Lotus Elan

Running rich

PostPost by: Charles73 » Tue May 03, 2022 7:54 am

After a long drive in my S4, with recently rebuilt engine running on Webers, I noticed that the exhaust had been spitting enough to leave black residue on the tail end. The same story where the manifold meets the head.

The car runs well, idles nicely, but does seems to lack in the bottom end when pulling in 4th.

I'm running the correct jets for the head, as advised by the chap who supplied the head to me.

Also running an electric pump with pressure regulator.

I'm yet to try to remedy the issue, but thought I see what people's thoughts are?


Many thanks
Charles
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PostPost by: rgh0 » Tue May 03, 2022 8:10 am

I would suggest
1, Check the jets for the cam you are using- if standard cam use the manual jetting.
2. If you dont know what cam you have, find out and people may be able to help from there
3. Take it to a weber specialist rolling road tuner
4. If you're into do it yourself look into Keiths Hypo jets

cheers
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PostPost by: Charles73 » Tue May 03, 2022 8:19 am

rgh0 wrote:I would suggest
1, Check the jets for the cam you are using- if standard cam use the manual jetting.
2. If you dont know what cam you have, find out and people may be able to help from there
3. Take it to a weber specialist rolling road tuner
4. If you're into do it yourself look into Keiths Hypo jets

cheers
Rohan


I'm running Q420 cams. All jets specified by the TC specialist who overhauled the head.

I intend on putting it on a rolling road once I've got it running the best I can.

Is too higher fuel pressure a possibility? Or simply the mixture screws need a wind in? I'll give it a try anyway.

Thanks
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PostPost by: Charles73 » Tue May 03, 2022 8:20 am

The jet sizes are:- Chokes 34mm, Emulsion tubes F16, Mains 140, Airs 155 , Idle 45F8, Pumps 40.
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PostPost by: TBG » Tue May 03, 2022 8:23 am

I posted this elsewhere but you may find it useful. I had a new big port big valve QED head , 420 cams - and yes I needed a mortgage!!

I went through all the recommendations from all over the place and as you can see went through a lot of changes to get it absolutely right for me. Incidentally the mpg has risen from just under 21mpg to 28mpg during the process and that is not when hanging about!! D

Spot jetting.jpg and


QED 420.jpg and
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PostPost by: nmauduit » Tue May 03, 2022 8:37 am

Charles73 wrote:The jet sizes are:- Chokes 34mm, Emulsion tubes F16, Mains 140, Airs 155 , Idle 45F8, Pumps 40.


I suppose you don't have a lambda sensor installed (very usefull to assess richness during all driving conditions) - also, spark plugs need to be in top condition for that kind of tuning, they need to be cleaned once they've been blackened before the next test or it may be biased (not colder than NGK BP6ES for road use).

I would think black deposit on the bumper are more likely to come from low speed low revs, hence would first try to reduce the idle jet one notch (40F8 instead of 45F8)

you may then want to try reducing a bit the main a giving it a bit more air at full throttle (main 135 / air 180) - but this is at play only above 3500 / 4000 rpm

as stated above, if you're after a near perfect tune, it's almost impossible to obtain without a rolling road (or accurate tools like a lambda sensor)

good luck
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PostPost by: pptom » Tue May 03, 2022 1:06 pm

I've been on a rolling road with both 360 and 420 cams with otherwise the same engine.
Same as TGB's post, the QED supplied jetting figures were way too rich. I seem to remember even the 34mm chokes weren't ideal and I would have been better sticking with the original size.
From memory it was too rich bottom end, the chokes also made the bottom end rubbish, almost right mid range and then too rich up top.
Carbs were rebuilt, but ultimately, they're 50 years old and every engine is a bit different.
The timing figures weren't ideal either, I went with something Rowan advised on here.
Even the max bhp was very optimistic on the spec sheet
Come to think of it, other than info on the cam measurements, I deduced that everything else on the spec sheet could be ignored.
That was with Omex crank triggered + mapped ignition. I've never been happy with the Weber's, too compromised, and have since gone fully computerised and fitted injection. Night and day difference and it seems like I've doubled the mpg.

Big valve, ported head, same car, same rolling road (Northampton Motorsports)
Q360 cams - 118bhp
Q420 cams - 128bhp
Q420 + Injection - 140bhp + much more driveable.
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PostPost by: promotor » Tue May 03, 2022 1:37 pm

pptom wrote:I've been on a rolling road with both 360 and 420 cams with otherwise the same engine.
Same as TGB's post, the QED supplied jetting figures were way too rich. I seem to remember even the 34mm chokes weren't ideal and I would have been better sticking with the original size.
From memory it was too rich bottom end, the chokes also made the bottom end rubbish, almost right mid range and then too rich up top.
Carbs were rebuilt, but ultimately, they're 50 years old and every engine is a bit different.
The timing figures weren't ideal either, I went with something Rowan advised on here.
Even the max bhp was very optimistic on the spec sheet
Come to think of it, other than info on the cam measurements, I deduced that everything else on the spec sheet could be ignored.
That was with Omex crank triggered + mapped ignition. I've never been happy with the Weber's, too compromised, and have since gone fully computerised and fitted injection. Night and day difference and it seems like I've doubled the mpg.

Big valve, ported head, same car, same rolling road (Northampton Motorsports)
Q360 cams - 118bhp
Q420 cams - 128bhp
Q420 + Injection - 140bhp + much more driveable.


pptom - for others reading this regarding expected horsepower figures with 360 and 420 cams can you advise of what spec the head was when either of those cams were fitted? Ie head chamber size and valve size / porting etc?
With relevance to this post, can you advise of cam timing settings used as cam timing may also affect what jetting (and ignition advance) is needed.
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PostPost by: pptom » Tue May 03, 2022 3:06 pm

Sorry, promotor, can't be specific with numbers as I can't remember 100%.
Head was standard valves when I obtained the car. I had it machined for the larger standard exhaust valves and it was sent, by the machine shop, to a chap who apparently had a role in the SAS head production. He ported the head and polished the combustion chambers. I have never measured chamber size. Other than the cams and springs, the head was unchanged.
Timing setting for the Q360's were QED spec with offset dowels.
Timing for the Q420's started out at QED spec, but as I had fitted adjustable pulleys I changed them to 107 inlet, 110 exhaust (95% sure!) And gained a couple of hp.
This is the graph between QED timing in red and 107/ 110 in black
Attachments
IMG_20210624_125758.jpg and
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PostPost by: Charles73 » Tue May 03, 2022 10:08 pm

It may also be worth mentioning that I was experiencing a flat spot when accelerating in third, around 3-4k. Also a chugging/stuttering in the bottom end.

At that point, I still had 30mm chokes installed. I thought I'd try the specified 34mm chokes and see what affect they'd have. I then took her out for a long drive and experienced zero flatspots. It was running very nicely.

Apart from the current lacking in 4th, it still does perform well. But is definitely running rich. From looking at the plugs, it's worse on 2 and 3. I'm going to start by starting again with tuning the carbs to the best of my capabilities. If not satisfied I'll try different jets as per your suggestions. Whilst running, I looked inside the intakes and no.3 had fuel dripping out the jet and fuel sitting in the venturi/choke area. I'll check floats and make sure they're OK.


Thanks
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PostPost by: promotor » Wed May 04, 2022 5:53 am

pptom wrote:Sorry, promotor, can't be specific with numbers as I can't remember 100%.
Head was standard valves when I obtained the car. I had it machined for the larger standard exhaust valves and it was sent, by the machine shop, to a chap who apparently had a role in the SAS head production. He ported the head and polished the combustion chambers. I have never measured chamber size. Other than the cams and springs, the head was unchanged.
Timing setting for the Q360's were QED spec with offset dowels.
Timing for the Q420's started out at QED spec, but as I had fitted adjustable pulleys I changed them to 107 inlet, 110 exhaust (95% sure!) And gained a couple of hp.
This is the graph between QED timing in red and 107/ 110 in black


Thanks for the info. I wonder if your low figures for the 420 are as a result of compression ratio being a bit low due to the combustion chambers being slightly bigger than normal and using standard pistons with no increase in intruder size?

Charles73 wrote:It may also be worth mentioning that I was experiencing a flat spot when accelerating in third, around 3-4k. Also a chugging/stuttering in the bottom end.

At that point, I still had 30mm chokes installed. I thought I'd try the specified 34mm chokes and see what affect they'd have. I then took her out for a long drive and experienced zero flatspots. It was running very nicely.

Apart from the current lacking in 4th, it still does perform well. But is definitely running rich. From looking at the plugs, it's worse on 2 and 3. I'm going to start by starting again with tuning the carbs to the best of my capabilities. If not satisfied I'll try different jets as per your suggestions. Whilst running, I looked inside the intakes and no.3 had fuel dripping out the jet and fuel sitting in the venturi/choke area. I'll check floats and make sure they're OK.


Thanks


Are you saying that at the same revs 3rd gear pulls better than in 4th gear?
At what revs are you getting the issue?
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PostPost by: pptom » Wed May 04, 2022 6:04 am

Linered, so standard bore with QED Omega pistons, but it is quite possible the comb chambers are a bit bigger. In retrospect, I wish I'd measured them.
Didn't measure the compression ratio, but I would imagine the head has been skimmed a few times. I do remember the last skim kissed the little core plug which I had to replace.

May just be that the Rolling road I used is quite conservative, though I did visit there once when a +2 used for sprinting was on the rollers. Think the engine was supposedly built by miles wilkins, that made 145bhp on carbs, but don't know the spec of it.
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PostPost by: pptom » Wed May 04, 2022 6:59 am

The chugging / stuttering sounds very familiar Charles.
I would say it's definitely worth spending £2-300 on a rolling road with someone who knows DCOE's, drop in the ocean compared to the problems which could occur if it was too rich / lean.
Especially since it's been rebuilt.
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PostPost by: rgh0 » Wed May 04, 2022 12:43 pm

I would not worry much about the rolling road HP numbers which have some unknown correction factor applied it appears and focus on getting the engine running as best in relative terms as you can

Running rich with no flat spots will not cause much power or torque loss unless its so rich it is misfiring. Mileage may be poor and bore wear greater due to excess fuel washing oil off the bores but this does not cause power loss.

The QED cam timing recommendations for the 420 cam are strange and inconsistent with all other cams of this sort of lift and duration so i would treat then with caution as you appear to have done and look at moving to something closer to what others recommend ( e.g. Kent 144 cam timings).

Then a good rolling road session to get the advance sorted and jetting right from someone who knows what they are doing . For road use 33 or 34 mm chokes should be optimum. You can try 35 or 36 but not really needed unless you have a steel crank bottom end going over 6500 rpm and seeking more top end power. The rolling road session should be able to also determine the best advance curve for your engine and fuel based on holding the engine at steady revs in steps across the rev range and full throttle and then tweaking the advance for maximum power. This may then need the dizzy to be recurved to suit the dyno optimum advance as the revs increase.

cheers
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PostPost by: Charles73 » Wed May 04, 2022 4:24 pm

After another fiddle with mixture screws and slight adjustment to the balance, I've improved it.

It now pulls better in 4th, and no apparent hesitation. Seems fine in all gears at all rev ranges too. But I still feel there's room for improvement.

The only issue I'm noticing is that it's varying at idle, not massively so, but it's not 100% steady. Maybe too much air?!

I've booked in for a tune up with Peter Lander at Sigma Engineering as he's not too far away.

I'm just hoping I haven't caused any excessive wear due to the fuel finding it's way into the sump...I've done around 300 miles since the rebuild, but have changed the oil twice!


Thanks
Charles
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