Wade, Any suggestions or recommendations on what you did or what. The float height was 48mm & 58.5, Im not sure I want to mess with that as I surely don't want it to overflow! Remember I don't have any extra parts laying around so would need to order them. Plus also remember it is fine at idle and WOT just that small transition where I am having an issue. Thanks for elaborating!
I would start by changing the accelerator pump nozzles. I believe they are 45, go to a 50. That will help when you step on it. The float level change is more delicate, you need to see where it is now and then look at the emulsion tube and see where the level is riding on the tube. Based on that information, you can decide if a change will help. You may be able to raise the level of fuel in the bowl and cover another hole in the emulsion tube. That will change that hole from an air hole to a fuel hole and richen the mixture. You may also pick a completely different emulsion tube that has a different hole configuration. This gets more complicated as the number don't follow an easily understood progression of change. Sometimes you just need to look at the tube and decide for yourself what the hole changes are going to do. Now, having said all that, it may be best if you bought a gauge with a wide band O2 sensor and hang the sensor in the end of the tail pipe and see what it is actually doing. It would be better to weld in a bung at the end of the collector but if you want it to look original, you can make do with it in the pipe, the readings are just slower. Doesn't carb tuning sound fun? You could just buy the Jenvey DCNF throttle bodies and put a self learning fuel injection system on it, plug it in and go drive the hell out of it. It will figure out the rest for you.
Wade and all, Finally got some time to work on the car, it turned out to have 2 pump jets nozzles plugged (cylinders 6&7). Could that little difference been causing my symptoms ( hesitation off idle)? What is the accepted way of cleaning those out? I called and talked to Mike at Pierce Manifolds out here, to get some parts, and he was surprised that I wanted to change parts, his thinking was my idle settings were off and suggested opening them up 3/4 turn (!)? This car was set up on a sniffer, I wish I could post the photos of it running on the stand before installed in the car, but gave up! I marked the idle screws for reference, and turned them all in and was amazed that some screws varied from 1.5 turns out to 3? The book says start 3 full turn out, with the average running setting around 1 turn?? Shouldn't they all be closer?? Rob Image Unavailable, Please Login Image Unavailable, Please Login
Based on your drawing, the non working squirters can only be a clogged nozzle as each carb has one pump and control. The nozzle has two outlets and if only one works, it is a clog. Clean the nozzles and see what happens. As for the idle screws, I start at 1.5 turns and adjust from there. If I go more than 2.5, I then up the idle jet and go back to 1.5. Unless you are sniffing each cylinder, it is not an advantage to have the idle screws that far off. 1/8 turn is an acceptable adjustment on idle screws. It doesn't take much to make a difference.
Assuming valve clearances and cam timing are ok. Distributor advance curve needs to be checked and verified. An ultrasonic cleaner is great for carbs. Correct float levels are important. To get the air flow correct across all carbs you need a Uni-sync ( or 2) , get all the slack out of the linkages, then fine tune the air bleed adjustmenst on each carb to get airflow the same on each carb. Once the airflow is consistent the idle screw adustments will all be a lot closer to each other. Once the carbs are set properly the tune remains quite stable - the points will wear out eventually etc. Good plugs are essential, eg NGK's. A hotter plug, ie -6's I find are more suited to "normal" driving with speed limits less fouling ( the recommended -7 heat range are OK for 4 hours flat out on the Autobahn in the 1970's .) These cars ran perfectly when they were built. My completely stock euro 'glass GTB runs clean to the redline, idles all day without fouling the plugs and starts easily.
Wade and Michael, What is the accepted way on cleaning the pump nozzles? I soaked them in alcohol overnight and blew air through them. I didn't have anything thin enough to stick in there and did not want to do that anyway! Could those only 2 nozzles plugged up caused my issue? I have a unisync and all throats are at 3.5 except the right rear carb at 4.0. The 3 float levels I checked were perfect. The car idles instantly, warms up to 1000 rpm and screams once off idle the only issue I have is a slight hesitation off idle when moving forward. Thank you for all your suggestions. I am having a hard time working on the car because of my neighbors, and work but will solve this. Rob
As it is a really small hole, check it by blowing air through it. I use low pressure and a rubber tip nozzle. I then hold it close to my cheek to feel the air. If it won't flow or is damaged, just replace it. You have to have that fuel shot on acceleration for this to work well. wrxmike is right, they will run great once you have them right. Just be patient and hit all the steps.
Hi all I appreciate this is quite the thread resurrection! Does anyone know if the timing on early carburettor cars could vary by load, and if so have any details on this? I know that the later cars used vacuum to detect load and advance the timing - again any details of that to the extent it would be relevant to an earlier 308 would be much appreciated. I now have programmable ignition on my 79 Euro 308 and am just wondering what to set it at beyond the settings at idle. It’s booked in for a tuning session, but that’s a way off and I’d quite like to see how well I can get it running beforehand. Many thanks.
No particular knowledge of the 308, but it is indeed more advance under high vacuum. This being said, that's not manifold vacuum, that's carb ported vacuum (sorry for the poor english). Not easy to retrofit on carbs that to do not have it already. If you want to add ignition advance based on vacuum and maybe knock management, you could give a try to J&S safeguard?
No, it's strictly just a mechanical advance (dependent only on engine RPM) for a carb 308, and what they did was just be very conservative such that the advance in the mid-band is always retarded like it is at high load. Assuming that you are completely emission-free (no cats, no air injection), you might consider starting with an ignition map something like that used on the euro 308 GTBi/GTSi shown on page 76 of the 195/80 OM, Fig 59: Image Unavailable, Please Login If you plot the 155/78 OM euro carb 308 advance curve: 1000 RPM = 6 deg BTDC then straight line to 1800 RPM = 16 deg BTDC then straight line to 6000 RPM = 39 deg BTDC then constant at 39 deg BTDC above that on that graph, you'll see how it's basically all below the heavy load line 1 (low vacuum) of the euro 308 GTBi/GTSi ignition advance map (except at high RPM).
