Brief Pictorial - Idle Jet Cleaning on Weber 40 IDA 3C

[Lapkritis]

Had a recent experience with the engine missing at part throttle, still business as usual at WOT. Suspected idle jets and had some assurances from others on the board that was likely the case. Weber 40IDA3C, 40 IDA 3-C etc... not sure if the layout is the same on 46's. Anywho...

Very basic procedure but if you haven't done any carb fiddling then it can be a bit daunting with the dated materials on the web for determining exactly where to find the idle jets on the carb body. Lots of brass screws on the outside to choose from and the widely distributed diagrams on the web are primarily from the other side of the carb body. Hopefully this saves someone some time/head scratching and deep reading.

Plan about 30mins for the job, including re-hydration pauses.

Tools for the job:


Pop the lid:


These are the idle jet holders, circled in red. I recommend to clear them one at a time for the sake of organization.



I found a chunk of fuel line rubber (I believe) lodged in the opening on cyl #1.



Here's the idle jet complete with the older:


Pulls apart with bare hands:


Gently clear the blockage by the means you choose. I used a safety pin as I had it on hand to poke only the rubber before clearing with carb clean and compressed air. Take care not to damage any of the metal.

If you have gum/varnish or other deposits then now might be the time to soak the jet with carb cleaner. Clear through:



When reinstalling, I used a very light coating of oil on the o-rings and took care not to over-tighten. These are only gently snug, not "guten tighten". As the age of my rubber fuel lines is unknown, I'll plan on replacing these in the next week and adding fuel filters closer to the carbs perhaps. Paul/1QuickS mentioned enhancing the sealing of the air filters around the edges - I'll likely pursue that as well.

[rbogh901]

Can't get enough of this kind of basic info. Well titled for future searches. Hopefully the photos won't disappear after a while, like they do too often on Rennlist and occasionally here. There are many great threads with holes in them now just because they were written some time ago and the pictures were not saved.

[Lapkritis]

I hope so as well. De-mystification of even the most basic tasks on these cars will help everyone out. A picture is worth a thousand words especially with the new generation of owners who often don't have the attention span to read walls of text... the "tl;dr" types who prefer photos. I'd like to see more learn to live with carbs than swap to EFI.

[KTL]

Yes the same applies to the Weber 46. The 46 is basically a just a bored-out 40 carb.

That's a big chunk of rubber! Definitely get some inline filters just ahead of the carb inlets and of course its time to investigate the source of that chunk.

I'd also recommend the PMO fuel bars on the carb fuel inlets. At each carb they eliminate two potential hose leak points and also a section of rubber fuel line. You can also add fittings to the rearward ends of the PMO bars and join the two carbs with a section of hose. Of course doing that adds back more hose/leak points! But its not a bad idea to do to get some crude circulation between the two carbs on a deadhead-type system.

[Geneman]

THIS IS SUPERB LAP-DUDE!.. Thanks. can it be translated to PMOs also? is the jet in same place and same structure?

btw i have a single inline filter that is positioned before the regulator: should i also put individual inline filters to each bank?

kev chime in

thanks ! frank

[Lapkritis]

I think it's from removal/re-installation of the fuel hose at the regulator on the firewall during my engine drop in 2012. They had a bit of memory and maybe chaffed on re-installation a bit.

I think I'll pick up the generic metal filters from local auto parts along with new hose this afternoon. I can't imagine the clear plastic filters would be a good idea with this engine bay and the temperatures after shut-down.

[Lapkritis]

Hi Frank,

The Webers pictured are a PMO kit from the 1990's on my '74. Should be the same for some other vintage PMO but not positive about the current PMO offering. Perhaps someone else can confirm?



-Andrew

[bhaubold]

The idle jets on these Webers are so small, it doesn't take much to clog them. They are so easy to remove and clean, I clean them about every six months to keep things right. It's amazing how bad your car will run when they get clogged.

[Lapkritis]

Bob,

Agreed. The car shook like a sleeping bag in a washing machine with 1 cyl down due to the clog. I'll start servicing these annually when coming out of storage I think.

[gordner]

I have a CHT and EGT set up on mine since installing the webers, and I find myself cleaning the idle jets quite frequently due to cold cylinders at idle. It is amazing how small a piece of debris will upset them, and I can tell you from experience that you can't really feel it until they are basically completely clogged. I honestly can't feel the difference idling on 6 or on 5, it remains remarkably smooth. The temps tell all!

[ganun]

Great pictures Lap, but just a word.... you do know that its not a good idea to clean jets with a steel pin, they come in half mm increments and just a bit too much pressure and its a different size. Ultrasonic cleaning or plastic bristles is the way to go.

[Lapkritis]

Hi George,

Yes indeed - I was careful not to ramrod the jet with the pin. I only used it to coach the rubber back out of the hole as it was sorta snaked in awkwardly. Very gently and then spray/air once the object was out.

[Geneman]

Gordner what are you using to detect and record egt? Do you have it on every cylinder? Very useful in small planes. Would love to have it in race car.

Thanks frank

[Lapkritis]

Hi Frank,

I can answer that question from a general perspective. You can monitor wideband for up to 8 cyls and egt for up to 8 cylinders using this product:

http://www.diyautotune.com/catalog/canegt-channel-thermocouple-interface-p-542.html

Very cool system in my opinion... Cheap too but of course you need all the sensors/controllers as well.

-Andrew

[jmz]

Computer key board cleaner air can and/or carb cleaner with spray tip works well for me.