A/F Rich when cruising

Baja_Tommy · Posted: Mon Jun 15, 2015 7:04 pm Post subject: A/F Rich when cruising

Question first: Is it acceptable for the engine to run rich (around 11:1) at a light cruise and lean out at 12:1 to 13:1 under WOT?
I recently installed a wideband sensor in my bug, and after some tuning, those were the numbers I got. While doing my research, I came accross this point in another thread:

[email protected] · Posted: Mon Jun 15, 2015 7:27 pm Post subject: Re: A/F Rich when cruising

What elevation and emulsion?
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Baja_Tommy · Posted: Wed Jun 17, 2015 10:31 am Post subject:

800 feet elevation and f11 emulsion tubes.

After some more driving it seems to run at about 12:1 when cruising in town. Cruising out on the highway (60 mph and ~3200 rpm) it can run as low as 10.5:1, but goes back to ~12.5 when I punch it.

[email protected] · Posted: Wed Jun 17, 2015 10:34 am Post subject:

F11 is the problem, it comes in sooner than the proper F7s. Put F7s in for center mount IDFs.
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Baja_Tommy · Posted: Wed Jun 17, 2015 10:51 am Post subject:

Thank you! I will definitely be making that adjustment!
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Baja_Tommy · Posted: Fri Jun 19, 2015 1:02 pm Post subject:

Put in the F7s and it ran rich on the mains at WOT. At 65mph and 3500rpm it even dipped below 10 and misfired, puffing black smoke.

I tried a smaller main jet, but it ran way lean above 4500, leaner at idle, and still rich at a cruise with misfiring when I tapped on the throttle.
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mikedjames · Posted: Fri Jun 19, 2015 1:58 pm Post subject:

I would expect to see those A/F ratios with the choke on for the first few miles. They seem rich to me.
Then switch to 11:1 to 12:1 wide open throttle going up a slight hill and 14:1 to 15:1 on level road cruising and sometimes even leaner going downhill.
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[email protected] · Posted: Fri Jun 19, 2015 3:02 pm Post subject:

with an emulsion tube change you are going to have to re-start tuning from scratch.

I'd start with an air jet in the 160-170 range. With 34-35mm venturis try a 135 main.
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Baja_Tommy · Posted: Fri Jun 19, 2015 5:16 pm Post subject:

I've done some more thinking and tweaking. My problem is that no matter what jetting or what rpm the engine is at, it runs rich at about 10% throttle.

The F7s seem to make the problem slightly worse. With the F7s, its running best at about 55/140/175, but It now runs rich enough at 65 mph and 3500rpm to cause a misfire. The ratio is getting into the nines! Other than that, my readings are the same as the ones I originally posted. Maybe a bit leaner overall.

Could it be a wrong float bowl level, lack of vacuum advance, or something fundamentally wrong in the carburetor?
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[email protected] · Posted: Fri Jun 19, 2015 5:19 pm Post subject:

If it's rich at 10%, go down on the idle jet, since 10% is being metered by the progression holes.

And yes, you need to make sure these basics are good

fuel pressure
float level
engine compression
no throttle "flutter" which causes pump squirt

The engine can run fine without vacuum advance, so it's not that.

What plugs are you using?

Are you sure the "140" main jet is really 140, or is that just how it's marked? Don't assume anything!

Understand that if your A/F is reading 9s or 10s, it's probably accurate. The question is where is the fuel coming from? It doesn't necessarily have to be from the aux venturi (main jet), if the carb is sloshing, spilling from a high fuel level or fuel pressure, or pump flutter. Widebands can easily "False lean" for a variety of reasons, but they never "False rich".
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modok · Posted: Fri Jun 19, 2015 5:24 pm Post subject:

The correct jetting for a single IDF is a problem that has never been fully solved. There is no single right answer!
f-7 works good sometimes, but if you use a isolated manifold of smallish diameter then f-7 goes too rich at high rpm.

A custom emulsion tube might be a good idea, but emulsion tubes are always the LAST step. Choose manifold carefully (correct size for engine), hook up pre-heat if you ever plan to drive in even mildly cold weather, try a few jetting combos and figure out the right venturi size, then lets talk about emulsion tubes.

Baja_Tommy · Posted: Sat Jun 20, 2015 2:55 pm Post subject:

compression: 165-182 psi (can't run straight pump gas or it diesels)
fuel pressure: 5 psi (too high I know, but my pump is rated at 2.5 to 4.5 psi and if I turn my fuel regulator down any, it starves the float bowl under WOT)
the float is set so that it stops letting in fuel when parallel with the ground. it doesn't sputter around corners.
Plugs: NGK B7HS

With a 50 Idle jet, I get no noticeable improvement. As I push in the throttle to accelerate, it still stumbles when it reaches about 10%. Messing with the idle adjustment screws doesn't seem to help either.

The engine has had a thing where if I go WOT under 2000 rpm, it stumbles rich. I don't run it that low anyways, but I thought it might be related.
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[email protected] · Posted: Sat Jun 20, 2015 2:58 pm Post subject:

REMOVE that POS "fuel pressure regulator", since it doesn't work. It's the chrome one with the dial/arrow right?

You can't go any further until you get the pressure properly regulated.
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Baja_Tommy · Posted: Sat Jun 20, 2015 3:43 pm Post subject:

Yeah. In my experience it doesn't change the pressure so much as restrict flow. I've known it's garbage, so I guess now is the time to swap.

A Holley 12-804 sounds good. Set it to 3 psi, and see what I can do with the adjustments then.
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If you're too old for dirt bikes, get a Baja Bug!

Baja_Tommy · Posted: Tue Jun 23, 2015 4:24 pm Post subject:

Fuel pressure is now set at 3 psi. This has mostly corrected the richness under 2000 rpm.

The problem with running over-rich at partial throttle is still the same. I tried different jetting, but it ran too lean or too rich. With a 130 main, The partial throttle richness did get better, but it was way too lean at WOT. I noticed It stumbles and lurches more at light throttle with the smaller 50 idle jets. It Goes
WOP WOP WOP WOP WOP down the road, loading and unloading the drivetrain.

I ended up back where I started with the F11 tubes and 55/150/185. With every other combo I've tried, the car just doesn't feel as good or get the right A/F ratio.
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A Baja Bug with some power is like a dirt bike. Quick not fast. Fun at low speed but scary at high speed.

If you're too old for dirt bikes, get a Baja Bug!

[email protected] · Posted: Tue Jun 23, 2015 4:39 pm Post subject:

why are you running 50 idles with a 44? Should be 55-57.5.

This is what I mean by you have to start over from scratch. No information you got from before (with the bad regulator) is useful. Start over.
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MURZI · Posted: Tue Jun 23, 2015 7:29 pm Post subject:

Also verify you have in fact a carb designed for use as a single. Does it have the 2mm holes in each throttle plate? If not you are probably opening the throttle plates too far at idle to make it idle... Exposing progression ports and jacking up the mixture. Just something to check........
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Baja_Tommy · Posted: Thu Jun 25, 2015 7:21 am Post subject:

No throttle plate holes in my carb.
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A Baja Bug with some power is like a dirt bike. Quick not fast. Fun at low speed but scary at high speed.

If you're too old for dirt bikes, get a Baja Bug!

MURZI · Posted: Thu Jun 25, 2015 7:28 am Post subject:

OK close the throttle plates completely. Screw in the speed screw 1/2 turn after it hits throttle arm. Now unseat the air bypass screws(ones by idle mixture screws with jam nut) 1 turn and see if it will idle. Adjust idle speed here to get it to idle first. By doing this you have covered the progression ports at idle(the way it should be) and created an air leak to allow it to idle.

Now you need to start the jetting process all over again.
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Tim’s welded heads
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Fk44 cam

[email protected] · Posted: Thu Jun 25, 2015 8:15 am Post subject:

You can put a gauge on the SVDA port, if you have vacuum from that port at idle the throttle plate screws are in (open) too much. Back the idle speed screw until the vacuum is gone.

Now, if the idle speed is too low, you can fix this issue by opening the air bypass screws. Open them up a bunch. If you can't get enough idle speed via the bypass screws, you'll need to drill the holes in the throttle plates to get more air in. But MOST engines will work fine with the bypass screw adjustment.

Of course, make sure the idle timing is correct before you do any of this stuff, and adjust the idle mixture after everything is done.
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