Use 4th gear at WOT
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22's 1980 xs650 build thread
- Thread starter Twenty2
- Start date
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'd follow your plan. If it doesn't respond look then. Better to remove IMO.
Doug has a good point too. A true test of final jetting needs some load; 4th gear a long sloping straight-stretch
Doug has a good point too. A true test of final jetting needs some load; 4th gear a long sloping straight-stretch
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....
If your shifting to 5th at 3000 the engine hasn't started to work.
Stay in 4th and as mentioned a long slightly uphill slope and wind it out then hit the kill switch, (with the bike clutch pulled in), Brake to a stop then check the plugs
Stay in 4th and as mentioned a long slightly uphill slope and wind it out then hit the kill switch, (with the bike clutch pulled in), Brake to a stop then check the plugs
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 .....
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.
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 .....
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.
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 just got back from a good test with the 132.5 mains and the needle at slot 3. The stumble exists at WOT and 4,000 rpm but I believe it's better than when I had the 135 or 137.5 in. I think I orginally misdiagnosed a stumble for a flat spot and figured I was too lean on the main, also everything I read said I would at least need a 135.
So given I still have a minor stumble with the 132.5, my next move is to lean the needle clip 1 step to slot 2.
The bike otherwise pulls very strong through the whole rpm range in all gears, I know you guys say you need to get near redline to really test the main but that thing is moving in 4th gear and around 6000rpm.... I can't imagine getting it up to 7000rpm, but maybe I just haven't gained the confidence in a 40+ yr old bike that I took apart and put back together as my first bike project.
Thanks for all the help and for helping me really understand the ins and outs of this carb. I think I'm almost there and with the leaner needle I hope it's bang on.
Somebody's sig "Never ride faster than your guardian angel can fly"
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.
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.
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 don't think the profile or taper on the Canadian needle differs much (if any) from the U.S. spec needle, it's the shorter length that makes the difference. 2mm is a big change in needle height (5IX11 in it's center slot).
I think you're right; you've got the carbs as good as it gets. I didn't want to muddy the water before, but how you were getting the stumble - shifting to 5th, then snapping WOT from 3K - is, um, too extreme.
Good job!
Edited to include "snapping"
Good job!
Edited to include "snapping"
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Yes, you'd be going pretty fast by then, lol. I usually do my midrange to main transition testing in 2nd or 3rd gear. From about 3K, I roll the throttle open fully and run it up to about 5 or 5.5K, watching for any stumbling or break-up. These CV carbs are rather forgiving and will mask over minor jetting glitches unless you push them hard. So for jet testing, you have to do that. You won't normally drive the bike like that but have to for testing.
I do that 3-5.5k once a ride just to hear the pipes.
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.
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.
Yeah I'll take a look today.
Also, yesterday my turn signals started turning off on their own, which made me think I have a loose connection but I started reading and now I'm questioning, does the 80SG actually have a self canceling feature that I had never noticed before or all of a sudden started to periodically work yesterday? Mind you it was not consistent at all and often turned the signal off before I turned hence why I thought it was a loose connection. I'm kind of puzzled on this one because I've been turning them on and off manually since I got the bike about 800 miles ago.
Yea, I never trusted those things. But, we've all seen motorcyclists riding along with the signal flashing away
In addition to the "cancel unit" there is a "reed switch" in the speedo that supposed to sense distance traveled (W/G wire).
In addition to the "cancel unit" there is a "reed switch" in the speedo that supposed to sense distance traveled (W/G wire).
