TheSamba.com :: View topic - Jetting dual two barrel Weber carburetors on a Berg 1776 motor

Fri Jul 27, 2018 4:39 pm

I recently aquired a 1972 Superbeetle. It's equipt with dual two barrel Weber 40 idf carbs on a motor with a Gene Berg 1776 upgrade. I would like to know from anyone with this setup what they jetted the carbs with. Thanks for your time.

Sat Jul 28, 2018 7:27 am

Have you done a search? Theres a lot of info out there and I have gotten some great advice from John at aircooled.net for various IDF anf HPMX jetting questions. There are also quite a few jetting tables online, but some of the suggestions are questionable....

Sat Jul 28, 2018 8:39 am

I have been scouring the net looking for info, as you wrote, there are more than a few tables that contradict each other, that's why I was hoping someone was running this setup.

Sat Jul 28, 2018 9:49 am

Get yourself a Weber tech manual by Bob Tomlinson

Sat Jul 28, 2018 1:58 pm

loungewizard wrote: Gene Burg
And learn how to spell the mans name. If it was your name, you would care.

Max

Sat Jul 28, 2018 5:07 pm

A good starting point for jetting would be,
50 idle
125-130 main
180 185 air correction.

Good Luck.

Sat Jul 28, 2018 6:18 pm

Post all of your engine specs

Sat Jul 28, 2018 7:23 pm

67rustavenger,

Thank you!

74 Thing,

The car was given to me by my cousin. He had the motor built, put about 100 miles on it and then it sat in his garage for three years. I've been trying to get more info on it from him, but details are a bit sketchy. I'm told that it was built with the Berg kit and is all new except for things like the coil, and other miscellaneous parts. The dual Webers came off the motor when it was a 1650cc. I had to pull the left intake manifold and replace the gasket do to a leak. I checked the compression on the three cylinders I could get to and they were all at 120 psi on a cold motor. What other specs would you like.

Thanks for your help!

Sun Jul 29, 2018 12:47 am

The cam plays a critical role in your jetting requirements. Also learn how to do sparkplug readings.

Sun Jul 29, 2018 2:30 am

Without knowing exactly what cam is in the beast, I can say it's a mild street cam, there's nothing radical about it. I was a full fledged motorhead 30-40 years ago and was adept at jetting Holley four barrels and Quadrajet carbs by spark plug color. Since I don't have a box of Weber parts and have to order what I need to dial these 40s in I'm looking for a starting point. That and it's a huge pain in the ass to pull them since there's no room to work in this situation.

Sun Jul 29, 2018 6:07 am

lounge, did you happen to check the current jets and the venturi size on your left IDF when you took it off for the head flange gasket? That would've been ideal because getting at either of the idle jets with the carb installed is nearly impossible. You can still easily get to the main jet with the carb installed, because it is at the very bottom of the two large tall brass tubes which stick straight up from the carb body and have a large slot in the top of the tube. This tall tube is generally known as the jet stack. Just unscrew one of the entire stacks and look at the numbers stamped into one of the hex sides of the main jet which is located/pressed into the bottom of the stack. The other pieces of the stack are also important for jetting and contain numbers. Here's a Gallery shot of the stack from a larger Weber, but on yours they would be pressed together the same way. Main jet stack on right, idle on left.

The venturi size is usually cast into the top rounded shoulder of the venturi if dealing with an OEM part. Typical numbers for an engine of your general build would be 28 or 30, indicating the diameter in millimeters of the narrowest part of the venturi. You can see it with flashlight by taking off the carb top which you'll have off anyway to unscrew the jet stack. Then just look down the carb throat beyond the auxiliary venturi. No disassemby required. If you don't see a size cast into the top shoulder, then it's likely that the venturi is not an OEM unit and was simply a machined piece which did not get the size stamped in. Then you'd have to remove it from the carb (not hard to do but must take the carb/manifold out of the car) and measure.

In this Gallery shot for general orientation you can see such sizes on the 3 OEM venturies in the top row. The left one is "24". The center and right are "28".

All that would take you at most 10 minutes, so that all you'd still need would be the idle jet size.

Sun Jul 29, 2018 7:34 am

Rome,
Thank you for your info. I didn't have a rebuild kit on hand when I pulled the left manifold so I was reluctant to disassemble the carb. At that point I thought my only issue was the manifold leak, I've come to know better.

Sun Jul 29, 2018 7:39 am

lots of things affect jetting....not just whats in your engine but also where you live....elevation above sea level and local gas formulation are contributing factors....suppliers of carb kits either send the carbs out with what they came from the factory with for their original application(usually too lean) or try to come up with a "one size fits all" jet size for the whole country (usually too rich)....and unfortunately many suppliers will take the original jets (lets say marked 115) and just drill them out to 130 or so(not just the mains but idles too)....so now you go in completely the wrong direction when trying to tune them....and you just bought 50 bucks worth of useless jets....so get a jet gauge and find out whats actually in there before you waste any money....many jet recommendations come from books that are 30 yrs old when gas was very different...my old shop in ny was at sea level with metropolitan area oxygenated gas with different winter and summer blends....now i'm in the foothills of north carolina where we have non ethanol premium available....and the jetting is about 20 points different with similar engines....so asking someone from across the country what size jets do i need might not lead you in the right direction

Sun Jul 29, 2018 8:09 am

X2 on jet gauge. Also look into a micro drill set and/or jet file kit. As mentioned , unless you measure the jets, you don't know what you have. What sucks about Webers is that it's expensive to play with them. A full set of jets will set you back around $70 and you still need a gauge, file/drill set etc. I havent added it up, but when I got into Webers/HPMX carbs, I am sure that I have spent a couple hundred just getting a proper kit and tools together for them. But, I have a shop and have worked with several Weber/HPMX cars so the expense was spread out. If you have any car buddies that mess with carbs or look into any local VW clubs or groups you may have some help out there.

And knowing the venturi size is critical since all of the jetting revolves around that. I totally agree that the tables are all over the place. Getting the book suggested is a good idea for a starting point. Also, I don't remember if you have 40s or 44s. Hope you have 40s.

One more thing, if you don't have a synch tool, buy or borrow - the cheap $20 one works pretty well. Synching is critical.

So, no easy solution...wish there was a quick and cheap answer. But will reiterate that John at aircooled.net was a huge help on the last car I worked on. Was a really messed up combo and his initial suggestion was amazingly close to what we ended up with (tuning on a chassis dyno)

Sun Jul 29, 2018 8:10 am

lounge, you don't need a gasket kit to check the main jet size and the venturi size. Just take off the top cover of either carb with the carb in place on the engine. The air filter element can remain in place, though if in the way you just pull it straight up. Then you'll see the two brass jet stacks between the velocity stacks just like shown here. Remove either jet stack with a medium blade flat screwdriver. This is why I mentioned that determining the main jet size and the venturi size should only take 10 minutes.

Years ago I transferred a set of 40IDFs from my mild-build 1641 dual-port with stock valves sizes, to a 1776 that had similar specs. Did not change any jets since I kept the 28mm venturi size. IIRC the engine ran well immediately.

volksworld makes valid points about encountering main jets that have been drilled bigger than their stamped size.

Mon Jul 30, 2018 9:01 pm

The carbs are 40 - IDFs, the centuries are 28s and the main jets are marked 115. I'm guessing that's why the mechanic who put this together had the idle mixture screws out eight full turns. When I pulled the left carb I set it to two turns from seated and that side was running very hot. I'm ordering a set of 130 main jets, hopefully this will get me closer to running right.

I have a unisync, getting ready to use it is how I found the manifold leak. The question I have now is, for those of you who have this configuration in a type I, how do you go about syncing the carbs? Do you bring it up to operating temp, take a reading, wait an hour plus to make your adjustments, bring it back up to temp, check and repeat till it's properly set? I have a hard enough time getting my hand in to make adjustments with a cold engine, I've burnt my hand trying to do it when I haven't waited long enough for it to cool down. I confess I not very impressed with this configuration in this vehicle. If I was sitting on an extra $500/$600 I probably wouldn't hesitate to go to a single carb.

Again, I thank all of you for your input. It is greatly appreciated.

Tue Jul 31, 2018 2:30 pm

YOU get the car warm, put it one one side and adjust so the plug thing rides in the middle. Check the other side. and adjust. Dont know what linkage you have, but assuming its hex bar. If so, you leave it disconnected on one side and use the idle stops to balance them. Then you adjust the linkage so there is no change when you connect it.

Didnt see what your idles are. You tweak those based on how far you have to adjust the mixture screws.

Tue Jul 31, 2018 2:53 pm

Thanks,
I haven't pulled the carbs apart as yet to find out what the idle jets are. I'm going to order a set of jet drills since they will double as gauges. I can't really see spending north of $50 for a gauge I hope to only need once. Yes, it is a hex bar.

I miss the simplicity of my 1970 beetle. I had the stock motor rebuilt when I bought it and put 100k miles on it doing all my own work with the aid of "How to keep your VW alive." It wasn't pretty, but that car went from Copper Mountain Colorado to NY to Ft Lauderdale, back to NY and DC dozens of times, back and forth to Vail from Fort Lauderdale on four occasions. It's one of the best cars I ever owned. A friend was a mechanic for the air Force working on jets, he got me the relief tube from a fighter. I installed it under the dash, it cut my pit stops in half when I was traveling cross country.

Again, I greatly appreciate you help.

Fri Aug 03, 2018 12:40 pm

After years and years of working with dual single barrel Kads, I got thrown into Webers/HPMX carbs a year or so ago. Had a lot of learning to do and don't regret working with them. But the complexity can seem intimidating and there is so much conflicting info out there that it makes it even more challenging.

And I will tell you that I totally hate the hex bar linkage. There are better ways to do it. But this is what you have and you can make it work. There are some articles from Redline that help with set up, in particular the idles that will help. Good luck.

Fri Aug 03, 2018 5:15 pm

Ok andk5591.
So what do you recommend for dual carb linkage?
I have been having a heck of a time lately with my CB hex bar setup.

I actually sent a message to sync-link last night. I got a response back today complete with install instructions. The sync-link is a pretty complicated system to initially install. But from what I have read, once installed. It's spot on and works flawlessly.

What do you like?