Tuning the webers…. advice/experience requested..

You're on the right track. Start with checking the balance on the carbs, so grab a balance meter, a good one, not the one with the ball in the tube.

Check the balance with slight throttle opening as well, say about 1400-1500rpm. This is to make sure the carbs are all working together.

Once that's balance stuff is set, turn in each idle screw slowly until the cylinder it controls stops firing, then back the screw out about half a turn so it fires again.

 

That's the gauge I use. I put it right in the horns. It works just fine.

If there were taps on each header I'd suggest using an exhaust analyzer but my cars don't have those. Just measuring at the tail pipe is waste of time IMHO.

Check the ignition timing first. Is the distributor advancing properly?

Get the carbs fundamentally balanced and yes those barrel to barrel balancing screws will help. The DCOEs on my Espada don't have any!

Keep in mind that as the car warms and cools some of this is going to change due to the expansion of everything so don't go nuts.

Then when doing as suggested by Ferraripilot above I like to used a digital rpm meter, I have a small heathkit one from a lot of years ago, and then I can watch the rpms rise and lower as I lean out and then enrichen each circuit.

Use a big fan in front and at the engine compartment or the damn thing will get very warm. Early spring or late fall is a whole lot more fun!

I had to change the idle jets and accelerator circuit on my Espada from stock because of the alcohol in the gas. Does you Bora have any hesitation or lean out at speed as you ask for more gas? That was what min was doing but DCOEs aren't DCNFs.

 

Lucky you with the gas. I just did a tankful for my Jag S-Type R in PA about a month and a half ago and wow what better mileage and the engine was zippier too. We are getting screwed on gas and food because of this stupidity.

So stop letting the "transients" lean on your Bora, they might dent it ...

There's a Yahoo Groups website call Side Draft Central for side drafts (duh!) but you might pick up some pointers on there for the DCNFs and tuning out that condition anyway.

 

My best advise is don't touch the carbs until you are sure everything else is working properly. THe carbs rarely change adjustment. THe points wear in the distrubuter and cause the car to run poorly and make sure the compression is good on all cylinders.

 

I think that synching the carbs is a must. It is a straightforward job and makes the engine a lot smoother. If your car has been standing still like mine, clean out all the jets by soaking them in carby cleaner overnight and then set to work. This article sets about going through the steps for a 308.
The tool shown is available on Ebay for about $40

[ame=http://www.youtube.com/watch?v=G7GG9ylOhpQ]Maserati Ghibli DCNL carburetors after synching - YouTube[/ame]

Good Luck


Julian

Carb synch tutorial: 308 Series

 

Try this: Weberology: Tuned Induction I & II. Here is the link,

https://www.youtube.com/watch?v=dBs7GzSLLCc

Ciao,
George

 

I think that synching the carbs is a must. It is a straightforward job and makes the engine a lot smoother. If your car has been standing still like mine, clean out all the jets by soaking them in carby cleaner overnight and then set to work. This article sets about going through the steps for a 308.
The tool shown is available on Ebay for about $40

While this is true IMO it is a waste of time to try to adjust the carbs if the rest of the engine is not healthy. And since he just had an expert clean and adjust them in 2012 ago he is more likely to make them worse. If you have a valve leaking you are not getting the full vacuum that these meters need to balance the air flow.

 

I can't see how synchronising the carbs would harm if the engine is in good shape. I agree that messing with the mixture is a black art but its pretty easy to check the airflow into each airintake. They are either close to eacj other or not

 

There are two meters one is good the other is bad because it restricts flow


I am also a big fan of the colortune it is very easy to use on the Maserati and is accurate showing you the perfect burn ratio when tuning.
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Of course everyone has correct points.

Engine health should be established first with a leakdown test. Given all is well in that department, next is making sure the carbs have integrity. If not, a rebuild is in order. Tuned induction is the next step. Balancing and synchronizing are a must. Final step is the air/fuel mixture. Counter intuitive as it may be, when the DCNFs run too lean, the plugs will appear as having a too rich mixture.

Unless you have access to each primary tube and a digital A/F meter, the Gunson ColorTune is a good starting point. Once you get a blue flame, then work the A/F screw outward by 12% turns till the plugs show a spot on burn.

The link I posted shows you what the synchrometer should indicate on a correctly idling engine, specifically a Merak SS engine-with 44 DCNFs.

Just Sayin!!

Ciao,
George

 

Art has been around the block a few times already. He probably won't toot his own horn though.

 

Bad gas is another problem, In CA the gas is only good for 60-90 days, another issue with Weber's their need to have very clean fuel. Old cars and clean fuel are not always easy to do. Check the tanks, fuel filter in the tanks, fuel filter outside the tank, fuel filter in the bottom of the fuel pumps, fuel filter inside the Weber's.

 

Excellent point!

Ethanol free fuel is the only way to go. More and more stations are offering this type of fuel. The ethanol gas will make things stick, like the needle/seat assembly in your carburetors-not good!

Ciao,
George

 

Art,

As a 75 your car is pointless isn't it?

BTW, Dave and I are on the same BiturboZentrum website and he's coming down to Pocono at the end of August to run his Biturbo on the track there so I'm going to try and see him there. I think my AC belt drive issue should be fixed by then and I WILL need AC at that time of year too. No track duty for my 84 though. It's a very small community at times isn't it.

 

Hi, the sync of the carbs is a process requiring several steps. Always start with making sure that the car is parked on an even surface and the throttle cable has the right operation, the proceed to adjust the linkage to the carbs butterflies to make sure that the butterflies start to open at the same time when you push the accelerator. Use one of the middle carbs (carb 2 or 3) as a reference and start to fine tune with the small venturi adjustment screws to active the same vacuum on the two throats of one carb. Then move on to the next pair, and no 1 and 4 carb. It is a good idea to run the car inbetween the adjustments so the engine doesnt get too hot. Use a separate rev meter so you can monitor the rpm. When you have achieved the same vacuum in all the 8 throats, then you can move on to adjusting the idle richness with the 8 needles on the carbs. I use the rev meter to lean out each cylinder until it doesn't fire anymore and then I give it more fuel so that it starts fining again. Again you need to run the car a few times to get rid of excess fuel and to keep the right temperature. The last step is to adjust the idle speed using the stop screws for the butterflies. Then verify the vacuum for each cylinder once more and maybe adjust. Before you do all this you have to verify that the ignition is spot on (timing (and dwell if you have the points)).

The carbtune (with the ball) works fine if you take the readings quickly and use a bit of foam in the middle to separate the trumpets from each other.

heres a link to a manual, page 34 Ivan the car nut

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

cheers, Göran

 

Unisyn always worked for me....GREAT tool.

 

I was reading the valuable comments on the adjustment and decided to write down my experience over the years and share it with you. If you have any contributions, please share?

(Maserati) Weber Carburetor adjustments 42 DCNF
Based on my practical experience herewith a check list, point 1 to 10 must be OK before fiddling with the carb adjustment:
1. Camshaft timing and valve clearances to be to spec.
2. Compression, turn engine on starter engine with coil cable or rotor off: The engine shall rotate even with an even compressing sound per cylinder. If in doubt: Compression check with a warm engine with a tetster, should be within 15% equal to each other.
3. Ignition timing static and dynamic. Ignition needs to be working well!
4. Sparkplugs, cables, plug-caps(!), and distributor-cap. Check for unwanted sparks between elements of the unit in the dark!
5. Fuel supply pressure: 1.000mm< X <2.500mm water column.
6. Float-level: 48 (European) or 50mm (USA) both +/- 0,5mm, see manual.
7. Dripping nozzles in the inlet:
a) Leaking float needle: dripping when engine is NOT running! Mix a can of injector clean and run the engine, if no improvement: change needles.
b) Dripping when running: change diaphragms of acceleration pumps. Make sure that the covers are flat! (Eventually flatten them on a piece of glass cover with fine sand paper and oil. Mine were not air tight with new diaphragms!)
8. Air-filter cleanliness: running rpm with or w/o lid shall not vary!
9. Little balance tube on the inlet manifold under No 1 & 8 carb and the air inlet box to be connected! If not: irregular running at idling.
10. Acceleration nozzle capacity: equal quantity at opening butterflies.
Note: Advise by the master Sg. Tralli: Accelerator pumps: are always too rich shorten leverage effect to 2nd hole smallest capacity!
11. Synchronize individual carbs left and right inlets by special mix screw(with lock nut); one side stays closed!
12. Synchronize carbs at idling on the adj. screws and on the accelerator pedal: all equal suction by measuring device and listening: all same &#8220;hiss&#8221;.
13. Check leakage of the axles by spraying brake cleaner on the axle: if RPM increases false air is sucked in: renew bearings and seals. Quite a precise job to do that right!
14. Run engine under load for minimum 30min to clean plugs! Also during long adjustment session! Faul plugs do interfere with the adjusment!
15. After 30min running: Check synchronization again and adjust.
For the basic adjustment I use a product named Color Tune: a transparent spark plug which shows you the color of the burning process. I only use one set and do the cylinders one by one.
16. Color Tune at idling: constant spark and firing with white/blue ring visible in CT plug: more to the rich side as to the lean side. Change rich or lean burning by individual idling air mixture screw. I recommend to adjust the mixture at idling on the rich side: tending to a shade of orange/brown.
17. Same as 16 but &#8220;on the accelerator pedal&#8221; around 1.000-1.300RPM. I made a little device to keep the RPM stable whilst adjusting. l Popping of exhaust at constant RPM means rich burning cylinder(s)! ) One can find the too rich cylinder by taking the spark plug cap off during running, wear a glove for insulation!
Check too lean burning by holding a piece of carton against exhaust pipe: if it hits the pipe: too lean cylinder(s)! Pull caps off one by one till the carton does not hit the pipe anymore; increase mixture of that cylinder ¼ turn; richer and check again.
18. Popping on the overrun (deceleration on the engine while driving the car) means lean burning cylinder(s); run car for 30min and take the plugs out, check the color&#8221;(should be coffee with milk): for the too light colored plug: increase mixture of that cylinder between 1/8 and ¼ turn; richer and check if the backfiring/popping stops.
The 1/8 turn on one cylinder may be the difference between smooth running and irregular running!!! Those little pushes in the back that you may experience while driving at 2000 rpm. That is how sensitive the adjustment is!
19. One may have to repeat the points 16, 17 and 18 a couple of times but patience pays of! It took me a while to figure out the above but now my V8&#8217;s are running like a dream! Enjoy the process and the driving!

At least the above will keep you out of the bars for a while...

Saluti,

Bart

 

I wonder how critical airflow balance is when tuning.

The reason I ask is that I got mine perfectly matched a week ago, both between each set of venturii and across all carbs, it took quite some time. But I managed.

Now, while making a quick check yesterday after a longish drive, they're unbalanced again! Between throats is still ok, but now one reads 5.5kg/h, another 4.75kg/h and the others 5kg/h, which was the original reference point they all were set to.

I'm wondering how precise one should be, and how much "slop" or drift one can expect from the linkage (since the carbs are all controlled from the linkage and locked together as one unit).

How much variation is allowable while still having things tweaked to perfection?

 

Don't go nuts. It's a rather sloppy mechanical system that will drift with temperature.
Tune it when it's warmed up not cold or very warm and that's about all you can do.

Just praise heaven the Maserati V8 linkage is so simple and compact. The old Lamborghini V12 linkage is a nightmare by comparison.

 

I saw the YouTube video on multiple Weber tuning by the guy with the Jalpa who machined a new linkage setup for his car that made a lot of sense and made tuning and syncing much, much easier.

I wonder if a more stable linkage bar and adjusters would work on the V8, and more importantly if it would really make any difference.