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Our bugeye came to us with a Weber 40 DCOE. Never owned a car with Weber’s before, but hey? It started with no choke and ran. What more could one ask?
OK – it ran. But it hesitated a bit when I floored it, and what’s up with the starting without needing the choke. And if you do use the choke – wow. Instaflood – and let it sit for a while and try again. And let it sit for a while….
Our bug came to us with a 1275 engine, 8.5 to 1 compression, freshly rebuilt. For a variety of reasons, I chose to have the engine built again, this time as a 1380 with 10 to 1 compression, an aluminum head and a mild cam upgrade. Idles reasonably nicely, though not as smooth as the original build with its milder cam.
NTL, when cold, the car just didn’t want to idle. And pulling the choke was the kiss of death. What the heck?
I did my usual “let’s check the web to see what I can see”. Sort of like picking up a piece of plywood to see what is under it. Turns out that the way to do a snake survey is to lay a piece of plywood on the ground on a pleasant day and come back later to see what has hidden under the plywood. And, like searching the web, you really never know what you will find. And if it will try to bite you.
I began to learn that most folks view the “Fuel Enrichment” circuit on a Weber DCOE as a useless item. Here is a typical comment – found on this forum from back in 10/19/2005 (thank you Alan Myers).
“I've had a pair of DCOE on my TR4 for 25 years and the chokes have never been operated (there's not even been a cable connected). The "choke" on a sidedraft Weber is really more like a small, separate carb or enrichment circuit, not really a choke. It's also pretty much worthless.
Since DCOE and similar have an accelerator pump, the method I use (and I've heard widely recommended) is to just forget about using the "choke", fully pump the pedal two or three times, then hold so that the throttle is slightly open. Crank the engine and it should kick over, but might run a little rough at first and not want to idle. Use the pedal to hold the throttle slightly open for a minute or so, until the engine settles down and wants to run and idle more smoothly.
If it doesn't start first try, repeat up to three times.
After that it's likely the engine is flooded and might be necessary to clear it by holding throttle wide open (no pumping... just slowly press the pedal to the floor) and turn the engine over, releasing the pedal partially as soon as the engine starts.”
I can see my wife doing the “hold the throttle wide open” part. And starting the engine. Hmmm. Or is it OH MY GOD!?
Alan is right – as delivered, the choke on our DCOE was useless. But, well, our cam has a bit of an attitude. It didn’t want to idle unless one held the throttle open for a while. Until the engine warmed up a bit. So, a real while. Which is ok if you have a cup of hot tea and biscuits. Otherwise, a bit of a pain in the tush.
None of this made a lot of sense to me. Carbs have chokes so they will start when cold. All the previous carbs I’d worked on had chokes. Including the many SU’s I’ve tuned.
When we wanted to start our ’69 XKE with triple SU’s on a 20 degree F morning, I pulled the choke. It started. It fast idled. I went back into the cabin and had tea and biscuits.
Granted, some are called chokes, some are called fuel enrichment devices. Oh, even more confusing: Turns out Weber’s do have chokes – that is what they call the venturi inside the barrel of the carburetor – the part that narrows down the throat of the carb. And you can choose different sized chokes depending on whether you want low rpm grunt or high rpm ponies.
My gut level thought was that the jets for the fuel in the fuel enrichment device, or starter circuit, or whatever you might want to call it (as long as you don’t call it choke) were too big. Here is a diagram of a DCOE to further confuse you. Ignore all but item 16.
Turns out if you take the top off of a DCOE you can find all kinds of things – much like picking up a piece of plywood on a sunny day.
Item 16 – the Starter Jets.
Out of curiosity I checked to see what sizes were available – typed in 85F9 (what came in our 40 DCOE when purchased new a couple of years ago) in the search box on www.carburetion.com. “Sorry, part unavailable”. So I called them. Yup, part unavailable.
I get the idea that the 85F9 if the standard starter jet supplied in new 40 DCOE’s. I guess it doesn’t really matter since folks seem to believe that fuel enrichment devices don’t work. Hmmm. No fuel jet options and the devices don’t work. Wonder if they’re not working might be because the 85F9 jets are not right for every application for 40 DCOE’s?
So, more looking under plywood, and low and behold, found a YouTube video on “Tuning the Weber 40 DCOE Cold Start Choke Circuit”.
Wow. Harwinder (guy who produced the video) was asking the same questions I was asking. He figured the fuel jet in the cold start circuit was too big. So, he made it smaller. Granted, filling the jet with copper wire, soldering it up, and re-drilling it with a smaller hole is not the most elegant solution. But IT WORKED FOR HIM.
Fast forward to my shop. I am a watch and clock guy. As in, I can make really small things really precisely. For me, it was pretty much trivial to replace the 0.85 mm fuel orifices in the original starter jets with 0.30 mm holes. Why 0.30? Because it was the smallest standard bushings I had in my bushing kit. 0.85 was obviously way too big – 0.30 is about a third as big – what the heck – I could always ream it out if needed.
Note – 0.3 mm is pretty small. As in, a sewing straight pin is about 3 times that diameter. It is a pretty darned small hole. But then, so is a 0.85. Flip side, I routinely work with pivots on clock gears that are as small as 0.3 mm.
Install the modified starter fuel jets, pull the choke, and bam – engine starts right up and idles at 1400 rpm. Cold. Perfect! Much like Harwinder found when he started up his engine at 4:10 in his video. It just worked! First try.
With our performance oriented cam I can now start the car when cold and walk away. It idles!
I hope this slightly tongue in cheek article makes sense, and perhaps even helps someone understand why the fuel enrichment devices on Weber DCOE’s “don’t work”.
OK – it ran. But it hesitated a bit when I floored it, and what’s up with the starting without needing the choke. And if you do use the choke – wow. Instaflood – and let it sit for a while and try again. And let it sit for a while….
Our bug came to us with a 1275 engine, 8.5 to 1 compression, freshly rebuilt. For a variety of reasons, I chose to have the engine built again, this time as a 1380 with 10 to 1 compression, an aluminum head and a mild cam upgrade. Idles reasonably nicely, though not as smooth as the original build with its milder cam.
NTL, when cold, the car just didn’t want to idle. And pulling the choke was the kiss of death. What the heck?
I did my usual “let’s check the web to see what I can see”. Sort of like picking up a piece of plywood to see what is under it. Turns out that the way to do a snake survey is to lay a piece of plywood on the ground on a pleasant day and come back later to see what has hidden under the plywood. And, like searching the web, you really never know what you will find. And if it will try to bite you.
I began to learn that most folks view the “Fuel Enrichment” circuit on a Weber DCOE as a useless item. Here is a typical comment – found on this forum from back in 10/19/2005 (thank you Alan Myers).
“I've had a pair of DCOE on my TR4 for 25 years and the chokes have never been operated (there's not even been a cable connected). The "choke" on a sidedraft Weber is really more like a small, separate carb or enrichment circuit, not really a choke. It's also pretty much worthless.
Since DCOE and similar have an accelerator pump, the method I use (and I've heard widely recommended) is to just forget about using the "choke", fully pump the pedal two or three times, then hold so that the throttle is slightly open. Crank the engine and it should kick over, but might run a little rough at first and not want to idle. Use the pedal to hold the throttle slightly open for a minute or so, until the engine settles down and wants to run and idle more smoothly.
If it doesn't start first try, repeat up to three times.
After that it's likely the engine is flooded and might be necessary to clear it by holding throttle wide open (no pumping... just slowly press the pedal to the floor) and turn the engine over, releasing the pedal partially as soon as the engine starts.”
I can see my wife doing the “hold the throttle wide open” part. And starting the engine. Hmmm. Or is it OH MY GOD!?
Alan is right – as delivered, the choke on our DCOE was useless. But, well, our cam has a bit of an attitude. It didn’t want to idle unless one held the throttle open for a while. Until the engine warmed up a bit. So, a real while. Which is ok if you have a cup of hot tea and biscuits. Otherwise, a bit of a pain in the tush.
None of this made a lot of sense to me. Carbs have chokes so they will start when cold. All the previous carbs I’d worked on had chokes. Including the many SU’s I’ve tuned.
When we wanted to start our ’69 XKE with triple SU’s on a 20 degree F morning, I pulled the choke. It started. It fast idled. I went back into the cabin and had tea and biscuits.
Granted, some are called chokes, some are called fuel enrichment devices. Oh, even more confusing: Turns out Weber’s do have chokes – that is what they call the venturi inside the barrel of the carburetor – the part that narrows down the throat of the carb. And you can choose different sized chokes depending on whether you want low rpm grunt or high rpm ponies.
My gut level thought was that the jets for the fuel in the fuel enrichment device, or starter circuit, or whatever you might want to call it (as long as you don’t call it choke) were too big. Here is a diagram of a DCOE to further confuse you. Ignore all but item 16.
Turns out if you take the top off of a DCOE you can find all kinds of things – much like picking up a piece of plywood on a sunny day.
Item 16 – the Starter Jets.
Out of curiosity I checked to see what sizes were available – typed in 85F9 (what came in our 40 DCOE when purchased new a couple of years ago) in the search box on www.carburetion.com. “Sorry, part unavailable”. So I called them. Yup, part unavailable.
I get the idea that the 85F9 if the standard starter jet supplied in new 40 DCOE’s. I guess it doesn’t really matter since folks seem to believe that fuel enrichment devices don’t work. Hmmm. No fuel jet options and the devices don’t work. Wonder if they’re not working might be because the 85F9 jets are not right for every application for 40 DCOE’s?
So, more looking under plywood, and low and behold, found a YouTube video on “Tuning the Weber 40 DCOE Cold Start Choke Circuit”.
Wow. Harwinder (guy who produced the video) was asking the same questions I was asking. He figured the fuel jet in the cold start circuit was too big. So, he made it smaller. Granted, filling the jet with copper wire, soldering it up, and re-drilling it with a smaller hole is not the most elegant solution. But IT WORKED FOR HIM.
Fast forward to my shop. I am a watch and clock guy. As in, I can make really small things really precisely. For me, it was pretty much trivial to replace the 0.85 mm fuel orifices in the original starter jets with 0.30 mm holes. Why 0.30? Because it was the smallest standard bushings I had in my bushing kit. 0.85 was obviously way too big – 0.30 is about a third as big – what the heck – I could always ream it out if needed.
Note – 0.3 mm is pretty small. As in, a sewing straight pin is about 3 times that diameter. It is a pretty darned small hole. But then, so is a 0.85. Flip side, I routinely work with pivots on clock gears that are as small as 0.3 mm.
Install the modified starter fuel jets, pull the choke, and bam – engine starts right up and idles at 1400 rpm. Cold. Perfect! Much like Harwinder found when he started up his engine at 4:10 in his video. It just worked! First try.
With our performance oriented cam I can now start the car when cold and walk away. It idles!
I hope this slightly tongue in cheek article makes sense, and perhaps even helps someone understand why the fuel enrichment devices on Weber DCOE’s “don’t work”.
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