ANOTHER jetting thread. I know what I'm talking about now... I think...

21mm with the gasket is fine. And you measured these just when the float begins to touch the float needle, but not pushing down on it, correct?
The 145 is the main. (which is what I use because I am at sea level). Absolutely, positively no 2 bikes are the same.
The main has nothing to do with idle. The pilot jet is under the rubber plug, which controls idle to 1/4 throttle.
Don't worry about the air jet right now.
 
When I got my bike it was jetted with 145 main, 50 Pilot. It had short pipes with baffles in them and pods. It seemed to run find but had really bad vibrations above 60MPH and popped on decel. I'm blaming the bad chain for some of the vibes.

I've changed the carbs from BS35 to BS38, longer pipes, new chain, 18/30 sprockets, and getting new pods without the ridge in them.

With the stock jets in the 38 it would not run above idle. I purchased the 145/50 and the next size down for testing. Soon as I get my charging system fixed, I'll be working on this too.

So I'm following this thread close. I also have the carb PDF to read over and over until it gets into my head.
 
Guys, you need to stop trying to apply mechanical carb throttle-and-range charts to BS-series vacuum carbs. You can whack the BS34 or BS38 throttle plates wide open at low rpm, but the slides won't open to match till rpm's are well north of 4K. The importance of getting the pilot circuit right can't be overstated.
 
Yep, floats were just resting. I'm doing compression test now, barley under 150psi in each. Can someone explain leakdown test? I was doing something that I think was that but I don't know for sure. I've already proved I don't know what I'm doing. I can only do so many things wrong until people give up. Haha.

Also, for plug chops, should I be in 5th? Or is it just dependent on rpm?

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Yes, good compression. A leak down test is used with a gauge that pressurizes the bore to 100 psi or so and you see if it leaks.
When I test my plugs, I'm in 5th gear, wide freaking open with the throttle pegged and then pull in the clutch and hit the kill switch.
 
Jawknee21, Yes, Changing the pilots changes the mix, so you need to adjust the mix screws.
Phill, The bike won't run ell if the battery gets low, so fix the charging system or it may never run right.
Leo
 
Got my charging system fixed. It was running pretty good, then my left side starting popping and not running right. Pulled the plugs, left side is black, right side looks good. Looks like I'll be doing some carb tuning after all. Off to read the carb guide again.

6534275651_94b1819f8d_b.jpg
 
Phill, what year are your BS38 carbs? Depending on the year a 145 main is way huge. A 50 pilot can also be a way big.
The 76-77 carb set had a 122.5 main and a 25 pilot. The 78-79 set was 135/27.5. The 74-75 set had about the biggest pilots. with small mains, 127.5/45 the 70-73 was 130/42.5.
So you can see that two steps up on the mains and one step up on the pilots vary quite a bit from year to year.
Leo
 
Read the carb guide, you need it, lol. You don't have a clue what you're doing. You're just taking shots in the dark here. You "think" you have '79 carbs? You can't jet them properly until you KNOW which ones they are.

A note on the pilots in these 650 carbs. If you just glance at the sizes, you might get the impression that some years run much richer ones (in the 40s) compared to other years (in the 20s). Actually, the overall fuel flow through the pilot circuit isn't much different between the two. Pilots sized in the 40s are the BS30/96 type. They flow the already made gas/air mix. Pilots sized in the 20s are the VM22/210 style and flow straight fuel. The air is added after the jet meters the fuel. So, the overall flow is about the same in the end.
 
So i got my jets today and i put them in, 137.5 and 45. I went back to stock with the air jet too, 135. I tried to kick it and at least get it to idle and it runs like crap. i might have to put baffles back in. im gonna mess with the idle air screws tomorrow. Dead cylinder method. haha. but i gotta get it to idle first dont i? I can get it to idle with the choke out and pretty close to all the way in on the idle speed. open pipes dont seem to be the right choice...
 
A running stock bike is the best place to start with any change ups, stock being the key word.
On my bike I had to do a top end/carb rebuild and some electrical repair before it would run at all, then once running with the 2 into 1 exhaust there were flat spots and poor throttle response. Picked up a set of stock exhaust and it was a totally different machine. At that point I finally had the platform for proper change....if something didn't work out I knew what I could go back too.
You're getting there.
 
You've made no mention of what condition your mix screws are in. They and their components need to be in good shape and assembled in the correct order or they will not meter or adjust up correctly. The o-ring needs to be good and the assembly sequence needs to be correct .....

MixScrew80-on.jpg


After you verify that the screws are good, I would set them to 3 turns out and not worry about the dead cylinder method at the moment. The bike should start and idle with that setting. Your jetting should be pretty close now. Maybe you'll need slightly bigger on the mains for the pipes but that shouldn't be affecting your idle and low speed.

Back to the dead cylinder method. I don't feel it works all that well with the BS34s. They're too E.P.A. stifled. I set BS34 mix screws by engine response using throttle blips. I know they like about 3 turns out minimum so I start there. I then turn them in 1/4 turn and blip the throttle. I'm watching for popping and idle speed hanging (slow to return). I keep turning the screws in until I get this (1/4 turn at a time). This usually happens at not much below 3 turns on the 34s and indicates you're too lean. I open the screws back up from that point 1/4 turn at a time until the popping and hanging idle speed goes away. If it takes up near 4 turns or more for this to happen, I'll try a larger pilot or smaller air jet. Do both carbs at the same time, in unison, keeping the screw settings equal to each other. You can't do just one at a time this way.
 
I bought those screws new but mine looked ok. I guess there's no point of buying them and not using them. I'll put them in and try again. Thanks for the help. So no dead cylinder? And can I go down on air jets instead of going up on pilots to get similar results?

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As 5twins states, that little O-ring, if missing or in poor condition, will make those carbs run like complete shit. Most of the time it is stuck down in the mix screw port, all beat up and nasty.
 
I pulled them both out and they didn't look bad. Going to take the carbs off and do those screws right now...

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You guys are geniuses! I put the new screws in and went down on the air jets and 2 kicks and it actually idles now. haha. Gonna go take it out and see how it is. It does seem like it does hang a little, just above idle. i did a 1/4 each way on both carbs (in/out) and it didnt seem to get better. just worse.

Another question. On the idle air screws, the position of where the screws stop arent the same on both carbs. is this normal? my left stops at 3 and 9 o clock. the right stops at 12 and 6. thanks for the help guys. I really appreciate it...
 
Good.
If it is still hanging, then turn the problem cylinder screw out, counter-clockwise, about a 1/4 turn, let it idle for a a bit, then crack the throttle again. Turning them in, clockwise, makes it leaner. Turning out, counter-clockwise richens the mixture.
Sometimes they will not be even if you are lining them up by the head slot. Just go off of the fully seated position, then backing out evenly.
But as 5twins said, going past 4 turns out is not good. The spring stops doing it's job and the mix screw will back out on it's own. Anything above 4 turns out is in need of a larger pilot.
 

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