Regarding my Standard Specification (Euro) 1979 308GTB: I have rebuilt the four 40DCNFs and the car runs GREAT, but it has an idle problem. With the air cleaner base off and the engine cold-to-warm, it behaves perfectly and idles at 1000rpm, once off the coolant-temperature-operated warm-up cam. However, with the air cleaner base back on and the engine at operating temperature, the engine is very slow to return to idle (1000rpm decrease / second), and then the idle speed is too high (perhaps 2500rpm). A blip of the throttle makes no difference, but if I pull the engine speed down by leaving the clutch engaged until about 1200rpm, the engine speed will stabilize just fine at a slow idle! This all makes no sense to me. I have eliminated all the usual suspects; Italian cruise control (floor mat on throttle pedal), vacuum leak at carb base (new heat insulators installed), sticky linkage, etc.. It seems that the problem is related to heat, not the air cleaner base installation. Still, I will check that. I'll also check that the cold idle cam isn't reengaging when the coolant is hot (rather than just warm). I also hope to disconnect the brake booster vacuum line and seal it for testing. Any advice you choose to share is appreciated. I will proceed with the tests outlined above and post any relevant information. Thank you. -rick / cross-posted from Portugal section
setting the idle mixture and idle speed must be made when the car is full operating temp or the car will not idle properly.
When in this condition, what is the individual barrel air consumption in Kg/hr as measured by STE Synchrometer?
Good question, really good question! Thanks. At idle, proper idle, when warming up at about 1000rpm, the Synchrometer reads 5 on all eight chokes.
Too high IME -- i.e., not all cylinders are contributing at idle (but they may be at higher RPM). On a 308 with the 1000 RPM idle timing at your 155/78 OM spec of 6 deg BTDC, the air consumption per barrel should be more in the 3.5 Kg/hr ballpark.
check to make sure the linkage has slop in it, the set screws for the ball/cap assembly should not be screwed in tight, rather there should be some play. If they are too tight, the heat expands the rods and f's with the idle. where are your idle mix screws set?
Birdman has a great tutorial on his web site at: Carb synch tutorial: 308 Series I used this method to set up my carbs after a full engine/carb rebuild. Run the engine until warm, and remember the key starting points: *Close all air by-pass screws *Open all Idle mixture screws three turns (as a starting point) *Turn the throttle stop screws just until they touch the butterfly lever, and go anther half turn (Make sure that this adjustment does not alter the mated carb's throttle stop screw setting Also see Birdman's note (in the article) about increasing your idle jets
Did you remove the throttle plates and shafts when you did the rebuild. Are you sure they are centered and free to move and were installed it the same locations and with the same face direction. Also when I dismantled the chokes I also backed out the screw for the cold start idle valve. I found that this mechanism had a tendency to give me an erratic idle. It makes for a little difficulty in starting but once warmed up it sits at 950 rpm. I have an old Sear tach/dwell meter that I set the idle with as I had found the stock tack to be 100-150 rpm higher then actual.
I had a similar problem with my 328. High idle, blip the throttle it wouldn't go down, etc. It was sticky linkage. Cleaned up the linkage with some carb cleaner, and the car immediately returned to normal. I had visions of a major mechanical problem, and it turned out to be as simple as cleaning things up. Hope yours turns out to be as easy.
Hello Everyone, I write today today to thank everyone for their suggestions regarding my '79 Standard Specification (Euro) 308GTB's idle problems. I have to admit, I did not search for the problem scientifically. Rather, I followed everyone's advice, at the same time. 1. Rebuilt carbs WITHOUT removing the throttle shafts or plates. (Previous work.) 2. Installed new heat insulators with integral gaskets, below the carbs. 3. Replaced the fuel hoses. (Previous work.) 4. Cleaned and lightly oiled the linkage. 5. Assembled the ball joints on the linkage with 'considerable play'. 6. Ran the engine until at operating temperature, before tuning. 7. Followed The Birdman's carb synch guide to the letter. 8. Verified that nothing was binding as the air cleaner went back on. 9. Tested, and retested the idle as each part went together. 10. Went for a long test drive. 11. Perfect performance!!! Thank you, everyone. -rick
