Bing Fine Tuning / Idle to Mid-range Transition

[Mike V]

Trying to get back into the swing of things after total knee replacement surgery.  Better than ever now, but a story for another topic thread.

I've been struggling with the transition from idle to mid-range ever since the 81 R65 restoration and had to put it on hold until now.  Up till now I've tried almost everything in regards to adjustments with stock jetting and fitment.
 
Here's the existing info and fitment:
Carbs: 64/32/325 & 326
Slide: 906-1
Main Jet: 145
Needle Jet: 2.64 (Bing Manual calls for 2.66)
Jet Needle: 241
Atomizer: 591
Idle Jet: 40
Clip Position: 3

Let me explain what the condition is.  Idle circuit and full-throttle circuit is great.  Problem is that pesky transition from idle into the mid-range.  It's a lean condition and will cough, and sputter just enough to be a nuisance and danger in traffic.  Bike runs fantastic once beyond the mid-range. The bike is completely stock with fully renewed top end job fitted with unleaded Welltite valve seats and Swiss Intervalve valves via the Beemershop.  Stock Electronic Ignition.  Intake collars are new and well clamped.  The pulse air system has been removed and all vacuum fittings well blocked.  But, I'm thinking the new SS Keihan exhaust headers and mufflers may have altered the volumetric efficiency in contrast to the stock exhaust system.

I noticed the ride to higher elevation +3200 feet smoothed the bike out and the acceleration response was greatly improved at higher elevation.  Which leads me to believe it's a lean condition.  Plugs look great, valves and timing are right on.  Electrics are all in perfect order.

My first exercise will be to remove the carbs and check for any debris in the jets and small orifices. I noticed some very fine red tank liner material in the bottom of the bowls from my numerous tank flushings.  I've installed a paper in-line fuel filter instead of the small sintered filter.  I experimented with a larger main jet (150) only because I had one on hand. It improved the transition a smidgen but basically made the bike run richer throughout it's entire range.  I've tried setting the idle jet to it's richest setting hoping for some residual fuel to roll into the mid-range...wrong.  And I know another needle position will be too severe an adjustment.

So...I'm going to try some 2.66 and 2.68 needle jets since it seems like the stock 2.64 is even smaller than the Bing Manual prescribes.  If this doesn't work, I'm totally out of ideas!  Have any of you encountered this problem with a result of aftermarket exhaust and experimenting with needle jets?  Think the larger needle jets will solve the problem?  Any ideas?  Help!

[Semper Gumby]

What you need it a slide with a richer cutway.  Not a problem on AMALs but Bings I just dont know.  By richer I mean that there is more slide showing on the up wind side of the slide so that less air gets in for the same amount of fuel being metered.  Another way to get around this is to have a needle with a different taper.  But how this would be accomplished on the BING is unknown to me.  What you would need is a chart of needle tapers that show amount of fuel being metered as the throttle slide is lifted.  You would pick one that meters more fuel where you want it. Unfortunately this would probably be a compromise as you would also probably get more fuel where you didn't want it in another part of the range.

Sorry not too much help here.  

hey mike put that 2.66 needle jet back in.  That will meter more fuel as well as it is a larger diameter.

[Mike V]

hey mike put that 2.66 needle jet back in.That will meter more fuel as well as it is a larger diameter.  

Bill,
I'm thinking this will do the trick.  I have no idea how the 2.64 got there.  I'll try both the 2.66 and 2.68.  Curious what kind of impact 0.02 of additional jet opening will have on the responsiveness and acceleration.

-Mike V.

[nhmaf]

I'm thinking the 266 may do the trick too.   And/or you might just try tweaking the air mixture screw just 1 "blade width" clockwise to make it slightly richer overall - might not be too much to make the idle any less smooth.    Also, make absolutely sure that you've got the throttle cables on either side as close to perfectly synchronized as possible with equal amount of slack - I've noticed that 1/16" off can make the off idle transition a bit of a lurch as one cylinder start to pull before the other.

BMw definitely experimented alot with the jets/needle sizes in the 80-84 range as they tried to work out meeting new emissions requirements, etc.  Some of the experiments were less successful than others and are harder to tune in.

[Mike V]

maf,

I've tickled the idle mixture screws with almost every combination possible.  I had them enrichened to the point of stumble then back clockwise about a 1/16 or a blade width.  But it had no real affect on the transition point.  Carbs are balanced.  It just feels and sounds like it's starving for fuel to me.  I have to guess the Keihan exhaust backpressure is just different enough to upset the stock fuel/air mixture settings.  I'm curious if any of you out there with the same year, model and carbs as mine have the 2.64's or 2.66's as stock jetting.  I also have a pair of 2.68's to experiment with also.  I'll definately report back after I get the carbs apart and the new jets installed.

[Barry]

Mike

The transition problem you have is that just off idle which might suggest partially blocked idle bypass ports.

or I think more likely

Is it somewhere around 2000 - 3000 rpm which is the point that the tapered part of the needle starts to rise out of the needle jet. If this is where you are getting a lean mixture then the needle is not rising out soon enough at least with 2.64 jets.

I have heard of 2.64 needle jets being used but the needles had to be pushed up to position 4. Might be worth a try before changing to 2.66 jets

[montmil]

Lemme chime in, too.

My 1981 did exactly the same thing after total Binger cleaning, rebuilds with new, stock spec jets, o-rings, needles, gaskets... everything, and a lengthy session with balancing. All was most wonderflous except the stumble issue was making me crazy until...

...I moved the needle clip one notch away from spec. I'm now trying to remember what position cured it but I think, think, I'm in the top notch one up from the manual's specification. I'm afraid to lift the tops as the carbs are perfect.

Don't know why it needed that needle alteration but that's the case with my 1981. The experiment is easy and no cost but your small amount of time.

Monte

PS: Wasn't rehab fun?  

[Mike V]

Monte-Barry,

The stumble problem seems to be too great for the adjustment of the idle jet, I've tried everything with the result only affecting the idle and not improving the transition.  It's possible there could be a blockage in one or more of the ports from the tank debris.  That's why I'm going to remove the carbs and give them another good prodding with wire strands and compressed air.  I thought the movement of another needle position would be too great.  That is until your post Monte.  Very interesting stuff.  I may first try the larger needle jets (2.68) at the #3 position and if that doesn't work I'll try the last needle notch (#4) with the original jets.  Monte, do you have stock exhaust?

Monte your comment about rehab leads me to believe that's the voice of experience?  No pain...no gain!  I still have a ways to go.

Thanks for the help guys, all good info and help.

-Mike V.

[montmil]

... Monte, do you have stock exhaust? -Mike V.

Had OEM R65LS muffs on the bike when I did the Bing adventure. Now running some Dunstall-pattern EPCO(USA) stainless steel mufflers. No change in carb tuning needed. Sounds pretty throaty.

Monte

[donbmw]

I had a similar problem on mine after clean carb with spray can cleaner. I did notice the turning the Idle screw had no affect. Removed the carbs and soaked in carb cleaner and then blew through all the passage ways and everything work fine after.

Don

[Mike V]

Don,

That's the part that is troubling me, I have completely gone through the carbs and installed a rebuild kit during the restoration.  I only have about 1k miles since the restoration.  A strong possibility exists that some of the red lead primer from the tank after I flushed it has found its way into the carbs since I've noticed very very fine residue in the bowls.  This material got past my small bullet style in-line sintered fuel filters.  I've since replaced them with the paper element filters.  I will first re-clean the carbs with carb cleaner, wire strands and compressed air, then try some experimentation mentioned in previous posts.

Interesting clip (portion) from Bum on the Airhead LIST regarding this subject back on 11/27/09.  Thought I would include it in this thread...

<snip>
"Each needle notch is roughly the equivalent of three steps (2.64;
2.66; 2.68....) in the needle jet.  Thus, a needle notch is a
relatively coarse adjustment.  Needles are made in both different
lengths and tapers to match the carburetor and engine requirements;
and I absolutely do NOT recommend changing from the stock needle to
any other needle number; doing so would open a Pandora's box of
problems.  Changing the stock clip position or needle jet, is not in
that category........

The Bing CV carburetor needle and needle jet operate primarily in the
mid-range of throttle position, that is, roughly from 1/4th to 3/4
throttle, ...with some effect lower and higher.  The needle and needle
jet have very little effect at full throttle; and only a small effect
below 1/8th throttle."

I'll report back after some work develops in the shop.  Thanks again for the input.

-Mike V.

[Red_Hen]

Mike,

Your problem sounds like mine.  According to Ron, from Judson Motors, there was a tiny air hole, behind the throttle slider that was blocked  I believe there are (2) holes on that sit on the bottom of the carb interior.

After soaking it, boiling it and stomping up & down, Ron bought a small ultrasonic device from Harbor Freight and that did the trick.  Prior to that, he could not get the right carb to idle properly.

From what I recall, your bike sat dormant for many years.  Moisture, ethanol, corrosion - these are the gremlins that can block these tiny, tiny passageways.

Sounds like your on the right track - also, have you called the guys over at Bing?  My experience over the phone with them has been positive.

Let us know how you solve the problem.

[Mike V]

Ken,

You and some others may be right. This could be nothing more than a blockage problem and not jetting.  I pulled the right side carb apart this morning and besides the bottom of the bowl showing way too much sediment the jets were pretty messy with crap.  Especially the needle jet and jet stock.  I even found some bits in the idle jet which was tough to dislodge with the finest of copper strand. I have no idea how all this garbage got into the system, I had just rebuilt these carbs not too long ago.  Even the needle had build-up on it that I could scrape with a thumb-nail. Only thing I can figure out is a lot of debris got past the small bullet sintered fuel filter.  I've since replaced that with a fabric filter for the time being. I'm getting a new rebuild kit (o-rings) and will reassemble. I'm anticipating big improvements from just a simple cleaning...again.

-Mike V.

[Red_Hen]

I'd asked Matthew Parkhouse (Keep 'em Flying) about the blockage and he suggested using steel fishing leader to free the blockage.  I'd passed that suggestion along to Ron at Judson motors but he felt the Ultrasonic would be less invasive and not do any damage to the small holes.  In the end, the ultrasonic worked.
If I were doing what you're about to do (buy a new carb kit from Bing) I'd definitely buy or borrow an ultrasonic from someone you know or Harbor Freight.

[donbmw]

I normaly would never use a wire to clean out jets or other passageways.  This would be a last option. I have only had to do this a couple of times. Most of the time carb cleaner that you let soak in will clean every where.