40 IDF jetting advice needed

[Glauco]

Ok,
I know there are some weber goeroes on the forum so I hope you can help me out:
I used the settings provided in the bob tomlinson's original weber tech manual -super tune-up guide for vw and porsche engines-. to set up my dual 40 idf's.
but I feel there is a lot of room for improvement.
this is the engines setup:

1641, mahle B&P
SCAT CW-crank
SCAT connecting rods
engle FK65 with 1.4 rockers
stock heads with stainless valves and 3 angle valve job
1 1/2 merged header with S&S dual quiet pack
dual italian 40 IDF's
Mallory dual point ignition
compression is 7.3 to 1

this is what I have for jetting:

28mm venturi's
140 mains
200 main A/C
F11 emulsion tubes
55 idle
50 Pilot jet

under 2K it seems like nothing is happening, higher in the revs it gets better, but still not like it should be..
Is there a guideline for initial setting?

thank you,

glauco

[alex d]

im not an expert but 140 mains is for sure way too big for 28mm chokes!

[Glauco]

im not an expert but 140 mains is for sure way too big for 28mm chokes!

that's the problem, me neather. I just copied what the book told me and hope for the best.
didn't hope hard enough?

here is what the book says, was hoping that somebody could push me a little closer to the right set-up..

[ Attachment: You are not allowed to view attachments ]

[Andy]

I take it this engine is in your Ghia.

First off I would fit 30mm Venturis , these will give more power, and do the jetting around these.

A lambda sensor and wideband gauge kit will be a good investment, then you can see what is happening when you do jet changes.

Make sure you are not getting extra fuel from leaks or the choke circuit this can make it pig rich.

Is your distributor a mechanical or vacuum advance, with a vac advance you can go leaner on the idle jet, it might be worth trying 52 idles

Main jets I would agree a 140 is rich, my bug has 44IDF's with 36mm Venturis and has a 135 main jet, tuned with a wideband .  My bus has a near stock 1600, 36 IDF's 28 Venturis and has a 125 main jet and going by the black tailpipe is still a bit rich.

Try a 130 main but your best bet is tuning with a wideband.

I have forgotten what air corrector jets I am running

[Glauco]

I take it this engine is in your Ghia.

First off I would fit 30mm Venturis , these will give more power, and do the jetting around these.

A lambda sensor and wideband gauge kit will be a good investment, then you can see what is happening when you do jet changes.

Make sure you are not getting extra fuel from leaks or the choke circuit this can make it pig rich.

Is your distributor a mechanical or vacuum advance, with a vac advance you can go leaner on the idle jet, it might be worth trying 52 idles

Main jets I would agree a 140 is rich, my bug has 44IDF's with 36mm Venturis and has a 135 main jet, tuned with a wideband .  My bus has a near stock 1600, 36 IDF's 28 Venturis and has a 125 main jet and going by the black tailpipe is still a bit rich.

Try a 130 main but your best bet is tuning with a wideband.

I have forgotten what air corrector jets I am running

It is indeed the engine in my ghia. I will get 30mm venturis and 130 mains and start from there. I've tried with 50 files, but almost nothing changed.
Distributor is mechanical advance, choke circuit is blocked. Don't think there are any fuel leaks, carbs are rebuilt.

Maybe I should be looking into getting a lambda and wideband gauge..
Thank you for the info!

[alex d]

oh, yeah, the jetting recommendations in that book are a little questionable to say the least

[Glauco]

oh, yeah, the jetting recommendations in that book are a little questionable to say the least

Apparently. I was sure that the settings wouldn't be spot on, but nog I feel there is a lot of lost power in the engine.
I tried the explanation from aircooled.net and that gives me the following initial settings:
idle = 1.25xthrottle size, so this gives me 50 Idles
main = 4.1-4.3x venturi size. I'm going for 30mm venturis now so this gives me 126, I'll try 130 mains first
for emulsion tubes I'm going to start with the F11, I still have F7's as well, because I have the feeling that it's to ritch in low RPM's now.
I hope to get some more feedback from the engine with the new venturis and smaller mains..

if anybody else has a better idea for my initial settings that would be great, I'm trying to learn as I go here...

[Andy]

A wideband set up is the best thing for tuning carbs now they are available inexpensively. I suspect the recommendations in the book are a bit rich to stop people running lean , causing damage and complaining to the author.

Have you backed off the nut of the accelerator pump, if it is adjusted too tight it may pump more fuel than is needed, giving a rich condition.

[Glauco]

A wideband set up is the best thing for tuning carbs now they are available inexpensively. I suspect the recommendations in the book are a bit rich to stop people running lean , causing damage and complaining to the author.

Have you backed off the nut of the accelerator pump, if it is adjusted too tight it may pump more fuel than is needed, giving a rich condition.

didn't touch the accelerator pump after rebuilding the carbs, might be worth taking a look at, thank you for the tought!

[Jim Ratto]

Hello, I would change your venturi to 32mm to wake up your engine. Though the duration of the FK65 is modest, the lift isn't and to realize more potential, larger venturies are suggested. The 28mm venturi truly will limit any mid and upper end breathing, and will contribute to richness, as it is probably over-accelerating air speed. The 140 main is much to rich for 28mm unless you were running alcohol.
I would try the 32 venturi, with 55 idle, 130 main, your F11 tubes, and 180 air correctors. Before doing any of this, make sure your float level is 100% per Weber specs or the emulsion tubes won't "know what to do."

Let us know how it runs.

Jim

[Glauco]

Hello, I would change your venturi to 32mm to wake up your engine. Though the duration of the FK65 is modest, the lift isn't and to realize more potential, larger venturies are suggested. The 28mm venturi truly will limit any mid and upper end breathing, and will contribute to richness, as it is probably over-accelerating air speed. The 140 main is much to rich for 28mm unless you were running alcohol.
I would try the 32 venturi, with 55 idle, 130 main, your F11 tubes, and 180 air correctors. Before doing any of this, make sure your float level is 100% per Weber specs or the emulsion tubes won't "know what to do."

Let us know how it runs.

Jim

I was waiting/hoping you would respond.  
Thanks for the info!
I checked and rechecked the float level and I'm sure they are spot on. I'll order new venturis and jets tonight and let you know how it turns out.

[Jim Ratto]

Hello, I would change your venturi to 32mm to wake up your engine. Though the duration of the FK65 is modest, the lift isn't and to realize more potential, larger venturies are suggested. The 28mm venturi truly will limit any mid and upper end breathing, and will contribute to richness, as it is probably over-accelerating air speed. The 140 main is much to rich for 28mm unless you were running alcohol.
I would try the 32 venturi, with 55 idle, 130 main, your F11 tubes, and 180 air correctors. Before doing any of this, make sure your float level is 100% per Weber specs or the emulsion tubes won't "know what to do."

Let us know how it runs.

Jim

The 32 will work well with the size exhaust you are using. Should sing like an opera.


I was waiting/hoping you would respond.  
Thanks for the info!
I checked and rechecked the float level and I'm sure they are spot on. I'll order new venturis and jets tonight and let you know how it turns out.

[Bruce]

IMO a tiny little 1641 with stock heads is massively overcarbed with a pair of 40 IDFs that have 28mm vents. Bigger vents don't make up for restrictive ports.
My suggestion is to wait on the bigger vents and try what you have now.
115 main jet
F11 tubes
200 Air
50 idle
50 pump

[Bruce]

here is what the book says, was hoping that somebody could push me a little closer to the right set-up..
[ Attachment: You are not allowed to view attachments ]

I'd say throw away that chart, it's worthless.  155 mains with a 28mm venturi, what a joke.

[Glauco]

here is what the book says, was hoping that somebody could push me a little closer to the right set-up..
[ Attachment: You are not allowed to view attachments ]

I'd say throw away that chart, it's worthless.  155 mains with a 28mm venturi, what a joke.

I'm starting to think I would be better of if I would just throw away that poor excuse for a book.

IMO a tiny little 1641 with stock heads is massively overcarbed with a pair of 40 IDFs that have 28mm vents. Bigger vents don't make up for restrictive ports.
My suggestion is to wait on the bigger vents and try what you have now.
115 main jet
F11 tubes
200 Air
50 idle
50 pump

I'm going to try the setup Jim suggested first. the heads are mildly ported, so they should flow a little bit better than pure stock.
I know dem has got a 1679 with DCOE's with 32 venturi's in his karmann and that car goes pretty fast for a little engine..

[Jim Ratto]

The 32 will work. I've run 40IDF on 87 x 69 with 32 vents, though with slightly hotter cam timing, but less lift.
"mathematically" your engine would be ideally set up as such:
87 x 69
8.9:1 CR
35.5mm intake valve with 32.3mm ID port in head
Cam timing as such:
intake open 15 BTDC
Intake close 43 ABDC
exh open 51 BBDC
exh closes 7 ATDC
Which means a cam ground @ 108LC will be 4 degrees advanced 238' @ 0.050", 276' @ 0.020", around 0.490" lift
32mm venturi for street use (race use we would up CR and open port up to 32.8mm, and use more overlap/longer duration cam, with 34mm venturi or larger)

Personally, I'd opt for a little hotter cam for the street too, many years ago I ran this same size engine in my daily driver (only car) with 256' @ 0.050" x 0.470" lift but with 39mm valve. Same CR and 36DRLA Dellortos with 30mm throats. I was too young to know any better.

Have fun
Jim

[Glauco]

The 32 will work. I've run 40IDF on 87 x 69 with 32 vents, though with slightly hotter cam timing, but less lift.
"mathematically" your engine would be ideally set up as such:
87 x 69
8.9:1 CR
35.5mm intake valve with 32.3mm ID port in head
Cam timing as such:
intake open 15 BTDC
Intake close 43 ABDC
exh open 51 BBDC
exh closes 7 ATDC
Which means a cam ground @ 108LC will be 4 degrees advanced 238' @ 0.050", 276' @ 0.020", around 0.490" lift
32mm venturi for street use (race use we would up CR and open port up to 32.8mm, and use more overlap/longer duration cam, with 34mm venturi or larger)

Personally, I'd opt for a little hotter cam for the street too, many years ago I ran this same size engine in my daily driver (only car) with 256' @ 0.050" x 0.470" lift but with 39mm valve. Same CR and 36DRLA Dellortos with 30mm throats. I was too young to know any better.

Have fun
Jim

this is some very usefull info! thank you, again
I'm aware of my "bad" cam choice. The 1641 was built as a learning proces so I wouldn't mess up the bigger engine I have planned.
 I wanted something with more power in the low revs and that's why I opted for the FK65. Didn't know enough of cams to know what would be best.  Still don't know enough to be honest, but I'm pretty happy with how the engine runs so far. I'm going to make the best of it with what's in it. might consider raising the cr a little, seeing the engine is out of the car now because there were 2 plugs behind the flywheel that were leaking. should have it sorted by the end of the weekend.

thanks again,

glauco

[Jim Ratto]

The 32 will work. I've run 40IDF on 87 x 69 with 32 vents, though with slightly hotter cam timing, but less lift.
"mathematically" your engine would be ideally set up as such:
87 x 69
8.9:1 CR
35.5mm intake valve with 32.3mm ID port in head
Cam timing as such:
intake open 15 BTDC
Intake close 43 ABDC
exh open 51 BBDC
exh closes 7 ATDC
Which means a cam ground @ 108LC will be 4 degrees advanced 238' @ 0.050", 276' @ 0.020", around 0.490" lift
32mm venturi for street use (race use we would up CR and open port up to 32.8mm, and use more overlap/longer duration cam, with 34mm venturi or larger)

Personally, I'd opt for a little hotter cam for the street too, many years ago I ran this same size engine in my daily driver (only car) with 256' @ 0.050" x 0.470" lift but with 39mm valve. Same CR and 36DRLA Dellortos with 30mm throats. I was too young to know any better.

Have fun
Jim

this is some very usefull info! thank you, again
I'm aware of my "bad" cam choice. The 1641 was built as a learning proces so I wouldn't mess up the bigger engine I have planned.
 I wanted something with more power in the low revs and that's why I opted for the FK65. Didn't know enough of cams to know what would be best.  Still don't know enough to be honest, but I'm pretty happy with how the engine runs so far. I'm going to make the best of it with what's in it. might consider raising the cr a little, seeing the engine is out of the car now because there were 2 plugs behind the flywheel that were leaking. should have it sorted by the end of the weekend.

thanks again,

glauco

For your conservative compression ratio, I don't think you made a bad choice.

[Glauco]

I cc'd my heads this weekend, turns out they are 51cc, piston deck clearance is 1.55, so that should give me a cr of 7.8, not sure if that changes the settings a lot..?

glauco

[Greg Ward]

I agree with both Bruce and Jim with their above comments.

My only concern on trying to tune that engine at all is the compression ratio.

7.3:1, why so low?

 I have an FK65 that I haven't used yet, but it's minimum when I do use it will be 11:1

The efficiency in combustion will make tuning a lot easier.

Cheers,

Greg

[LGK]

Glauco,

Exactly what Greg said,your compression is way to low for this small bore engine,i've build Dem his 2.1L engine,ask him to get a ride and UP that compression to at least 9/1

You need in short;

Bigger venturie,max 31mm, a 125 mainjet,180-220 airjet,but most importantly up the compression and  you need an engine dyno-session

good luck.

Steve

[Glauco]

Glauco,

Exactly what Greg said,your compression is way to low for this small bore engine,i've build Dem his 2.1L engine,ask him to get a ride and UP that compression to at least 9/1

You need in short;

Bigger venturie,max 31mm, a 125 mainjet,180-220 airjet,but most importantly up the compression and  you need an engine dyno-session

good luck.

Steve

hello Steve,


I've had a ride or two in dem's beetle, I'm very aware of the power that 'little' engine makes  +
and it's absolutely not my hopes to get the same feeling out of my very humble 1641. I for first hope it gets me true next summer after ten years of working on the car 
but it might be a good idea to up the compression, thank you for the info!

Glauco

[Martin S.]

Instead of looking at as upping the compression, think of it as tightening up the chambers.
Focus on a deck height value, and build your engine around that. Don’t worry about the CR value.
Adjust the ignition advance to not ping with your gas and enjoy a more efficient engine!