Tuning shop AFR set up :shock: and advice needed

[[email protected]]

with an exhaust leak your #s are worthless. All you know is the #s might be accurate or richer than shown, which doesn't help much.
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[Marv [UK]]

Rightio - UPDATE o Clock

Just a small one for now, I have some issues to work out but I will touch on them and see what you think.

Firstly, carbs... I'm now running 55 idles and 140 mains (almost where I started )...... It idles at 15.5 when cold but at 14 when hot (I'll get to this in a minute) then lean idle at 16.2 ish up to 12.9 at WOT.

cruising at 60 odd at 3500 ish revs I can cruise at 16.5... result.... 360 - 380 farenheit on average cruise but still peaks at over 425, CR got to go down I reckon

Straight off idle, I mean cracking the throttle a fraction, it runs at 17 - 18... changing the accelerator pump nut changes nothing... this confuses me.... It was worse before I 'upgraded' my BR8 distributor... once again, more on this later

Overrun gets me up to about 21

running downhill with my foot off the pedal but in gear got me off the scale!!!! past 45 and all the way back to 08 there is a hole in the exhaust by the feckn donut clamps AGAIN!! makes a great noise in tunnels though, really scared a chav in a saxo

Now, I know this is just a bit odd, but by accident I think I might have stumbled on why..... while it was idling with the air filters off, I felt a wind in the engine bay... Lo and behold, just by my breather tower.... Turns out that at idle, I have a veritable gale issuing from the crankcase

All of this lovely burnt air is recycled down the air filters and into the carbs.... this is seriously going to crap about with my AFR.

So.. leakdown test is the next port of call for this engine. I've got to buy the kit to do it yet, but it's necessary unfortunately...

OK so here's the rest.... If i need to replace the piston rings (the barrels and pistons were used from the get go so it's likely) I'm going to shoot for a different scope for the engine.

It's a C35 cam so I'm going to shoot for a static compression ratio under 8.5 but I'm going to down grade my carbs to a 30mm venturi or less. that way it's going to be more user friendly and produce less heat. I want to be able to crack the pedal a bit more than a gnats weight to accelerate, it's a bit on / off for the bus.

Since installing the BR8 it's been a different animal to drive. Idle is rock steady with no scatter, nice and steady at low revs but hit 2000 and it'll take off without care in the world. It makes first gear town driving a pig though. TO solve the really low down stumble I had, I butchered the vac can off the 034 and it fits.

Retimed to 7.5 BTDC (hoses off) and it runs up to 29 (with a bit of scatter) and with the can connected it gets up to 36, so I get 7 degrees of vac advance... I think there is a bit of geometry to be worked out but I reckon I could wring a couple of degrees more. Could be that the BR8 attachment point is a bit further out from the spindle than the the 034, but I didn't have my calipers with me when I was camping.

But hey, it works

[[email protected]]

lean the idle jet first, THEN try the smaller air. You are on the right path!
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[bigsid]

Have been working a similar issue on my 1745 bus engine

I'm not perfect yet but getting close with John advice.

DRLA 36's. Currently at 50 idles, 122 main 180 airs

Lean cruise is around 16.5: 1 ( 17:1 - 18:1 on overrun)
WOT is 12.5 leaning out to 14:1 at 5000 rpm

Just off lean cruise ( going up a hill on the motorway is aroun 15- 16:1

Lean cruise in a 72 bus can be sustained on the flat up to about 55 - 60mph . By 60mph mains are having an effect and start dropping the AFR.

Head temps are fine, but sustained 60 up a motorway hill will push 220 deg c if the hill is long enough ( so I just ease off) . Lean cruise head temps are about 160 - 170 C

MPG on a long run has climbed from around 27 up to low 30's (UK gallons) with the improved jetting.

Next move will be slight move down on the airs to delay the mains coming in a little, and I'm going to try a 47.5 idle.

[[email protected]]

I have spent a lot of time tuning a buddies 36DRLAs, and his tune used 50 idles at sea level, as virtually perfect. He MIGHT have been able to use slightly smaller with more work. We are at 4300', and used 45s, which is ~50 sea level.
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[Marv [UK]]

cool, i've got loads of air jets, only in 20 steps and short though

might have to leave it for a few days though, i'm on holiday. the other half might have a few words to say otherwise

so if i go to 200 airs and 148 mains (the biggest i have to hand) that should get me out of the death zone. wouldn't going the other way do the same thing?

[[email protected]]

the solution is simple. Your error is you do not realize the air jets dictate WHEN the mains come in. If you have a Death Zone condition, go up on the airs to make the mains come in sooner. You'll also have to go up on the mains to Keep A/F the same, since you went with bigger airs. Go up 15 on airs and 5 on mains and re-try.

John
Aircooled.Net Inc.
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[Marv [UK]]

back to 55 idles and 145 mains tomorrow. that gives wot of 12.2 to 3 and lean cruise near 16.5 when mixture set at 14 ish

all that said though, a main of 128 would have seen wot at 15.5 with 17 at 4000. an idle jet of 60 or over may have dealt with the enormous lean spot right off idle of near 19 and maybe work on the pumps.

it would take more work than i can do here, but i'm convinced carbs could be tuned for 16 - 17 in all areas. i reckon they would need modifying first though. who knows. i think i'm going to stick with conventional wisdom for now though. it ran like a dog . . . . .

[Marv [UK]]

unfortunately there is middle ground no matter how it's tuned.

with wot at 11.9 and progression at 16.5, 3200 - 4000 still waver between 15.2 and 14.2 give or take.

with the 32 vents, it just seems my driving style hits the hot zone every time

either i need to reduce compression so cooling can cope with the heat produced, change vents or carbs or the motor entirely. the cheap option is of course, drive differently

[[email protected]]

"lean cruise" depends on your speed. In a bus, you ain't gonna get a lean cruise over 60mph, it's too much work to move all that air in front of the bus. Mark Harney should pipe in with his bus, which is tuned about as good as it gets. At what speed does he leave the "lean cruise" zone (17:1) and move into the main circuit (12.8-13:1)?

If you "cruise" at 70mph you can forget running lean, you have to go for power. You can do it in a bug, but not a bus.

You want a carb tune that runs lean OR power, and avoids the Death Zone of 13.5-15.5:1, which is where it runs hottest. Ideally the carb will flip from 16+:1 to 12.8:1, and back again, no middle ground.

John
Aircooled.Net Inc.
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[Marv [UK]]

yeah, i have been trying to tune it backwards and it's just not having it.

seeing as i'm on holiday for a while, i'm going to put it back to the best i've come across so far, which is 55 idles and 145 mains. idle set to about 14, wot comes in at 12.2ish with progression cruise at 16.2 or thereabouts.

i've come to the conclusion that i either drive sensibly at 60 or tear into the engine and lower the compression ratio. i don't know my current numbers, i've lost the sheet and my builder can't remember either, but i've changed the goalposts since it was built.

c35 cam, going to aim for 7ish dynamic.

it needs to be done it seems. too much heat. a.

[krusher]

So are you trying to set up the mains for lean cruise.

Your whole tuning sounds backwards.

When your in a light load cruise, (little accelerator and little power needed) you can cruise on the idle circuit at 16 to 1.
Because of the lean mixture the charge is harder to lite this is where you get a high vacuum and can use the early 40ish degrees of advance of a sdva to set this charge burning early for a complete burn.

You now see a hill or want to over take , this is going to be a high load situation where your going to floor it go onto the mains and need a denser charge, so the mains need to be 13 to 1 ish.

if you have set the mains to but lean then when your pulling a hill i'm not surprised your doing over 400 on the head temps.
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[Marv [UK]]

im posting this from my phone somewhere in a field in cornwall so forgive the lack of correct grammar.

New distributor reduced head temps by 20 degrees tried several different jet combinations today but, like you, figured my lean cruise would always be on the main jet. 138's made things a whole lot worse but 132's gives me 16.2 at 4000. my next available jet is 125 which is way too small so i'm ordering some 130's and 128's monday! they'll be here thursday.

i now have a bottom end problem (no laughing at the back!)

55 idles at 13.4 but a huge lean spot as soon as i feather the throttle. no adjustment of the accelerator pump has made any difference. now turned in 9 turns. not sure what's going on but might stick the 58's back in.

running temp still a little high at 400 - 42 at above 3500 but hopefully that will come down with a smaller main. still manage over 460 at Wot going uphill, but that's at low 15's AFR so again. smaller mains should do the trick.

i need to post out the idle cir

[krusher]

I dont know if i have this right or not so correct me if I am wrong.

The way your trying to set up is lean idles to get around 16 to1 and then mains to get around 13.

If to cruise at your normal 3000-4000 you have to go into the main circuit to get enough power to push the brick through the air at that speed then there is never going to be a lean cruise , because your chosen cruise speed isnt possible on the idle circuit.

Whats head temp changed have to seen with the new distributor?


keith
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(06:31:07) RoachGhia: "i drink dick way too fast"

[Marv [UK]]

hmmm

142 mains has leaned out the 3000 - 4000 rev range holding at about 15.2 AFR

accelerator pumps are still not doing their thing, 2 more turns in i think

Looks like I might have to go back up to 55 idles though, it's just getting a bit too lean at times

Soooooo, next step, 55 idles, 138 mains....

[Marv [UK]]

well, It's astonishing the difference a distributor can make.

I decided not to faff about with the 009, it's a bosch one, but doesn't say made in germany so i decided to give that a miss. So it is on with the VJU 4 BR8

What a difference! idles bang on 7.5, solid as a rock and advances to 28, no more, no less. It's totally differenct ball game to an 034. The scatter is tiny in comparison. It's actually possible to tell the max advance without having to average it out

Anyway.... back to point.....

Idles at 13.9 when hot
still overlean when accelerating on minimal pedal so I need to screw my accelerator pump nuts in a couple more turns
still at stocih when at 3500 ish and holding, and when going up hills and stuff, so I'm going to go down to 142 on the mains and see how that fairs

Overrun is OK, a bit lean and freewheeling downhill in gear gets me backfiring at 18 to 19 AFR.... I guess thats a problem from having no vac advance

as an aside... I did notice that I can swap the original vac can from the BR8 to the vac can from the 034 with some minimal work... thats something for the future!

[Marv [UK]]

[[email protected]]

1/2 your problem is your timing is set completely wrong. It should be around 8 BTDC at idle, 28-30 full advance hose off. If #s deviate from this the distributor has something wrong with it.

John
Aircooled.Net Inc.
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[Marv [UK]]

Proper update this time, been for a 70 mile drive on the motorway...

52 idles are looking ok... It idles at 13.9 +/- 0.1
750 revs but a bit of an uneveness in there...

1000 revs and increasing on the pedal gets about 16 - 17 AFR

2000 revs gives me late 15's early 16's

2500 - 3000 revs is late 15's

holding constant 3500 to 4000 revs on flatish roads gets me slap bang in stoich again. WOT is 11.9

Damn, I wish I'd only changed the idles, not the mains too...

So, what next?

I'm going to go back down to 140 mains and see if I can hold at 4000 at 16 AFR or more as thats where I do most of my motorway cruising.

I'm going to leave the 52's in there for now

I'm kinda hearing a little pinging in there when I hold a hose above the velocity stack.... hopefully thats just the valve closing

timing on the 034 is set at 30 ish at max advance... comes in at 2*BTDC at idle which is far too early in my mind.... it's a mexi bosch I'm packing my fake 019 (Bosch cast iron VJU 4 BR8) so I was thinking of plumbing that in at 7.5 BTDC at idle and seeing where that gets me. OK, no vac can attachment and re springing yet, but that will come with time

OK, so.... How do you lean drop tune for idle mixture with 4 vac gauges???? It's too damn noisy in my engine compartment with that damn EMPI phatboy

[Marv [UK]]

OK, so another update

52 idles are in.... can't get lean drop idle right, I'm having a bad day... 4 1/2 turns out on 1 through 3, but 6 out on #4 and seemingly no effect... not sure how many threads are left!

I'm going to have to learn to do lean drop idle on my bank of 4 vac gauges Anyone done this before? Know of a link or something to what I should be seeing on the gauges?

Anyway, idle at about 13.8 to 14.5, some stumbling and occasional 15.. It's not set right at all, I just can't hear it on this small a jet and lean running

low acceleration, about 16 give or take,

adjusted the accels to 1 turn in which solved the lean accel prob

still runs at 14.X to 15.2 while i'm maintaining speed up a hill

mains now at 148, down to about 11.8 when I'm on the gas

running at speed with foot off the gas, it rises to around 19 and pops like mad. I'm adling at 750 though, so maybe I ought to crank up the idle screw and just uncover the vacuum port a bit more, maybe I've half mooned it.

Still gets over 400*F on a couple of miles uphill

typical though, I hunt around for an hour looking for my 50's... no idea where they've got to. Damn, In go the 52's.

Spend a couple of hours fannying about, go to clear up some stuff ready for going camping this weekend, and the 50's fall on my foot!!! It's just one of those days