More on IDF 40 twins project

[oebb]

Hi guys!
Decided to go for the "twins" - a pair of used IDF40 with Alquati manifold. The rest is a 2.0 - pretty much stock - but with a 1800 head.
Got everything in place with linkage and so on and the sound is awsome. Have som issues though:
1. When I accelerate smoothly there is a noticeable dip or stall around 2000 rpm - if I press the trottle further the response is great. Any ideas what this might be? The jetting is main 130 emulsion F11. I havent checked the needles (didn't want to start tearing everything apart..)

2. I've got no air filter or ventilation filter. I'd like something in chrome that fits. I guess they must be quite low and narrow. What do you guys use (and where did u get them?).

Cheers!

/Mikael

[MNspiderman]

go to http://www.webercarbsdirect.com you will find air cleaners there at a great price, Chrome rectangles. Thats the ones i have on my 44IDF's 3" tall fit under my hood with the 1.8 engine. They also have tech help on how to adjust webers. which are fairily easy once you do it. But you cannot really get a good job until you purchase a synchrometer. you can get it pretty good but not all the way good. they also have every part you can imagine. good luck, let me know how its going.

[mdrburchette]

Once you get those carbs dialed in you'll love them. For the stumble you're talking about, if you arent' getting a pop through the carb or a backfire, it could be they're not quite tuned correctly or it may be the wrong size bleedback jet inside the bowl of the carb. If you take the top of the carb with the float off and look into the bowl, you'll see a jet in the very bottom. I run a 00 in my IDFs and don't have a stumble. That jet has something to do with how much fuel bleeds back into the system. I'm no expert so maybe someone else will chime in that knows a bit more.

[engineerted]

Mikael, Welcome to the world of Twin carbs. Can you post some info on your setup?

Main Jet size ~ 130
Air correctors ~ ?
Idle jet size
bleed back
Idf type 15/13 or 70 series?

key point to remember, make sure the carbs are clean inside and out, then do it again, then one more time. It took me three tries to get all that little crap out of the ports. What you will find is that those small transition holes next to the butteflies tend to get plugged with crap causing a lean conditon thus stumble, but after everything is cleaned out this is a non issue. I have been running my set for 4 years with no issues. If you still have a stumble you may have a too small of an idle jet and or wrong size bleed backs, or miss adjusted accelerator pumps.

Ted

[oebb]

Hi all and thanks for the feedback.
This is fun! I tried to determine the IDF type - I'm not sure how to do this but it looks like the linkage between the two carbs are original. That would make them of the 13/15 type - but I'm not 100%.
Tried to identify the jettings:

Main 130
Emulsion F11
Aux venturi 4.5
idles 60
pumpjets 55
bleedback no markings

The bleedback was at the bottom in the bowl of each carb with some kind of valve function. Theyre identified as No 13 "pump spill" in the carb schema in Bradley Artigues excellent guide.

Don't know if it's possible to say something about the jetting with this data only - comments apreciated

I found something though. Two of the pump bolts - that also have some kind of valve function (with no 10 Pump Demand Valve) were stuck, and one of them seem to have been soldered/tampered with. Maybe this is the problem...

Thanks for the pointer to Weber Carbs Direct - seem to be a great source for parts and more info.

Cheers

/Mikael

[mdrburchette]

The easiest way to tell a 13/15 from a 70 series is if the carbs have an adjustable arm going from the pump diaphragm to underneath the carb it's a newer 70 series.
What size air corrector do you have? You'll find this jet on the other end of the emulsion tube once you pop off the holder.

[oebb]

Hi again.
There is no adjustable linkage from the accelerator pump. It's a fixed linkage so I guess it's the older version.

The air corrector (thanks for pointing them out) have size 210.

Called my local Weber dealer and they told me that the Pump Demand Valve is not in the parts list or in any service kit - guess I have to chase for a used one. Anyone have a scraped IDF 40 or 44 layin around I'd be happy to buy the parts or the whole carb.

Regards

/Mikael