Want to kick my bike in the carbs

[retroLS1]

I do have mains from 137.5 up to 145 or 147 I believe. I was thinking of taking them down some, but I haven't done any wide open throttle runs to see how it goes on the top end yet so I didn't want to just guess.

I just read and downloaded your carb guide bible and will be re-reading it quite a few times. Tomorrow I will pop the 45 pilots in and see where that takes me. I would go back to stock jetting and adjust from there, but I don't have all those available to me unfortunately. I'll have to rig up one of the yard stick sync tools too to see how the synchronization is. Thanks for the help (and that guide)

 

[angus67]

its not the jets you have to match when u switch to Canadian needles, you have to get the Canadian emulsion tubes.
Maybe someone already asked but have you done dead cylinder method?

 

[retroLS1]

I have not. I just read about it in 5twins' carb guide so I might give it a shot. Sounds a bit tricky but I imagine it sounds worse than it really is.

 

[5twins]

Most of the time, you can tune the BS34s without the need for that Canadian needle and needle jet. I would suggest just changing mains and pilots for now. Usually that works but occasionally, a tough case comes along. Then you might need that Canadian stuff.

 

[angus67]

I put them in friends 80 . he wanted open pipes. now he wants it quiet. here we go again.

 

[retroLS1]

Well small update. Had the carbs off and swapped the 42.5 pilots for some 45's I had. I had turned the mix screws out to 3.75 before, but turned them back in to 3 since I put in the bigger jets. My mains are already larger than stock - they are 145's.

Got them back on the bike and rolled it out to start it up. Started up like normal (maybe couple more kicks than usual since the carbs had been off). It was still doing the same "hiccuping" as before, in the video. I didn't know if that was because of the lean condition, so I turned the mix screws out to 3.5 turns out. Took it out for a few mile spin and it went much much better than before. No hanging throttle/revs. Didn't have the same bogging/hesitation off idle as it did before and no popping/hesitation while riding. Seemed to accelerate quite well. I didn't get to go full wide open throttle but got to maybe 3/4 and it felt good.

Good start, for sure. I had an order I was placing with Mike's XS anyways so I put a pair of 47.5 pilots on there. I figure I could possibly put those in and turn in my mix screws back closer to 3 but we'll see. Either way definitely happy. Will keep putting it through its paces and see how it all works out. Thanks for the help everyone.

Edit: When I get my new exhaust I'll probably have to do a little fiddling too since it won't be just a short dump out to the street. They are Pandemonium Ya Mama pipes but I am thinking about cutting off the turned out tips in favor of straight ends so I can fit a baffle in there. Not sure I could with the turn out tips otherwise I would leave them.

 

[5twins]

There's something you have to realize about these CV carbs. They're very easy to over-jet on the mains because they work on engine demand. Even though you may whack the throttle wide open, the slide isn't going to necessarily lift all the way. It will only lift as much as the engine can use. Your mains can be too big and the bike may still seem to run halfway descent. That's because the slide isn't lifting all the way and those large mains aren't flowing at their full potential.

So, even if the 145s you have in there now seem to test out OK, the only way to be sure if they're right is to try the next size up or down for a comparison. Do the testing back to back so the feel of the one jet is still fresh in your mind. In other words, don't test one size tonight and the next tomorrow or a few days from now. Do it all in one tuning session.

 

[retroLS1]

I'll definitely do that. I didn't have much time tonight, and my particular setup here isn't really conducive to easy wrenching (condo complex) so next weekend I will probably bring my bike over to my parents' house and wrench in the driveway. I have a few smaller size mains - 142.5, and 140 I think. I also have one size larger, 147.5 - but I doubt I would need to go that far. I will try what you said - smaller and larger back to back, and see what kind of results I can get.

 

[retroLS1]

Didn't get to ride it to work today (40% chance of isolated storms... hate those forecasts) but I took it out tonight for a bit. Rode for about a half hour, about 12.5 miles.

Though I didn't think it was bogging when you first get on the throttle, I think it might be just a little bit now after getting some more miles on it. Not a lot, but a little noticeable. Mid range felt pretty good. I got a chance to get on it a few times at WOT or close to at least, in 3rd and 4th gears. Definitely was breaking up when you opened it up pretty good. Sounds like I will have to play around with the main jet?

I noticed when I got home that I had a little bit of an oil leak (smelled it first). I'll have to investigate that. I pulled the plugs to see how they look and it's hard to tell if they still look lean or not. I didn't have my phone on me to grab a pic but I will next time I am working on it.

 

[5twins]

Yes, break-up or stumbling under heavy throttle in the upper midrange is a sign that your mains are too big, or that the midrange needs leaning. Unfortunately with the BS34s, you can't adjust the midrange. However, 142.5 or 140 mains should be more than big enough and down-sizing to one of them will help eliminate that upper midrange break-up.

These CV carbs are very forgiving and will mask over minor jetting errors unless you push them hard. So yes, be sure to do some of your testing using large amounts of throttle, even full throttle. If you don't, you may not notice the jetting glitches.

 

[retroLS1]

Thanks for the advice. I know I have 142.5 mains and I believe 140's but I'll have to check. I'll pop the carbs off and swap them out and see how it goes.

As for the small flat spot off idle, without swapping to the Canadian needle and jets, would shimming the factory needle with a small washer help? I took one out when I had my carbs out last but I couldn't see how to shim it. The plastic washer that the needle had on it had some sort of small locating pin that made it sit correctly, so I couldn't put a washer under that. Also, what a PITA it is to get the spring and cover back on over the needle haha

 

[retroLS1]

So I put in the 142.5 mains tonight and took it for a spin. Was about to go wide open once or twice and it felt MUCH better. Did not break up, just pulled nicely. Do not know what RPM's as I don't have a tach. I am also now experiencing missing/stuttering/hesitating (whatever you want to call it) at low RPM's. I am doubting it's related to the mains since it's on the other end of the throttle spectrum but who knows. I did however turn my mix screws in 1/4 turn (I just remembered this as I type).

Tomorrow I have some parts coming from Mike's XS, including a pair of 47.5 pilots. I will try throwing them in and see how they are, and compare to the 45's in there right now. I thought I had 140 main's as well but I only have 132.5, 142.5, 145, and 147.5. It had 145's in it when it was breaking up at high RPM's, and the 142.5's right now. I will leave that as-is until I order more stuff and will pick up 140 mains and see how they fare in comparison.

Slowly but surely getting there. Feels good to ride around. I just had to keep it in a little higher rpm/lower gear tonight to keep it out of the hesitation zone.

 

[5twins]

You can shim the bs34 needles but only richer and not by too much or they'll bind in the slide. You would need to place the washer between the e-clip and that thick plastic spacer .....

 

[retroLS1]

Ah ok, gotcha. Thanks. Might try giving that a whirl this weekend. I am already dreading getting that retaining plate back in.

 

[retroLS1]

Ho boy. Here we go again. Just took it out for another ride. Back to square one in some aspects...

I have some parts on the way (speedometer, cable, pilot jets) and I wanted to give it a ride before I put anything in so I could see any changes. Got out of work early and it's a nice afternoon so it was perfect. Unfortunately UPS doesn't deliver til about 5:30, but anyways...

Last time I was out, the top end felt good but low end was missing/stuttering/whatever. Before going out this time, I backed the mix screws 1/2 turn out to see if I would have any change. I had also removed the outermost red filter layer on my UNI filters (dual layer filters) to give them a little more room since they were kind of crammed in there. I remembered the low RPM badness started after that at some point, I figured I'd try putting them back on.

Started it up and started riding. Felt a little "fat" in the low RPMs, and still doing the missing/bucking/whatever you wanna call it. So I started out on a good cruise and a little over 8 miles in is where my first issue arose - the RPM's ran away on me again when coasting up to a red light. Pulled over, let all traffic pass by, kicked it back up and it was ok.

Rode another 2 miles. Again, coasting up to a red light, clutch in... 1st or 2nd gear (same as before)... RPM's rise up on their own and hang til I kill the bike. Luckily I was next to a gas station so I rolled in and kicked it back up. Ran ok.

Just wanted to get home at this point and I was still about 5 miles away. Stayed on small backroads to avoid much traffic interaction in case it did it again. I was rolling up to a left turn and clutched in in 2nd gear I believe (might have down shifted to 1st, can't remember.... a car in front of me was turning left too so it was taking longer than if it was just me) and the RPM's took off on me again. This time instead of killing the bike I slipped the clutch a little bit and let it take me away instead of getting on the throttle.

I started to notice a little trend - it was always slowing down/coming to a stop, clutch in, in either 1st or 2nd gear... most likely 1st. What I did from that point on was roll up to a stop in say 3rd or 4th gear with the clutch in, and then just downshift into 1st once I stopped. Seemed to work ok.

The other issue was the bike does not seem to slow down all that much when you just let off the throttle when riding. Maybe it's just the nature of this bike, but all other bikes I have ridden you can practically come to a stop just by downshifting through the gears. I found myself having to hit the brakes a lot more as it was almost like I had cruise control on in 3rd and 4th gears sometimes when I would let off the throttle.

I am leaking oil pretty good from my left side engine cover. I noticed it before but didn't know it was that much but once I got back from my ride, I noticed it dripping from the left side cover. I'll have to pull it off and investigate. Could this all be somehow related? I'm at a bit of a loss with these runaway RPM's. Could it be something like the clutch not disengaging enough or something like that? I could have sworn at one light I was waiting at, the bike wanted to lurch forward a little bit (in 1st gear) but I couldn't tell if I was on a hill or anything...

 

[5twins]

I think you're experiencing a combination of the lean pilots and the advance unit doing it's thing. If you're lean in the idle circuit, that can cause the RPMs to hang or be slow returning to idle speed. Your advance unit slowly advances the timing starting about at 1500 RPMs. As the timing advances, so do the RPMs. More RPMs increases the advance more, which gives more RPMs, which advances the timing more, etc. Eventually you end up at full advance and it's associated higher RPMs, and it can happen without you touching the throttle. It's sort of a self-feeding problem. So, the lean pilots are causing the RPMs to hang and those higher RPMs are starting the advance on it's way.

What happens when you start the bike, let it idle, and blip the throttle? Do the RPMs hang or drop back down quickly to idle? They should drop back down quickly. If they don't, your pilots or mix screw settings are too lean. Until you get bigger pilots, about the only thing you could try to alleviate the problem would be to open the mix screws way up. Open the mix screws 1/4 turn at a time and test with throttle blips. Keep going until the revs drop quickly for you. You may not be able to fix it this way because the mix screws are for fine tuning and only control about 1/4 of the flow through the pilot circuit, but it's worth a try.

 

[retroLS1]

At idle, after blipping the throttle it returns back down pretty normally. What you described - the advance unit and rpm increase - sounds like what is happening. It doesn't just all of a sudden go full-bore, it gradually goes up - albeit in a short period of time - I can tell when it's happening in the course of a few seconds.

I have no idea at what RPM my idle is set at right now since I don't have a tach... I basically have to go by ear and feel. I did turn it up a smidge as I didn't know if it was going to stall on me with the skipping I was experiencing.

 

[5twins]

Well, that could be another thing adding to the problem. If your idle speed is set too high, it may be starting the advance into doing it's thing. Turn it down some and see if that helps. These are old bikes. They don't have electronic gizmos and fuel injection that will compensate for idle speeds at cold and hot engine temps. Set correctly, the engine will idle very low when cold, maybe barely at all, and idle at the spec (1200 RPM) once warmed up. If you set the idle speed so it idles at spec cold, it will idle too fast once warm.

 

[retroLS1]

This bike has more ups and downs than a heart beat on a monitor.

Big brown truck showed up with some goodies. It's been raining a little bit off and on, but I still wanted to get the work done. I wanted to ride the bike in to work tomorrow (first time) and after the ride earlier I was not feeling it. Got a mini speedometer, speedo cable, handlebar clamp, and 47.5 pilot jets. Speedometer install was painless and easy. I didn't wire up the illumination on it yet - I will do that tomorrow. Just wanted to get it hooked up.

Pulled the carbs again and swapped the new 47.5 pilot jets in. Left the mix screws the same. Turned the idle down 1 full turn to start. Got everything back together and waited for the rain to stop so I could take it for a spin.

Ran much better this time. Idle was not doing the missing/hesitation as far as I could tell. Idle was still a bit high (according to my ear) so I lowered it some more. You mentioned it's supposed to be on the verge of dying when the bike is cold, so I tried to get it pretty low when I first started it. Blipped the throttle, came right back down.

Went out for a short ride, only about 3 miles. Acceleration seemed fine - no noticeable new flat spots or weird hesitations. I also noticed that when letting off the gas while riding, the bike actually slowed down (like I mentioned all the other bikes I've ridden do). Felt good! Got on it pretty good once and still felt plenty strong. Can't wait til I get my new exhaust (Tuesday) and then when I figure out some baffles for it to get a little torque back hopefully.

After my ride earlier I kind of walked away with my tail between my legs since a lot of those stupid problems were happening. This one left me feeling good - pretty nice feeling. Thanks again for all the help 5twins - you're the man. I owe ya a beer or 5.

If the rain holds off, tomorrow will be a good test. My work isn't far, only about 8 miles or so each way but I plan on taking the "long way" home to stretch its legs.

 

[Nolan_B]

Keep me updated on how those new pilot jets work out. So far every problem you have described, my '77 (with cones instead of airbox) is going through. When I first bought it, it would cough and bog around 5000 rpm, went up on the main jet and it fixed this problem. After that, I was experiencing this carb backfire worse and worse, until last week when the bike stopped holding idle altogether. On two occasions, I was smashing down the highway and the bike hit a flat spot at high rpms and completely gave out until I decelerated.

Also, this out of control stuck rpms at 3000-4000 happens to me still. Was running it anyway, the problem seemed to come and go. I've done that advance test and everything seemed to be fine. Though it's quite dirty and greasy in there.