DCNL carb question

a grove. there should b no fuel bypass. lot of cars lost for that reason.

 

You either have a piece of dirt in a needle valve, or failed needle valves. Replace them all if they are very old. They should not leak in normal usage.

 

but on the Merak thread someone made a very improved version

 

Meraks and Boras use DCNF carbs, not DCNL .... they are very different.

Ivan

 

Grose jet.

I don't know if they fit DCNLs?

Cars in good nick that are run regularly don't have these issues anyway.

I thought he'd rebuilt the carbs? That would include this?

 

Probably so unless there's evidence of a somewhat recent rebuild. The float needle & seat valve are typical replacement item in a rebuild kit. As already noted it can lead to fires on some cars. You can buy the pieces separately and assemble a rebuild kit yourself. I did that for the six DCOEs on my Espada and it was cheaper than buying "kits" but check around. There are plenty of folks making parts for Webers so be careful. I also had the steel parts replated and replaced any damaged items.

 

I bought this rebuild kit, as far as I could find it was cheaper than many others and seems to be of decent quality: Maserati Enthusiasts' Page (next to last post from the bottom)

I also ordered Grose replacement jets instead of the needle type. They're supposed to be an improvement compared to original.

 

Do they supply for DCNL 5? The kits I could see were all for DCNF. Different beast.
I am contemplating refurb. of my DCNLs too, with complete strip and ultrasonic clean.
Pierce manifold have the requisite kits here:

38-40 DCNL


I have not taken the plunge yet but seem to recall from previous posts that they have a
Solid reputation. Anyone with first hand experience?

Cheers all.

Mark.

 

Mike Pierce has been a friend and business associate for almost 30 years. He is a straight-up guy. Honest and very knowledgable. They now have the largest Weber inventory in the world.

 

A quick comment about Grose Jets. I am suprised you could find them, as the man who made them has died and the business is closed. He just operated out of the basement of his house. Unfortunately, I have switched back to Weber needle & seats, as I found the ethanol fuels caused the Grose Jets to glue themselves closed if the car was not run for a few months over the winter. The fuel pump pressure was not enough to pop the ball off it's seat, and I would have to take the top off the carb to free the ball. After a few years of this, it just got to be too much. However, we still use them in our race cars, as we run race gas and they do provide better fuel level control.

 

I hate that ethanol in gas! I have been using ethanol free gas in my Merak, so the Gross jets have behaved well. The Gross jets are available for the DCNF carbs. I'm not sure how well they cross reference to the other Weber carburetors.

Also, a list of all ethanol free gas stations in the U.S. is available on the Merak Group website under the links tab. The Gross jet is also listed under the products/parts tab. You can just Google "Merak Group" and it will lead you to the site.

Ciao,
George

 

I bought mine here: Marketplace:John Titus - Citroen-SM-wiki

As far as ethanol is concerned, it's usually marked on the pump, and I try and avoid it as far as I'm able. Additionally, I've found that the car *hates* to sit unused, so I try and go for a drive at least once a week. It seems to help keep things working, it's when the car sits unused that stuff breaks!

 

DCNL's are very diffrent than DCNF's

Mine were on a very early Ghibli and only a few cars used them. I think one Lancia model.

The bodies were sand cast and they lacked a air bypass adjustment, this caused a lot of extra work. In order to get the air bypass balance between the four carbs you had to "tweek the butterflies by hand. To do this I took the carb off and hooked my wife's vacuum cleaner hose to the bottom side and a Weber Synchrometer on the air trumpet end. This allowed me to see the air flow and make adjustments to all carb's butterflies before they went back on the car for final tuning.


I found the colortune worked really well tuning the Ghibli

Pierce is the best place for parts and I did order rebuild kits from him 10-12 years ago.



On another note these carbs hate dirt even if it is microscopic.

Make sure you check ALL your filters there could be a gas tank filter, a fuel pump (or pumps) filter, a engine compartment filter and the filter in the carb. They all need to be spotless.

Carefully check your whole fuel system, this can save you a lot of time in the long run.

 

Excellent points! Gas tank must be relined and an extra glass see through fuel filter wouldn't hurt either. The air filter should also spotless. In the late Merak SS model, it is possible to run 2 small K & N filters in the air intake snorkels [while still using the stock configuration] in conjunction with the stock air filter to keep things ultra-clean.


Ciao,
George

 

Life gets tough when your balls get stuck ...

So you experienced some benefit using these?
I had them in my Bora a t a time when I was chasing a much bigger gremlin and just took them back out to eliminate that as a possible suspect so I can't say I had a positive or negative experience with them.

 

Hi Bob,

I have had the Grose jets in use for about 6 years with no issues of any sticking even when I was using the 10% ethanol based fuel. Regular driving is certainly a very big plus. With the Grose jets there is never a worry of fuel starvation no matter what the demand, no matter what the bank.

Just Sayin!

Ciao,
George

 

Any thoughts on using a vane style tool vs. a mercury column one for setting airflow and tuning/syncing carbs?

Either way is fine for me, just wondering what the pros/cons of each type are.

This is for the 42DCNF on a 4.9l V8, btw.

Thanks!

 

You are confusing matters.

The colourtune is used to set the idle mixture.

The mercury columns or any other vacuum/flow measuring device is used to synchronize the airflow between the throats.

Best,

Jack.

 

Maseratisti,

My advise before even touching the carbs:
1. Set the valve clearance correct than the valve timing.
2. Make sure the ignition is set correctly.
3. Check the leads and put new plugs in.

Only then start playing with the carbs.

4. Make sure the carbs are absolutely clean inside!
5. Start with the synchronisation first per carburettor, left and right intake shall be equal!
6. Then fix the accelerator cable at a ~1.500rpm level and check / adjust the air flow to be exactly the same between the 4 carbs. This excercise is time consuming because every time you do and undo the nuts on the linkage the stuff resets itself a little different.
7. Now go to idling RPM and check the airflow again, use the adjuster screws for the butterflies per carb. After all this you can start playing with your colortune to set the idling mixture.
Be aware that if you foul a plug you need to run the engine under load for at least 30minutes to clean it up and be able to progress playing with your settings!
Quite an excercise but it pays off to have your engine running smoothly.

Ciao,

Bart

 

+1 very good suggestions.

Here are a few other tips:

Before you start adjusting the carbs do a compression test. Setting the carbs to all draw equal amount of air is fine if the compression is consistent across all cylinders but not so good if you have most cylinders at 150 psi and one at 120 psi. You will want the lower compression cylinder(s) to draw a little more air to compensate.

A Colortune is a great tool to verify that the carbs are working properly. You should be able to screw in the idle mixture screw in all the way and see the spark but the cylinder not firing. As you unscrew the mixture adjustment screw the flame will initially be white, then turn blue and finally turn yellow. I set them just as they go from blue to yellow.
If you cannot get the cylinders to burn with a blue flame using the Colortune (ie: the cylinder goes from not firing to a bright yellow flame), it is time to rebuild the carbs.
For those not familiar with Colortune it is essentially a see-though spark plug. You temporarily replace the standard spark plug with the Colortune and then you can see what is happening inside the cylinder while the engine is running. You do this one cylinder at a time. Simple and effective.

Once you finish with the Colortune idle jet adjustments, disconnect the spark plug lead one cylinder at a time and note the RPM drop. Use a heavy rubber glove when disconnection the wires! I use the digital RPM indicator on the ignition timing light for this test. You want each cylinder to have approximately the same RPM drop when disconnected. Adjust the idle mixture and/or air flow to achieve this.

As Bart mentioned, this is very time consuming but will make a huge difference in the way the engine runs.

Ivan

 

Ok, ok,

my typo.

I didn't mean colortune (even though I wrote it, and yes I will buy one of those too), I meant "carbtune", as produced by f.x. Morgan and many others. Mercury (or not) filled columns to measure vacuum and sync carbs together. I've seen these kinds, as well as the vane type that looks like a wine cork with a meter on it, sits on top of the velocity stack.

As far as the other things go, the car has been gone through, has excellent compression across all cylinders, no loss on leak down test and the valve clearance/timing has been set. The people at the dyno place found that 2 spark plug wires were not providing spark under load, all wires have been replaced and tested as ok. They also found that no. 2 carb (from the firewall) is leaking, and wanted the carbs rebuilt before doing a dyno run.

The carbs were rebuilt by the PPO, but that's beginning to be quite a few years by now, over 5. Plus the fact that they're leaking tell me that it's time to go through and make sure they're ok.

Thus my question now, which carb sync unit do I want, and why. Yes, I'll get a colortune too for the idle mixture .

(and thanks for the tips Bart and Ivan, they'll come in handy when I get that far!)