What size Webers & Chokes?

joseph222 · joseph222's Garage

I've got 48IDF webers with 37mm chokes in a 2.0L with a hot cam. I need to drop the choke size down to help cure a low rev stumbling problem. Since they go for about 100.00 a set, I was hoping to find out what most of you are running choke size. I realize that what works for one particular engine will not necessarily work for another, but just looking for some feedback to see what's in the ballpark. Thanks.
Joseph

John Rogers · 01-19-2003, 04:27 PM

I am guessing the carbs are a little too large. The rule of thumb in the San Diego area is 40mm for 2.0l, 44mm for 2.4l and 48mm for larger. I have a 2.8l stroker and use 48IDFs with 37mm chokes and it is just right with max power at about 5200 RPM. I think that the engine will stumble at low RPM no matter how small the chockes are with 48IDFs. Good luck.

joseph222 · joseph222's Garage

John,
Just to clarify for me, are you saying the 48IDFs have a limit of correction choke wise, or just that with my particular combination, the problem will still persist? What I was considering were 34 or 32mm chokes, possibly combined with different jets, emulsion tubes, etc. to get to where I need to be. Maybe simpler than buying new IDF kits, installing, cleaning up & finding a buyer for my old ones, shipping, etc. Bad Idea???

MJHanna · 01-20-2003, 05:21 AM

I go with John's advice; I don't think you can choke them down to get them to work properly. On my track 2.0 with flowed heads big valves, big cam etc. I run 44's I can't even imagine running 48's. Fax Roger at PMO, but I think your pushing the wrong end of the stick.

JWest · 01-20-2003, 05:40 AM

I had a 2056 with a 286 duration cam and 45mm Dellorto carbs. I had 34, 36, and 38mm venturies. I would change them out depending on my mood, but even with the 38mm vents I could pull the motor down to 800 RPM in 5th and floor it - it would smoothly accelerate through the whole range with no problems.

While smaller carbs might match your combination better, I still think your setup will run fine if dialed in. I also ran 45 Dells on a 1776 bug motor with no drivability issues.

I think you need to look at your jetting. I would look at enlarging the idle jets first to richen up the progression fuel. A little more info on when the stumbling occurs might help (part or full throttle, load, RPM, etc.)

joseph222 · joseph222's Garage

The car stumbles at low revs (under2500RPM), under load (at part or full throttle). To avoid it on take-off, one must keep the revs up by riding the clutch a little. Of course, at street lights, everyone thinks you're challenging them

During AX slow turns, when in 2nd gear, again, one must ride the clutch to avoid the stumbling, or just slowly feather it up (not real desirable for AX!). We have measured the amount of fuel "squirted" upon acceleration - it measures to an acceptable amount. So the thinking is the motor simply doesn't suck in enough air to pull fuel in the the low revs - thus a need for smaller chokes? I am going to look at the jets, emulsions tubes, etc. to see what's in there. I don't know what the typical base line combination is, but it will be a place to start. Thanks to all for your invaluable advice. I'll let you know what I learn.

JohnConnolly · 01-20-2003, 10:07 AM

I'm running 48 IDFs on a 1914 at 4500' above sea level with no hesitation. In fact, I can drive away from a stop in 3rd gear no problem.

You just need to tune the ones you have. Almost all webers I see have some sort of setup problem (even new out of the box).

If that doesn't do it, we are finishing a run of venturis from 32-45mm for the 48 IDF, so you'll be able to step down if you need to. We will also have a huge assortment for the 40 and 44 IDF, and 48 IDA.

John
Aircooled.Net Inc.

joseph222 · joseph222's Garage

John,
Do you have a target date when you will have a selection of 48IDF chokes available? Thanks.
Joseph

John Rogers · 01-20-2003, 01:33 PM

I imagine that the barrel size could be anything you wanted as long as the chokes are sized for the engine and the RPM where you want to make power? The folks at Weber told me to figure size , you take engine displacement (2.0l) and then select RPM where you want power to peak at (roughly) and then take that choke size x 1.25 to get barrel size. I guess the internals might be different on different sized IDFs but I've never tried to measure things like that? The chart I have says for a 2.0l engine @5000 RPM use 32mm, 5500 RPM use 33mm and 6000 RPM use 35mm. If you multiply those by 1.25 you get 40mm bore for the 5k, 41.25mm bore for the 5.5k and 43.75mm bore for the screamer, remembering you have to rev past the peak power some to shift! Good luck.

JohnConnolly · 01-20-2003, 05:22 PM

What size? They were due around X-mas, and are running late. We are doing largest sizes first (45mm), but we expect the 45, 42, 40 (IDA only), 36, 34, and 32mm for the 48 IDF and 48 IDA to be done soon.

John
Aircooled.Net Inc.

joseph222 · joseph222's Garage

I would be looking for 32 or 34mm chokes for 48IDFs. Can you email me direct with a way to check in with you @ a later date when they might be finished? AX season starts for me next month and I'd like to have the 48s either tuned or sold by then. Thanks.
Joseph

JohnConnolly · 01-21-2003, 09:49 AM

I suggest you e-mail me directly. I get over 600 e-mails a day, so I don't have time to check a "to do" list, it's best you just keep checking in every week or 2.

John
Aircooled.Net Inc