weber 38 jetting tales

[falcon fanatic]

I've been getting pretty awful mileage since I installed my weber, about 13.5 mpg. Since I installed that carb like three or four years ago, that's a lot of gas down the tube. So, I decided to install a wide band 02 sensor with guage, because I thought I might be running a little rich. The result, oh, about 11:1 . I guess I have some jetting to do...

 

[Anonymous]

Just out of curiousity..I was wondering what guage you are using. I have been thinking of doing the same thing to dial in the 5200 on my 200.

 

[fordconvert]

Here is the one I have, its my first so I dont have anything to compare it to.

Innovate LC-1 $199, Im using it with a Megasquirt EFI system so I didnt need the gauge. It has 2 analog outputs that can be programed to do or simulate just about anything so they can hook to stock ECU's and other brands of gauges. The also have sets for $289 with gauges. From what I read before I bought it seemed like the best value with the best reputation. The sensor itself is for 2000ish volkswagons and can be bought from just about any parts store for around $70 IIRC if you ever need to replace it. Some of the other ones were much more money and apparently only available mail order from the original vendor. They even have a clamp on bracket so you can temp install it in your tailpipe.

http://www.diyautotune.com/catalog/inno ... 3e054d496e

 

[falcon fanatic]

I'm using this one from AEM:

http://www.aempower.com/ViewCategory.aspx?CategoryID=67

I got it for $225 on ebay, delivered.

It's very helpful. I took a long drive last night, was able to get my idle at 14.5 - 15:1 and my half and 3/4 throttle cruise is around 15:1. It's only my 1/4 to 1/3 throttle that's rich, at about 13:1. So, I'll put in a smaller idle jet today and that should get me close to perfect.

I think my accelerator pump is too big, because it jumps to 11:1 when I pump it. Also, full throttle acceleration is rich at like 12:1, but I'm not sure what jet governs that. Anybody?

My overall goal is to run lean-of-peak except when accelerating. I'm trying to maximize mileage, and still get max power when I mash it.

 

[fordconvert]

The accel pump volume is usually controlled by the stroke of the pump. How that is done varies from carb to carb and how far you need to adjust it. In some cases you do need to mod stuff. From what I have read and seen so far with my setup 12:1 should still be fine for performance especially for a brief period. Im dealing with Megasquirt EFI where you can easily adjust any and everything and I have not been able to get rid of small spikes like that. I would assume with a carb its going to be even more difficult. If you can get your cruise in the 15+ range and good drive ability over the rest of the range I wouldnt worry too much about a few rich spikes here and there. Have you messed with your ignition much? I have not gone to electronic timing yet but have had to change the range of my vacuum advance a few times because of detonation problems. I had tweaked the curves with the carb on the same car before and was happy with the performance. When I went to EFI and started working closer to 14.7 or leaner I started to have detonation issues. At first I just turned back the whole dizzy which solved the problem but performance started to suffer so I ended up putting a washer in to limit the travel of the vacuum advance and was able to advance the dizzy again. Since then its been running great.

 

[cfmustang]

When you get it dialed in, it would be nice to see a list of your jet sizes. Lots of people have listed the jet sizes for their 32/36's, but there isn't a whole lot out there for those of us with 38's.

 

[falcon fanatic]

will do, chris. Right now I have

Mains 145
air jets 185
idle jets 50 (had 55)
emulsion tubes F-50
accelerator pump jet: 70

This setup is close. I'm thinking one size bigger mains, and one size smaller pump jet.

 

[cfmustang]

Good information to know!

I've noticed poor mileage myself and figured it was the carb running too rich. However, it has been running good enough to push it off till later. Maybe this weekend I'll look at my jets and see where I am at.

Thanks!

 

[falcon fanatic]

FYI, I've made the following changes to great effect. The car is now mostly between 13.5:1 and 15:1. Idle is dead on at 14.7. I still need to get it leaner at the low revs and richer at the high, but this is a big improvement in both power and fuel economy. I can power out the tail around corners, finally justifying the trak-loc. Car runs much smoother now and I've discovered that the awful rattle that I was having at WOT above 3000 rpms was detonation due to leaning ouch! Doesn't happen any more.

Mains: 155 (up 2 sizes)
air: 185 (same)
Idle: 45 (one down)
emulsion: f-50 (same)
accelerator pump: 60 (one down)