I just saw the other 308 thread regarding not running smooth at cruising speed, and the responce answers one of my two problems. My unsolved problem: My '78 308 GTS starts right up after the start up ritual of letting the fuel pump run for 20sec, three pumps on the gas pedal, and fire it up. After up to a minute, the car settles in at a smooth idle. Problem is when the car is at operating temp, and parked for half hour or so, on restart, I cant seem to get the idle to settle in. I come to a stop; it will idle, and then slowly drop to stall if I dont keep the gas on. This can be challenging when the stopped is on a hill. The problem will correct itself, only after I continue to drive at a steady speed such as the freeway where I hold the throttle fairly steady. Then when I come to a stop, idle is fine. It appears that the stop and go driving is the problem here. I also noticed this a few times even without stopping for that hour. The car idles fine, then if I proceed thru some canyon route, with a lot of throttle modulation. When I come to a stop, it doesnt what to settle into an idle. Easy solution would be just dont stop, but, sometimes that is not rational solution. I have stock jets, car has the emission equipment fully operational and the engine smoothly pulls thru the rpms, Carbs were rebuilt, they dont leak, new plugs, new wires, fully tuned by one of the better shops in So Ca . Any thoughts would be much appreciated- Thanks in advance Dave
At what RPM? At what RPM? Over what durration of time, and at what RPM does the engine drop off and die? Over what durration of time? At what RPM? It settles at what RPM, and then over what durration does it drop off and die? Sounds like the idle mixture is not correct, and maybe the idle speed is not set correctly. How does the warm engien take an application of throttle--like a jab? Comming to an idle and then slowly dieinig is a sign of too rich* on the idle mixture, comming down too slowly is a sign of too lean on the idle mixture. Your descrip[tion above is not precise enough to tell from this distance. Are you absolutely sure the startup circuits are completely off after the car is fully warm? (*) or a lot of other things....
When a hot engine is turned off it doesn't start cooling immediately. There's a period where heat sink increases the engine temp. Both circumstances you describe sound to me like overheating affecting the tune. What is your normal indicated running temp and what temp is showing when your idleing issues arise? Are your cooling fans coming on and is your system bled of air?
From the posted data:: I think that you have the idle mixture too lean and that you are hoping that the 975 RPM settling point is where the idle RPM is set. I suspect that it is really set (now) at that 600 RPM point, where the motor is not making enough power to run itself. This leanness is confirmed by the jab on the throttle at idle, 3200 RPMS, and gone away by 3600 RMPs. What I would do first:: set the idle RPM so that the (warm to very warm) motor runs at 950-975 RPMs for 5 minutes without dieing. {Might want to put a 3" box fan on the radiator to help the motor from overheating.} Now go out and run the car for 5-10 minutes to cool it off, and to verify that the idle speed is such that the motor does not die on you. While cruising, take the car out of gear and watch the descent of RPMs towards idle and then the stability at idle. This will tell you how the engine is idling with cool airflow. Then come to a stop and watch the same descent of RPMs and the stability at idle. This tells you a little about the heat soak idle properties of this carb setting. Now just sit at the stop for a while (1 minute) to see if the stability is long term. I will be back later after I think about the carb tuning and refer to my Weber manuals. Do you have access to a set of manometers (manifold vacuum gauges)?
The only way to start with this problem is to synch the carbs, check the idle mixtures and properly set the idle speed. If you just go through this procedure, the car will run right. It's not hard. I suspect that your carbs are not synched well enough. Don't accept that because a better shop "fully tuned" the car that they synched the carbs properly. You would be surprised how few shops have someone that knows how to do that anymore. The fact that you are on the original jetting in this day of ethanol fuel probably means the car is running lean to begin with. Poor synch is going to make the car run poorly from idle until the main jets start to come in (3000ish RPM). Use the procedure on my website. Virtually foolproof! It ain't rocket science. http://www.birdmanferrari.com/service/sync/carb_synch_tutorial.htm Birdman
in all situations where the Rpms just drop, the temp is not over the operating temp. The water runs at 195. the oil at 210. after the car sits for the 45 min, and then on restart, there is no noticiable increase in engine temp, if anything, it is sometimes cooler. Even in the hottest days of summer, water temp gets above the 195, oil is above the 210, i still have a steady idle.
Mitch, on steady driving, rpms at 3200+, then go into city stop and go- the rpms DO NOT DROP. engine will idle steady at 950/975. it will idle at that for as long as i sit there at idle. I could pull into my garage, leave the car idleing for 5 to 10 min (note i would never do that due to cooling issues) and it is rock solid - 950/975. Issue is at re start, where it doesn't hold at that 950/975 rpm, but will drop steadly to zero or the engine stalls. I don't want to give you the empression that, the idle goes to the 950/975 range - but then wants to "settle" at 600. The idle really just drops steadly off the 950/975 mark until the engine stalls --- i don't let this happen, because i just modulate the throttle-
Birdman and Mitch, sounds like you both are thinking carb adjustment issues. The carbs to me, sound like a lean issue with the comments from Mitch, and the issues, where quick, hard jab on the throttle causeing imediate stall. I did have car tuned and adjusted in order to get smog test. The carbs were readjusted to run better after the test. Birdman, i need to get some equiment to complete your carb synch. I'm thinking prior to getting the equipment- since its late saturday, maybe, i just give each carb a 1/4 turn on the mixture, to go with a richer setting. i realize this will be not too accurate, but if there is a small noticable change in the "quick jab' issue, then possibly that is the direction to proceed. complete carb synch would then be the next step.
The quarter turn is only going to affect idle mixture. So not quick jab. Quick jab is affected by the accelerator pump and its jet (for each throat). Getting yourself a flowmeter to synch the carbs and adjusting the idle mix and speed as per Birdman's info is just a start. I recommend you get the Haynes Weber book and get your head around how their various sections work because I agree the idle issues are an indicator that changes in fuel have brought your carbs tune close to the edges of its envelope. It would be interesting to know what jets, emulsion tubes etc they have currently.
My guess would be that you have worn carb linkage causing some binding or drag. If you slowly modulate the throttle when coming off the gas and the idle is higher than when you take your foot off the gas more aggressively then that's a sign your linkage needs some love. As birdman suggested, go through the full drill of checking the linkage and synching the carbs.
