B20 DHLA 40C problems solved almost.

Dellorto, Weber, trycka eller suga?
Miksa89
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B20 DHLA 40C problems solved almost.

Inlägg av Miksa89 »

Set up is:
B20 6-bolt original
44-40 valves,ported head and chambers modified,height 83mm
Scat single springs.
11:1 comp
Modified dizzy with 15 deg mec-advance, 18 idle - 33 max at 4000rpm
R-cam
Stock exhaust manifold+2.5" exhaust
Long Misab manifold + DHLA 40C carbs with trumpets.

32 choke
135 mains/185 air
5. e-tube
55 idle with 1. holders
38 pump jets.

Fuel pressure 0.25bar + 120l/h elect.pump.

Fuel levels 31mm measured from maintube hole,at lower section from float bowl top.
Level is visible at idlejet holder hole bottom conical part.

Afr at idle is 13.

When accelerating at part throttle afr goes like this:

Idle 13
2000rpm 12
2500rpm 10-10.5
3000rpm 12.5
WOT afr stays 12.5-13 3000-6500rpm

Problem is that rich peak at ~2500rpm and goes like "prapprapprap " and when revs gets 3000rpm starts acting normal.

Tried with 13. e-tubes but was even worse.
Also tried with 50 idle jets and 2. holders but no change,other than mixture screws 5 turns open to idle acceptably.
Now with 55 idles screws still over 4 turns open to nice idle.

Other problem is when decelerating at 4.th gear and slightly pressing gas it spits at carbs. if pressing more gaspedal theres no problem,only when just hitting barely after deceleration.
Afr goes 14-14.5 when decelerating.

Thank if someone can help me and sorry for bad english.
Senast redigerad av Miksa89 den mån mar 07, 2022 4:35 pm, redigerad totalt 1 gånger.
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fredde_vit_pv
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Re: B20 DHLA 40C problems.

Inlägg av fredde_vit_pv »

First, how is air-synchronation ? even between flyers in same carb.
it can be to small chokes so the main jetting overlaps low trottle system !?

/F
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

fredde_vit_pv skrev: tor dec 02, 2021 7:41 am First, how is air-synchronation ? even between flyers in same carb.
it can be to small chokes so the main jetting overlaps low trottle system !?

/F
Sync is in the sweet spot, checked with "snail-type" synchometer. All are equal.

Spitting stopped when changed idle jets 55 -> 60.

Tomorrow need to try 55 again with richer holders just for fun.

Problem perhaps is just that what u say,mains come in too early.
Ordered 6. e-tubes because they should come in the play later, 5. and 13. come in earlier so that may be the case.

Other fix may be bigger chokes to weak vacuum at that point?

E: Played with fuel levels too and reduced fuel pressure 0.25 to 0.2bar because 250 needles to close for sure.
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fredde_vit_pv
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Re: B20 DHLA 40C problems.

Inlägg av fredde_vit_pv »

a little more advaced way that can work is to block some progressionhole/holes
if you block some hole far down from trottleblade the the low end system fades out earlier.

in that case you might must go to bigger low-jets (65 maybe!?) but that also makes the idel adjustment more
responsive and easier to adjust (like Webers :) )

note that dellorto carbs have have alot of different models so holepattern can be different

marked progress_hole.jpg
marked progress_hole.jpg (67.39 KiB) Visad 2250 gånger
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

fredde_vit_pv skrev: fre dec 03, 2021 10:27 am a little more advaced way that can work is to block some progressionhole/holes
if you block some hole far down from trottleblade the the low end system fades out earlier.

in that case you might must go to bigger low-jets (65 maybe!?) but that also makes the idel adjustment more
responsive and easier to adjust (like Webers :) )

note that dellorto carbs have have alot of different models so holepattern can be different


marked progress_hole.jpg
Mine have five prog. holes like in the pic too.
Mayde i wait to get new 6. etubes,they will arrive next week.

I think blocking holes can be way to go if nothing else helps.
What would be the right way to block?
Just solderin with solderin iron and tin? :D

And thanks for your replies 8)
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fredde_vit_pv
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Re: B20 DHLA 40C problems.

Inlägg av fredde_vit_pv »

i just coned a weldingrod and plugged it,like a very small whinecork
so you can take them out if not working
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

fredde_vit_pv skrev: fre dec 03, 2021 12:23 pm i just coned a weldingrod and plugged it,like a very small whinecork
so you can take them out if not working
Thats good idea,thanks 😊
Need to try it in the weekeng for curiosity.
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

Tested fo fun without mainstacks.

Still AFR gets 11 at part throttle 2500rpm when gently increasing revs without load.

Does the choke size matter way or the another when on progression stage? Does bigger choke make progression leaner or does choke size have no effect on progression afr?

Now i have 60 idles with 1. holders and idle screws 4 turns open and Afr is 13 at idle.
Earlier tried 55 idles with same holder but mixture screws need to be over 5 turns open and still so lean at idle that it was spitting 4.th gear at light throttle after deceleration.

Maybe in now going to try with 55 idles with .2 holders if that makes any difference.

If that doesnt help need to try that prog hole plugging.
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fredde_vit_pv
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Re: B20 DHLA 40C problems.

Inlägg av fredde_vit_pv »

you can say that progression-system is trottle-controlled and the main/choke is flow-activated
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

fredde_vit_pv skrev: mån dec 06, 2021 9:25 pm you can say that progression-system is trottle-controlled and the main/choke is flow-activated
Okey.
Same problem still occuring.

Tried with 6. emulsion tubes but same thing.

Feels like problem gets in the play after driving few seconds at part throttle ~2500rpm.

When after decelerating and turning at 2. gear and try accelerate part throttle car goes "praprapra" banging at the exhaust like launch control 2500rpm.

Yesterday looked at progression holes and when idling first hole is completely on the engine side of the butterfly. And second one is on the line with butterfly??

Need to try fix that before other things.

E: Now only first hole is half way on the wrong side.

Better but far from good.

Ordered 36 chokes and will try those.

Now with 55 idle jets + 2. holder its driveable,need to fiddle with acc pedal to get over the rich phase.

Maybe timing advance is part of the problem too,because even when afr stays over 11 at 2500rpm when playing with pedal still feels like strugling in that point and sound is like uneven prompromprom not wroom like upper revs.And you can feel the struggle when driving yourself.

Hard to describe with my bad english.

Going nice with 4.th gear like 1300-2000rpm but when reaching near 2500rpm sound and afr gets funky.
Works nice when WOT at least. :doh:

Advance is now 20 @ idle
25 a 2500rpm
30 @ 3000rpm
and max 35@ near 4000rpm.

Numbers are with litlle errormargin because measured with timing light but not many degs faults i think.

Dizzy is -077 with hot spark pointless and decreased sentrifugal advance and no vacuum advance.
All done by me,maybe thats one reason for poor working. :roll:
jonny
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Re: B20 DHLA 40C problems.

Inlägg av jonny »

You probably have to high fuelpressure , 0,18 bar maximum for Dellorto , set fuelpressure at 0,15 bar and try .


Then with right fuelpressure I think you will need 65 idle jets .
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

jonny skrev: fre dec 17, 2021 8:45 am You probably have to high fuelpressure , 0,18 bar maximum for Dellorto , set fuelpressure at 0,15 bar and try .


Then with right fuelpressure I think you will need 65 idle jets .

Lowered pressure to 0.18bar week ago,no big difference.

Lowered it today to 0.15bar but was too lean,so screwed it back to 0.18bar. Maybe its no litlle higher than before because funky spot is worse than before.
Tomorrow need to set it between .15 and .18bar to find the sweet spot.

And need to play with advance tomorrow too.

Now with 36 chokes,135 mains and 150 airs works way better than before.

Afr stays between 11-14 at normal driving at part throttle,except the funky spot between 2000-2500rpm sometimes drops to 10.
Wot afr is 12-12.5 and over 5000rpm goes near 13,i think that is acceptable range?
Thunderbo1t
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Re: B20 DHLA 40C problems.

Inlägg av Thunderbo1t »

I would think, when you say "too lean at 0,15 bar" you would need bigger jets? I would not adjust AFR with fuel pressure on a carb?
Miksa89
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Re: B20 DHLA 40C problems.

Inlägg av Miksa89 »

Thunderbo1t skrev: sön dec 19, 2021 5:14 pm I would think, when you say "too lean at 0,15 bar" you would need bigger jets? I would not adjust AFR with fuel pressure on a carb?

Why change jets for 0.15bar fuelpressure if worked acceptable with 0.18bar? :?:
Is there reason why should use 0.15 instead 0.18bar if theres no difference in the problem area?

Im not adjusting afr with fuel pressure,i mean if lowering the fp makes difference in the funky spot more or less. Now fuelpressure is little bit higher than it was in "best working order" so im going to lower it where it was or a little bit lower IF it helps with funky spot but not so low that all jettings needs to be done again.

Need to try again tomorrow with new plugs if there is real difference in afr with fuel pressure changes because todays test was just quick test :D
Thunderbo1t
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Re: B20 DHLA 40C problems.

Inlägg av Thunderbo1t »

Fuel pressure should never affect AFR when using a carburetor, if it does, for example, the fuel pressure is wrong, or fuel delivery is restricted, or needle valves leaking for some reason, worn, vibrations etc.
Float level affects AFR a little.
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