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Author Topic: slow acceleration to 1/4 throttle.......then WOW!!!  (Read 1965 times)

tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #15 on: August 02, 2013, 12:39:24 PM »
Not really UNDERSTANDING ALL THE CAPS, but I am pretty sure its not an o-ring. its about a 1/4 inch thick, plastic and sits under the notches on the slide needle inside the slide. I am not making this up, there is a plastic ring (plastic not rubber like an o-ring) under the notches on the slide needle that seats inside the slide.  There is no disrespect meant in this post, just trying to clarify. I am talking about the inside of the slide, not the screw on the outside of the carb.

          Yes. Now we're on the same page.

           That's what I asked you in my original post & I quote from it now (go back & read it):

                  "Did yours have a plastic collar permanently covering the needle height grooves"?

             I think where I got thrown off was you said it was at the "bottom of the needle". To me it's at the top of the needle as the carb is held in its normal position.

              OK. Anyway. Where are you now? What are you trying next?

               In thinking about it over night, I think we may both still be running lean in the mixture screw setting along (I think our Pilot jet & needle heights are damn close). I'm going to try at least another 1/2 turn rich next, maybe even a full turn. On my last ride I was less than 2 turns out from bottomed.

               Our glitches are both similar: You have a flat spot right off throttle & I have a slightly slow to return to idle problem. Both indicate lean.

               Can't do anything today - pouring rain.   
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tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #16 on: August 02, 2013, 12:51:47 PM »
Ooops.  Yep, wrong carb.  Glad I don't have one of those. Threw one from my old Suzuki in the trash.

       Yes, it's an old design pulled out of the closet & used for those couple years by RE to pass Fed Emissions before the UCE EFI was ready. It's not the greatest carb, but once you've had it apart a dozen times tuning for changes in exhaust & intake & understand it, it's a perfectly serviceable carb for just regular riding. Plus it has the advantage of being a forgiving CV type that's not so touchy with changes in temp, humidity. The magic diaphragm smooths things out. It suits me just fine the way I ride now plus I like things I can take apart whenever I feel like it.
2008 RE AVL Classic
1977 Shovelhead Hardtail Bobber

D the D

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #17 on: August 02, 2013, 02:29:37 PM »
 tooseevee
Just about every carb has it's lovers and haters.  Many HD owners think the CV is the bomb.  I'm just too wed to Mikuni.  I didn't care much for the Carter on my Sportster either! ;-)
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tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #18 on: August 02, 2013, 04:32:57 PM »
tooseevee
Just about every carb has it's lovers and haters.  Many HD owners think the CV is the bomb.  I'm just too wed to Mikuni.  I didn't care much for the Carter on my Sportster either! ;-)

           CVs on harleys can help cover up other small problems (especially with kick onlys) like slightly out of whack valve timing or ignition timing or mixture. They're more forgiving & they also don't fart as often when you hit a pocket of cold air. 'Course they're all fuel injected now & I don't care.

            I've had S&S Super Es on three kick only harleys I built since the mid-'70s & I love them. Others hate them (like you've said).

             
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tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #19 on: August 03, 2013, 03:31:53 PM »
    General carburetor question for the experts:

     If the "sweet spot" for the mixture screw on the Mikuni BS-29 with a stock (15) Pilot Jet is 2 1/2 turns out, what does it become when you change to a 17.5 Pilot to rejet for removing all exhaust restrictions?

      Should the sweet spot now be closer to 3 turns out or fewer than 2 1/2 turns out? Seems to me it should be fewer turns out, right?

       Here's what I have & I can't seem to work it out:

         Bike kickstarts perfect & idles perfect. Runs perfect out on the road & around town, never dies, never farts. Purrs like a kitten at 50 in 4th OR in 5th (only 766 miles, ain't gonna go no faster yet). I have jumped it to 55 & 60 a few times & it's fine. Solid as a rock.

         Here's the ONLY problem I have & I can't work it out:

            It's slower than it ought to be returning to a dead idle. There's a 3 or 4 second delay (say at a stop sign) when it hangs onto a high idle, THEN it drops to the normal idle. It's reeaally aggravating.

            This would indicate that I'm still lean, but I've been out to 3 1/2 turns on the mixture & in to only 1 turn out & it makes no difference. Still returns to idle too slowly.

            I have no intake leak & no binding cable. It returned to idle perfectly as it should (quickly) prior to the hot tube removal & pilot jet change (the silencer is also pretty much wide open). 

             What should I try next? Ideas?  20 Pilot maybe?
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DanB

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #20 on: August 03, 2013, 04:25:33 PM »
1/4 throttle responsiveness.

I've had the same issue. Drop the needle one notch richer. That plastic washer will spin and then you can push it anyway you want. It moves once you free it up. Also, our UK brothers have shaved about .7mm off the bottom of the slide allowing a richer condition which may solve the slow to return to idle condition. I'm running a 17.5 pilot, 120 main now , richest notch, about 1/2 turn on the mixture screw.
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tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #21 on: August 03, 2013, 05:50:56 PM »
1/4 throttle responsiveness.

I've had the same issue. Drop the needle one notch richer. That plastic washer will spin and then you can push it anyway you want. It moves once you free it up. Also, our UK brothers have shaved about .7mm off the bottom of the slide allowing a richer condition which may solve the slow to return to idle condition. I'm running a 17.5 pilot, 120 main now , richest notch, about 1/2 turn on the mixture screw.

           Hey, Dan

                     Thanks for the quick answer. When I hit Send on my post I was going to go for a ride, but then it started raining again so I've been watching a round table discussion on Obamacare for an hour & a half. It's a huge mess of a stew & all the chefs are lunatics. Now I can go pull my carb & do something useful.

                      Anyway. What you say above is just about what I wanted to hear because futzing with the mixture screw wasn't getting me anywhere & it was curdling my mind logicwise.

                      But don't you mean raise the needle a notch richer, not drop the needle a notch richer?

                       Just askin'.  Also, could you discuss a little how shaving the bottom of the slide richens the mixture? I can't see it in my head.   
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High On Octane

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #22 on: August 03, 2013, 07:49:33 PM »
  ...........But don't you mean raise the needle a notch richer, not drop the needle a notch richer?
Just askin'.  Also, could you discuss a little how shaving the bottom of the slide richens the mixture? I can't see it in my head.   

A bigger cut-away on the slide leans out the mixture.  Most times, a larger cut-away is needed when drastically increasing the main jet size.  Also, lowering the needle will lean the mixture.  You will want to raise the needle, probably to the highest position from what you're describing.

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DanB

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #23 on: August 03, 2013, 08:37:08 PM »
Hope the rain stopped. It's beautiful by me and I'm out the door soon to ride!

I'm not a slide expert by any means, but Scottie said it.  By shaving the bottom our our BS29 slide, we reduce the size of the cutout thereby richening things up. The combo between slide and needle really effect that 1/8 to 1/4 throttle response I believe.

I always get by terms mixed up on the needle notches. Scottie's explanation is what I meant to say, but he's done a much better job.  ;D
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tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #24 on: August 03, 2013, 11:39:26 PM »
Hope the rain stopped. It's beautiful by me and I'm out the door soon to ride!

I'm not a slide expert by any means, but Scottie said it.  By shaving the bottom our our BS29 slide, we reduce the size of the cutout thereby richening things up. The combo between slide and needle really effect that 1/8 to 1/4 throttle response I believe.

I always get by terms mixed up on the needle notches. Scottie's explanation is what I meant to say, but he's done a much better job.  ;D

            Answering both you & Scottie:

               Couldn't get back to you before this. The twin granddaughters (12yo) stopped by.

                I see what you're saying now about increasing the cutout area on the slide. Hope I don't have to go there. Or drilling out the two holes in the bottom.

                Here's what I did before the girls arrived:

                 I pulled the carb & raised the needle 1 shim (.002") or 1/2 a notch. I set the mixture at one full turn out. Started 1 kick & sat there at a perfect idle.

                  Went for a ride. Didn't feel right. Stopped & came out a 1/2 turn on the mixture. Felt happier. Ran well around town under all RPMs AND out on the road at 50 in 4th & 60 in 5th. It's running really, really well again & going between buildings is eargasmic.

                  Came home & the idle drops to dead low in less than 1/2 the time than before PLUS the engine now reacts to the mixture screw way better than it did before. I came out almost another 1/2 turn & the idle increased. I dropped it again with the idle speed screw & left it 'til tomorrow. I think I just need to concentrate tomorrow on finding that perfect mixture screw position & I will be home free.

                   If not I can throw another shim in in 10 minutes & see what that does.

                   Thanks guys. I've really enjoyed the process of learning this Mikuni (& the whole bike) which I've been doing since December 2010 when I bought this never-sold, not running, dry as a bone, no electrics, all bulbs blown, orphan '08 Classic. I knew nothing from nothing about this bike. And I couldn't have done it without Pete Snidal & whining to all you guys ad nauseum.   

                PS: I have no problem leaving that damn collar on the needle alone & using shims. I think there are 3 in there now. If I move (or remove) the collar now, I'm back to square one in finding my correct needle height using the grooves again, and shims. (For those reading this who don't know - this hard plastic  collar on the needle of the BS-29 covers the 2 lower height grooves on mine. As I have freed up my intake & exhaust I've raised the needle progressively using .002" shims under the plastic collar. My needle is 3 shims (at least) higher now than it would be with an e-clip in the bottom groove). This carb was created to give an engine just barely enough fuel to run on, hence AVL Lean Burn.

                 Those carbs (BSs) were on bikes (Soozookies for one) & other small tools back in the '80s. Whose idea was that solid collar on the needle? Was it a Federal emissions thing? It must have been because the mixture screws were also plugged or capped in those days.

           

                 
« Last Edit: August 04, 2013, 12:00:33 AM by tooseevee »
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DanB

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #25 on: August 04, 2013, 12:27:58 AM »
Excellent!  Sounds like your very close. I find can't leave mine alone   :o

Enjoy 2CV
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D the D

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #26 on: August 04, 2013, 12:31:11 AM »
EPA required manufacturers make their carbs "tamper proof" starting in the mid to late 1970s.  I think bikes came after cars and were probably a Cali requirement first.  All bad things are a Cali requirement first.  :(
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tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #27 on: August 04, 2013, 03:29:16 PM »
Excellent!  Sounds like your very close. I find can't leave mine alone   :o


           Just to close out my part of this thread:

                  I rode 12 miles this morning with both around town & out on the road miles.

                   It could not BE any better. Raising the needle that one shim did it plus I stopped twice & tweaked the mixture screw, then again when I pulled back in the driveway 12 miles hot. I could not be any happier with this bike now. At 50 in 4th or 5th & at 60 in 5th it purrs so I'm not going to worry about the main jet until over 1,000 miles. It's got 785 now & I'll very seldom be over 45 the way I ride now so I'm not too worried about running lean at "high speed".

         Maybe tires next? ;>)

 
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kfthompson

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #28 on: August 04, 2013, 11:51:38 PM »
How many turns out on the mixture screw? How many did you start @?

tooseevee

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Re: slow acceleration to 1/4 throttle.......then WOW!!!
« Reply #29 on: August 05, 2013, 02:12:01 AM »
How many turns out on the mixture screw? How many did you start @?

           I just went down & checked (just fer you  ;) ) & found it had settled in at just a bit more than one full turn out on the final tweaking (12 miles hot) in the driveway. It was at 1 1/2 turns out when I first left the driveway. The setting now seems reasonable with the larger pilot & the needle raised one shim higher than before.

           This doesn't mean yours will be the same. Depends on your needle height. 

           I need 250 more miles now & I can go ahead & work out my main jet size.
2008 RE AVL Classic
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