Jetting recommendations for Weber 40 IDF's

Gabe · Post by **Gabe** » Thu Mar 23, 2006 1:01 pm

I've searched around and found varied suggestions for jetting Weber IDF carbs, but not all of the suggestions mention engine size and altitude level. What idle/main jets would you folks recommend for the following cominations:

1. stock 1600dp, pair of Weber 40 IDF's, 28mm venturi's, close to sea level (Maryland area), DVDA/SVDA distributor, header/QP muffler.

2. mild 1776, otherwise same condition as "1" above.

Thanks!

RoWaMe · Post by **RoWaMe** » Thu Mar 23, 2006 1:15 pm

Gabe, I had very similar setup on 40 IDFs on my 1600, stock internals, 1 3/8" header, 009; and also the 28 venturies. After some tuning with main jet sizes, I ended up with 115 mains and either 50 (I think that's the one) or 55 idles. Car ran great. Put same carbs on a 2-liter (78x90.5) and did not have to change anything!! The 2-liter was very "mild", having stock-valve heads and also using the 1 3/8" header. Go figure... Yeah, I'm at sea level too.

Gabe · Post by **Gabe** » Thu Mar 23, 2006 6:27 pm

Sounds good. The set I picked up have a 130 main and 55 idle. What issues would I run into if I left the main and idle as they are? Too lean/rich?

David Miskov · Post by **David Miskov** » Fri Mar 24, 2006 3:57 am

Too rich. Are the venturis 28mm?

Gabe · Post by **Gabe** » Fri Mar 24, 2006 5:13 am

Yeah, the venturis are 28mm. Better rich than lean I guess.

David Miskov · Post by **David Miskov** » Fri Mar 24, 2006 5:23 am

Read this:
http://www.aircooled.net/gnrlsite/resou ... etting.htm

You would be closer with what Rowame suggested.

500LbGorilla · Post by **500LbGorilla** » Fri Mar 24, 2006 5:40 am

Gabe wrote:Yeah, the venturis are 28mm. Better rich than lean I guess.

Better correct than not. The difference in how it will run is substantial, and your economy will go up.

Personally I think 28mm vents should be left to bone stock 1600's. If you run a 1776, consider at least a 30mm vent, more if your engine is built to breathe. 4-6mm smaller than the intake valve on milder engines. 2-4mm smaller on powerhouses, and even more on all out drag and insane street engines.

There's no good way to tune it without a good wideband though, unless you have a dyno or access to one. The wideband AFM will tell you what you need to know for economy for sure, and will give some good guidelines for power. Now that I have one, I don't know how I got on without one.. I am sure it could have really helped me in the past.

RoWaMe · Post by **RoWaMe** » Fri Mar 24, 2006 11:22 am

Gabe, my IDFs came with 135s. The engine ran, but at higher speeds it seemed like something was holding it back. Also remember smelling gas in the exhaust!! At night on the highway, with cars behind me, I could see exhaust smoke in their headlights as I nailed the gas. Next jet size ws 125; definite improvement as the engine felt "freer". Went down to 115 with no loss in performance, the "exhaust smoke" stopped, and no pinging/popping due to lean condition. I stayed at that size.

I realize that when I installed these carbs on my stock-valve headed 2-liter, I could've gained some performance by going to 32mm venturies which I had ordered. But the dang engine developed low oil pressure very quickly, requiring removal before I could try the larger vent's.

Gabe · Post by **Gabe** » Fri Mar 24, 2006 2:59 pm

Looks like I'll have to order some jets. Following the advice from everyone and the calculator in that article (4.1-4.3 x venturi size for mains) I think 115 or 120 should be a good start, since I'm close to sea level and I don't want to risk going too lean initially. Probably leave the idles as they are at 55. Thanks guys.

500LbGorilla · Post by **500LbGorilla** » Fri Mar 24, 2006 5:03 pm

What are your float levels, btw? They need to be about 11mm. If they're not it won't tune right. That and fuel pressure are critical factors.

Bruce2 · Post by **Bruce2** » Sat Mar 25, 2006 1:45 pm

Gabe wrote:Looks like I'll have to order some jets. Following the advice from everyone and the calculator in that article (4.1-4.3 x venturi size for mains) I think 115 or 120 should be a good start, since I'm close to sea level and I don't want to risk going too lean initially. Probably leave the idles as they are at 55. Thanks guys.

Your fears are unfounded. By using the jets Roland stated you will not be lean. When Weber ships 40IDFs for VW use, they install:
50 idle jet
28mm vents
115 mains
200 airs
F11 tubes.
This always works in VWs. I ran that combo in my 40IDFs on my 2 liter and made 120hp. It would rev to over 7000 rpm, so the small vents didn't restrict top end power like some will tell you. Although larger vents would make more hp at the expense of bottom end torque.

Sixty3GL · Post by **Sixty3GL** » Sat Mar 25, 2006 6:50 pm

500LbGorilla wrote:What are your float levels, btw? They need to be about 11mm. If they're not it won't tune right.

That is what I set my 40 and 44's to (following your directions) both were set way off.

Gabe · Post by **Gabe** » Sat Mar 25, 2006 7:06 pm

Just started taking apart my carbs, and when I pulled the F11 tubes, I noticed that the mains are 115's. Surprise to me, since the box for the carbs had a sticker on it stating that "The jets in this carb kit have been drilled to: 130 Main jets, 55 idle jets" (the numbers were written in). These were from CBPerformance. Seems like I won't have to spend any more $$$ for new jets.

Bruce2 · Post by **Bruce2** » Sat Mar 25, 2006 9:46 pm

Have you measured the jets? If the label says they were drilled, they probably were.

Gabe · Post by **Gabe** » Sun Mar 26, 2006 8:35 am

Aww, Bruce, why did you have to bring me down to reality. I thought so too, but I don't have a measuring device that small to confirm that they are 115 or 130. I'll probably install them as they are and feel how the engine runs. If too rich, I'll order a set of 115's and see if they make a differnce. Going to try to finish up cleaning the carbs and setting floats today.