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We've all been there.

Running great. Then - all of a sudden - not so great.

Ah, dirty idle jets in the Webers! Pull them, clean them, reinsert, and - no difference!

And you didn't see any dirt in the jet, anyway, right? And you blew out the 'hole' the jet goes into with carb cleaner, too.

 

WTF?

 

This video explains why you probably didn't find any dirt and what's really going on.

Also, without saying so directly, it shows why tweaking a mixture screw might sometimes have no apparent effect on how the engine is running.

Best video I've come across that shows how the whole idle circuit works. There's a lot more to it than just the jet.

Make some popcorn and watch.

 

 

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Another source of contamination-- the fuel itself.

Ethanol is corrosive, and will eat rubber and phenolic bits (like your floats). There's nothing as awesome as picking out chunks of float from the progression ports (the 4 holes the narrator was talking about). I've always wondered how stuff can get past the idle jet, but it does-- an often lands in those ports.

I'm thinking the cat's meow would be a threaded plug, rather than that press-fit deal. Plug up the idle circuit? Spin out the plug and clean out the progression ports.

Hmmmm. Now to check McMaster Carr for the proper stuff...

There hasn't been much on the list about this issue lately. Maybe some of you are suffering through it alone.

This is a very good video.

The way these carburetors are designed there will always be stopped jet issues. The float chamber is open to the atmosphere inside the filter. Dirt can also enter around the main jets, through the carb top. You see in the video that he replaced the top without removing the main jets. Unless you have HEPA filters there will be some dirt. I have not upgraded to the K&N filters.

I made several modifications to my carbs to help with the problem of dirt entering the float chamber. If dirt can't get in the float chamber it can't get into the jets, but it is not possible to stop it all.

The carburetors are installed, what to me, seemed backwards. All of the adjustment screws and access to the idle jets are toward the fender wells. You can't see what you are doing. So I turned them around (see my post about that project). Now, I can see the adjustment  screws and idle jets.

I installed Jaycee Jet holders making dealing with the idle jets much more simple. Also installed were Jet Doctors. These move the intake for the idle jets up and inch or so from the floor of the carb top. The last thing was to install a neoprene gasket between the filter body and the carb. Paper gasket no good here.

These things have virtually eliminated airborne dirt getting into the carb.

 I have read/heard about others complaining about the additive but I have not had any issues with the ethanol fuel. My car is driven year round. My engine runs fine.

In the course of getting all of this done, I cleaned the carburetors. My personal eye witness opinion is that ethanol will destroy the carburetors eventually. You can never be sure that all of the white residue is cleaned out. I ran the parts through Gunk carburetor cleaner (gallon can) several times and had to scrape some tite areas to get what I could see out.

One last thing. Idle speed screws can NEVER be turned in more than 1/2 a turn from stop or the "cursing ports" he shows in the video will be exposed and you will NEVER get the engine to run correctly.

Drive on...

 

 

 

 

Last edited by Jim Gilbert - Madison, Mississippi

I'm not griping about E10 fuel. It's here to stay. I build for it, cope with it, and accept it for what it is.

That being said, most of my issues come from the floats breaking down. I run giant filters, make sure I've got great gaskets, have run K&N filters, and everything one is supposed to do.

After a few years of E10 fuel, the floats start breaking down. New ones are not cheap, but worth every penny.

That was a really good video !  The secret revealed is the way to blow out the air/fuel circuit backwards. I hat to say this but I have been to some carb repair shops and watched some technicians unknowingly make the mistake of trying to blow out all the passageways by whatever method they seem to think "may" do the job.  Jet doctors are a good-cheap investment as well.  I also like the Jaycee idle jet holders with the hexagonal body. This eliminates using a screwdriver to R & R the holders because you then  use a 1/4" drive 1/4' socket for R & R. This makes it much easier  no mater how your carb is oriented............Bruce

That's funny, I still have the original Spanish Weber floats in mine from 2002.

Jim, you are right on the money on all points. Jet Doctors and a good air cleaner, also sealing the air filter base are all crucial. Idle speed(throttle plate screw) exactly: just off closed.

The only error in the video above is that the "mixture" screw is not that, it is a VOLUME screw, the air and fuel are already mixed before hitting the volume screw. Those screws should be about one turn out, from 3/4 turn to 1 1/4 turns. Any more than 1.5 turns and the idle jets are too small.

Some of you remember, in Carlisle in 2007 I had a plugged jet that wouldn't unplug on the way to the All-Star Cafe on Thursday night. I pulled the offending jet and the VOLUME screw(making sure I didn't drop the O-rings or springs) and blew the circuit out both ways with carb cleaner. Started it back up  and reset the volume screw. Elapsed time about 5 minutes. Problem solved.

I didn't have any problems the rest of the weekend. 

Since then I've installed Jet Doctors, and only get dirt when I futz with the carbs. As long as I leave them alone, they are trouble free. I use Stabil every fall, and as far as ethanol is concerned it's a non-issue.

@DannyP posted:

That's funny, I still have the original Spanish Weber floats in mine from 2002.

 

Maybe modern-era Webers have better floats? No idea, as it's not my thing.

As Dellortos haven't been made in 100 years, it's hard to say how old the floats are in my various carbs-- and for whatever reason, they aren't included in a rebuild kit. The floats in my 45s disintegrated and sent lots and lots of black "worms" through the idle circuit a few years ago. There was zero problem for several years, then it was constant, until I figured out what was going on.

Alfa1750 on ebay has stuff nobody else does. I got new ones from him, and should probably have another set for spare.

Last edited by Stan Galat

 

FWIW, my Spanish IDF 40's were new in 2013, and have seen about 30k miles on two engines over the past seven years.

The carbs were just torn down (for new needle valve seals) and put back together with rebuild kits. The floats showed no noticeable deterioration and weren't replaced.

The car does gets driven regularly almost year round, so the gas is relatively fresh most of the time. And, I always top up the tank after a drive.

Also, so far, I've had almost no issues with dirty idle circuits.

Spark scatter, yes, but not dirty idle circuits.

 

@Sacto Mitch posted:

 

As long as you're tapping and threading that plug, Stan, there's no reason not to run a line from there to a solenoid-operated valve that then leads to the intake manifold.

Dirt in the system? Tap the under-dash switch and use intake vacuum to flush it out.

Why waste valuable cruise time stopping by the side of the road?

 

Dude I see what you are doing and it is evil. Stop.

 

Damn, Ed, go and spoil my fun, why doncha?

See? "A neat little response" was "all written out".

So close. Stan was already halfway down the rabbit hole.

I knew our master pipe fitter would see the obvious flaw in my proposed solution. The upstream side of the clog would be at the same pressure as the intake manifold, so there'd be no net pressure difference to flush anything.

Sure, you could run the downstream line to the manifold of a different cylinder (one of the cylinders being on the compression stroke, when the other was on intake), but that's still not the cowboy way.

We'd need a dedicated, high-pressure vacuum pump. Which could be actuated by the same relay that controls the solenoid valve.

And, once you're in for a dime, why not automate the whole thing? Pressure sensors in the intakes, some simple circuit that activates the valve on any cylinder with suddenly less vacuum than the others, and bam!

Any old-school 911 driver has a dry sump. How many have idle jets that clear themselves?

 

@Stan Galat posted:

I'm not griping about E10 fuel. It's here to stay. I build for it, cope with it, and accept it for what it is.

That being said, most of my issues come from the floats breaking down. I run giant filters, make sure I've got great gaskets, have run K&N filters, and everything one is supposed to do.

After a few years of E10 fuel, the floats start breaking down. New ones are not cheap, but worth every penny.

I stopped using it last summer. Here ethanol-free "Clear" gasoline is the same price as premium. I've run it in my Spyder and 99 Ducati forever, but last summer I did a little test and found I get 2-3mpg better mileage than premium in both my Mercedes and my Smart, so it's all I buy anymore. 

Before i I started using Clear in my Ducati, it would always take me several hours to get it running in the spring. With Clear, it just takes about twenty minutes. 

Last edited by dlearl476
@Stan Galat posted:

I can get it easily here as well-- but if I'm building to drive across the country, there's no way I'm going to be able to find E-free gasoline all along the way.

Injection would solve all of the issues. 

You'd be surprised. 

Pure Gas app

Plus, I don't think running a tank or two of E10 would matter much. AFAIK, it's the ethanol sitting in the carbs and lines that dies the damage. 

Last edited by dlearl476
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