Use 4th gear at WOT
You had to put that thought in my head haha, is it possible to take the needle jet out without taking the carbs off?The only fly in that ointment is if a previous owner ordered a jet kit and put a US needle jet in there. That'll cause issues.
I usually use 4th and 5th. My usually strategy is shift to 4th and immediately crank the throttle wide open.... it pulls great from wherever the rpms are when I shift it, let's call it 3000rpm.... pulls great until it gets to around 4000 then stumbles 2, 3 maybe 4 times then begins to pull hard again up to say 6000, I've never gotten close to redline....Use 4th gear at WOT
The bike was very stock when I bought it aside from aftermarket mufflers and the plug in the air screw had been removed so maybe some jets had been changed but it came with 132.5 mains and 135 air jets (at least that's what I wrote down when I cleaned the carbs last summer, I'll double check the air jets next time I take the carbs off). The needles were set at slot #3.I'll just add a few things about CV carbs in general, and your Canadian BS34's in particular, maybe it'll help. So yes, first of all, on a CV carb full throttle doesn't necessarily equate to full slide lift. The throttle cable isn't directly connected to the slide and also, CV carbs work on engine demand. The slide only lifts as much as the engine can use or demands. This fact explains why it's easy to over-jet CV carbs and still have them run fairly well. The slide isn't lifting all the way so that too large main jet isn't flowing at its max.
Now let's talk about your Canadian BS34's. The fixed U.S. spec needle, the 5HX12, measures 50mm long from it's single clip slot to the tip. Your Canadian adjustable 5IX11 measures 50mm from it's top clip slot to the tip. Mikuni clip slots change the needle height by 1mm so set in the middle #3 slot, your 5IX11 would be the equivalent of 2 steps richer than the fixed 5HX12. That's a pretty big change in a needle setting and may explain your stumbling. You may need to lean it, set the clip all the way at the top.
I've never run across any jet specs for the Canadian BS34's, like from a Canadian manual or something. The only other spec listing I've ever seen besides the U.S. model one came from a Japanese home market manual, and it's not really a spec listing, just a parts list. I assume these are the "world" specs, what other markets around the world and outside of the U.S. got .....
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They list the main as a 130 but it seems most Canadian carb owners report finding a 132.5. They also list a 130 air jet. That would be 2 steps smaller than the 135 we got in the U.S. There is no needle clip setting mentioned and while the middle #3 slot is often the norm, that's not always true. For example, the '75 and older BS38's came with their needles set in the #4 slot stock.
So maybe you can help fill in some blanks here? Like, where did you find your needles set at and what size air jets do you have.
Yeah this is all definitely true for my bike, the canadian needle must be quite a bit richer, at least in my case. The step leaner on the needle to slot 2 is definitely better, almost perfect, I can sometimes feel a very short minor stumble but I'm inclined to say that this is as good as it'll get. I could maybe try a washer shim to go slightly leaner but honestly if I'm not looking for the stumble I'm guessing I wouldn't even notice it. I would only look to add the shim washer if there is any potential for damage? Otherwise I'm going to call the carb good to go and just ride it the rest of the season, it's spinning great and wayyyy better than when I bought it so I'm pretty happy. Thanks again for all the carb help everyone!I consider 4000 to 4500 RPMs the upper part of the midrange, right where you're transitioning into main jet territory. Break-up there under heavy or full throttle usually means your larger mains are bleeding over into that area and making it too rich. Yes, the usual "fix" is to lean the needles a step.
Being in the States, I've never dealt with jetting any Canadian spec BS34's. I know the midrange is richer because of that 5IX11 needle and the Canadian needle jet (336-Y-0). Let's talk about that needle jet for a moment. In the States we got a plain Y-0. This designates the size. Since the Canadian jet has the same Y-0 designation, I'm pretty sure the metering orifice is the same on both jets. The difference between the two is the number of small air bleed holes running down the sides. The U.S. spec Y-0 has two rows of 3 and two rows of 4 while the Canadian 336-Y-0 has two rows of 4 and two rows of 5. So, since it's letting more air in, it would seem the Canadian jet is actually a little leaner than the U.S. one. But, with the Canadian needle being 2mm shorter when set in the middle #3 slot, which makes it much richer, the overall effect is a richer midrange circuit.
Richer midrange circuits usually get paired with smaller mains. That could explain why you're having to go so small. The one up and two up from stock (135, 137.5) that the U.S. spec bikes like may not work well on yours.
This is exactly it! Mind you I was thinking today which sound do I prefer, from 3 to 5.5k or rolling off the throttle from 5.5 down to 3k, the commandos sound great when you roll off full throttle.I do that 3-5.5k once a ride just to hear the pipes.
Yeah I'll take a look today.They look very good, very clean, maybe too clean? What you need to do is look down inside the plug, at the porcelain. You want to see a dark ring of color at the bottom of it, maybe coming up about 1/3 of the way at most.
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