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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!

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Old Jul 20th, 2022, 20:24   #11
Burdekin
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Thanks, Ron, I always love your tips.

Yes, when compared to one another, if I push them up at the same time, they have the same amount of resistance and they fall together when I release them.

My initial setting was at 12 flats, but I believe they are currently sitting at 14 flats. That's right about where they were when I set up my 1800S with the identical engine and carb setup.

The air cleaners are currently off, but I have a set of CNC machined aluminum velocity stacks that allow me to quickly remove a modern conical air cleaner for carb service. Removing the velocity stacks makes no change in behavior.

(For those interested, these velocity stacks were made by namvet6970 on eBay.)
To set idle mixture wind down the jet increasing fuel mixture until revs stop increasing then just back up one flat is the best and most accurate without using a O2 wideband sensor and gauge. A SU should idle rich, about 13.2:1. A wideband O2 sensor and gauge is ideal for checking driving mixture.

I have velocity stacks as well and found they definitely weakened the mixture when under load and had to fit a richer needle. The car was slower with them with the standard needle. I experimented with the O2 sensor and timed runs to get it right.

One other thing is check the direction of the fuel filter and have you got the spacer behind the fuel pump?
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Old Jul 20th, 2022, 22:19   #12
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Just to be certain remove vacuum advance and plug manifold end, any difference?
Will it rev past 4k with no load if yes it's likely fuel or a blockage of intake or exhaust if no it's likely ignition related
Other thing to try is drive the car trying to get it past 4k and do an ignition cut that's ignition off and clutch in at same time and coast to. a stop, pull the ugs and see if its rich lean or ok, sounds like fuel starvation so it should rev higher under no load and the plugs should be light grey to white

Last edited by Rustinmotion; Jul 20th, 2022 at 22:25.
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Old Jul 20th, 2022, 23:40   #13
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To set idle mixture wind down the jet increasing fuel mixture until revs stop increasing then just back up one flat is the best and most accurate without using a O2 wideband sensor and gauge. A SU should idle rich, about 13.2:1. A wideband O2 sensor and gauge is ideal for checking driving mixture.

I have velocity stacks as well and found they definitely weakened the mixture when under load and had to fit a richer needle. The car was slower with them with the standard needle. I experimented with the O2 sensor and timed runs to get it right.

One other thing is check the direction of the fuel filter and have you got the spacer behind the fuel pump?
I definitely observed the lean condition with velocity stacks when I ran them on the previous B18 engine originally fitted to this car. I did my best to set that one up rich before biting the bullet and switching needles. I currently have KD needles in these carbs.

Yes, the fuel filter is in the correct orientation and I have the plastic spacer behind the fuel pump. I've seen so many local shops who don't understand these cars try to install a pump without the spacer and snap off the lever. "Must be a defective pump."
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Old Jul 20th, 2022, 23:48   #14
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Originally Posted by Rustinmotion View Post
Just to be certain remove vacuum advance and plug manifold end, any difference?
Will it rev past 4k with no load if yes it's likely fuel or a blockage of intake or exhaust if no it's likely ignition related
Other thing to try is drive the car trying to get it past 4k and do an ignition cut that's ignition off and clutch in at same time and coast to. a stop, pull the ugs and see if its rich lean or ok, sounds like fuel starvation so it should rev higher under no load and the plugs should be light grey to white
Thanks Rustinmotion,

My distributor does not have vacuum advance, it's purely mechanical. It does not rev past 4,000 RPM in neutral without load. I just checked timing at 4K RPM and it showed 33-34 BTDC. I pulled the plugs yesterday when I ran a compression test and they looked normal, not wet or covered in oil. They have approximately 3 miles on them.
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Old Jul 21st, 2022, 06:52   #15
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Thanks Rustinmotion,

My distributor does not have vacuum advance, it's purely mechanical. It does not rev past 4,000 RPM in neutral without load. I just checked timing at 4K RPM and it showed 33-34 BTDC. I pulled the plugs yesterday when I ran a compression test and they looked normal, not wet or covered in oil. They have approximately 3 miles on them.
I'd look at the coil and ignition, if it was fuel you would have a different max rpm with and without load
As you have already tried a distributer with points I'd look at coil and HT leads, also check a good 12v supply to coil
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Old Jul 21st, 2022, 12:51   #16
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Bork;

I had more thoughts about what could be causing RPM limiting...both Ignition related...

What kind of noise does it make when it hits that RPM limit? Does it sound like a Rev-Limiter, with intentional cylinder drop-outs, or does it still run true and smooth, but just doesn't want to go higher (which is what I expect a flow-restriction would sound like). A short video would be helpful...

Has the Distributor been apart? Getting the clocking of bottom driving shaft, and upper Lobe-shaft wrong on reassembly, can cause Rotor to align fine with plugwire stations at idle, but not at higher RPMs as Cent Advance moves Rotor earlier and earlier misfires would result...this would effectively result in a mechanical rev-limiting (sounding like a misfire at that time).

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Old Jul 21st, 2022, 13:41   #17
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Your Brazilian coil may pass the tests but in use may fail badly. It doesn't have to be Bosch but I would try another. Just make sure it is 3ohm and not 1.5ohm. One from a good MGB dealer or Moss should be OK. If you have an old one lying around just try that first. Swap one in from a friend with a similar car?
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Old Jul 22nd, 2022, 00:46   #18
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Bork;

I had more thoughts about what could be causing RPM limiting...both Ignition related...

What kind of noise does it make when it hits that RPM limit? Does it sound like a Rev-Limiter, with intentional cylinder drop-outs, or does it still run true and smooth, but just doesn't want to go higher (which is what I expect a flow-restriction would sound like). A short video would be helpful...

Has the Distributor been apart? Getting the clocking of bottom driving shaft, and upper Lobe-shaft wrong on reassembly, can cause Rotor to align fine with plugwire stations at idle, but not at higher RPMs as Cent Advance moves Rotor earlier and earlier misfires would result...this would effectively result in a mechanical rev-limiting (sounding like a misfire at that time).

Good Hunting!
Thanks Ron,

To me, the engine sounds completely flat at 4,000RPM; with that signature B20 tractor noise. It doesn't seem to have that rev limiter bounce or crackle sound I have heard other cars make when redlining.

I made a short video with a friend this afternoon, I will try to find a host and link it later today.

As far as I know, this distributor has never been apart, but it the springs feel good and the shaft has no noticeable play. My other distributor set up with points is in similar condition.

Before bed last night, I thought that maybe my velocity stacks were just not the right pairing for the modified B20, Isky VV-71 cam, and KD needles. As I understand it, velocity stacks behave differently at certain RPMs based on shape and length, so perhaps these were okay with my stock B18D with a stock cam, but not for this modified B20. In my mind, I thought they could have leaned out the fuel mixture at 4,000RPM, while behaving normally at lower RPMs. Thinking that was the most simple thing to try, removing the velocity stacks was first on my to do list for this afternoon.


Today I did the following:

Removed the CNC velocity stacks and drove the car with the Bosch Blue coil. No change.

Removed the Bosch Blue coil and replaced it with a used Pertronix Flamethrower. No change.

Replaced the coil again with a new NAPA coil (OEM Bosch, made in Mexico). No change (the RPM hang appeared more at 3,800RPM vs 4,000RPM). *This is when I made the video.

I swapped the IPD silicone leads for used Bosch leads. No change.

Put the newer IPD leads and Bosch Blue coil back. No change.
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Old Jul 22nd, 2022, 00:50   #19
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Your Brazilian coil may pass the tests but in use may fail badly. It doesn't have to be Bosch but I would try another. Just make sure it is 3ohm and not 1.5ohm. One from a good MGB dealer or Moss should be OK. If you have an old one lying around just try that first. Swap one in from a friend with a similar car?
Hi Derek,

We're on the same wavelength. After I removed the velocity stacks this afternoon, I tried a Pertronix Flamethrower coil with no change in behavior. I also went to NAPA and purchased an OEM Bosch coil with a NAPA label (made in Mexico). This was a 3 ohm coil, but actually performed a hair worse than the Bosch Blue coil I had before. (3800RPM vs 4000RPM). I also changed the leads to the used Bosch leads I had before returning to the IPD leads, with no change between the two. I have since returned to the Bosch Blue coil and IPD leads.
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Old Jul 22nd, 2022, 02:07   #20
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...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...
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