Weber 40 IDF help, My usual guy had back surgery and can't help now Options

[mmichalik]

Hi everyone,
My 75 is ready to drive again. I fixed the oil leak from the main seal a couple of weeks ago and all is good.
As I continue to do the shake out of the car, since I'm on the tail end of the restoration, I've had one problem the entire time and I need to get it fixed now.
Cold or hot, as I'm driving there's a flat spot when I shift between gears. It bogs and then picks up again.
It's particularly noticeable from 1st to 2nd and 2nd to 3rd. Sometimes even when starting for a dead stop.
I know NOTHING about carbs but I'm willing to jump in.
Does anyone have any experience with these symptoms? Is there a write up on the world that I've missed?
Would anyone be willing to work for high end craft beer and good pizza (along with an hourly rate) (IMG:style_emoticons/default/smile.gif) I'm in north county inland San Diego (Valley Center)
Mike

[technicalninja]

First thing I'd check is if the accelerator pump circuit is working on both carb.

Operate linkage while looking down carb bores.

Should see a squirt.

Old version IDF have a linkage that can be misaligned which might cause this.

New version has an adjustable rod linkage that cannot disconnect (without parts loss) but CAN be adjusted down to the point of almost no spray.

[Superhawk996]

What are you using for ignition? The reason I ask is the Bosch 009’s have some flat spot lags that align to your comments that are related to ignition advance. They feel an awful like carb issues but they are not.

[porschetub]

Hi everyone,
My 75 is ready to drive again. I fixed the oil leak from the main seal a couple of weeks ago and all is good.
As I continue to do the shake out of the car, since I'm on the tail end of the restoration, I've had one problem the entire time and I need to get it fixed now.
Cold or hot, as I'm driving there's a flat spot when I shift between gears. It bogs and then picks up again.
It's particularly noticeable from 1st to 2nd and 2nd to 3rd. Sometimes even when starting for a dead stop.
I know NOTHING about carbs but I'm willing to jump in.
Does anyone have any experience with these symptoms? Is there a write up on the world that I've missed?
Would anyone be willing to work for high end craft beer and good pizza (along with an hourly rate) (IMG:style_emoticons/default/smile.gif) I'm in north county inland San Diego (Valley Center)
Mike

You are most likely lean on the idle jets , check the size and IDF guys will step in cause I work on Dellorto's mainly but principles are similar .
In the rev range you are talking about it will be pre transition to mains I would think.
Supply some more details and you will be better off in the long run ,cheers.

[mmichalik]

What are you using for ignition? The reason I ask is the Bosch 009’s have some flat spot lags that align to your comments that are related to ignition advance. They feel an awful like carb issues but they are not.

I'm running a Bluetooth 123ignition

[mmichalik]

Hi everyone,
My 75 is ready to drive again. I fixed the oil leak from the main seal a couple of weeks ago and all is good.
As I continue to do the shake out of the car, since I'm on the tail end of the restoration, I've had one problem the entire time and I need to get it fixed now.
Cold or hot, as I'm driving there's a flat spot when I shift between gears. It bogs and then picks up again.
It's particularly noticeable from 1st to 2nd and 2nd to 3rd. Sometimes even when starting for a dead stop.
I know NOTHING about carbs but I'm willing to jump in.
Does anyone have any experience with these symptoms? Is there a write up on the world that I've missed?
Would anyone be willing to work for high end craft beer and good pizza (along with an hourly rate) (IMG:style_emoticons/default/smile.gif) I'm in north county inland San Diego (Valley Center)
Mike

You are most likely lean on the idle jets , check the size and IDF guys will step in cause I work on Dellorto's mainly but principles are similar .
In the rev range you are talking about it will be pre transition to mains I would think.
Supply some more details and you will be better off in the long run ,cheers.

I'm not sure what's in there right now but I did purchase a bunch of idle jets from size .40 up to .65 so I could test that.
I also bought a jet gauge and some jet reamers as well.
I'm running the tangerine racing cable linkage and the engine started life as a 1.8 but is now a 1911 with a mild custom Schneider cam in it.
let me know if there's any other info I can supply that might be useful

[nditiz1]

So 2 things will be needed, 1 of which is easy and the other will require a purchase and some welding (well they do make a bolt on bung)

1st we need to know what jets are in there now. Pull one from the side (idle jet), pull the top stack (main, air, emulsion). If these are brand new Weber IDF or even old stock ones you are probably running something like this:

50 idle
115 main
180/200 air (can't remember which one came factory)
F11 emulsion
28mm venturis

The 2nd item that is needed is an AFR gauge. I usually use an AEM UEOG wideband, but you can use whichever you like. They even have a fancy bluetooth one that shows on your phone so no need for an additional pod. You will need to have a bung welded into your muffler or exhaust. Preferably both sides, but one in the muffler should suffice. There is another option in LM2 (if memory serves) that connects to the end of the muffler tip to get a reading on AFR. Never used that one.

OR you can just keep making minor changes until it "feels" right, but you could be overly rich and not know it.

[Superhawk996]

The 2nd item that is needed is an AFR gauge.

Awfully nice to have but not a must have. There were no affordable AFR gauges back in the day and we got by just fine reading plugs, using the assometer, CHT’s, and monitoring fuel economy.

Glad to hear the ignition is 123 - makes life a whole lot easier.

Per Porschetub’s comment above, need a whole lot more detail on speed, RPM ranges, throttle position, and load (flat vs hill) to advise. Your gut instinct is correct; it is a lot easier if you can find someone local that has carb tuning experience vs doing it via internet advice.

Regardless of how you go about this - I highly suggest you keep a journal / logbook. Time / date, temperatures, jetting changes, ignition advance curve used, CHT’s, any details. Things can get very murky after a few days. Humans are not terribly good at recalling how one change vs another felt after only a few hours between changes. Doesn’t need to be overly fancy or complicated but document your baseline and what changes you make.

[930cabman]

The 2nd item that is needed is an AFR gauge.

Awfully nice to have but not a must have. There were no affordable AFR gauges back in the day and we got by just fine reading plugs, using the assometer, CHT’s, and monitoring fuel economy.

Glad to hear the ignition is 123 - makes life a whole lot easier.

Per Porschetub’s comment above, need a whole lot more detail on speed, RPM ranges, throttle position, and load (flat vs hill) to advise. Your gut instinct is correct; it is a lot easier if you can find someone local that has carb tuning experience vs doing it via internet advice.

Regardless of how you go about this - I highly suggest you keep a journal / logbook. Time / date, temperatures, jetting changes, ignition advance curve used, CHT’s, any details. Things can get very murky after a few days. Humans are not terribly good at recalling how one change vs another felt after only a few hours between changes. Doesn’t need to be overly fancy or complicated but document your baseline and what changes you make.

All good information and try to make just ONE change at a time to keep things in order

[densible1]

From my experience with 44 idf's and a bluetooth 123 the flat spots could be tuned out in the tune mode on the phone app. I note what rpm range the hesitation starts and bump the advance up till the flat spot levels out. Note the amount of advance in the tune mode and then with engine off but ignition on reedit the curve that is loaded. Then write that curve as a new curve and load. If close to idle hesitates bump low rpm advance to 8-10. I don't know for a 40 idf and your displacement/elevation if a 115 main is too low but my 44's at sea level needs 140 mains your other jet values seem right.

mark

[Superhawk996]

One thing that is critical to tuning IDF’s is to understand the transition ports and that in light throttle / light load you are running on the idle circuit and transition ports more so than the mains.



Take the time to read the Weber tuning manual to get a baseline understanding of the transition ports. The manual isn’t specific to IDF but the principles are the same.

https://www.lainefamily.com/images/WeberTuningManual.pdf

[nditiz1]

A great tip that John from ACN told me was to remove the main stacks and drive the car around (caution no big inclines) You get to feel where the idle port drops off. The car will fall on its face. This gives you an idea of your idle jetting and the transition to the nonexistent mains.

[dtmehall]

did the car ever run correctly with the webers and the 123 ignition?

i agree with Superhawk996 and densible1. the type of behavior you describe can often be caused by ignition issues

[flxzcat]

Drilling new progression holes is a last resort and not for the home mechanic unless you have a mill to put them in a precise location in each barrel.

Spanish version Weber 45 DCOE's of the mid 2000's were notorious for this particular progression problem and the only solution was to drill an extra progression hole exactly like the original Italian 45's.

You might Google for pictures of 40IDF progression holes in an original Italian version and compare to your carbs.

[dtmehall]

if you want to investigate weber carb options cb performance has recommendations and sells jets and emulsion tubes

https://www.cbperformance.com/Weber-Carbs-s/152.htm

[Superhawk996]

Drilling new progression holes is a last resort and not for the home mechanic unless you have a mill to put them in a precise location in each barrel.

Spanish version Weber 45 DCOE's of the mid 2000's were notorious for this particular progression problem and the only solution was to drill an extra progression hole exactly like the original Italian 45's.

You might Google for pictures of 40IDF progression holes in an original Italian version and compare to your carbs.

There is no need to drill anything on IDF’s to get them tuned for a 914.

[dtmehall]

(IMG:style_emoticons/default/agree.gif)

[mmichalik]

Going to pull the emulsion tubes and idle jets to get the sizes listed on them Will report back.
Thanks everyone for the help and advice!

[Superhawk996]

Need the Venturi size too!!

Very often the venturis shipped in IDF’s are too large for good street driveability and lead to bogging similar to your description.

[CCE]

Hi everyone,
My 75 is ready to drive again. I fixed the oil leak from the main seal a couple of weeks ago and all is good.
As I continue to do the shake out of the car, since I'm on the tail end of the restoration, I've had one problem the entire time and I need to get it fixed now.
Cold or hot, as I'm driving there's a flat spot when I shift between gears. It bogs and then picks up again.
It's particularly noticeable from 1st to 2nd and 2nd to 3rd. Sometimes even when starting for a dead stop.
I know NOTHING about carbs but I'm willing to jump in.
Does anyone have any experience with these symptoms? Is there a write up on the world that I've missed?
Would anyone be willing to work for high end craft beer and good pizza (along with an hourly rate) (IMG:style_emoticons/default/smile.gif) I'm in north county inland San Diego (Valley Center)
Mike

As you I know NOTHING about carburetors and had some similar issues 2 years ago, my mechanic saw the motor and modifications it had, 44mm twin webers cbperformance distributor and my main issue was jetting and high altitude in Mexico City. He recommend cbperformance black box for timing and a Weber update kit (Like black magic) had no more issues with timing, jets or venturies. And the car motor is very happy now. Here is a picture.