Apparently there is a guideline: Small carburetors (with a long intake path) smoothness at low revs. Large carburettors and a short intake path for high revolutions and speeds. And how does that work with a 750 cc side valve with a nominal 23 hp?
With the standard carburetors
When rebuilding my side valve, I opted - in consultation with Richard Busweiler - for Pekar K68s as carburettors. With an adapter set to turn the mounting threaded ends 90 degrees and with an Inertial Supercharger set between the heads and the carbs, this was otherwise a plug-and-play process.
That poor guy's turbo, the Inertial etc. is nothing more or less than a balance hose between the two carburetors. The system must be doing something somewhere, because you also saw something similar with Japanese multi-cylinders until the eighties or so.
Only the piping on the suction side had to be adjusted slightly. Stairs, walk, go! I felt like the boxer ran nicely and all kinds of wild things happened at 'high' speeds. In short: I got the idea that 750 cc would certainly produce the once specified 23 horsepower.
There were some critical comments on those K85s from UralDneprClub Netherlands man Benno van Ham. According to Benno, the K68s were too large in diameter. As a result, the gas flow would actually not get going properly in the (low) speed range to which side valves actually owe their reputation.
Through some searching in the box with various things and a donation of parts from Benno, I was able to put together two K302 carburetors (after the parts had been given an ultrasonic bath. The tip is 'put a generous dash of Dasty in the bath water').
What the real difference would be remained a secret for a while. But the optical difference was enormous. The K68 are enormous, sturdy gasworks and in combination with the turbo hose, the Uralblok looked like a serious engine room. The K68's have a passage of 30+ mm. The K302's breathe easily through a 27 mm hole. The 302s look a bit shabby compared to the K68s. Less tough. How substandard. But if originality is your thing, they are part of the block.
The area of a circle is the radius squared x 3,14. And if you calculate that for 27 mm and 32 mm respectively, you see that there is quite a big difference between those two carburetors in passage > flow rate > filling of the awkward combustion space of such a side valve. In terms of suction, it is similar to inhaling through a straw or a PVC drainpipe.
With the K302s the engine room looks less impressive. The turbo hose adapter no longer fits because its thickness pushes the 302s so far back that the carburetor body touches the crankcase.
The connection between carburetor and air filter still requires some TLC.
But then? With the K302s just tested, the twin starts exemplary and immediately goes to a neat idle. The ride is… Softer, smoother from the lowest revs. And will the full 23 hp come out? The engine, the throttle response with the K68's feels 'rougher'. To get around with the K68s, things really had to be kept up to speed, whatever that's worth with such a side-valve engine.
In terms of brutal acceleration and absolute top speed, the engine running on the 302s yields to the double-muscled version with the turbo hose and the big K68s. Bottom line, in both versions you are fast enough to be the first driver in any traffic jam.
There is a difference. But is that important?
It's the difference between fun and fun.
And no matter how satisfied I was with the 68's, Benno's approach is absolutely flawed. Bottom line, I can now choose each day which carburetors I attach to the boxer. This is how I created my own win-win situation by listening to men who know more about it than I do.
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Because whether it's on the toilet or on your bedside table, reading from paper is more fun, but...
Funny to see that the spark plug wire and 'garden hose' have the same colors as the Ukrainian flag😉
It was brought to my attention! But I'm too politically unaware to come up with something so subtle myself!
So you can see how great insights can be gained with real motor spirit and key skills. It takes me back to the development process of 'Blauwtje' from a powerless R45N to a brighter R65 that can even handle the 33/11 final drive of an R100. That R45 was born as an 'N' version. The N stands for 'Nichts' or 'Niks'. Lethargic with 27hp. The power has now more than doubled and 32mm carburetors were also required for this. I received this through a good friend of mine who, as a wonderful person, has good contacts in the motorcycle world. Those 'gas factories' came from an identical R65 model series. The nozzles of those 32mm Bing's turned out to be much too small in my setup. Main jets thus went from #125 to #145! To achieve the desired 'scavenging' effect while maintaining the tame camshaft, both balance pipes in the exhaust were replaced with expansion dampers. At the bottom, Blauwtje still performs well and smoothly, firmer from 3000 rpm and from 5000 rpm it takes off like a rabbit. And all with surprisingly little vibration! The compression ratio eventually went up from 8,2:1 as R45 to 12,5:1 as R65 equivalent. With Doppelzündung and a completely modified ignition curve it is finished. There's nothing more to it. All this with a consumption of 1:18 – 1:19 and with a fairly loose wrist. What I want to say with all this is that the whole is the combination of all facets. And engine manufacturers are smart people who produce excellent power units from the factory. A side valve is known for being strong at low revs. Blauwtje cannot offer this. Dolf's side valve will definitely be the king there. I think it's beautiful, just the way you handle it Dolf. Have fun planning, trying and messing around. Beautiful!!
They explode at high speeds!
As soon as you go off-road you don't want that Pekar, you miss the grind of the side valve at low revs and that is just what you need. Deni PZ28 is also a good side valve carburetor, but the idle jet is often too small and because it is pressed you cannot replace it very easily. It works, but requires some thinking and tinkering.
Drilling with a 0.35mm drill bit is also possible.
The Pz is indeed a very good alternative.
Thanks for this additionQ
I keep learning! Nice! Thank you!
It just depends on how you use the tricycle; If you want a friendly character, also easy in [s]city[/s] village traffic, then the little ones underneath.
If you go for sprinting on the country road, then drop the 68's...
I wanted a bit of both on the AWO, so I took the original 22mm off and threw a 26mm Jikov (Jawa) on it..
Does the poor thing have a little more breath?
Be sure to book something at the bottom...
That Awo is great! But chasing my bullshit on the highway? A little fat biker is faster!