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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars |
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I've never had so much trouble with SUs before, please help!Views : 5251 Replies : 42Users Viewing This Thread : |
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Jul 22nd, 2022, 05:22 | #21 | ||
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Jul 22nd, 2022, 06:51 | #22 |
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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 Last edited by Rustinmotion; Jul 22nd, 2022 at 06:54. |
Jul 23rd, 2022, 13:03 | #23 | |
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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. |
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Jul 23rd, 2022, 14:33 | #24 |
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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. |
Jul 23rd, 2022, 14:38 | #25 |
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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.
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Jul 23rd, 2022, 14:45 | #26 | |
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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. |
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Jul 23rd, 2022, 14:52 | #27 |
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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? |
Jul 23rd, 2022, 18:05 | #28 |
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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?
Last edited by Rustinmotion; Jul 23rd, 2022 at 18:31. |
Jul 23rd, 2022, 18:29 | #29 | |
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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. |
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Jul 23rd, 2022, 18:33 | #30 |
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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 |
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