I've never had so much trouble with SUs before, please help!

[Bork Volvo]

Originally Posted by Ron Kwas

...maybe its time to loose the Pertronix and return to a standard Points based Primary circuit...I'm thinking the dwell and time of charging the Ign Coil may be being limited by the module...

Thanks Ron, that was one of the first things I considered. As I said earlier in the thread in response to Groundes-Peace:

I thought that was the case at first, so I tried to rule it out by installing a stock points ignition with new cap, rotor, condenser, and points, but it actually reduced max RPM at WOT to 3,500. FWIW, my 1800S has the same exact Pertronix and coil setup and it was totally plug and play.

Both distributors I tried in my car are aluminum bodied Bosch: JF 4 / 0 231 178 007 with mechanical advance. I have several other Bosch distributors in my inventory, both steel and aluminum, but they are either incomplete, untested, or have a vacuum unit. I know there are dozens of Bosch distributors with different pros and cons; if this "007" model is not a good one, please let me know if there is a better one I should look for.

[Rustinmotion]

If your not using vacuum advance and you already confirmed with a strobe the max advance is being reached I don't think distributer is the cause, fuel starvation would show with lower max revs driving under load than revving it on the drive, coil has been swapped
Have you confirmed a healthy 12v it doesn't drop for some reason at 4k?
On all situations have you been using the same electrical ignition? If yes put the points back in to rule that out. Have you measured valve lift, are they opening to specification

[Bork Volvo]

Originally Posted by Rustinmotion

If your not using vacuum advance and you already confirmed with a strobe the max advance is being reached I don't think distributer is the cause, fuel starvation would show with lower max revs driving under load than revving it on the drive, coil has been swapped
Have you confirmed a healthy 12v it doesn't drop for some reason at 4k?
On all situations have you been using the same electrical ignition? If yes put the points back in to rule that out. Have you measured valve lift, are they opening to specification

Voltage to the coil is around 14.2V at 4k RPM, tested with a multimeter.

I measured valve lash when I assembled the engine and again when it was hot. I will need to buy more tools so I can accurately measure lift.

[Derek UK]

Something to check as you say you have fitted new dampers to the SU's. It is possible to use dampers with a bleed hole in the top if there isn't a hole in the dash pot casting just below the threaded hole for the damper. You mustn't have a hole in both or you wont have enough vacuum to raise the piston sufficiently. It may raise it about half way and this could be the reason you only get about 4k revs. Early dampers have a brass top, usually with a hole. Later ones have a black plastic top and I think these don't have a hole. If that is the case there should be a hole just below the threaded area.
There is also the possibility that the dash pot and pistons have been swapped over and are now mismatched. Easy to do during a rebuild. They come as a pair and must be kept together.

[Bork Volvo]

Originally Posted by Rustinmotion

On all situations have you been using the same electrical ignition? If yes put the points back in to rule that out. n

At this point in my troubleshooting, I have swapped the Pertronix distributor for my points distributor several times. Both units are Bosch: JF 4 / 0 231 178 007 with mechanical advance. My experience with the points ignition in this car is that it consistently lowers the max revs to about 3,500 RPM. Cap, rotor, condenser, and points are new OEM Bosch. I tried the points distributor in my friend's 122 with a B18 and it appeared to perform normally for him. Pertronix is giving me the best performance.

[Bork Volvo]

Originally Posted by Derek UK

Something to check as you say you have fitted new dampers to the SU's. It is possible to use dampers with a bleed hole in the top if there isn't a hole in the dash pot casting just below the threaded hole for the damper. You mustn't have a hole in both or you wont have enough vacuum to raise the piston sufficiently. It may raise it about half way and this could be the reason you only get about 4k revs. Early dampers have a brass top, usually with a hole. Later ones have a black plastic top and I think these don't have a hole. If that is the case there should be a hole just below the threaded area.
There is also the possibility that the dash pot and pistons have been swapped over and are now mismatched. Easy to do during a rebuild. They come as a pair and must be kept together.

Good point. The dampers I have fitted are brass with a bleed hole. As far as I can tell, my carbs do not have a bleed hole in the casting. The original black plastic dampers that came with my carbs also had a bleed hole; the reason I swapped them is because one had damaged threads and would frequently back out after ~200 miles of driving.

I'm aware about the piston match for tolerances, I feel like I was pretty careful to do each carb individually so I wouldn't accidentally mix and match, but I can try swapping them around and see if it makes a difference. Perhaps there was an error under previous ownership.

[Bork Volvo]

I wanted to add that I checked the fuel pressure of the new OEM Pierburg pump. Many of the pressure testers at my local parts store were for modern systems, but I found a low pressure tester kit that measure from 0-10psi.

According to the fuel pressure tester, I have an average fuel pressure of 4.5psi at idle or under load. As I understand it, SU carbs are very sensitive to fuel pressure, and work best between 1.5-3psi. Could this be be contributing to my problems?

[Rustinmotion]

Originally Posted by Bork Volvo

Voltage to the coil is around 14.2V at 4k RPM, tested with a multimeter.

I measured valve lash when I assembled the engine and again when it was hot. I will need to buy more tools so I can accurately measure lift.

Your not looking for super accurate a tape measure or a piece of wood marked at fully closed and fully open, do the penta engines have different rocker arm geometry, this would effect maximum opening and restrict RPM edit just read your first post again and I think you had this engine running ok before rebuild, one more thing to try, with someone holding accelerator to the floor and engine running a 4k max what happened if you slightly lift the SU piston with a long screwdriver? Do the revs rise?

[Bork Volvo]

Originally Posted by Rustinmotion

Your not looking for super accurate a tape measure or a piece of wood marked at fully closed and fully open, do the penta engines have different rocker arm geometry, this would effect maximum opening and restrict RPM

I thought you measured lift using a dial indicator like this.

As far as I can tell, there is no difference in geometry between the AQ130 and B20 rocker arms, and they have the same amount of adjustment as the B20F. I had one of my 6-bolt B20Fs torn down side by side with my AQ130, they are almost identical, except the AQ130 had the following:

Steel timing gears
Different head casting: it had larger exhaust valves, better porting, and stiffer valve springs, but I needed to machine holes for the water pump and heater pipe.
Volvo C-Camshaft
Different timing gear cover

I chose this AQ130 over my B20F because it was absolutely clean inside. The 70k mile B20F was very dirty and had some heavy sludge/buildup on the crankcase. The Penta engine looked almost new inside, and it was obvious that the bottom end was recently rebuilt. I located the shop who did the engine work for the previous owner, and hired them to modify the head for road use.

[Rustinmotion]

See my edit
Re valve lift you'd be checking for significant difference so if you should have 10mm and it's only 5 that would show up with a tape or piece of wood marked, I don't think it's valve lift