| Author | Message | ||
| '75 308 GT4 (Peter)
|
What about the little ball valve in the acceleration system? Any excess fuel and/or vapour is discharged through a calibrated hole into the float bowl, which is operated by that ball valve. If its getting stuck, it could be allowing that extra fuel to continue to flow, making the engine run on further even though you backed of the gas. | ||
| Robert Johnson |
OK I give! I reset the carbs again with the Synchrometer. They were not off by more than a fraction. The linkage is free, air flow at progression is exact and the throttle returns to the stops immediately. The distributor advance and return is spot on. Still the problem persists. The car runs fine, it just takes a few extra seconds between shifts (very annoying!). Any fresh ideas are appreciated. Thanks, Robert | ||
| Robert Johnson |
Thanks for all of your input. The last paragraph from the info from CraigFL sounds like a good description of the problem. I bought a Synchrometer today and will recheck the carbs again. I have been using the other type of flow meter. It was ok for my Lotus (twin DCOE's) but may not be accurate enough for the four DCNF's on this V8. The Synchrometer is no doubt more accurate. Thanks again to all and I will post the results here when I am finished. | ||
| Steve Magnusson (91tr)
|
Robert -- why not get the dist advance performance checked/verified. Even if it's OK, it's no sin to have this done every decade or so. If you pull and reinstall the distributors yourself, the labor should be only a couple/few hours (you may need to put a point set back in for the dist machine to use). JMHO, Steve M. | ||
| rocco
|
If the ign is okay, then the idle mixture is off. the throttle flap may be opened too much and the carbs may be drawing fuel from the progreesive circiut. | ||
| CraigFL
|
For some reason my message didn't come thru with the image.... Whenever I hear the RPM doesn't settle back down to idle, I think of vacuum leak. The Weber carb book leads you in this direction as well as things inside the carb. | ||
| Steve |
Robert I have a 77 308 GTB and I discovered while I was doing a cam cover gasket change there is a FAST idle valve that sits in the center of the top of the block. It is a valve assemble that is in the alum. water pipe that goes in between the carbs. The throttle cable pulls this link arm. Its purpose is when the engine is cold you are supposed to adjust the throttle linkage(there is a screw adj. here) to 2000rpm.When you pull the choke lever this valve goes to the cold setting. I found that this gets STUCK and doesn't bring the engine to idle quickly. So because you don't want to use the choke you need to de-tune this valve so it doesn't work. Check it out it may be the problem. You can see it on page 72 of your owners manual if you have one. Good luck Steve | ||
| CraigFL
|
C:\pagisinbox  webercarb1 | ||
| '75 308 GT4 (Peter)
|
Pretty tricky one. Thanks for the great detail. When you say that your linkage is free, is the cable a bit slack? The cable shouldn't be taut, I noticed the one on my car was slack, I've never had a problem with my car the way you described it. | ||
| Robert Johnson |
I have a 308 GTB (carbs). The problem is that it takes about 20 to 70 seconds for the RPM's to return to idle when the throtle is released. I have overhauled the carbs, including changing the intake manifold gaskets and the throttle shaft bearings. The carbs and linkage are free and return to the stops fully upon release. The throttle cable is new. The carb balance is exact and the float level has been rechecked twice and is exact. The fuel pressure is regulated to 1.5 lbs. The brake vacume booster and hoses hold vacume with no leaks. Timing is exact. Distributors have been converted to Crane XR700 units (the problem existed prior to the conversion) The motor mounts and torque strut are fine. When I check the mechanical advance on the distributors it does not fully drop until the RPM's drop. The counter weights are clean and greased. The car runs better than ever! The idle just will not drop properly between shifts. This may be ok for club day at the track, but for Sunday drives it sucks. I am confident that the problem is not carburation. I am thinking that the counter weights are the only thing left that may be the problem. Any suggestions on how to isolate their operation short of putting the distributors on a distributor machine? Any help or suggestions will be greatly appreciated! Thanks. Robert |