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.

 

 

Original Post

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...

 

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?

 

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.

Also, I second the use of CB space-saver manifolds. They work GREAT with a 911 shroud, but the number one and two cylinders are difficult to get to with a regular Beetle shroud.

@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

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. 

@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

Here's some of the stuff needed to build a "DCIJBS" (driver controlled idle jet blowout system) Couple this with a 6 cu. ft. compressed air tank and a 4 port manifold and you got it ! Two types of 12 volt valves are shown. A light weight one for Al's car and a heavy duty one for Stan's..........Bruce

Attachments

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Or you could remove the air cleaner on the offending side (found by releasing one plug wire at a time until you find the dead cylinder) then rev the engine to 2K rpm and slap your palm over the dead cylinder’s velocity stack while letting off the throttle linkage.  That will often suck any crud in the jet/passages/transition ports through and clear up the stumble.  If it’s stubborn and doesn’t clear with 2 or 3 tries, then go to plan “B” and blast out the passages and ports with aerosol carb cleaner or compressed air.

I did this for John Estes one time at Carlisle and it worked like magic.  I tried it on Pearl when Chris had it for a weekend and it didn’t clear the stumble but THAT was caused by a broken mechanical part.  Still, it’s easy and worth a try when out on the road.

Last edited by Gordon Nichols
@PaulEllis posted:

You can also find the dead cylinder by touching the exhaust and finding the cold pipe.

There's a 300% chance you will get it wrong three times. 100% on the first try, 100% chance you'll get it wrong the second time, and a 100% you'll get it wrong on the third try.

Last edited by Robert M

There is 75% chance you’ll get it wrong the first time and 100% chance you’ll get it right the last time...because you’ll have found it.

It’s akin to finding something like your 10mm socket in the last place you look...because you found it there!

Paul Ellis: interesting comment.  Have a solar system for a well system pump at a ranch, with a back up propane powered gen set.  Problems with the gen set on a control panel, and had a Kohler rep come up to replace.  Started gen set after the panel replacement, and as a civil engineer and I celebrated after the gen started, the rep said something's wrong, it doesn't sound right.  He tapped one side of the 2-cyl exhaust pipes, then the other and said, this side isn't firing.  Probable fix, a coil. But his ear and a finger tap on the cold pipe was an impressive troubleshooting technique based on experience.  Really, we thought it sounded fine.  A simple finger tap said no.  Shows you what we knew about rpm and sound.

Finally took the time to watch the video.  Great find, @Sacto Mitch- very valuable info there!!!  The guy had put a lot of thought into what what was going on and broke it down so it was easy to follow.

One can also accomplish the same thing with CHT gauges on each cylinder, although a $10 non-contact temp probe seems easier than either my way or Paul's.

Finding the dead one gets you half-way to fixing it.

@Robert M posted:

There's a 300% chance you will get it wrong three times. 100% on the first try, 100% chance you'll get it wrong the second time, and a 100% you'll get it wrong on the third try.

There is also a 100% chance you'll burn yourself. I put my hand NEAR the exhaust right by the head, engine running. I promise if you touch it you'll be sorry!

You could drip or spray a little water on the exhaust near the head, that works too.

Also, if I pull a plug wire I'll definitely get shocked, so no go on that.

What I do now is screw the idle mixture(volume) screws in one at a time until there is no drop in rpm, there's your winner! Obviously turn the screws back out to where you started on the cylinders/jets that are flowing.

Last edited by DannyP
@Stan Galat posted:

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.

That's Gabrielle in Italy; where I got my Dell 40s from approximately 15 years ago. Still ticking. The guy is awesome. And yes; I got the Jet Doctors right away along with the intake manifolds, air cleaners and linkage from CB Performance. Good call.

Last edited by Impala

I found it very interesting that both Dave and Justin at Blackline Racing, the guys who rebuilt and set up my 40mm Dells, did NOT like Jet Doctors.  I had them installed since the first days of running my Dells for all of the same reasons; they push the air inlet to the jet way up at the top off the air cleaner so “less dirt can find it’s way in”.  That’s the story I believed.

Dave said he has seen a lot of problems with jet doctors and doesn’t recommend them for his clients (sorry, I can’t remember specifics).  I had the original, shorter jet holders from when I first set up my Dells and sent them along with the carbs for their rebuild and Dave installed the originals, set everything up and sent them back.  They’ve been running flawlessly ever since.  I mean, I am amazed at the difference before and after rebuild.

Now, in the 18 years I had been running my Dells with the jet doctors, I had exactly one instance when I can point at something and say “that, there, is a clogged jet”, unclogged it and it got better.  

Once.

Other than that, they ran OK, just tended to lean out during transition off idle and I couldn’t cure it on my own.

I got my Dells back from rebuild around the end of last August and, so far, haven’t had a single issue with them, even with the shorter jet holders.  And believe me, they’re running so well I’m not gonna touch them!

Last edited by Gordon Nichols

I found it very interesting that both Dave and Justin at Blackline Racing, the guys who rebuilt and set up my 40mm Dells, did NOT like Jet Doctors.  I had them installed since the first days of running my Dells for all of the same reasons; they push the air inlet to the jet way up at the top off the air cleaner so “less dirt can find it’s way in”.  That’s the story I believed.

Dave said he has seen a lot of problems with jet doctors and doesn’t recommend them for his clients (sorry, I can’t remember specifics).  I had the original, shorter jet holders from when I first set up my Dells and sent them along with the carbs for their rebuild and Dave installed the originals, set everything up and sent them back.  They’ve been running flawlessly ever since.  I mean, I am amazed at the difference before and after rebuild.

Now, in the 18 years I had been running my Dells with the jet doctors, I had exactly one instance when I can point at something and say “that, there, is a clogged jet”, unclogged it and it got better.  

Once.

Other than that, they ran OK, just tended to lean out during transition off idle and I couldn’t cure it on my own.

I got my Dells back from rebuild around the end of last August and, so far, haven’t had a single issue with them, even with the shorter jet holders.  And believe me, they’re running so well I’m not gonna touch them!

A friend of mine installed the Jet Doctors and noticed the car didn't run as good as when it didn't have them.

The carbs need to be reset after installing the Jet Doctors especially on Webers. The whole idle air intake path is changed. I had to reset mine, and had a terrible rich bog from 1500-2500. I put my wideband A/F meter on and found out why. The short velocity stacks were interfering with the idle air BIG time. I installed the original taller velocity stacks and air cleaners and the problem disappeared, back to running flawlessly.

As an aside, the Jet Doctors may be a better idea on Webers than on Dells, but I only have a lot of experience with Webers and their clones. Not much time working on Dells.

That’s cuz few people ever have troubles with their Dells.

They just work.

BS. They're just not as many Dells out there versus Webers, Gordo. And people get frustrated with Webers(all the while learning) then buy Dells. I'm living proof that it ain't the carbs, it's the knowledge(or lack thereof).

So remind me again how great Dells are after you've struggled for all these years and finally sent them out to Blackline?

I haven't had a plugged idle jet in YEARS.

Last edited by DannyP

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