1700 XFlow AFR setup

[Mudder]

Dear Seveners,

 

I've been tinkering with my 40DCOE's for quite a while and I think I am getting quite good at it.

However I would like to get a little more analytical in regard to AFRs.

 

I am running a stock 1700 Super Sprint.

My compressions are excellent and the engine is timed properly.

I optimized my 123 Ignition on a rolling road and both of my DCOE's are new (40 DCOE 151).

 

The engine pulls pretty well, but at my elevation of 8000 ft, I would like to tweak the carbs based on proper AFRs.

 

Does anybody in our group have experience with installing an AFR sensor in a classic dual Weber, 4 in 1, no cat setup.

Essentially I am running four small 425cc engines which can all be tweaked individually ;-).

A single sensor wouldn't really work IMO.

 

Please fire away!

 

Cheers

Wolfgang

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[MV8]

What makes you think the jetting is incorrect? If burning ethanol mix, it is helping offset the altitude.

I suggest setting them the same based on a single wide band sensor. You can check pipe temps individually with a laser, water bottle, or run egt probes in the primaries and temp fit four gauges under the dash.

 

 

Edited September 12, 2025 by MV8

[CarlB]

You might look at Performance electronics or Innovate motorsports.

[Mudder]

54 minutes ago, MV8 said:

What makes you think the jetting is incorrect? If burning ethanol mix, it is helping offset the altitude.

I suggest setting them the same based on a single wide band sensor. You can check pipe temps individually with a laser, water bottle, or run egt probes in the primaries and temp fit four gauges under the dash.

 

 

Well,

1. revving the warm engine at idle creates black puffs out of the exhaust

2. gas mileage went down to about 15mpg from 20 mpg

3. very black spark plugs

4. fuel droplets on my right clamshell

 

Funny enough it runs fairly well, no real flat spots.

2-3000 rpm, putzing through 30 mph zones it becomes a little erratic.

 

 

I pulled the floats (plastic, about 19grams each) and reset the height to 13mm and travel to 25mm (measured in the middle of the flat side)

I was surprised to see some marring on the needles (1.75, 3000 miles) 

 

I synchronized the carbs a couple of days ago and my idle screws are about 2-2.5 turns out.

 

New needle valves (1.75) are on order.

Pierce Manifolds recommended a 60 F8 idle jet and I will install a Malossi Fuel pump and regulator.

The Holley regulator  I installed 2 years ago is inconsistent (measured by my fuel pressure tester)

 

Carb Setup:

 

40 DCOE 151 (Spanish), new from Pierce Manifolds:

Mechanical Fuel pump (very consistent 3 psi out put)

 

Choke            32mm

Idle Jet           50 F9

Emulsion T.    F11

Main Jet        120

Pump Jet       .45

Needle Valve 1.75

Air Corr.        170

 

Cheers

 

[Mudder]

1 hour ago, CarlB said:

You might look at Performance electronics or Innovate motorsports.

I talked to Innovate and they couldn't tell me where to install the AFR sensor on my 4/1 no cat setup.

The Tech Guy was worried about wrong readings.

I'll try Performance Electronics next.

[MV8]

Under what conditions is the psi increasing? How much? How are you checking it? Which holley regulator are you running (they all look about the same).

 

What part numbers did you change? Was it running well before? Might try 115 if not running ethanol.

 

Cat or not has nothing to do with it. You can run a single wide band.

 

 

 

 

Edited September 12, 2025 by MV8

[toldfield]

I installed an AIM AFR on my twincam.  Had a bung welded beyond where the two into one connection was.  It works well, I'm just too illiterate to figure out how to log the data.

[jbcollier]

Weld the bung in right where the four pipes join.  One sensor is all you need.

 

Dial in your mains first. WOT up a hill @ 4500 rpm (mid 11s)

 

Then air correctors.  WOT up a hill @ just below redline (mid 11s)

 

Next your idle jets, set mix screws to fastest idle + a smidge and then light throttle at 30 mph/50 KPH (13.0 to 13.5)

 

Now you are mostly dialled in.  Drive it and watch carefully for transient lean spots.  Use different idle jets and/or emulsion tubes to reduce/eliminate them.

 

Now run your engine for a couple thousand miles/kilometers.  Check your valve clearances.  Stayed the same?  You’re good.  Valves tighten?  Richen your mains one step and do it again.

[IamScotticus]

On 9/12/2025 at 2:05 PM, Mudder said:

Well,

1. revving the warm engine at idle creates black puffs out of the exhaust

Normal

2. gas mileage went down to about 15mpg from 20 mpg

Normal

3. very black spark plugs

Normal

4. fuel droplets on my right clamshell

Normal

 

Wolfman,

It's a 1960s engine.   It's a dirty engine and it likes it that way.

I saw something on the FB Webber group,  take it with caution...

Someone had DCOE carb spitting and solved it by drilling a hole in the back cover plate. Don't know why it works. 

 

Two kinds of meters

Air/Fuel Ratio meter- gives actual O2 readings.  Need to know what to expect for your fuel type, altitude, etc.

 

Wide band O2 / Lambda?

A system that shows you the perfect AF reference point (stoich) and where the current AFR is in relation to that point.

I don't know how the system knows the Stoic point for any engine,  but it makes tuning more simplified.

There are portable systems to stick in the pipe.

I believe the Innovative LM1 was such a tool. @jbcollier uses one. 

 

JB gave really good advice a while back:

"Get a O2 sensor bung welded into the exhaust right after all the pipes come together but before the muffler.

 

Then buy an Air/Fuel Ratio gauge with a wide-band 02 sensor. I haven’t bought one in a while so I can’t give you any current advice there. I use an Innovate LM1 which is out of production now. I’m sure someone will chime in with more current recommendations. There are bluetooth gauges you can run off your phone. No need for a dash gauge. You’re going to dial in your carb and then unplug everything so no need for anything fancy, just functional.

 

Warm up the car thoroughly. Then fit the O2 sensor and hook up your gauge per its instructions. Now go for a drive. Here are the critical modes to test:

 

- part throttle, low rpm, steady state, between 25 and 35: in other words just moseying along.

- part throttle, steady state around 50.

- part throttle, steady state at hwy speeds

 

In all these cases you want mid to low 13s. Anything exceeding 14 is too lean. This is mostly adjusted using the idle jets

 

- medium acceleration from a rest to 35: low 13s to high 12s. Watch for faltering and lean/flat spots which may indicate too small an accel jet.

 

- WOT, hard acceleration 3000 to 5000 rpm: low 12s to high 11s. This is all on your main jets.

 

Once the mains are set, then:

 

- WOT, hard acceleration 5500 and up: low 12s to high 11s. This is where you set your air correctors. A larger air corrector leans the mix.

 

I rough set my idle jets and idle mix so it is ok. Then I dial in the mains. Next the air correctors. Finally I go back and fine tune the idle jets. Time spent here can find valuable fuel efficency.

 

Side draft carbs can have a seemingly infinite variety of jets, chokes and nozzles but really you find the recommended settings and are just using the AFR to fine tune things for your local climate and driving style.

 

Downdraft carbs are easier and harder in equal measure. Easier because there just isn’t as many options available, and harder, you guessed it, because there aren’t as many options available. You’ll have to compromise as you can’t nail it like you can with a sidedraft. Just remember, always err on the RICH side, never lean!

 

Just one more thing, carbs transition from idle to progression to mains. It all blurs from one to the other. In those transitions, you can get fleeting lean spots. Watch carefully for them as we commonly drive with the engine in those transition zones. Lean = heat = burnt valves and holed pistons. While you certainly will toast an engine quickly being lean at WOT, you can do it just as well being lean at part throttle. Just takes longer."

Edited September 15, 2025 by IamScotticus

[jbcollier]

I’d forgotten about that post, like I do most things.  Just some additional info on downdrafts:

 

The commonly used 32/36 DGV and derivatives is designed to run lean at part throttle.  No amount of fat idle jets or rich idle mix settings will correct it.  Fortunately, there is a primary emulsion tube that helps.  Replace the stock F6 with an F66.  This brings things down from the 16s to the 14s.  Still not ideal but much better.  I haven’t yet but you can do better by filling or reducing the holes in the emulsion tube.  Upper holes affect part throttle, lower holes full throttle.  The holes let in air so more and/larger holes is leaner and vise versa.  The transition from idle jets to mains is also shifted a bit, fewer/smaller upper holes means an earlier transition point.  The auxiliary venturi is the primary method of shifting the transition point but they are hard to find and only make big “jumps”.  Note: changing the float level will also shift the transition point.

[Mudder]

18 hours ago, MV8 said:

Under what conditions is the psi increasing? How much? How are you checking it? Which holley regulator are you running (they all look about the same).

 

What part numbers did you change? Was it running well before? Might try 115 if not running ethanol.

 

Cat or not has nothing to do with it. You can run a single wide band.

 

 

 

 

I temporarily plumped a fuel pressure tester right after the fuel pump and my mechanical out put is 3 psi, revving it to 2000-4000 RPM

With the Holley regulator in line my pressures are bouncing between 2 and 3 psi in the same Rev. range

The regulator is a Holley 12-804 .

 

It's difficult to get ethanol free gas around here. 91Octane comes as E10.

 

I am at high altitude (8000ft) and I will try to jet it down a bit.

 

Thanks!!

 

 

[MV8]

Remove the regulator.

[IamScotticus]

The OEM mechanical fuel pump does a good job of self regulating but can induce surges with throttle.  There is a Solex pressure stabilizer available for this.

https://www.piercemanifolds.com/product_p/b26570.htm

Edited September 13, 2025 by IamScotticus

[Mudder]

1 hour ago, MV8 said:

Remove the regulator.

Removed!

[Mudder]

Thank you so much to everybody who chimed in.

Still trying to find a cost effective AFR logger.

The Innovates are kind of up there.

well, it will be a worthwhile investment.

 

[slowdude]

22 hours ago, Mudder said:

Thank you so much to everybody who chimed in.

Still trying to find a cost effective AFR logger.

The Innovates are kind of up there.

well, it will be a worthwhile investment.

 

AEM or Amazon have stand alone AFR gauges. @NSXguy has a similar standalone setup on his kent.

 

@IamScotticus, those AFRs seem very rich. I just got my wideband (Spartan) setup off my emerald and its running to AFR targets setup by my engine builder for my cams. My idle is at 14.5, through to 13.2 at full throttle for when the cams come on. Over 14 is OK, its when you get above 15 that you risk running leaner. Running super rich at idle (especially at start up - sub 14), you risk carbon build up due to intake/exhaust valves. Anything around stoich should be fine.

 

Since youre not running an ecu to measure voltage on the sensor, check the manual of whatever sensor you get and see if there is a calibration process. Make sure you also check which wideband it is, there are a lot of 4.2 clones, while most newer widebands can run 4.9 and 4.2's.

 

Check the manual as well for the sensor heater, so you know when the sensor is ready to go so you dont fry it. Make sure the sensor isnt wet and cold or it will fry.

 

I just spent too much time learning about all of this with my emerald ECU, but I am very happy with how it turned out.

[MV8]

I would have been tempted to swap in smaller chokes, giving up having near zero vacuum at WOT at 6000 for better part throttle operation covering 90% of normal driving. One could look at a typically combo with the smaller chokes as a starting point.

 

You could get new chokes of your choice for about $150 shipped on ebay from Italy (not counting tariffs). Czech Republic has insane shipping.

[IamScotticus]

Still a lot of questions here.

If Mudder puts in a logging AFR, it only shows his O2s based on what?  An AFR meter doesn't know what test of fuel, altitude, compression ratio,  blah blah blah...Murder needs to know what his ideal AFR should be based on his variables first, and it may not be the perfect stoichiometric ratio of 14.7:1. So Mud needs to determine his Stoich point before an AFR is useful. 

hey, I say if you're blowing smoke, that's good 

Edited September 15, 2025 by IamScotticus

[jbcollier]

On a Kent engine, it would never be 14.7, too lean. See details above.

 

A Zetec or Duratec would a different matter entirely as they were designed for the higher temps — both cooling and combustion — of emission controls.