Acrid smoke and low vacuum

Talk about the E-Type Series 3
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lowact
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#21 Re: Acrid smoke and low vacuum

Post by lowact » Sat Mar 10, 2018 4:07 am

I know it runs rich; I often wondered, if I hung an old paint tin off the end of the exhaust, would I capture enough to run the lawn mower?
A friend has a portable wide-band A/F meter, we bolted it on and went for a drive. At idle, 40, 50, 60 mph in 4th gear we were getting 12.7, 12.4, 13.0 and 13.3. So we adjusted the needles, afterwards we got 12.7, 13.8, 13.7 and 14.7. Somehow this also improved the vacuum to -14inchHg, still too low and made no difference to the acrid fumes making clothes stink.
Recapping from previously: all cylinders firing sweetly, timing is 12 deg BTDC at idle, no vacuum advance, plugs are black, exhaust is blue, compression is 150 psi ±7%, 98 ROM fuel.
Also, bypass valves on the carbs are completely removed, blanked off. Carb needles are original, B1BH, spark plugs are N9YC's, I'm thinking of trying 11's?
Regards,
ColinL
'72 OTS manual V12

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jagwit
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#22 Re: Acrid smoke and low vacuum

Post by jagwit » Sat Mar 10, 2018 8:41 pm

Colin, its noteworthy that the mixtures at idle did not change despite having fiddled the needles. This already hints that something is not as it may seem. Also consider that depending on where you installed the O2 sensor, and the exhaust configuration, you could be getting an AVERAGE reading from two or more carbs.

With all the EFI projects I have done, I have seen that an engine can tolerate rather lean mixtures at low throttle openings. E.g. My Jensen with the old tech Chrysler 440 runs happily at AFR16 when cruising on the level at 2000rpm. My pre-HE V12 XJS likewise. The HE V12 engines were cruising at 17!! At full throttle though it is imperative that the engine gets all the fuel it wants for an AFR of at least 13.5.

I now work on the basis that these old tech engines need the following AFRs (as a guidline):
0-30% engine load: AFR 13 (this is overrun / engine braking conditions)
30 - 55% : AFR 16 (light cruise)
55 - 75%: AFR 14 (maintaining speed up a slight hill)
75 - 100: AFR 13 (basically full throttle)

I can not see that a hotter / colder spark plug is going to make any difference in your situation.

A last thought: Can you measure vacuum levels while driving? If so, what's the max vacuum you get, say, at 2000rpm on overrun?
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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#23 Re: Acrid smoke and low vacuum

Post by jagwit » Sat Mar 10, 2018 8:48 pm

Here is the AFR map for my Jensen (Chrysler 440). The X-axis is RPM and the Y-axis is engine load in KPa. 100Kpa is full throttle and 20Kpa is 0 throttle. (The engine never pulls more than 20kpa vacuum, and idles at 40kpa).
AFR map.png
AFR map.png (144.96 KiB) Viewed 606 times
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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muz122
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#24 Re: Acrid smoke and low vacuum

Post by muz122 » Fri Nov 08, 2019 7:47 am

Hi Colin, did you ever get to the bottom of this?

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lowact
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#25 Re: Acrid smoke and low vacuum

Post by lowact » Sun Nov 10, 2019 1:00 pm

Not yet, but I must be getting close ...
Image
The clatter returned (so wasn't just the air pump) and became continuous, no longer stopping when the engine had warmed up. Good reason to start the HE upgrade. I'm suspecting the acrid smoke was due to old valve seals, all other rubber and plastic is perished/brittle/cracked, valve stem seals won't be an exception. The clatter was regular and tied to rpm, i'm imagining may (?) be a dropped valve seat, both these would also cause poor idle vacuum? Thx for the interest, i'll update after i've stripped the heads.
Regards,
ColinL
'72 OTS manual V12

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#26 Re: Acrid smoke and low vacuum

Post by jagwit » Sun Nov 10, 2019 6:52 pm

Timing chain tensioner good?
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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Woolfi
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#27 Re: Acrid smoke and low vacuum

Post by Woolfi » Mon Nov 11, 2019 10:11 am

"I now work on the basis that these old tech engines need the following AFRs (as a guideline):
0-30% engine load: AFR 13 (this is overrun / engine braking conditions)
30 - 55% : AFR 16 (light cruise)
55 - 75%: AFR 14 (maintaining speed up a slight hill)
75 - 100: AFR 13 (basically full throttle)"


I think that from 0 - 15% engine load the AFR shall be AFR from 13 - 14. With an engine load of 15% a V12 motor can "produce" 268 x 0.15 = 40 hp. With 40 hp the car can drive roundabout 65 - 70 mph. At this speed / load the motor can run with AFR 15 - 17 without problems, to ignite the load. AFR 13 at 30% engine load seems much too fat for me. The motor runs will with AFR 13, but with a higher AFR the gas consumption is lower.

My own 6,0L HE motor in the E-type is running from 40 miles up in 5th gear with a AFR of roundabout 15.5 - 16. In the past the motor was running good also with a AFR of about 17 at the load. With a higher AFR the motor is producing less bad exhaust smell, caused by unburned HC.

With a constant depression carb there is one problem with a high AFR. If the needle is a little bit thicker and therefore the mixture is a little bit leaner at a low load, the mixtures is staying too lean, when pressing the pedal full at low revs of roundabout 1200 - 2500 rpm. If I "tailor" the needle a little bit thinner, the mixture at cruising is less lean and the mixture is also less lean when accelerating strong. A CD carb is not able to deliver a lean mixture at low revs AND becoming immediately fat (AFR of less then 14.7) if the throttle is opened suddenly full.


Regards
Wolfgang Gatza

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jagwit
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#28 Re: Acrid smoke and low vacuum

Post by jagwit » Mon Nov 11, 2019 1:49 pm

lowact wrote:
Sun Nov 10, 2019 1:00 pm

Image
Those cylinder tops also look very black - as if the engine was running very rich (as suggested by thread title), or it was burning a lot of oil, or both.
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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lowact
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#29 Re: Acrid smoke and low vacuum

Post by lowact » Tue Nov 12, 2019 7:04 am

jagwit wrote:
Sun Nov 10, 2019 6:52 pm
Timing chain tensioner good?
Thought it was, but i was wrong. Couldn't tell by looking but as soon as I tried to ease off a bit of tension it fell apart. No flex there at all, Should have known, 50 yo plastic ...
Image
Time for a beer while I ponder my next move.
Regards,
ColinL
'72 OTS manual V12

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#30 Re: Acrid smoke and low vacuum

Post by jagwit » Tue Nov 12, 2019 7:30 am

Look how those crank sprocket teeth are worn...

New:
sprocket
Tensioner
Cam sprockets
Chain

Might be cheaper to buy a parts engine
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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