CHANGING IDLE JETS

Short answer 1: Not neccesarily - if the needles are kept constant they generally all are richer to the same degree.
Short answer 2:Not neccesarily. Should leave air clener off when first starting the motor with the new idles to check for leaks.

It has been my experience that if you touch nothing else in the linkage, the idele will be quite sinilar abd just the one odle set screw in the middle will do.
60's are quoite rich and you may expect smoe blue exhaust (very rich). Your transition will be smoother and you will definitely not need to use the starter enrichment when you start - at any temperature - if the rest of the carbs are stock and operational.

If you are having a transition stumble around 2800 0 35oo, I would suggest you consider keeping the 55 idlea and raising the main jet size instead which will bring in the main circuit earler.
Good luck and let us know!!
best
rt

 

60's are very rich and may require a hotter plug, say NGKBP5. i ran 55 /135 idle and main jets in all of my carb cars. i had the individual air filters on 2 of them. i would be careful to keep an eye on your plugs as 60's in any of my cars gave me fits. i would be inclined to increase the main jet and go to a richer air corrector before putting such a large idle jet in.

my .02

 

I tend to agree...on a '79 308, the cams are pretty mild and I would be surprised if you really need .60 idle jets. The early 308s ('76-'77) often respond well to .60s because of the cams, but I would suspect that .60s on a '79 would be really rich. Of course, you can tweak down the idle mixture screws to lean it up at idle, but once you start opening the throttle you get the full idle jet mixture. This should help your transition but it may foul plugs like crazy.

I would just check the synch at idle once you change the jets, and then set the idle speed before putting the airbox back on, just to test things out.

Birdman

 

But imagine the education and confidence you would gain screwing with it a day or two by yourself!

 

I am running 55 idles but I think it would be worth at least trying the 60s. They aren't that expensive plus it doesn't take long to change them. If I had a set I would give it a try. Change them out and drive the car. It is runs better keep them in if not change them back to 55s. IMO it is worth trying.

 

It's absolutely worth trying the .60s. I am just surprised if a '79 wants .60s but hey, what the heck do I know??? It won't hurt anything. Worst case, it runs a bit rich.

My '77 loves the .60s and everyone told me they were too rich too. It might be, but the car runs better with them without a doubt.

Birdman

 

Furthermore, it is my experience that most dealerships (yes even Ferrari) and most independents (I'm sure not all) haven't the slightest idea what they are doing with carbs anyway. Maybe Algar has a carb guy that knows his stuff, but there are very few shops locally in this area that have anyone that knows squat about Webers on 308s.

Birdman

 

Would consider 135 mains, F36, 200+/-10 Air correctors and 55 idles. This will save some gas, but yet bring in the main circuit sooner.
Good luck!

 

exactly. this is a near perfect combination. . 60 idle jets are too big for a 308 with no internal engine mods. i gave away the set of them that i took out. jets, spark plugs and accuracy of the advance wieghts in the dizzys are critcal to a happy carb car. i detest points ignition, so that would be another point to improve upon.

been looking for another carb 308, havent found one i like yet. lambo is gone, the 911 is fun, but it aint no Ferrari. it is cheap to play with though.

 

Currently, my '78 has 135 mains, F36, 200 AC and 55 idles. I do have a set of 60 idles that I will try when I get a chance. It is a simple job to R&R the idle jets. I do have individual filters, opened exhaust (no muffler), and an Electromotive ignition.

Henry

 

it probably sounds a bit out there but have you checked any of the other basics.cap ,rotor grounding out.ht leads plug condition and gaps.do you do alot of short runs.try closing the plug gap by .004 .a closer gap will give you more spark duration.if that fixes it the coil could be weak.if its a flatspot check your accellerator pump .is it pumping to little.too much can give you a similar feel as you have too much fuel mixed with a certan amount of air.get the emissions checked out.it will tell you alot

 

NO muffler??? WOW! That sucker must be LOUD!

 

WHAT?!? Did someone say something?

Actually not too bad. I've got the cats on and the Ansa tips muffle it a bit. It's a little louder than some Tubis I've heard on 308s.

 

I had to smile hearing you talk about the inside jets. I also have developed a new vocabulary. I made a dinky little tool just for those with a removable screwdriver head and a socket and some tape. I am also glad tha Pierce sells the little o-rings cheaply. I keep a supply.

Glad to hear it went as expected. Richness covers up that transition between idle and main circuit making it much more livable. As I said before, you may eventually want to try 135 mains and back down to the 55 idles.

That slight break-up is probably in part due to those 125 mains you are running. If you are set on keeping the 125 mains, would suggest richening the top end with an air corrector of about 190 or so.

Your idle went down as it is a bit richer than it was - my A/F bet is around 11:1 to 12:1 from 13 or higher.

Again - glad to hear it is improved - keep us informed!!
best
rt

 

Alright! Good work Bob! Now sync the carbs and tweak the idle speed! What teh heck, the airbox is off anyway.

I have this fabulous 90 degree screwdriver that I have had for eons and I use it EVERY time I work on the 308. I'll post a pic. Very helpful tool!

Birdman

 

Hi Bob,
OK, first the idle. There are only two screws to adjust idle speed. These are the throttle stop screws, one on the forward pair of carbs, one on the rear. They just allow you to adjust how far the throttle will close when you take your foot off the gas pedal. They must be adjusted together and is best done with a flow meter so you can get them matched from front to back. This is the final step in syncronizing the carbs. I HIGHLY suggest that you take another hour once you have the airbox off and do the sync procedure. Really, it's quite easy, just follow my guide and do it outside so you don't asphixiate. I PROMISE you will notice the difference. It's a nice feeling to know that the carbs are synched and you can feel it in the way the car drives.

Adjust your idle FULLY warmed up, not just a drive around the block, or the idle speed you set will not end up there when the car is warm.

Once you have adjusted the idle once with the airbox off, so you know the linkage, it is possible to do it with the airbox on, using a long screwdriver, a flashlight and a mirror. It's not easy that way. I would still pull the lid off the airbox and use the flowmeter to get the front and back balanced. That's the best way to get it to idle perfectly.

The flapper in the airbox is to keep the stinky fuel smell from wafting out of the carbs into the atmosphere and the door is activated by a vacuum from the carbs, the same vacuum that runs the rest of the vapor recovery system ( i.e. the cannister you refer to). You can remove the vacuum line to the airbox, but you must plug the orifice that feeds the line, or you will have a vacuum leak and the car will run poorly. The cannister also is part of the fuel tank vapor recovery, so you don't want to remove it. It is harmless except adding a few ounces to the weight of the car. It actually does do something, which is to help keep your car from giving off fumes. You will appreciate it when your garage stinks of gas.


Congrats on your progress! You are on your way to being a carb guy!

Birdman

 

It all depends on what the mixture was before and what it is now. There is a happy medium in the ratio of air and fuel. When you change jets, you change that ratio and everything changes. You probably made it a little too rich at idle (for which you can compensate with the idle mixture screws) and that made it drop in idle speed. I find that my car likes to run a little better around town with a larger idle jet, which makes it a little rich at idle. So you make a performance trade off. I'll bet if you close down the idle mixture screws a turn or two, the idle speed will come up again. It's important to note that the idle mixture screws only adjust the fuel delivery at idle, with the butterflies closed. The progression circuit that feeds additional fuel in the transition period between idle and the main jets is VERY important to how the car runs, and those are fed directly by the idle jet UNAFFECTED by the mixture screw. If you look at a cutaway diagram of the carb, you will see what I mean. The fuel to the progression holes goes in a different path from the idle jet AROUND the mixture screw.

Once the idle mixture screws are open all the way, the idle mixture is limited by the idle jet. So if your car needs more fuel in the transition period, the only thing you can do is a bigger jet. Then if that makes the idle too rich, you just close down the mixture screws and lean out the idle mixture. In fact, the way you set idle on the car if you don't have an exhaust gas analyzer is to set the idle screws for the point at which they produce the highest idle speed. That is, in theory, the ideal setting where the A/F ratio is optimum. You would be surprised how close you can get it this way if you are careful. If you close them to much and go too lean, the engine slows and if you open them too much and go too rich, the engine slows. At the right setting, you hit a peak in the bell curve where the engine runs best.

Birdman