Workable Setup for 44 IDF on a 2 Ltr Pinto?

[Amateur]

Hi folks.

My Robin Hood Exmo has a 105 HP 2 litre Ford OHC engine. Standard, no (known) modification. When I bought the car, it was equipped with a 48IDF carburator. It took me ages to get that carb running decently. But I never managed to get good performance for lower rpm. The carburator is simply too big for that engine. Besides, the old 48s are old, worn and dirty.

To get a little better performance in lower rpm, I decided to buy 44 IDF instead. However, I failed to get the carbs running until now. In my garage, reving the engine, I get the 44 IDFs running decently within a range of AFR 12 - 15. But on the road, under load, the engine shoots to lean the second I touch the accelerator. I have to push the accelerator binarily (full throttle or none at all). Even when I try to just hold speed the mixture gets lean as hell (AFR 17+). I tried valve combinations getting fatter and fatter. But until now, nothing helped. My last setup is main = 150, air correction = 165. My feeling says, that's way to fat. But pressing the accelerator still makes the mixture go lean.

Does someone have 44 IDFs with the Ford Pinto engine and can tell me what valve combination works decently? That would greatly help me to get my beloved Seven back on the road...

 

Edit: just fixed my typos..

Edited June 19, 2023 by Amateur

[Foz]

I don't know a lot about IDFs but most Webers work on a similar principle - the idle jet controls the small throttle opening/low revs mixture until the mains take over at 2-3000 rpm.  The mixture screw sets the mixture at idle speed. 

Have a look at the idle jet size - you may need to increase this to get the mixture right on part throttle and low revs.

Everything tends to interact as well.  Do you know what size chokes are fitted - smaller chokes (and smaller jets) will give better bottom end at the expense of top end power, and vice versa.  On DCOEs you probably wouldn't want much bigger than 32mm chokes for a standard Pinto.  130 mains and 50 idles would then get it somewhere close. I suspect the IDFs are not a lot different, but I can't be sure.

Unfortunately you can easily spend weeks trying to get them set up (I've been there), but if you can find an "old school" guy who knows them he can probably do it in a couple of hours for you.

Steve

[Amateur]

Hi Steve.

Many thanks for the suggestion. But the idle jets are sadly not the solution. I actually had to make the idle jet smaller. When I bought the Webers, they were supposedly equipped for a VW Beetle or small Porsche. 36 chokes, 135 main jets, 210 air jets, 55 idle jets. That setup is what I started with, in the hope it would be a feasible start. Not the case.

With the 55 idle jets the Pinto runs extremely fat at low rpm. AFR falls below AFR 12 at .5 to.75 turns open, and below 3,000 rpm AFR drops below 11 with the foot off the paddle. So I put 45s in. This way, I can at least open the screw 1.5 turns to set AFR to about 13 and the fat mixture below 3.000 rpm mostly went away.

Without load, the engine remains inside the AFR rage 12 - 15. But on the road AFR jumps up to 17 and more the second I touch the accelerator.  Acceleration pump is in all the way. When I floor the paddle, that gasoline shot is the only thing that prevents the engine from choking. By the book that means that main jets are too small.  I tried 140 and 150 main jets in combination with the 210 air jets. I now even dropped the air jets to 160, only 10 points above the main jet (Weber manual suggests 30-40). That last step actually improved it a little. I now ordered 160 main jets and 170 air jets to go even bigger.

But I somewhat doubt such big jets are the right solution. The larger 48IDFs having 40 chokes worked with only 140 main jets, 190 air jets, and 50 idle jets. 

The only thing I have not yet altered is the fuel level. I set the floater to close at 10mm below the lid. Do you think it would do something to increase that level to 5mm or so?

[Foz]

I would be reluctant to set the float height to anything other than standard - it does have quite an effect of the mixture but not always in a predictable way.

I think your choke sizes are probably too big for a standard 2.0 SOHC Pinto engine - the original type of twin choke carbs fitted to these had 26/27mm chokes (or there abouts) and gave good results, but swapping chokes is a lot more expensive than jets, particularly if it doesn't solve the problem.

One thing I did wonder - is your ignition timing correct? and is the mechanical (and vacuum) advance working correctly?

If I think of anything else I'll let you know.

Steve