Weber 36 IDF rebuild project (updated 10/24/07)

Welcome to my project page for rebuilding a pair of old Weber 36 IDFs to work with small to midrange sized VW Type 1 engines.

These pages are a work in progress.

I recently bought a set of old Italian Weber 36 IDF carburetors.  The general condition was good but the fitment of them and calibration to a VW engine is going to need a few things to make it work as it should.

I will update this page as I get through the project.  Questions, contact me.

NOTE: The MODIFICATIONS listed here for the idle air bushings are SPECIFIC to these units, and to CERTAIN 40 IDFs that have the same style mixture screws, same size air bushings, and FIVE progression ports.. don't just do this because they are IDFs.  If you are not sure, ask me.  Send me pics of your carbs and I can tell you if they are subject to similar issues in individual runner or centermount application on the VW aircooled engine.

Inspection

I've started out with a set that looked like the pictures below.  These pictures show the general condition of the carburetors.

Note the use of the enrichment circuit.  Whatever car this was on was afforded that luxury.  You can also see the special barrel nut stud that was used to attach to the air cleaner most likely.

You can see from this shot that the fuel lines were different sizes going into this carburetor.  The lower one is what we're all more accustomed to.  I will probably plug the top one and use the lower one.

Not much to say here that you haven't already seen but it's another shot.  The underside looks good.

Here you can see that the butterflies are not damaged and are relatively clean.  Some normal deposit under the center holes of the throttle shaft.

Shot of the mixture screw cluster for one barrel.  This shot shows you a brass plug that hides the progression circuit holes into the barrel, a CO tube for calibrating mixture (not a way we use that much anymore, I prefer Air-Fuel meters and flow meters to do the calibrating), a lead plug in an unused air bypass circuit to the right of the mixture screw, and finally, above and to the right of the CO tube, is the boss for a vacuum line suitable for a vacuum advance pot on a distributor.

This shot shows the other side of the same carburetor, mirror image, sans the vacuum port boss.

This shot shows how the throttle shaft is terminated on the "back" side.  These two carburetors are an opposed pair, so when installed, they both have this plate on the firewall side of the engine, and the speed screws, return springs, and arms are all on the service side.  Nice feature, saves reconciling that or having to do a Weblink conversion.

Top of the carb - again not much to say here.

Tear down

 After taking off the top, jet stacks and enrichment control, I see that inside is basically very clean, and does not have evidence of contamination or water damage at all.  Some slight mineral deposits on the paper gasket, but not much of anything else.  The complete idle jet stacks were missing from this carburetor, so I will have to source those if I can.  I have an extra set on a core, but I don't like to sacrifice what parts I can source.

Jet stacks were 135 main, 220 air, and F50 emulsion tubes.  This is not the ideal setup for VW Type 1 engines, and I will explain more about that later, relative to the behavior of these.

Another picture of the cover.. the floats were not bad off for measurement and the condition is great.

Picture of inside.. really pretty clean.

These have been sitting where a spider could find a home and spin a web.  Note the design of the acclerator pump jets.  If you have ever had a set of Weber ICTs, these will look quite familiar.  They are sealed using o-rings, and there are no valves in them  The valve is similar to the setup used in Dellorto DRLA carbs in that there is a ram and a ball bearing that avoids reversion of the shot into the bowl on each side, as a check valve.  These have them under the nozzles whereas the DRLA has them under an access screw.

Something else of interest here, the idle air bushings (little brass opening to the right of the accelerator pump nuzzle) is LARGE compared to what we see on Spanish and other Italian models of the IDF.  These are about a 2.00mm opening!  The regular size we deal with is about 1.15mm.  The other difference that is related is that this carburetor has 5 progression ports, whereas the later models have 4, and sizes of the ports vary quite a bit.  This model is very close to the Dellorto DRLA carbs in terms of air bushing and progression ports.  I'm sure they will respond better with smaller idle air bushings.  These typically run kind of lean in the transition area.  After they are cleaned, they will get soldered, re-drilled at 1.20mm, and tops will be resurfaced.  If the bushings are too small at this point, then I will drill them larger, to about 1.50mm and try that.

Shot of the spot where you would expect to see a removable bypass valve.  What is here is fixed and really non-serviceable without a lot of work.

Shot of the linkage arms on the carb.  Some of that is not necessary for our use.

Shot of the model number.  There are many different IDF bodies out there.

Shot of hte body nearly torn down all the way.  Enrichment circuit guts are next.

Another shot down the barrels.

Venturis are 30mm and aux vents are looking good on the sealing area.  32mm vents will go back in these.

The three pieces on the right will not have to go back on the throttle shaft.

Accelerator pump jets are snap in style like the ICT, and are sized very small.  With the spring style acclerator pump rods, this is a good size for carbs this small.  You can crank down on the springs and get a little more spray if you want it.

Shot down the acclerator pump circuit.. the item in the hole is the end of one of the brass rams pictured below.  Under the ram is a steel ball that serves as a check valve.

Lose any of this and you have a problem.  Modern versions now have the check valve in the bolt that holds the nozzles.  Both systems work well.

Going in the tank

Here are the parts going through the first aqueous cleaning process.  This process removes oils, greases, dirt, and other stuff stuck to the outside of the parts.  The circuits don't get much but a rinse from this process.  The solution is Simple Green cleaner mixed at about a 10:1 ratio with water (water is the major).  The solution is heated to about 150 degrees and the parts are dropped in for about 15 minutes.  Parts will turn dark if you leave them in too long.  The rinse is a hot water rinse for several minutes with submersion on the complex parts.  Parts are blown dry with compressed air.  Simple parts like screws and such don't get blown dry, only vents, jets, bodies, tubes, etc.

Into the hot tank they go.  I have a small tank, so I have to change the chemicals out frequently.

Cook it up!

After cleaning cycle. Here is the whole carb minus idle jets and holders, mixture springs, and disposables.

After this process, I went ahead and closed up the air bleeds and re-drilled them to 1.20mm.  They look like ass, but they're better than the pics look.  The holes on air jets do not have to be as precise as fuel jets, IMO.  They are within 0.05mm I am sure. 

After the parts were degreased, they were put in the tank with ultrasonic cleaning solution. They come out looking a lot the same, with the exception of carbon deposits and hard stains greatly reduced.  Carbon deposits are all removed.  I've put pistons in this cleaner for 30 minutes and had them come out literally looking brand new, sans scuffing and such.

The parts that can still use some cleaning are brass parts.  They just don't get that gleam they had out of the box.  Using my secret formula, I tank the brass parts, and they come out looking new inside and out, no etching, no dimensional changes, just CLEAN.  I scrub the throttle plates to check for burrs and such.

Now inspection and reassembly is next!

Covers   

Now that the parts have been cleaned up, it's time to reassemble them.

But, first things first here.. these covers have two fuel fittings each, and I only need one on each.  You can either leave two on one of the covers, and use that in lieu of a "T" fitting, or you can eliminate one on each and use them with a "T" fitting.  I prefer the latter.  So to remove the fitting, I just cut it off and drill it.  It can't be pulled out due to the way it is installed.. I'll show more about that later.

Here is the cover with both fittings.

After taking a cutoff tool to the fitting, and then using a disc to sand it flush.

Fixtured and ready to drill.

Let the chips fly!  Use WD40 or something to keep things slippery during the cut.

All drilled out.

This is the remainder of the bushing as it slipped out with the bit during one of my retractions.  The right side is the end of the fitting and the left side is the end closest to what I cut off.  See the groove in the fitting?  That was held in by swaged aluminum from the cover, like a retainer, hence difficult to remove any other way without risking damage to the cover.

Cleaned, tapped, cleaned again, and ready for a plug.

All plugged with an iron plug.  Brass or aluminum will work too.  For those of you that want to go on about expansion rates and such, do the math, figure out how little it matters here, and then figure in the thread sealant, and get outta my way.  :)

Now we'll move on to assembling the cover and setting the float.  This is perhaps the most overlooked and ironically the most important part of calibration.

The standard 40/44/48 IDF rebuild kits are NOT the ticket on these carburetors.. you have to get the kits that are SPECIFIC to 36 IDFs.  Here is such a kit.. Weber does not offer them anymore.

Nice Italian kit.. yay!

Now, reassmbling the cover starts with flipping it over, installing the filter, drain plug, seat assembly, and top cover.

See how the cover gasket is different?  Compare it to a typical IDF gasket.. different hole patterns.

A comment about the needle.  Look at the picture and you will see that on the non-business end of the needle there is a steel ball captive in the needle.  Under it is a spring.  All IDF needles are like this.

When you adjust your float, make sure that the tab is not compressing this ball!  It's all in how you hold the cover when you measure.. just let the float tab REST on the ball.. not compress it.  Some are more sensitive than others, but the rule is the same.  Yes, my fingers are a little dry.  Get over it.

After preassembly, install the float and get out your measuring equipment

I like to use calipers to do the measurements.. You can either use the depth gauge, or the ID measuring tool.

Measure from the paper gasket to the bottom edge of the float.  SPRING NOT COMPRESSED!

Experience has told me that THESE particular carburetors seem to respond best to floats set to roughly 9mm.  Most others are better at 10-11mm, but these seem to do pretty good at 9mm.  I've never tried to figure out why, but I am sure it has to do with something related to the jet well and aux vent attitude.  This picture looks a little funny, like the instrument is not resting on the gasket, only because I had to hold the cover and tool with one hand while I took the shot.  Rest assured that I did it right when I put the camera down.  The distance you measure is from the gasket face to the bottom edge of the float, at the right most edge in this picture.

Almost done with the cover.

Notice that the stud holes for the air cleaner studs are NOT drilled and tapped on these covers.  They have to be drilled the rest of the way through and tapped for studs.  The way the air cleaners attached to these in the standard application was by the other two studs, and a larger screw that went down into the center cover screw hole.  On the end of it there was a barrel nut body complementing long studs on the other two holes.  Then nuts held down the air cleaner on the studs, and a bolt or screw most likely threaded into the barrel stud.  So now we have to tap the two stud holes, and source a larger screw (probably 6mm) for the center cover hole.

Rather unceremoniously, I will say I drilled and tapped them, and here they are tapped and then new studs installed.

With that, they are nearly done, and ready to go.  I spared you the reassembly - it's the reverse of disassembly.

Next we'll fit new throttle plates, bench test and check the float levels with fuel in the bowls, and finally leak test, install, and road test/tune.

Ready to go

All done with the tops, it's time to put them on the bus.

Whew.. look at those monsters.

Installed.  Here are the pics!

Driving, first impressions: With F11 emulsions, and 135 mains and 200 airs as a starting point, the light midrange and WOT were quite rich, as well as the idle circuit.  I removed the 52 idles and installed 50 idles, and that helped keep the numbers in the reasonable range, but these carbs were still all over the map, between 12 and 15 on the AFR scale.  Switching to 47 idles helped a lot. 

Final tuning depends on the engine, but this got me in the ballpark.  Smaller air bushings warrant smaller idle jets.

I hope you found this article useful.

Email harneyscarburetorclinic@gmail.com with questions or comments about this web site.
Last modified: 12/27/07