All Small Six Weber 38/38 DGES jets, emulsion tubes and settings

This relates to all small sixes

awasson

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Prompted by a recent discussion about the Ford 200, carbs, distributors and exhausts, I thought I’d create a discussion thread specifically about the Weber 38/38 to document what has worked and what hasn’t to add some knowledge. Hopefully we can add some good info others can refer to. Please add your experiences with the Weber 38/38.

Personally, I think the 38/38 is a fairly simple carb to set up on a relatively mild or stock engine but they do require fuel pressure regulation of about 3 lbs, the floats must be set right and in my experience, you need to keep the distributor timing in mind when it comes off idle onto the main circuit.

My car came with an uninstalled Clifford Performance, Redline 38/38 kit so when I rebuilt the engine, I installed the new carb (on the unmodified intake log using the Redline/Clifford adapter) along with an EBay header and single 2-1/2” exhaust to a free flow muffler. According to the documentation, the Weber Redline carb is set up for the Ford 200 and is a bolt and go kit. In my experience it was pretty much bolt on and go. Initially, it fired up and idled without any real adjustments, I only had to adjust the idle speed screw. My engine had zero miles on it, bored 60 over a little under 9:1 compression ratio with a small log head, a Clay Smith H-6474-0-B camshaft and an HEI distributor.

After the initial startup and shake down, I thought it was running rich at idle and cold start so did some reading and followed the setup described at Redline Weber: http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm

Following the setup, I changed the stock #55 idle jets to #60’s and adjusted the mixture to compensate. The following are some notes I took during my setup:
  • #55 Idle Jets: Idles not bad with mixture screws 5/8 of a turn out but will not rev smoothly; kind of fights itself. Could be more timing required by my cam? Need to investigate further with an AFR gauge.
  • #60’s Idle Jets: Set idle mixture to 7/8 of a turn and initial timing to about +16° to +20° advanced. It’s best low idle is at about 800RPM. This works well and seems about the best I’ve achieved to date. Vacuum advance is disconnected and it gets +14° mechanical advance which starts to come on shortly after the carb comes off idle. I’d like to get the vacuum advance into the mix so I’ve still got some work to do.
I’m going to do some more investigating in the Spring, when the weather in my area warms and dries up but I could drive this setup and be entirely happy with it. I’m going to see if I can make it happy with the #55 idle jets with a custom curve on the distributor.

Things I’ve Noted:

1)
Plenty of people have installed these carbs successfully but you must follow the base setup and don’t be tempted to try to adjust the idle speed screw until you have the lean best idle.

2) The vacuum port on the carb is “ported” vacuum. At idle there is no vacuum but when you open the throttle and it transitions to the main jet circuit, you get the vacuum. This is a good way to determine whether you’ve added too much idle speed via the idle speed screw; if you’re pulling vacuum on the port, you’re no longer on the idle circuit.

3) Getting the idle jets and idle mixture right improves the whole of the air/fuel system. My guess is that the idle circuit is always active and is additive to the air/fuel situation.

4) My engine seems to want a lot of initial timing and knowing that helped me understand what was a function of the carburetor and what was a function of the distributor. More timing, more fuel.

5) I don’t know how much of a difference it makes but I trimmed the intake gaskets that fit between the carb, the adapter pieces and the log to remove overhanging gasket material. It’s a bit like port matching an intake manifold gasket on a non-log head. I expect it makes some difference.

I haven’t looked at what the air corrector jets and main jets are in mine. They are whatever was installed by Clifford/Redline or Weber when the carb was manufactured. I’ll put an AFR gauge on mine in the Spring and look into dialing the carb in for the whole range from idle to WOT. In the meantime, it would be interesting how others have set up their Weber 38/38 carbs, main jets, air corrector jets, etc. If you’ve got a 38/38 Weber on your Ford 200, I’m looking forward to hearing about it.

Andrew
 
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Thought I’d come back and add a little more to the equation. We’ve had exceptionally clear and sunny weather for the last week so I did a little tweaking to my tune. It’s definitely winter even though it’s sunny. It’s below freezing.

My engine is bored 60 over a little under 9:1 compression ratio with a small log head, a Clay Smith H-6474-0-B camshaft and an HEI distributor and an EBay Header into a Y-Pipe, 2.25” singe exhaust into a simple non restrictive muffler, like a turbo muffler and of course it is fueled by the Weber 38/38 on the Clifford/Redline adapter plate.

I’m still using the #60 idle jets. Idle mixture is at 3/4 turns out.
Initial Timing is around +18 degrees advance.
Vacuum Advance is hooked up at +10 degrees advance.
Centrifugal Advance is progressive up to +14 degrees advance.

Idle speed is about 900 RPM when it’s warm and about 700 RPM when it’s still cold and warming up off the choke circuit.

At this tune with the engine at operating temperature, it’s seems to be the best I’ve had it. I will put an AFR gauge into my car so I can really dial it in but it sure seems nice at the moment. It’s great driving in traffic and really wants to get up and go when I have room to put my foot into it. I don’t even have 500 miles on the new engine yet so I can’t really get into it but this tune sure seems to be on the right track.

Also, for the record, my car does not enjoy starting in sub zero weather. When I start it, it still fires up immediately but it has a severe “lope” to the high idle for at least the first 60 seconds to maybe 2 minutes. Then it starts to smooth out into a fast idle at about 2,200 RPM. When it gets to full operating temperature and the log and head are at temperature, it’s happy and it revs out nicely.

Anyway, I’ll update further when I have more to say.
 
I'll share my own settings after I dig into the carb. Since I've only been moving the car around and not driving it, I haven't gotten around to setting up the Weber 38. One thing I've noticed in tuning the twin Webers on my Triumph is that a lot of the jets do not have proper numbers, or the stampings aren't legible. That has been very frustrating. These are Redline jets, and I expected better quality.
 
I'll share my own settings after I dig into the carb. Since I've only been moving the car around and not driving it, I haven't gotten around to setting up the Weber 38. One thing I've noticed in tuning the twin Webers on my Triumph is that a lot of the jets do not have proper numbers, or the stampings aren't legible. That has been very frustrating. These are Redline jets, and I expected better quality.
That sounds great. I’m really interested in what others are experiencing with this setup. I pushed mine around for almost a year before I was able to get it moving under its own power. Thankfully, it’s a relatively light car.

I’m out of town this week but I have a jet kit from redline for the 38/38. I’ll snap some photos when I’m back to see if they’re marked any better than yours are.
 
Thought I’d come back and add a little more to the equation. We’ve had exceptionally clear and sunny weather for the last week so I did a little tweaking to my tune. It’s definitely winter even though it’s sunny. It’s below freezing.

My engine is bored 60 over a little under 9:1 compression ratio with a small log head, a Clay Smith H-6474-0-B camshaft and an HEI distributor and an EBay Header into a Y-Pipe, 2.25” singe exhaust into a simple non restrictive muffler, like a turbo muffler and of course it is fueled by the Weber 38/38 on the Clifford/Redline adapter plate.

I’m still using the #60 idle jets. Idle mixture is at 3/4 turns out.
Initial Timing is around +18 degrees advance.
Vacuum Advance is hooked up at +10 degrees advance.
Centrifugal Advance is progressive up to +14 degrees advance.

Idle speed is about 900 RPM when it’s warm and about 700 RPM when it’s still cold and warming up off the choke circuit.

At this tune with the engine at operating temperature, it’s seems to be the best I’ve had it. I will put an AFR gauge into my car so I can really dial it in but it sure seems nice at the moment. It’s great driving in traffic and really wants to get up and go when I have room to put my foot into it. I don’t even have 500 miles on the new engine yet so I can’t really get into it but this tune sure seems to be on the right track.

Also, for the record, my car does not enjoy starting in sub zero weather. When I start it, it still fires up immediately but it has a severe “lope” to the high idle for at least the first 60 seconds to maybe 2 minutes. Then it starts to smooth out into a fast idle at about 2,200 RPM. When it gets to full operating temperature and the log and head are at temperature, it’s happy and it revs out nicely.

Anyway, I’ll update further when I have more to say.
A "lopy" cold high idle usually indicates excessive richness. It's bad for the engine, and wastes gas. Relieve some pressure on the choke coil, or increase the amount of choke pull-off, or however that carb works: reduce the amount of choking immediately after cold start.

Also- don't baby a new engine! Ring and bearing break in is quicker and more accurate with occasional WOT pulls up to the redline, beginning 1-3 hours after initial start.
 
That sounds great. I’m really interested in what others are experiencing with this setup. I pushed mine around for almost a year before I was able to get it moving under its own power. Thankfully, it’s a relatively light car.

I’m out of town this week but I have a jet kit from redline for the 38/38. I’ll snap some photos when I’m back to see if they’re marked any better than yours are.
The car runs and moves around under power. I have the hood, fenders and interior removed and the cowl is being replaced. It's hardly street legal. The electrician will be finishing up the garage today, so I should have some data on the carb later this week when I get the cars moved around.
 
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A "lopy" cold high idle usually indicates excessive richness. It's bad for the engine, and wastes gas. Relieve some pressure on the choke coil, or increase the amount of choke pull-off, or however that carb works: reduce the amount of choking immediately after cold start.

Also- don't baby a new engine! Ring and bearing break in is quicker and more accurate with occasional WOT pulls up to the redline, beginning 1-3 hours after initial start.
Yes, I was thinking that I should adjust the choke blades and have them a bit more open to see if that improves the cold start. I’ll do that.

This is the first engine I’ve built in 25-30 years. I used a ring set with chrome Molly rings and had the bores honed to suit. I’m pretty sure the rings set immediately. It’s used no oil during the break in period. I’ve taken it up to around 4,000 RPM for short blasts but no WOT to redline yet. I’m sure that won’t hurt at this point as I’m certain everything is happy in the engine now.
 
Thanks again @Frank. I reduced the tension on the spring that affects the choke blades and it smoothed out the cold start immeasurably. It didn’t take much adjustment to make it work. After a really good warm up of about an hour of driving I attempted to dial in the idle mixture a little more to get a “best lean idle” by adjusting in 1/8 of a turn increments and again, I got it dialed in a little better. Even though it’s at freezing or near freezing temperatures, I’m getting it more and more dialed in. It sounds great too.
 
Back again for a Spring 2025 update for anyone who’s following along.

I was really quite happy with my timing and tune. There was just a slight flat spot when going from idle to the mains but it didn’t really affect driving and the car really has some get up and go. Then, last week I unintentionally threw my tune off while experimenting with an electric cooling fan.

Running with the electric fan was not successful in that although the radiator cooled better, there was much less air circulation in the engine bay and it may have heat soaked the carb. In addition, I suspect the fan introduced EMF or perhaps was broadcasting digital noise that interfered with my HEI ignition; I’m not 100% certain about that but do intend to investigate further. I’ll start another thread about that.

Whatever the issue was, the net result was that I played with timing, idle jets and mixture and then when I removed the electric fan and put back the conventional fan, I re-tuned the whole shooting match again. So, here’s where we are at:

I removed the 60 idle jets I’ve been running and I put in the 55 idle jets.
+20 degrees initial advance with another +10 degrees on ported vacuum.
About 5/8ths of a turn out on the idle mixture screws.
Maybe 5/8 - 3/4 of a turn out on the idle speed screw.

With this tune, it idles around 650-700 RPM. It does not have the annoying flat spot when it goes from idle to the mains. I’ve had it in absolute hair pulling grid lock traffic and it behaved quite well. Didn’t stall, didn’t overheat, almost got some heat soaking but nothing to worry about. Put your foot into it and it really comes alive. After about an hour and a half of just horrible grid lock traffic I jumped on the highway and opened it up in second on the on-ramp, (3 speed manual still) and it absolutely jumped ahead without hesitation. I think I have nailed the tune and it’s as good as it gets.
 
Thought I’d come back and add a little more to the equation. We’ve had exceptionally clear and sunny weather for the last week so I did a little tweaking to my tune. It’s definitely winter even though it’s sunny. It’s below freezing.

My engine is bored 60 over a little under 9:1 compression ratio with a small log head, a Clay Smith H-6474-0-B camshaft and an HEI distributor and an EBay Header into a Y-Pipe, 2.25” singe exhaust into a simple non restrictive muffler, like a turbo muffler and of course it is fueled by the Weber 38/38 on the Clifford/Redline adapter plate.

I’m still using the #60 idle jets. Idle mixture is at 3/4 turns out.
Initial Timing is around +18 degrees advance.
Vacuum Advance is hooked up at +10 degrees advance.
Centrifugal Advance is progressive up to +14 degrees advance.

Idle speed is about 900 RPM when it’s warm and about 700 RPM when it’s still cold and warming up off the choke circuit.

At this tune with the engine at operating temperature, it’s seems to be the best I’ve had it. I will put an AFR gauge into my car so I can really dial it in but it sure seems nice at the moment. It’s great driving in traffic and really wants to get up and go when I have room to put my foot into it. I don’t even have 500 miles on the new engine yet so I can’t really get into it but this tune sure seems to be on the right track.

Also, for the record, my car does not enjoy starting in sub zero weather. When I start it, it still fires up immediately but it has a severe “lope” to the high idle for at least the first 60 seconds to maybe 2 minutes. Then it starts to smooth out into a fast idle at about 2,200 RPM. When it gets to full operating temperature and the log and head are at temperature, it’s happy and it revs out nicely.

Anyway, I’ll update further when I have more to say.
What are your main jets and air correctors? I have a 300 with a melling mtf-6, hedman headers that go to free flowing exhaust, and then a. Clifford intake with the dual Weber 38s.
 
What are your main jets and air correctors? I have a 300 with a melling mtf-6, hedman headers that go to free flowing exhaust, and then a. Clifford intake with the dual Weber 38s.
I'm not cutting in to interrupt awasson's jet question answer. Just tp point out, his jet info may not be that useful to you. Dual carbs changes normal jet strategies.
Hopefully you have an AFR gauge. ? Are you running lean with the dual carbs?

OH!, and nice set up BTW! (y)
 
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I'm not cutting in to interrupt awasson's jet question answer. Just tp point out, his jet info may not be that useful to you. Dual carbs changes normal jet strategies.
Hopefully you have an AFR gauge. ? Are you running lean with the dual carbs?

OH!, and nice set up BTW! (y)
It’s getting there. I’m able to get it idling with 55 idle jets. Air correctors are 180 and main jets are 155. I just got back from a test drive and there weren’t any flat spots in acceleration. I’m going to check the plugs when it cools down a bit.

It’s getting leaner. When driving it has a flat spot as I go into second and is worse when I get into 3rd. I’m going to have to look into getting an AFR gauge I think. At this point, I’m just trying to get it to drive decently and then fine tune from there.
 
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It’s getting there. I’m able to get it idling with 55 idle jets. Air correctors are 180 and main jets are 155. I just got back from a test drive and there weren’t any flat spots in acceleration. I’m going to check the plugs when it cools down a bit.

It’s getting leaner. When driving it has a flat spot as I go into second and is worse when I get into 3rd. I’m going to have to look into getting an AFR gauge I think. At this point, I’m just trying to get it to drive decently and then fine tune from there.
Not surprised to hear it's lean. The smaller the airflow being pulled through a carb, the vacuum signal is reduced and they go leaner. Dual carbs require larger jets than stock calibration calls for. Seems counter-logical: a big carb on a small engine will need a jet increase not decrease. Don't hurt the engine- you're running way lean. A lean flatspot is in the 16's:1 AFR range.
 
What are your main jets and air correctors? I have a 300 with a melling mtf-6, hedman headers that go to free flowing exhaust, and then a. Clifford intake with the dual Weber 38s.

I haven’t changed the mains or air correctors on mine. I’d need to check but I think the mains a 145’s and the air correctors are 185’s. That sounds like a really great setup on your 300. Mine scoots pretty nicely but at some point I’ll want to move to a better head and intake.
 
Time for an update…

I’m running the 55 idle jets. I’m at 3/4 of a turn out on my air/fuel mixture screws. It runs best at 3/4 - 7/8 out with the 55’s. I backed my timing down a bit. I’m at somewhere between 15 - 18 degrees initial timing (I should put the light on to see where I’m at.

I put in the light (gold) springs on my HEI distributor and all timing is supposed to be in at about 2,200 RPM. I can’t detect any detonation with this timing and I’m constantly listening for it.

I’ve got the 5-speed in now so on the highway I’m usually running between 2,000 RPM - 2,500 RPM (65 MPH - 85 MPH) and cruising in the city around 1,800 RPM unless I’m stuck in traffic.

My setup is running quite well now and I’ve put on some decent mileage since my last adjustments. I just checked timing and idle air/fuel yesterday after about an hour and a half on the road. It’s about as good as it gets without changing jets. It does not hesitate. It pulls silky smooth when it gets on the mains.

I put on a 6mm phenolic spacer to isolate the carb from the heat of the log. It’s improved things a bit. It is more responsive to the pedal. I might put the slightly heavier distributor springs back on just to make it a little tamer in traffic though. When it goes off idle it’s a pretty abrupt shift and it just wants to go.

The downside is that it smells rich. I don’t have an AFR but I know what rich smells like and with additives in modern gas, it’s worse than old school leaded gas was. I can’t get it any leaner on the air/fuel mix without affecting the idle in a bad way. I might see what it’s like with a set of 50’s for the idle jets. I don’t want to change the mains until I have an AFR to see where I’m at since it runs so nicely. If I drive it like an adult with a mix of city and highway I get about 23 MPG. If I drive like a hooligan, it gets much less. Probably closer to 14 MPG but it gets up and goes pretty quickly with the assistance of the 5-speed.
 
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