Ferrari Life Forum banner

Opinion as to what is fouling my plugs.

3723 Views 20 Replies 9 Participants Last post by  Magoo
I went to the parts store to pick up new plugs for my Ferrari. I had one of the old plugs with me. One of the guys behind the counter picked up the carbon fouled plug and said"I see you've been letting your grandmother drive your car."
1 - 20 of 21 Posts
He probably said that as he saw a heavy layer of soot around the thread body. Let me guess, the insulator is a milk-chocolat brown? Did you mention to the parts-guy that this is a plug from a carbureted car? Carb cars tend to leave thicker deposits on the plugs, because carbs do deliver a little more fuel than is needed because of a lack of finite control (which FI with its computers[and even older mechanical CIS] can vary mixtures to a fraction of a ml).

Our Webers are generously jetted, seeing as the best milage I can get out of mine on the highway is a little over 20mpg (don't even ask about how much around town...).
[quote='75 308 GT4 (Peter)]
Our Webers are generously jetted, seeing as the best milage I can get out of mine on the highway is a little over 20mpg (don't even ask about how much around town...).[/quote]

This is quickly becoming my favorite area of the forum. I'm a DIY type and this has been very informative. My question is what do you mean when you say "Webers"?
Weber is the manufacturer of the carburetors fitted on older Ferraris (and just about any other classic and sports european cars).

Jets are just little brass thingys with a precise diameter hole in the centre, varying the size of hole (by selecting and installing a different size jet), changes the amount of fuel flowing through it, leaning it out or enrichening it (going smaller or bigger respectively).
Here are pictures of one of the Weber 40 DCNF carbs on my car (I have four in total on the engine) and a picture of me removing the idle jet and its holder:
fuel injection

[quote='75 308 GT4 (Peter)]Weber is the manufacturer of the carburetors fitted on older Ferraris (and just about any other classic and sports european cars).[/quote]

Now I got it, thanks. My car is newer so I have fuel injection. Those are some excellent pictures and you know a wealth of information about how your Ferrari works.
"Modena": Yes, the 250 GTO uses six 38 DCN's, a model which is similar to this one (downdraught, dual-throat, forward-facing float-bowl, etc...).

Andrew: I have no other choice but to know how my car works. I earn a modest income, which cannot support the rates charged by Ferrari repair shops.... But even if I could afford it, there's no greater joy and satisfaction when you complete the job and it works perfectly.
No chocolate brown.

Peter those plugs were so black and sooted up even inside around the insulator. When I pulled them5 out of 8 plugs were wet. Remember I don't drive the car that much and also the trips I take are maybe max. 15miles then return. I also had it running in the garage checking the adjustments on the carbs. Put a new set of the NGK 5s and it seems much better. I laughed when that parts guy said that because I have not driven it as I should.
My carbureted jeep is the same way, I have a weber carb on it and I just put a high performance racing distributor on it last week (combines to make a beast out of the 4.2L inline 6). No matter what I did in the past some plugs simply came out fouled. There was no two ways about it and even though they were fouled they never really affected performance (no detonation, etc). One thing I do with it though is stay about from those small diode plugs, Bosch in particular, just to be sure.

My 308 (qv) I left the plus in for like 8K miles, pulled them and fouled somewhat, but not bad considering. 308s are supposedly prone to plug fouling, not sure how true that is, but have heard it repeatedly.
Plug fouling.

This is true Bret, But I find the carb. models have a lot more problems with this then the GTSi. I changed to a hotter plug Ngk No. 5 and so far so good.
My carb 308 does the same thing with the plugs. They are always a little black and sooty. I am using a Champion N9 which is equiv. to a NGK 6. I am thinking about going up a heat range as I would like a little more brown in my plug color. I tend to run my car a little rich also.
Hotter plugs

Rich, I changed my plugs from the NGKBPR6EVX to the NGKBPR5EVX and they burn brown on the insulator and electrodes. Car starts much quicker also.
Magoo, what do you think of the Bosch plugs. Do they make a plus 4 plug for our car?

My records show the plugs I have, have 8,000 miles on them and are 9 years old.

I've been thinkg about replacing them.
I have no missing, just going to do it.
What do you think???
Bosch Plugs

Hey Bud hows it goin'? I checked on those plugs when I got my NGKs and there were non listed for the 308s. My car had a rich condition and everything was dead on, floats, timing, mixtures etc.. So I changed out the coils for hotter ones and then went to a hotter plug the NGK5s and set the gaps at .035 to give a hotter spark with the hotter coils. I do not have a rich condition and the plugs don't soot up or foul out. I also have a better response on accelleration and the car starts easier and quicker.
I noticed this was another thread, which I had posted photos that got deleted. I have re-attached photos of my carbs and idle jet in that previous post.
Greetings, Magoo, peter, richelson,Bret and ed, I wondered where you guys were hiding. Sorry my post isnt technical.
wow, all of you guys are turning up over here, nice to see you. I havent heard from Bret in a while though, last time i saw him was at the WWoC tech session.

Anyway, your plugs will foul if you let the car idle for long periods of time. The best way to aviod fouling is to DRIVE THE CAR, by this i mean wind it out to redline every so often, dont worry, the car wont self destruct (unless you didnt put on new belts every 30k)
Magoo, you did just what you should have, the factory coils and ignition for that matter sucks. You are dealing with two problems here, lots of fuel and a week spark from out dated points and coils. If you retain the stock points as I have, hotter coils and larger gaps is the key. I will be updating my coils soon and putting in a fresh set of plugs. This should prevent fouling.
I agree Paul. I replaced my coils with just ordinary, off-the-shelf Neihoff's and it made a very noticeable difference in the way it ran.
1 - 20 of 21 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.