6 cyl draw threw turbo

[hiy_po]

Where I am at


Idle tubes 0.067" top 0.031" bottom
Idle Down-Channel Restriction 0.047"
Idle Discharge tube 0.118"
Upper Idle Air-Bleed    0.040"  (Air horn)
Upper Idle Air-Bleed body    blocked
Lower Idle Air-Bleed    0.065"
Idle Air By Pass throtle plate outlet 0.079"
Main Air-Bleed Airhorn 0.079"
Main Air-Bleed body 0.040"
Primary Jet 0.073
Primary Rod 0.048
Custom: / (2-5) / 0.900' spring
ATP 2 turns up.
Secondary Metering Rods   0.044' tip inch “DA” code
Secondary hanger bracket B
Needle-Seat 0.130"
Float setting 0.250.

[hiy_po]

Too ambitious ?? How small can you go?
Have the Idle tubes down to 0.023 jet. They look pretty small.

[Cliff Ruggles]

If you are using a .065" LIAB and .040" upper in the airhorn it will not need a lot of idle tube to put plenty of fuel to the mixture screws and transfer slots.

Marine carburetors used a similar set-up as they were not emission calibrated.  They also use very small idle tubes and generous idle fuel at the mixture screws.

It's remarkable how responsive Marine carburetors are if you test one.

If you look all the way back to early production Q-jets, you'll also notice that early units thru 1967 will also use less idle air and smaller idle tubes.......Cliff

[hiy_po]

OK I'll get em out today 6/6-32 & 4/8-32.

Thank you. They look alot better than my home made ones.

[hiy_po]

My latest carb setup

FIRST Carb (Stage Two Ver 6-1)
________________________

Idle tubes 0.063" top 0.024" bottom
Idle Down-Channel Restriction 0.041"
Lower Idle Air-Bleed    0.054" #54
Idle Discharge tube 0.118"
Upper Idle Air-Bleed    0.040"  (Air horn)
Upper Idle Air-Bleed body    blocked
Idle Air By Pass throttle plate outlet 0.079"
Main Air-Bleed Airhorn 0.064" #52
Main Air-Bleed body 0.040"
Primary Jet 0.072
Primary Rod 0.048
Custom: / (2-5) / 0.900' spring
ATP 2 turns up.
Secondary Metering Rods   0.044' tip inch

[hiy_po]

I did a trip yesterday. 200 km round trip.
Was happy with approx 17litres/100km highway travel. I use 98ron pump gas.
I do seem to have a lean cruise. At very light throtle, low load, level cruise the AFR meter goes off the scale lean. Still seems to cruise ok if maybe a little hesitant.
Adjustment to APT does nothing as Vac is about Zero or even possibly just positive.
Have I created a gap between main and idle circuit???
Am thinking slightly enlarging IDCR will allow more idle system fuel to be added longer maybe bring it back on to the scale at least, or be better to just go up one jet size. it does make sense to me to try close the gap with the mains system rather than Idle system.
It is worth saying that engine didnt have any bad effects from it running lean. just really good fuel economy.
Will also try going to blocked Idle by pass air as that controlled air leak may be contributing to the lean.

Current recipe

FIRST Carb (Stage Two Ver 6-3)
________________________

Idle tubes                               #52 0.063" 1.61mm top
                                             #73 0.024" 0.61mm bottom
Idle Down-Channel Restriction #59 0.041" 1.1mm
Lower Idle Air-Bleed               #54 0.054" 1.4mm
Idle Discharge tube                #32 0.118" 3.0mm
Upper Idle Air-Bleed               #60 0.040" 1.0mm (Air horn)
Upper Idle Air-Bleed body    blocked
Idle Air By Pass throtl plate    #68 0.310  0.79mm
Main Air-Bleed Airhorn           #70 0.0270 0.68mm
Main Air-Bleed body              #60 0.040" 1.0mm
Primary Jet 0.070
Primary Rod 0.048
Custom: / (1-4) / 0.900' spring soft thin wire
ATP 4 turns up.
Secondary Metering Rods   0.044' tip  “DA” code
Secondary hanger bracket M
Needle-Seat 0.130"
Float setting 0.250.
Idle Screw 2 turns out
Throtle stop 2.5 maybe 3 turns

Am I using the smallest Cubic Inch engine on the site??
Any other 6 cyls ??
Still havent bought another pump but may do it at end of week.

[Cliff Ruggles]

Tune for results not what a gauge is showing you.  If you are lean to a point where the engine doesn't like it, at light throttle for example, the engine will surge, lack power, "flat" with a little throttle movement, or even backfire up thru the carb if it gets way too lean.  So basically in certain scenarios you may see really lean on a gauge but the engine load is light enough it doesn't care. 

Every engine has slightly different requirements across the load/speed range but most will like similar numbers as a general rule.   Don't forget about ignition timing, especially the amount added by the vacuum advance.  It is a load sensing device and designed to add timing when engine load is light and engine vacuum is high.  This allows us to burn a much leaner mixture all else being equal, so don't forget to use it as part of your tuning......Cliff

[Chris_Oz]

Am I using the smallest Cubic Inch engine on the site??
Any other 6 cyls ??
Still havent bought another pump but may do it at end of week.

Is that in a VK? Looks like a black motor.

Sound like you almost have it sorted.
I am enjoying reading the progress.

[hiy_po]

Yes VK with a black motor 3.3

Quick question I am sorting the secondaries and have backed off the tension that holds the secondary air flaps closed until I am getting a slight cough back and splutter as I open the secondary throtle plates. Now I know I can just tighten them up again to get rid of it but I do want them open asap. Can I enlarge the secondary enrichment to compensate for the earlier openning of the air flap ??the secondary enrichment outlet seems to be about #70 0.028thou at the inner restriction.
Thanks.

[Cliff Ruggles]

I prefer to use a timed choke pull-off to keep the flaps from "whipping" open too quickly vs spring tension.  What I don't know is how intake pressure from using a turbo effects the drop in vacuum seen on N/A engines that allow the pull-off to dampen then fully open progressively based on the size of the restriction being used in it.

I wouldn't open up the POE system any if at all, at least not until you make sure the pull-off can't be used to delay the opening just long enough it prevents a lean condition.  POE fuel comes in pretty quickly, and the fuel in the main passages leading to the secondary nozzles adds some fuel as well going quickly to full throttle.

Since it isn't using an accl pump there is a very slight delay for POE so using the pull-off to hold things back for just an instant really helps.  There is of course some accl pump shot left over from the primary side to help out as well, so shorter pumps over there increase duration helping out even more......

[hiy_po]

Had to strip it down for some turbo repairs. Made a start up video once had it all back to gether. Idles average of 600 to 650 rpm does drop as low as 500 rpm. enjoy.

https://youtu.be/F4uTnM00Yas

I was thinking if I was to use the Pull off would use the same boost ref line the power piston is using. Havent put the pull off back on yet  but may do if I get the hesitation or stumble back as secondary air flaps open. Is hardly noticable atm.