365 GT 4 acceleration hole

There's another thing I'd like to have your opinion on. Since I've bought my 365 GT4 2+2 a little over a year ago, I had quite a lot of work done on it, since the car had obviously been standing for quite some time. I had the entire suspension, steering and brakes overhauled, got new ignition wires, rotors and points, installed two dinoplex units for better spark and had recently the carburators overhauled and valves and ignition adjusted. It seems to me that all work to make the engine run as good as possible has been carried out. The compression is fine, the engine revs and idles smoothly but there's still what I would call an acceleration hole somewhere around 3500 RPM. If you accelerate with full throttle from, let's say 2000 RPM it's not as well noticeable. However, when you slowly accelerate, with maybe half throttle, the engine revs to about 3500 RPM, then kind of "gulps" for a moment, before it continues revving up high.
In a thread about a 365 GTC4, that shares the same engine, this was mentioned briefly before. I would like to know from the other 365 GT4 owners if they expirience a similar problem. Maybe even the 400 GT owners. What do you do about it?

Howard

 

I'm afraid that couldn't be the problem. I did two trips to Italy last year and since I've had my carburators completely overhauled I did another 1500 mile trip to Switzerland just a few weeks ago.
It's not that it isn't any fun to drive but it seems odd that especially a 12-cylinder car doesn't have a smooth power curve all the way through.
Nevertheless, in this thread that I can't find anymore, one guy claimed that this was typical for 365 GTC4's and another one, as far as I remember, recommended to just turn the mixture richer, including using a larger jet.
I don't know if this makes any sense at all. I could maybe see that they had a minor problem with the 365 GTC4 but after over 500 cars somebody at Ferrari should have found a solution for that by the time they came out with the 2+2.
Another question I have is, how often do you change your points, or how often do you adjust the gap between them?

Howard

 

Thanks Russ for your help. I think this makes a lot of sense - I'll give it a try and let you know how it turned out...

 

Thanks snj5,

today I've changed the main jets on all carburetors from 125 to 130 and the problem has disappeared almost entirely. The car is so much more fun to drive.
However, I'm tempted to try 135's to see if I can get it even smoother...

 

This is really easy. You open the butterfly screw on top of the carburator - the two larger screws underneath it are the main jet assembly. Take them out and pull off the main jet from the large emulsion tube. You should be able to pull them off without the help of any tools. To put on the new jet (easily obtainable, just make sure they're for a DCOE carburator) might be a little trickier, since they're a little larger than the opening in the emulsion tube to make them fit as tight a s possible - you can carefully use a small set of pliers to make them fit. Put them back in, close the lid again - done...
It took me a little over half an hour to do all 12 jets.
However, before you do anything, I would suggest for you to wait and see which jets are really better. I now have the 130's and they're a great improvement. Nevertheless I'd like to try the 135's to see if they're even better. I'm ordering them today and should have a result by the end of the week.
What I'd like to know is, what ignition system did you get for your car?
When I got mine last year I got new rotors, points and cables and installed two dinoplex units with the coresponding coils, which improved the overall performance a great deal. However, I'm still not happy. There's still the occasional backfire when I'm accelerating into the higher RPM ranges and it doesn't go there as smooth as I would hope. There's always a slight "studder". Also, when I try to maintain a certain speed with anything over 3500 RPM, it backfires. Not badly but there's always that "crackle" that I think shouldn't be there.
The way I see it, I'm looking at either rebuilding my two distributors or getting myself an ignition setup that is entirely electronic, doesn't use any points and has no mechanical parts to worry about. My guess would be that the second option might be even cheaper but is way more effective.
The question is, what system to use. A while ago I started a thread on this but didn't get that much response. A lot of people, it seems, have converted their 308's to electronic ignition but I haven't found anybody who converted his 12-cylinder engine. Superformance in England, where I got my dinoplex units and who are exceptionally friendly and knowledgeable highly recommended a unit manufacured by BSM (http://www.blackstallionmotors.com.au/bsm_ignitions.html) which is sold in the US by Carobou. The price is fairly high at 1,100 BPD's over here but they seem to be the best choice I've seen so far. All alterations can be easily rebuilt to original spec with no traces left, it's programmable, fairly easy to install and it even has a toggle switch that lets you choose between "performance" and "emissions", which is definitely an issue over here in Germany.

 

I will keep you posted on the diffrent jets. What you bought from Lyle at ferraripartsexchange is exactly what I put into my car a year ago. He gets these units from Superformance in England, where, by the way, you can get them for 235 BPd's, so including shipping and customs you should end up in the lower $ 500's.
As I mentioned before, these units are a great improvement. The engine starts, idles and generally performs much better than before. Fuel consumption is down about 20%. I can't tell you at what exact RPM my engine idles because the rev-counter needs to be overhauled - The needle trembles at low RPM's. However, it idles perfectly at, so it seems, the right engine speed.
However, the disadvantage of this system is that it still uses the original distributors, points, rotors, etc.. These are all moving, mechanical parts, prone to malfunction or disadjust themselves in one way or another, sooner or later. I, in my particular case know that these distributors have some kind of problem somewhere because I've singled out every other possible source.
So now it's for me to decide whether I want to refurbish both distributors or if I instead go for a system that guarantees optimum performance, like a modern car, throughout all RPM ranges, practically maintenace free - both at probably the same cost. Well, you probably know my answer already. I'll probably go ahead and put in the electronic unit in september. I have a very good feeling about this. First I really trust these guys at superformance. Second, the system really does make a lot of sense. You should go and take a look at their website.

 

OK, I have now installed the 135 main jets and the car runs even better now. This was confirmed by a check of the spark plugs while the 130's were still in - they indicated a mixture that was too lean. However, I still have to check the plugs on the 135's.
Now that the car is running so well in higher RPM's, I suspect that the idle jets are a little on the small side as well. The car is a quite sluggish while accelerating out of the stand - once you get over 2500 or 3000 RPM it's a dream. It seems only natural to use a larger idle jet as well if the reason for this is really the different quality fuel we use today (btw, I'm using best quality 100 octane fuel).
However, all these changes have one negative effect: they increase fuel consumption. How much, I have not yet determined.
As I'm working my way into this rather difficult subject of finding the perfect jet setup, I'm thinking there might be also a different way to do this. Rather than going all the way up to a main jet of 135, one should be able to reach a similar result by using a different air-correction-jet. The air-correction-jet regulates the amount of air - the smaller it is, the richer the mixture gets while still using the same main jet and therefore the same maximum fuel consumption.
I think it would be very interesting to run a test on a variety of those jets and emulsion tubes and fumble with them. I bet you the results would be amazing. However, unfortunately I don't have anyone around here with those facilities.
Anyway, the results I'm getting with these small changes are amazing already. Wait until I have tried a larger idle jet and then you'll know what to use for your car. You won't believe what a difference that makes...

 

Hello Snj5,

since I will be away for a week, I have given the whole matter into the hands of my mechanic. Although the overall performance has significantly improved, I still do experience some problems in the high RPM's over 5000 - hesitant acceleration and the occasional misfire. So I'm having my mechanic go through the entire ignition setup before I continue to play with the jets. I suspect something to be wrong with the distributors, since the advance has just been set perfectly about 2000 miles or three months ago. I will know by the end of next week...
The original idle jet for my car is a 60 F8, so I went ahead and bought a set of 65 F8 which will be installed once we know that there aren't any problems ignitionwise. The immediate acceleration seems to be fine - until, as I mentioned, you get over 5000 RPM, when you feel that it doesn't accelerate as freely anymore and misfires occasionally.
On the lower end the engine only seems to idle well at higher than normal RPM's (hard to tell precisely, since the rev-counter trembles and seems to be slightly off). Also, the acceleration out of the stand seems to be very sluggish. I always use a lot of clutch which I'd rather not. Hence the idea for the bigger idle jets.
Let's wait and see what my mechanic comes up with. I'll keep you posted...