 (US)

My floats are all set to 48mm, the mechanic who recently did the valve job and cams said that's where they should be (spec is 48mm for Euro, 50mm for US cars).

Wondering how other people have set up their carbs.

 

Looking closer at the manual (while ordering parts from Pierce), I see that Maserati lists the following:

Choke Tube
Main Jet
Air Jet
Centering Guide
Chamber
Pilot Jet
Air Pilot Jet
Pump Jet
...
Idling Adjustment Screw Hole

A few quick questions -

The choke tube I assume is the choke/venturi diameter, and the Centering guide the auxiliary venturi located in the center of the main throat? Chamber must be emulsion tube.

Is the Air Pilot Jet the same as the idle jet holder, and on the DCNF does it actually let air in to mix with the fuel metered by the idle jet? I know that the IDA does, but it isn't clear to me if it actually works the same on the DCNF (and the car isn't close enough that I can go pull it and look). The main jet has an air corrector to mix air with the fuel in the emulsion tube, what about the idle jet? On one drawing I have, it looks like this is fixed, however another article would suggest that the idle jet holder does indeed let air in as well.

The fact that the manual specifies a size for the idle jet holder (if indeed that's what "air pilot jet" means), would also indicate that it actually allows air to enter and mix with fuel in the idle circuit.

Oh, and what's an "idling adjustment screw hole"? It sounds like the hole in which the idle speed screw fits, but that doesn't make any sense considering it has no other function but to set the idle speed, and doesn't need to be different between the US and EU markets.

Other than that things look pretty clear (and pretty identical between the US and EU versions), I'm planning on trying smaller idle and main jets as suggested, but will only make one change at a time to see how each affects overall smoothness of power, and mileage.

Thanks!

 

It's a simple mechanical advance, Bosch ignition box same as a 928 Porsche and with the USA emission models on your guys cars there's a vacuum retard that's engaged via a just off idle switch on one of the carbs. You should be able hear it click on and off. Hopefully both of you have eliminated this just off idle vacuum retard system. Best to just get a good distributor mechanic (with a distributor machine) and have them re-curve the mechanical advance to match the European advance curve of the earlier cars. Then it's vroom, vroom time!

Bob S.

 

.70 seems high for the 42 DCNF. I run three 44 DCNFs on my Merak SS and the idle jets are .70 as they originally came from the factory.

It seems the primary idle circuit is what is causing issues with the needed emission levels. Addressing the idle jets seems to me a good starting point. This is on the understanding that your carbs are not suffering from corrosion or contamination issues due to ethanol gas and that you are not having those common drip issues common to contamination. I have used ColorTune and it just gets me in a rough range of correctness, ultimately the spark plugs tell the whole story. Fuel pressure must also be correct as Webers are very sensitive to incorrect fuel pressure.

To anyone running DCNF carburetors, I would highly recommend replacing the fuel pump valve [sometimes referred to as the check valve] that Pierce Manifolds offers. These are newly machined valves with pressed in aluminum plugs rather than the lead plugs of old.

What can lead to catastrophic results is a hair line crack that occurs in the lead plug due to repeated heat cycles and just plain old age. Once that lead soldered plug is compromised, fuel will flood not only the engine but the cylinder as well causing a condition called hydraulic lock up - read broken valves. Imagine such an event happening during a 4500 rpm gear shift on the highway and one of those puppies lets loose. How do you spell Ouch?

Just Sayin!

Ciao,
George

 

Hey guys,

thanks for the suggestions. The engine has never run better than it has now, smooth, much quieter (the timing chain was loose), pulls evenly up to 3500rpm (haven't really taken it much higher, there's nowhere to drive that fast here).

Art, I get 8-10mpg, 11 on a good day of long distance cruising. 3 Other QP3 owners I know here in Euro-land get 15mpg on average, 20mpg downhill with a tailwind. So I still have a potential 50% improvement, meaning more power and lower fuel consumption. If I can hit 15-16mpg I'll be happy to call it a day and stop complaining ;-).

Colortune shows all cylinders a nice deep blue with a hint of yellow. 3-4 plugs look rich (black soot), 3 perfect (cappuccino) and 2 lean (white), but I want to put a new set of plugs in and go for a "spirited drive", cut the engine and read the plugs. Airflow is steady at 5kg/h at idle, and stays in sync at 1500, 2000 and 2500 rpms. And i completely agree, I'd rather have her running slightly rich than too lean, resulting in everything running hotter.

The carbs were rebuilt 2 years ago, soaked in carb cleaner, went through an ultrasonic bath, new gaskets, seals, accelerator pump diaphragms, etc, etc. Tightening the idle mixture screw kills combustion in the cylinder, and when they were rebuilt we inspected them to make sure there weren't any cracks or other problems (like someone over-tightening a mixture screw and breaching the hole in the casing).

We checked the timing and advance, and as far as we could tell (looking at the chart in the manual, increasing rpms and reading the timing light) it was according to spec, with 37 degrees of total advance. I'll check and see if there's anyone in the area with a distributor machine. The microswitch that vacuum retards the ignition has been disabled (removed), although I'm not completely clear whether there is any vacuum advance at all, or if it's all centrifugal. You have a good point Bob, to set the dizzy to whatever Maserati was using before emissions became a big issue. I have the Ghibli and Bora timings somewhere if I'm not mistaken and will compare them to the QP3.

I've got a set of 60 idle jets and 130 main jets on the way from Pierce and will try replacing idle jets first to see it it helps things any. Starting from Euro factory spec might not be a bad idea. Fuel pressure is a steady 2.5psi, I have an inline gauge between the regulator and fuel rail.

There are ethanol filling stations here, but I avoid them. Esso and Shell are still selling real 98/99 octane gasoline without ethanol, and that's all I put in the car. I have filled 95 octane when there was absolutely nothing else available while on trips in Europe, the car ran fine but mileage was even worse.

George, thanks for the tip about the fuel check valve, I'll look into it and see. That reminds me that I need to check my primary fuel pump, it's either got a clogged filter or has died, and only delivers enough fuel to idle (roughly).

Cheers!

 

My Espada uses DCOEs. What I finally had to do to make run right on gas with alcohol was to change the idle jets and increase the accelerator jetting a bit. It's done differently on DCOEs so it's not just bigger jet or an increase in stroke like on the DCNFs. But the point is I could NOT make it run right with the stock jets. Period. Once I changed the car is far better though a bit rich. But now I also cannot use pure gasoline in it because it is far to rich then. This "new" gas really screws with these cars but I'm sticking with the alcohol tune because getting pure gas is just too hard.