Crankshaft Question

comnoz said:

Are there any examples of 180 motors with a single carb?

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I don't know?

But I know a considerable number of Japanese four-stroke vertical twin engines had/have 360 degree cranks, so maybe the 360 degree crank configuration isn't so bad after all?

The 360 degree crank has been my favorite.

Wow! a clash of the Titans...

Great discussion, very stimulating, caused me to do some searching, the only 180 twins I could find that breath through one straw are boxer twins, like the Saito 90ts two stroke. I also thought that the XS 650 was a 180 twin, it came out in a burst of Honda 180 CB 350/360 twins (twin cabs).

I did find this: kawasaki 250s and 305s have 180 degree crank angle which means that there is an uneven firing order (each cylinder fires every 720 degrees in a four stroke) meaning a single carb, though it is possible to get runnng, will never run well, as one cylinder gets a 540 degree puff and the other only 180 degrees.

I think this explains why a 180 twin would have trouble breathing through one carb.

RS

RoadScholar said:

Saito 90ts two stroke.

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?


I don't know about any Saito engine (a model plane engine?) but there wouldn't be any problem with a 180 flat twin two-stroke engine running off a single carb, as I'd think both cylinders would share a common crankcase? A two-stroke 180 parallel twin will also run happily with a single carb.

There's no problem with a four stroke 180 degree crank flat twin using a single carb either, as one cylinder fires every 360 degrees, the same as a 360 crank four-stroke parallel twin.

L.A.B. said:

RoadScholar said:

Saito 90ts two stroke.

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?


I don't know about any Saito engine (a model plane engine?) but there wouldn't be any problem with a 180 flat twin two-stroke engine running off a single carb, as I'd think both cylinders would share a common crankcase? A two-stoke 180 parallel twin will also run happily with a single carb.

There's no problem with a four stroke 180 degree crank flat twin using a single carb either, as one cylinder fires every 360 degrees, the same as a 360 crank four-stroke parallel twin.

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My point...

Great discussion!!!

RS

What about the Honda CA72/CA77? (the Honda Dream or Nightmare as we used to call them). They were single carbed and I believe a 180 crank. I had a CL77 (305 Scrambler), but I was only 18 at the time and hard as I tried I could not come up with a reason to split the cases, but I'm pretty certain it had a 180 degree crank. The CL77, however had dual carburetors.

P.S. - Motorcycle Classics has a great article on a CL77 in the latest issue.

Ron L said:

What about the Honda CA72/CA77? (the Honda Dream or Nightmare as we used to call them). They were single carbed and I believe a 180 crank.

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http://en.wikipedia.org/wiki/Honda_CB77

The motor of the CA72/77 featured a 360 degree crankshaft and single carb.

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http://popular.ebay.com/motorcycles/honda-305.htm

The models of the Honda Dream are CA72-CA77-CA78. The Honda Dream has a 360 degree crank as compared to the 180 crank on the Superhawk.

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Leaning by your discussions. I believe some engines use air reservoir to allow enough volume to satisfy one jug trying to pull more than its fair share. i now my 360 Combat liked a bigger single better than two smaller duals for top end.

Here's example of Suzuki 450cc 180 crank that liked a single a bit better than dual carbs. go figure.
http://nswroadandtrackbikes.com/forums/ ... 14088.html

The only compromise to one carb instead of two is in the manifolding required to get one carb split between two cylinders. What many people do not understand is that the air speed through the carb is the same through a single carb as it is with twin carbs on a non overlapping intake pulse engine like a two cylinder.
With twin carbs the airflow only happens half as often and it is this longer time period between pulses that makes twin carbs more difficult to make run cleanly at low speeds. You have to get the fuel moving again after it has had time to stop and settle back toward the bowl. With a single carb there is only half as much time for the fuel to settle.
On a non-overlapping intake pulse engine such as a Norton there is no steady airflow through the carb. Air velocity in the carb is only determined by the carb bore size, the valve size, cam characteristics, the piston speed and cylinder bore. Not by the number of carbs. Jim

Yep sir, plenty of examples of single carbs on multi cylinder engines, mowers, tractors, cycles and cars trucks. Studying up on this shows that to feed a single jug by a single carb throat, to get max hp out requires a bigger throat than if fed by a single. The old mechanical fuel injection system like Hilborn learned about this.
Seems like that Comstock fella has also followed this path, bigger single throat over two smaller separated ones.