Wideband Results

[Alstrup]

[quote="topnotch"

I'm trying to get the engine in my bus running just right.

Its a 2078
stock heads (ported)
scat c25 cam
8.5 CR
twin dell 36s with 32 vents
123 ignition dizzy (vac and centrifugall - but can disable the vac) - max timing is 28 centrifugual and 10 added for vac.

[/quote]

You´ll never get that right. but you can make it driveable.
The engine will need "large" idles. Probably around 57 to make up for the displacement at lower rpm. Mains, I have no idea, but i would expect something like 135, E2´s and 180 main air.

You will likely see that the can does not release the vacum at WOT like normal, so you may have to go all the way down to approx 80 KPa to set 0 advance and then have a steep incline to max vac advance.
Also, 28 mechanicak is 90% not enough. I suspect it is built with a lot of deck height or even Semi hemi chambers to get down in static CR. Both scenario´s need more timing.
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[topnotch]

Yes- you’re not far off - I got it running well with 59/180/137 and that was pretty much bang on with mechanical only advance - 13afr all the time except on deceleration when it goes lean to 16

I built the engine myself - deck height is around 1.25mm and comp ratio is 8.5:1

It was built for torque not speed.

Mostly it’s pulling 60kpa on part throttle unless give it 100% in which case I get to 100kpa. I hardly ever drive fully throttle so I think I’ll have to stick with using the mech advance only and a richer idle circuit because of the way the vacuum is running unfortunately.

It’s ok though - it’s running pretty cool and AFR is good fit a a mech advance only timing curve

[tzepesh]

Small update on my issue: changed the fuel filter and it was not too clogged, so it was not fuel starvation. Next, I'll try the 50 jets, maybe it just does not like slightly lean... It was not running well today, strugggling to rev on idle circuit.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[Alstrup]

[topnotch]

Well - it’s hits 100kpa when I’m at idle with no throttle and 100kpa with the throttle wide open no matter the rpm

But I’m still getting 60-65kpa at 1/2 - 3/4 throttle

[Alstrup]

Thats because your butterfly´s are so small in relation to the displacement. What do you have on cruise?
50, 65, 70 and 75 mph?
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[topnotch]

I’ll have to get back to you on that as I’ve hurt my back quite badly and can’t get around at the mo.

I seem to remember at cruise (regardless of speed), I was seeing around 65kpa

[Alstrup]

You need to find out where the "picture" tips. Then add the map in a default setting. that will change the vacum again, so you will have to readjust to get a proper setting. Sometimes the drop of must be quite rapid. A friend of mine has a 180 hp 2275 fed by IDA´s in a split bus. He had the same problem with the vacum not letting go, so after a little testing back and forth they found the sweet spot. But the difference between full vacum advance and WOT is only 12 Kpa.
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[topnotch]

Yes agreed - it’s something that will take a bit of time and testing and watching the vac dashboard.

I think for now , I’ll leave as is and then when I’ve got some free time I can have another play with it.

Thanks for the advice though - appreciate it 👍

[tzepesh]

Another day, another test. In between Topnotch's posts .
I went for a ride with 48 idle jets, AFR was still around 15:1 and the engine struggled to rev up to 3000 rpm. So I swapped to 50 idle jets, and it is running much better. It stays in the range of 13.5-14.0, but I also saw periods of time with 14.5-15.0, I guess I was slightly letting off the pedal, as the revs were going down slowly (between 2000 and 3000 rpm). I still get some hesitation from time to time, it may be the advance not going up so fast (remember I simulated a 009, centrifugal only, not MAP/TPS). But overall it feels much happier.
So, 50 idle jets, 13.5-14.0 up to ~3000 rpm, 122 main jets, 12.5-13.2 all the way up. I guess the engine does not like that slightly lean AFR of 15:1, but it prefers the slightly rich one.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[oprn]

[tattooed_pariah]

I know I haven't posted in this thread in years, and to be honest, I didn't re-read everythig catch up.. I just wanted to remind everyone that your O2 sensor is a consummable item..

I put a wideband gauge in my car like 5 years ago, and didn't drive it much, and for the last few years was ignoring it because no matter what jet changes I made, it ALWAYS read lean/air.... I finally replaced my O2 sensor a month or so ago and learned that I've pretty much dialed in all my jets but my idles..

At idle, I still get lean/air, so I know I need to bump my idles up a bit, but at like 1/3 throttle or higher, I am between 11 and 13 AFR...

If your readings aren't making sense, think about how old your sensor is..
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-pariah (just a novice from "that other VW site")
'72 Volksrod "Effigy"

"Never worry about stepping on people's toes. People who get their toes stepped on are either sitting down, or standing still on the job."
-Admiral Arleigh Burke, USN(ret.)

[tzepesh]

@OPRN, you are right, it works well with that particular advance curve. But for the moment it's enough, I just want to drive it. When I have more time, I will get back to it, maybe add MAP back (I see many people having just a very small vacuum window, I thought I had an issue with the setup).
Also, I misinterpreted the tuning procedure, and I went for lean progression circuit. I had on and off TPS and MAP for so many times, that in the end I had the worst combination: lean progression circuit without engine load compensation. Reading again the wideband tuning procedure from John @aircooled.net, I now understand I should have aimed to 13.0 until the mains kick in, and that's what I found that worked very well just by swapping jets, seeing AFR, feeling the car. OK, I'm a bit leaner, but I do not have any jets in between 48, 50 and 52... Remember, 48 showed 15:1, 52 showed 9:1, 50 showed 13.5:1. That should do it.
It is not clear for me how the light cruise is set (if I would have MAP or TPS...). I guess jets remain the same as done in first phase, but just play with advance under load.

@tatooed_pariah, the readings did make sense, but I did not understand why it would not run with the same setup after rebuild. But it makes sense now, those worn parts made it run somehow, even if a bit lean.

Thank you all who supported with advice!

Anyway, I should really finish my 2056 type 4 fuel injected... I just need to put on the cooling. Moreover, the FI setup could be just installed also on the 1.6 type 1, I'm just lazy... And I fear that those 36mm throttle pates would not work on such a small stock engine.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[daos]

tuning a type 3 stroker with following spec:

2007cc stroker
standard heads with mild porting
dual dellorto 40s, balanced and linkages in order
web 163 cam
1,25 rockers, single HD springs
9,5:1 comp
4-2-1 exhaust
full flow + hoover mods
+ black box

gone through idle jet tuning, then mains + air. currently on the following:
54 idles
155 mains
185 airs
acc pump set to minimum.

AFR:
idle around 13ish
light cruise (80kmh/50mph) high 12s to mid 13s
light cruise (105kmh/65mph) mid 13s to low 14s
WOT around 13

runs fairly well but noticed a couple of issues, namely:

#4 is running 25% hotter (reading 130°C/266F near the exhaust port). found a vacc leak at the intake manifold, testing with with start spray produces a choking/lowering of idle speed. this i will fix to stop the lean issue.

#1 is running cold (60°C/140F), slightly more than half the temp of cyls 2 & 3 (110°C/230F). setting LBI is hard, i can turn mixture to zero on #1 with basically no change. did have clogged idles a couple of times which gave rough idle but even after cleaning there was still no change when adjusting mixture. need to address this issue before i go any further with tuning, not sure what i'm looking for. maybe something up with the spark plug?

also the engine wants to run on 3 cyls under light acceleration, pushing harder it runs fine. suspect cyl #1 is the culprit.

[Alstrup]

Unburned gas corrupts the reading. Get that idle fixed.
Then increase float height 1 mm.
Reduce exh valve lift with 1,1´s
Rejet. Your mains are crazy large compared to what I normally see, - assuming you use 34 venturies. (?) I would expect something like maybe 145, 148 at the most.
What is cruise timing at 80 kmh? 100 kmh?
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[daos]

yes, need to get idle sorted. really not sure what's up with #1 though.

re. the lower exhaust rocker ratio, what's the thinking behind that? higher exhaust gas velocity later in the piston cycle/better scavenging?

also, i'm running 32 venturis since i only have 32mm exhaust valves, would a switch to 34 be worth considering?

need to drive more w laptop plugged in and record timings at cruise, but want to fix the #1/#4 issues before driving more.

[Alstrup]

Your exh. look to be efficient in that rpm range, so you need to reduce scavenging.
Yes, 34´s should enable you to stay on the idles longer.
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[daos]

cool, thx. need to look around for parts. AA Performance should have rockers i think, i'm using their 1.25s.

not sure how to raise dell floats, the tabs are not bendable the same way webers are - at least the ones i have (alfa romeo). will have another look, only takes about an hour to get them off lol.

[mikedjames]

One thing I have seen a few times is that if you drive around at 11:1 or richer, eventually the AFR sensor starts to indicate leaner and leaner mixture, as it gets covered in soot. On my bus that happens if the choke heater wire has falllen off.


If you go too long like that, it never comes back. But if it happens for a day, you can usually burn it off by going back to leaner jetting, then the gauge will come back to working properly after a while.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Alstrup]