Idle Jets

Mike,

Ironically, I posted about my idle mixture setting a couple days ago. I have .57 idle jets and it is running perfectly now.

I have no cats now (but a set of Hyperflows on the shelf if ever needed), Tubi exhaust, and one set of points operating in each distributor. Sounds like you have a similar set up.

My 308 had .65 idle jets when I bought it and they were way wrong, then I went down to .60, then to .57. I believe the 1978 cars as originally shipped up had .55 idle jets, but I could be wrong.

You might try stepping up to richer jets from where you are now.

Jeff

 

My car runs the stock idle jets without issue. I recently upgraded my ignition system to an Elecromotive and it has no cats and a Tubi exhaust.

Looking at the shop manual, it says it came stock with .45 idle jets. I can not verify that is what I have or not.

On a side note, my main jets were upgraded to 135 from 125. Seems like a nice change and was made at the advice of a guy that used to race a GT4.

 

My 79 had 50 idle jets when I purchased it, later changed to 57 with a single distributor running Pertronix, no cats, Nouvalri exhaust the result was a significant increase in power. Euro cams are next.

 

57's running tubi with test pipes is perfect for me at sea level.

Idle screws at 2 turns out (euro screws without the tapered shoulder).

 

Fresh rebuild on 1975 308 GT4 with twin distributors as original 65 pilot 2 turns out at sea level. Ansa exhaust.

 

Geno, Which mains are you running? Jeff

 

my '79 GTS has '55 original on idle, have change jets to :
- idle '60
- main 125
- air 220
now is very well.

Stefan

 

I bounced back and forth between 125 and 135, deciding on 135 as the car just seems to rev "slicker" to redline. It was just a but starved with the 125's.

As i said before I switched to the non tapered euro mix screws and the result was that finding the optimum idle was easier as the profile of the euro screw is more severe, and gives it more of an on-off effect. Plus the screw isnt backed out 5 turns and nearly falling out...

My key for eliminating the stumble from through the 3-4k rpm range was to hold the thottle at the point where the car wants to stumble or cough, then back the idle mix screws out until the stumble smooths out (ie dumping more gas in through the idle circuit).

Geno

 

I'm running 130's and it revs beautifully to 5500 rpm, then, unless the engine is good and warm, will hesitate there like it is too lean. I've got a set of 135 jets coming now.

thanks for your info. Jeff

 

I check and adjust the mixtue each zylinder with ColoTunes.
Very simple solution for ideal mix adjusting, I believe, when the flame has a darkblue color is the best, after this I turn 90 degrees to left (rich) and that's it.

 

My 77 likes 60 idles & 135 mains, it was the Iridian Spark Plugs & Crane Ignition that finally got rid of the last rare annoying carb pop.