If you haven't changed anything on the engine, and you seem to have less power than before, I'd start with a thorough tuneup. You can't make progress towards getting more power unless you're sure everything is working as well as it can.

I much prefer the S.U. carbs, as they are dead simple and not expensive to work on. If you have some mechanical ability and a good S.U. tuning book, there's no reason you can't tune a set of these carbs.

The single carb setup was usually installed by owners who are intimidated by the thought of trying to synchronize two carbs. With the S.U.'s it's extremely easy, and you can even get a gauge that will help set things up.

Also, if you don't have the 4-2-1 exhaust manifold, I highly recommend you get one. Look at where the cast iron ends and the tail pipe begins. You should see two exhaust pipes that attach to the cast iron. This manifold works as well, probably better than the header systems, and if you want to go to dual exhaust, just have a shop remove that section of tail pipe that goes 2-into-1 and fabricate another pipe so you have two.

Another secret here is that these older Volvo's use both a muffler (under the passenger's front seat) and a resonator (behind the rear bumper). You can remove the muffler to reduce back pressure and just use the resonator, which sounds a whole lot better, too!

Referring to the valve adjustment mentioned below, you should also remember that these engines were manufactured at a time when 'unleaded' gasoline was unknown.

Without lead to cushion the closing valves, they can beat the valve seats in the head until they begin to actually recede into the head. You may notice your valve/rocker clearances seem to keep closing up. There are several good articles here about detecting this problem, and what to do if you find it exists on your car.

As far as the micro-gains in horsepower you can find in engine accessories, the thermostatically controlled fan blade is a good idea, but you will probably find that you don't have space for one. A good alternative is a Flex Fan, which flattens out as the engine gains RPM. I found a 17" Flex Fan (that's the maker's name) on eBay for about $12. Much better at cooling than the stock Volvo fan, and as I said before, it flattens out and minimizes power loss at higher RPM's.

If you prefer an electric fan, you can install two small ones on the front side of the radiator or one on the back side of the radiator.

An electronic ignition setup is much better than the old style points/condensor that the cars came with. You can spend a fortune on it, so do as I did and shop at the online auctions to find a setup that works for a 4-cylinder engine. My car came with an MSD-6A setup, but it died after about 5 years (of me owning it) and rather than try to diagnose it out in the cold, I simply bought a good used Pertronix unit and installed it for the time being. I also built a 'stock' distributor that I can just drop into place if I have further ignition problems. Since I'm in a wheelchair and there is no cellular service near me, a breakdown could be catastrophic! SO I carry a lot of small backup items.

BTW: I put together a complete original Volvo tool kit - for shows - and actually ended up using it when I accidentally left my toolbox at home and one of my carbs had a float problem. What they say about being able to completely rebuild the car with those few tools may actually be true!

Good Luck!

Steve in California
(Near Death Valley)
1964 Volvo PV544
1965 Volvo P1800s
1967 Fiat Abarth 100-OT Coupe