So now i have a Vintage speed silencer fitted i am toying with fitting a wideband afr meter. I know 14.7:1 is the optimal ratio but what would you want to run at on our old aircooled engines? Something slightly richer?
14.7 is ok for idle but I set my Della around 13ish around 55-60 mph . I have the inovate LC 2 set up . Used it on the bus with dells you get it as good as I could now it on the 914 as part of my micro squirt setup
14.7 idle, 16-17 cruise at.60- 65mph slight downhill, or pootling at 30mph 12-13 foot down hard, 20+ engine braking. 1641 with a progressive.
Mains... WOT AFR is all you need worry about as that's hole in piston territory. 12.8-13. Tickover...whatever. Get it idling nice. Note the AFR but don't tune for it. Some try and tune for a small idle for "lean cruise" to save petrol but it doesn't really work for a heavy bus and you must have an SVDA distributor to try this. If you get it really lean (tiny idle) without choke it won't start in the cold and messes with the idle/main x-over area such that fitting overly small Venturis is the only solution. Fine tuning that point with main airs won't be enough but if you're able get that right you'll find WOT or fast cruise gone wrong. One can waste a lot of time and money with AFR. I did. Now back to how it was when I guessed. If you have a stock engine the whole AFR journey is IMO a hideous waste of time. BUS before Garrick chips in - Beetles is different..
The main thing it does is show why no matter how clever carburettor designs are, they are all a compromise compared with EFI. Even with six orifices squirting petrol at different times, or together, its just never quite right. Progressive: accelerator pump jet, two idles, two main jets and a vacuum operated "power valve"
I suspect the power to weight thing doesn't help us either. When I give up camping I may put my engine in a Beetle.
Spending all your time with the outside front wheel smoking as you go into the corner.. it was a great day at the VWH 30th anniversary at Brands watching all the Beetles sort of on the edge, as modern Golfs just drove outside them on the corners.. and the splittie leaving an ever increasing oil haze on each lap...
if you can save hundreds by not buying an Afr meter and get a good set up count me in. I cannot see why they are so dear. The electronics cost next to nowt. When someone comes out with a reliable temporary test rig/meter for under £100 i will think about it. Then Rolling roads can pack up, they break engines with poor operators anyways ...
Slightly strange.. a modern lambda sensor should work over at least a 10:1 to 20:1 range. That is probably a narrow band sensor which means it will be reliable at 14.7:1 +/- a bit, and getting hopeless over near 10:1 ( which a VW air cooled shows with the choke on and a wideband lambda setup ) and 20:1 which my progressive provides engine braking down a steep hill.. I did pay only £23 on eBay for a Bosch LSU4.2 clone sensor..
Normal driving covers about the range of that sensor, but while tuning you may need more range. If you read the description, it can run on a battery.. so it is narrowband as the wideband ones need more like 20 watts to run the heater.. so a sign is it is wideband is if it says 12 volt power only.. Narrowband sensors have 2 wires. Just signal/ground Wideband have 4 or 5 wires... signal/ground/heater/feedback /calibration resistor. The feedback currentadjusts oxygen pumping into the sensor cell fed down the sleeve of the sensor cable to keep the mix in the sensor at 14.7:1.. It runs at 600 degrees C why it doesn't like water or condensation. Wideband is a narrowband sensor heated at startup so they respond before the exhaust heats up Their Wideband AFR gauge is quite expensive https://kosonorthamerica.com/product/wideband-airfuel-ratio-meter-7/
Would ove of these gauges work for adjusting the stock carbs on our 2L type 4? If so where would I mount the sensor? Or would I need 2 sensors? What is the best value (read cheapest that works) gauge/sensor?
If all you want to measure is idle mix then that cheap setup will let you set that. It depends on the exhaust, but on a stock exhaust you could fit an oxygen sensor bung to the tail pipe near the silencer end, just needs to be more than a foot from the end of the pipe where it meets the air. Or you make a temporary setup with a bit over a foot of pipe that fits well over the end of the tailpipe and carrys the O2 sensor attached to that extension. I use a PLX devices setup, more like £160 to £200, this measures 10 times a second, it's a wideband system. I have a single quiet pack on a T1, with a 4 into 1 collector arrangement, my sensor sits in front of the silencer so it picks up pulses from each cylinder in turn. Here you can see the black soot marks from the metal cracking away from the welds on the side of the stainless silencer box, after whacking a few things with it.. . As a result at idle RPM if there is one cylinder not firing right, the gauge 'flickers' it does not tell me which cylinder, only that there is uneveness in the combustion in different cylinders.
I made the tailpipe with the 18mm sensor bung about a foot from the end as mikedjames says. I know it needs decent heat to work so further back to head won't hurt. Just waiting for world/suppliers to do the right thing. Isn't it just a matter of measuring resistance with an ohm test meter, or whatever the gauge does in the proper kit?? These are more for permanent installs, they need to launch a cheaper removable test kit. Once it's jetted ok I don't need it in the van, it can sit on a shelf. Or someone provide a service hiring it out maybe...
