Idle mixture screws - in or out??

depends where you start from. both will work.

 

while very little scares me as a DIY'er, adjustment of multiple carbs is something I've found is not something your average enthusiast should do. You have to listen to the air flow at the neck of each carb to make sure they are all flowing the same amount of air and adjust them all the same for mixture. If you get it wrong you can run some cylinders too lean and burn a hole in a piston, lose power, have very irritating exhaust gases, etc.

Take it to a mechanic you trust and then LEAVE THE CARBS ALONE!

 

Hello,

this whole thing is NO black magic and with some patience and time can be done by a experienced home mechanic.
For adjusting the air flow ( synchronising ) there are several useful devices, so that one doesn't have to rely on listening to the air flow.
The carbs on the 308s are not very sensitive regarding idle mixture. Three turns out is often sufficient for a good result regarding smooth idle. Small increments can be done for decreasing CO.
More critical are internal carburettor faults like clogged main jets, false air through worn out or not sealed throttle bearings, faulty accelerator pumps and so on.
Or leaking lead plugs on the carburettor housings, which can lead to an engine fire if they eventually fall out after some 'carburettor specialists' have had the housings ultrasonic cleaned without restaking the plugs.
Also are the engines not sensitive regarding carburettor faults. If the carbs are very much out of tune, the engine may run crappy, but I have never seen severe engine damage due to carburettor reasons.
Unlike my '72 Alfa GTV, which answers with immediate piston holing on clogged main circuit or false air.

Best Regards from Germany

Martin

 

It's a very well defined procedure, but the airflow meter will help. Do a search on carb adjustment and you will find tons of information. The Weber carburetor book also has a very good procedure. It can be done, and you can do it.

The starting point is 3 complete turns out (from a totally closed position)

 

I'm in the process of rebuilding my 40 DCNF carbs and I am using an ultrasonic cleaner. How do you correctly "restake" the lead plugs and how do you check to see if they are leaking??? Also how many are on a DCNF?

 

Hello Doc,

I started a thread regarding this some months ago.

http://www.ferrarichat.com/forum/showthread.php?t=35524

to check if yours are leaking, simply fill the bowl with fuel and wait several hours, preferably over night and look. Badly leaking plugs will be damp then.
Although slightly leaking plugs may be dry and get damp after some warm/cold cycles.
So best is to check before cleaning of the carbs. Slightly leaking plugs show an oily, dirty residue around them.
How many on one carb ? I didn't count them, I can just guess. 20 - 30 plugs per carb.

Best Regards from Germany

Martin

 

In.

 

If your car has had a muffler installed other than the one it came with, and the carbs were not re-jetted, you will need to start 6 turns out rather than the recommended 3. I have been through this on multiple cars, and it always more than 3 when the exhaust has been opened up. It's always better to have it set slightly rich rather than slightly lean.
You will also need to clean your spark plugs after you are done with this procedure (Yes, you can clean them).

 

I ended up reaming all the lead filled casting holes in the carbs with an exacto knife - removed just enough lead so i can get a good hold with epoxy, but left enough lead in the hole to stop epoxy from getting too far in, then filling the holes with JB weld - works great - a few years back i used seal all. the seal all was not impervious to gas - so they all leaked again. so far, jb weld has kept gas from seeping out of the holes. and yes, there are about 25 plugs on each carb.....
john
78 euro carb 308
ps. i set the idle mix screws while the car is idling at its lowest possible idle (that way i can detect any miniscule change in idle when adjusting the idle mix screws). i then adjust the idle mix screws for maximum idle.

 

You will also want to use a tachometer hooked up to your coil, as it is rather difficult to detect the drop by ear until it has dropped significantly.

 

A trifle dramatic perhaps.
I have run my car with idles jets from 52 to 70. No difference in the quality of idle once warm. Off idle behavior / throttle response is markedly different.
BTW, I believe exhaust valves will usually feel the brunt of a lean mixture. Pistons (with added holes) usually reflect detonation.
Philip

 

I believe he was quoting the Alan Bishop Book. A great book, but I have never seen/heard of a piston burn through because of a slightly rich condition.

 

Martin
Thanks for your advise. I was worried about the lead plugs after using the ultrasonic but your thread made me feel better after I restaked the lead. I also used a drop of Locktite (penetrating type) on each one. I had it handy for use on the retaining screws that hold the throttle plates in the shaft. It should creep into any space around the lead and it is impervious to fuel. I'll sleep better tonight.

 

you're welcome. One question from me. Which type of Loctite did you use ? I'm just curious about the 'penetrating type'.

Best Regards

Martin

 

The green one, I assume.

 

Should be OK here but remember, Loctite doesn't like heat.

 

I've also always been taught that too lean a mixture UNDER LOAD (i.e. main circuit, not idle) will lead to problems. Many dyno techs have told me that at idle A/F's even above 14.7 are common on FI cars. Kjet Ferraris run right up on A/F 14.7 all the way up under load for emissions.
Detonation resulting UNDER LOAD will absolutely hole a piston.
Most performance carb settings aim to keep A/F around 12.8 - 13.8 under load on the main circuit for best power, a pretty safe range; idle jetting is as Philip relates, more of an issue in idle smoothness and off throttle behavior in my brief experience. And powerwise, in my brief experience, Ferraris are tolerant of a pretty liberal A/F range.
best
rt

 

Martin
I went out to my garage to see what I used and it was actually Permatex Penetrating Grade Threadlocker (Green) and one of the uses noted on the back of the container was for carburetors. I got it at Advance Auto. It also said in order to remove something treated with this you have to heat the application to above 500 degrees F. Sounds like it should hold up under regular use wouldn't you think?
Charlie

 

500°F. That are 260°C. That's hot And I think it will hold up. You also said, that you have restaked the lead plus. So I think, that you are 200% on the safe side.

Best Regards and good luck with your carburettor job.

Martin