Now that i have my AFR gauge set up i've been doing some reading on what i should be trying to get for best performance. Aircooled.net has a good write up that i've been reading: How To Use a Wideband To Tune Your Carburetor(s) On The VW Flat-4 Engine | VW Parts for Aircooled Volkswagens - Aircooled.Net WOT (or anything over 1/3 throttle) they are saying should be in the region of 12.8 – 13.2. Light Cruise with vacuum advance should be 15.5 – 17 Is this a good target range for a 2.0 type 4 motor? stock other than ict carbs.
It's good for ANY carbed motor. You're unlikely to see "light cruise" in a bus unless on the flat under 35mph, just tickling the pedal.
Yeah tbh I’m just trying to get the best WOT first, not that worried about anything else. As you say, bus aerodynamics means you usually have your foot in
A slight downhill at 60mph can also hit"light cruise", but generallly when its flickering around 17:1 suddenly at idle it means a spark plug lead has fallen off, as unburnt fuel/air has full O2. And a duff condenser moved the WOT to closer to 11:1 from the 12-13:1, when it was fighting to get to 50mph in 3rd on the flat.
Cruising at 50 on the flat at about 1/4 throttle i see about 14.5-15 which is ideal. Foot in up a steep hill around 12. I do have a slight flat spot on transition when it momentarily goes to 17-17.5 but I just drive through it.
With carbs you will really only have one area that will be what you want . I set mine to what it would do most ( motorway 60-65 ) everything else is a compromise… now my FI map is a different beast . I’ve also never had a spark plug lead come off ever
Thanks. My understanding is that tootling around town/ low speed its using the idle jets, and it drives nice already like this. The issue i'm targeting is it being overly rich at WOT, climbing long gradients on the m-way etc, bogging, using loads of fuel and not making the power it should.. which should just be main and air jets to change to get this right, and that those changes shouldnt' affect my low speed/town tootling where the main and air jets are not in play?
The point I was making earlier about low speed tootling is easy to verify with dells by removing the main stacks to drive only on idle jets, but also possible though much more effort with ICTs is that you'll find there are virtually no situations in a bus where you'll be driving only on idle jets. IME of doing this main stacks removed driving any more throttle than lightly touching the pedal - honestly just touching it - brings in the mains and kills the idles. In that respect you can go down to really small idles and it makes little difference to anything apart from making it hard to start. If you go really small it simply will not start in the winter from cold but you might see that low cruise high AFR thing. What am I trying to say? - Fit 55-57 idles and forget them and yes the main sizes will effect everything other than crawling along in a traffic jam. But that doesn't really matter as you won't have your foot in it most of the time so if it runs nice the AFR is immaterial. Which just leaves the WOT to contend with which as you know is where damage occurs at to weak mixture or it bogs with too rich. Get that right and live with the rest is my advice. OK there is one more thing - the overlap between idles and mains. This will make itself known in your tootling situation where you think you should be idle cruising but in fact you are on that cusp of the mains just starting to operate as the idles pack up - very little throttle. You'll have to see what happens there, but the usual 55-57 idles (quite large really) should work. You read that fitting larger main airs can help a lean overlap but this adjustment is very fine - it probably makes more difference getting your float right, fitting different emulsions etc. Too rich overlapI'd suggest fitting slightly smaller idles is the easiest way forward. All said and done this could drive you insane - It did me! In the end I went back to my guessed jetting before AFR when it ran great!!
great advice - thanks currently have 55 idles, its what eurocarb supply in new carbs and wayoutwestie also recommends. there's a few folks i've found who run bigger but no-one runs anything smaller as far as i can see - i'm not planning to change these.
I went down to 42 at one point chasing the elusive lean cruise. It ran as well as ever once warmed up but almost impossible to start when cold.
yes... .as Zed said i left my idles @55 and kept changing my main jets till the AFR read what i wanted at 60 -65 mph
I’ve been running DRLA’s for about ten years now. As they came out the box jetted to my engine spec by Euro Carb. Always been very happy with them but always wondered what was really going on so fitted an AFR a couple of years ago. Something else to look at and worry about now. It has changed my driving style. I find myself adjusting my right foot to get a better figure especially on long up hill driving.
As Zed says the more I looked in to it the more complex it seemed to get. Euro carb seem to have got it right for me and the AFR doesn’t show anything to worry about. At first I was hoping to have a nice steady figure like you get on a modern car diagnostic machine data list, but the old Dells are up and down like Bazza’s underpants.
...and what AFR did you want at 60-56mph? Mine went really well at 65-70 when I had no idea what the AFR was. It didn't want much throttle either. Turns out the AFR was about 13.5-14. Might have even been leaner. Would you say that's ok? Honest question.
Yep i can relate to this I find myself doing the same, economy driving to the A/F gauge. Although still only manage about 22mpg
Before doing any research at all I would have been happy with 14.7 at all times. It fluctuates a lot but generally hovers around 13. If it goes weak on an uphill climb I just give it more throttle and it riches up. Because of this I find myself driving harder and faster than I did before the AFR meter
I can’t remember where I did my research but 13.5 was my aim at those speeds .. it worked out at nearly bang on the 14.7 at idle and as rich as 9 /10:1 under WOT …
I did a tank driving like grandad and then a boy racer tank and there was almost no difference, perhaps 1 mpg. After that I just drove it.
