I have the jet kit and with a 160 idle jet in the primary,( the largest in the kit) it still stumbles a bit and backfires occationaly. I have heard of people drilling out jets, but i'm not ready to go there yet. Any thoughts? Thanks.

WEll, it stopped raining, so i'm back to jetting. After advancing the timing, the off idle hesitation is better, but it's running rich, so i'm going to start backing off and see what happens. That AF meter is sounding better all the time.

Please don't be offended if I state anything that may be construed as obvious--just want to be sure we're talking about the same things. You mentioned that your idle jet is the largest in the kit--a 160 in the primary. It sounds like you are actually refering to the main jet. The idle jets are located on the exterior of the carb, held in place by brass screw "holders"--one screwed into each side of the carb--and the jet slips into a recess on the inside. Normal range for the idle jets would be in the 30-50 area in increments of 5. The main jets are located in the float chamber, at the bottom, at an angle, one for each barrel with the primary (smaller of the two throttle plates) range in the area of 125-145 and in the secondary, 115-145. The air correction jets are found at the top of the carburetor body, alongside each barrel. You'll see numbers like 155-170. Under the air correction jets are the emulsion tubes which sometimes can be removed if the carb body is turned upside down with the a/c jet removed-but usually have to be fished out with a wire hook. The emulsion tubes come with different profiles and holes along their length and for the most part can be left alone-that gets into the area of very fine tuning-but if you have your carb apart you may want to see that they (and all passageways) aren't clogged. The accelerator pump jet which is also installed at the top of the carb body with its nozzles pointing down. They can be had in different jet sizes but what's more important is that they provide a good strong stream of fuel when the throttle is opened. That depends on the passageways being clear and the diaphragm in good shape (easy and cheap to replace). The problems you are having sound like something other than jetting issues. The condition of the distributor (bushings not worn, advance working, etc) and the rest of the ignition system being up to par are essential.

When I bought my Amazon it stumbled on acceleration and I wrestled with my Weber (came on the B20 in my Amazon when I bought it) for quite a while trying to get it right, and when it came time for a new exhaust system I had a port welded in so I could put a wide-band A/F meter in. Before you start drilling out jets, try going in the other direction. Now it is possible that there is something screwed up internally in my Weber (tough I've rebuilt it, new diaphram, o-rings, etc. etc.), but I have the absolute smallest primary idle jet available (I think) in mine and it still idles a little bit rich, but otherwise runs very well. I spent a lot of time fiddling with the carb and watching the numbers on the A/F meter trying to get things smooth and with good economy (last I calculated it I was getting around 29mpg, and had good power). Of course every engine is a little different, particularly with the various mods, exhausts systems, etc. one can put on, but here is what I currently have in my DGV according to my notes:
main idle 40, sec. idle 42, main 150, sec. 140, main air cor. 165, sec air cor. 180.
Per the A/F its STILL a little bit rich at idle and it gets a tad lean at highway speeds on a long, slow incline.

You need it to be a bit richer than 14.7:1 at idle -- that's just how engines work.

What brand of meter did you use? It seems this would be the least amount of trouble in the long run. I've read of several people who did this and it always gives a better running car. (even with SU's)!

Honeychrome--you've taken a much more scientific approach to tuning (as my son would at his Mini/BMW shop) than my own stumbling, seat of the pants experiments. When tuning, it's much easier to get it right if you go from rich to lean. Going the other way the car seems to run better and better--egging you on to make it richer still---wrong. Then you've gone so many steps too rich you have work to get back to the sweet spot. Going from rich to lean will make an overstep more noticeable--then back up one step. Your condition of leaning out on light throttle under load may be correctible by going a little smaller on the A/C jets. That's also the area that the emulsion tube plays a roll. I used to have the advantage of access to many scrapped cars for Weber hardware--and had accumulated a variety of jets, tubes, etc--with Weber guide in hand I examined the emulsion tube in a car with a similiar problem and a number of tubes on hand---picked a different profile-- solving the problem. Your symtom could also be caused by carb icing--an often overlooked factor. If you don't have some warm air already directed to the intake, try doing so--heavy duty aluminum foil and some appropriate tubing will work temporarily.

I did it 'seat of the pants' for years with my old BMW motorcycle- the A/F meter may have taken the art and mystery out of it, but it sure is easier! I actually got the car running quite well before I put the meter in, but I wanted to know what exactly was going on and figured I could get a bit better economy than I was getting, which I did after putting the meter in. The meter I bought is an AEM (I think). Think I got it from Summit racing for around $250 with the O2 sensor, if I recall correctly. There are much cheaper A/F setups, but those are not wide-band, and you really want a wide-band.

When the car comes out in the spring I'll fiddle with the emulsion tubes and see if that does the trick with the leaning out, which really isn't that much of a problem, but I'd like to get it perfect!

Thanks for the kind rebuke, yeah, it's a 60 in the primary idle side, 55 in the secondary idle, 160 main jet and 155 in the secondary main jet. When it stops raining, i'll mess with my timing.

My experience is that you have to get the idle jets right first. The right idle jet will get you to the point that it idles best when the idle screw is turned out about 2 turns. Then what I have found is that mine required a lot of advance to accelerate fine without hesitation. I cant explain why but when I went to almost 20deg of advance at idle, the thing pulls strong and runs well. I think I wound up with main jet around 160 and secondary jet at 150. Cant recall what air corrector jets I wound up with. But once you get it right....you never have to mess with it again.

Dean

20° advance at idle is about what it ought to be anyway.
--
George Downs, Bartlesville, Heart of the USA!

Well that's good to hear. My haynes manual says the B20B should be timed at 10deg BTDC at idle.

Dean

Yeah, I advanced the timing by ear, and got rid of a lot of the stumble. I'm going to mess around some more with the jetting.