PMO carb tune + hesitation at 4k RPM

[zenithblue71T]

I pulled the stuck main jet. .

Found out why it was stuck. Why anyone would use this broken jet is beyond me.

Like Ed said above, I unscrewed the rain shields, removed the air filters, unscrewed the air horns, found the 3 jet stacks in between and unscrewed them with a fat stubby flathead. Get you one with as wide a head as possible to not tear up the soft brass jet stack holders like I did. Then I took apart the jet stack and swapped out the 130 main jets for 125 and swapped out the 180 main airs for 170. Getting the broken jet out of the #4 hole was a bitch and the q tip with grease did not work. I had to remove another layer of the carb and then I used some long tweezers to remove the offender. Putting it back together was the reverse of the above.

I test drove today and have little to no hesitation at 4K RPM. That stuck jet was likely not seating properly and doing God knows what to my 2.2S motor.

[Brickdog]

This is a very interesting thread. I’m experiencing something similar on my ‘70 911 with the stock 2.2 and 40IDAs (1980’s era PMOs) I developed a stumble/misfire under load between 3200-4200 RPM. It can be driven through in a lower gear but if you select a taller gear and let it work a bit more under acceleration it’s quite noticeable. Carbs have been ultra sonic cleaned several times as well as all ignition parts swapped out to eliminate that. Recently I tried swapping the 125 mains for 130’s but it was still there although the car seemed to pull harder. Next I swapped back in the 125’s and tried switching the 180 air correctors for 170’s but found no improvement. Currently the emulsions are F26 and was wondering if I should switch out those. Although my situation sounds similar to the one posted mine seems to come on earlier in the RPM range. Anyone have any input/suggestions?

[zenithblue71T]

Brickdog, try f11 emulsion tubes and then F16. The best advice I got was to make one change at a time. I.e. don’t change jets and airs at same time to fix one issue.

I finally tuned out my PMO 40mm hesitation on my 1971 911 T motor with S pistons and hot solex cams. I went from F11 emulsion tubes to F16 and the stumble is now gone. The PMO tech bulletin suggests:
-60 idle jets but those made the car stall so I went back to my 55 idle jets
-125 mains
-180 airs

So happy to finally have a well sorted motor, 3 years later!

[Brickdog]

Thanks James. I will have to try different emulsion tubes once spring arrives and the snow is all gone here. It's really strange that this issue developed on the trip to Luftgekult in 2017 (previous to this trip it was amazingly smooth). I was blaming it on US fuel but once I got back to Canada and better quality fuel it never went away. I'm to the point that if the emulsions don't fix it I just want to send them to someone who is an expert on these and can run them on another engine to fix/tune them.

[chiroracer]

I got some f16 emulsion tubes to try this solution but I discovered another issue( venturis) I have some new f16s if anyone needs them.
Steve

[1QuickS]

Brickdog, E-tubes for PMOs do not work in your Webers. Even though your Webers were sold by PMO they are not PMO carbs.

If engine was good and suddenly has an issue then you have a debris issue to resolve. My best guess is one of your E-tubes has a hole that has a blocked orifice.

It is easy for debris to enter the air cleaner (imperfect filter sealing or corrosion of the housing that is undetected) which then enters the main air correction jets which secure the emulsion tubes in their wells. A small bit of corrosion/debris may then be drawn into an orifice in the body of the E-tube which can become lodged there. I personally experienced a RPM issue which was resultant from a tiny bit of paper towel stuck to one of my E-tubes.