of diaphragms and jet needles

[montmil]

The following successful tweaks on my 1981 R65 evolved from at least three different yet associated threads posted here on Disorganized. Bear with me as there really is a point to this post... eventually.

I recently overhauled the Bing CV carbs. Motobins and ChiTown BMW supplied all the tidbits while the R65 family and internet sources provided tech and morale support. No work problems.

The bike lit off with the first push of the starter button. Whoa! A DIY manometer got the carbs synch'ed and away we went.

But... there seemed to be a soft spot in the throttle up during rides. I had to maintain a half-lever of enrichener for 5-7 miles just to keep the engine smooth. The issue was not present before the carb job.

OK. To the point...

A prior post discussed the different diaphragms sold for the Bings. Some appeared to be a heavier material. I read all responses and stashed the info somewhere in my limited gray matter.

Another post discussed needles and needle jets; their position in "the clip" and other chatter. Stored it.

Enter English Lou with his six blazing two-guns. Stop the train! He's having acceleration issues with his bike after replacing the carb's diaphragms. Hum. Sounds like my issue, too. Lou cured his evil spirits by simply raising the jet needle one notch; the fourth from the top, Lou said.

I pondered all these previous posts and this morning, after thinking through my carb issues, went to the garage and yanked the carbs. Raised the jet needle to the 4th notch from the top and went for a ride. Urethra! So s-m-o-o-t-h  [smiley=clap.gif]

After comparing old to new, I'm pretty sure that my new diaphragms are of a slightly heavier weight material than the ones I replaced. If so, the vacuum required to raise the slide and the jet needle would be greater than with the old units. This difference might account for the lean running at partial throttle just off the idle jet where I had to maintain a half-lever of choke.

 

[Bob_Roller]

I'm wondering if your fuel mileage will decrease any noticeable amount with the needles raised one notch ?

[montmil]

I'm wondering if your fuel mileage will decrease any noticeable amount with the needles raised one notch ?

I'd considered this as a likely result. It's a trade off I'll accept. At any rate, I've never checked the fuel mileage on any of the bikes I've owned so have nothing to compare.  

Perhaps the new diaphragms will soften, over time and miles, permitting the needles to be dropped back a notch?

Monte

[nhmaf]

Seems like a reasonable deduction to me, Mr. Holmes!   Do chart your fuel mileage over the next tank of gas or two, as I suspect more of us will be replacing rubber bits in the carbs in the coming year or so.

The EPA has sponsored a bill that is still in the feedback collection state on capital hill to raise the ethanol percentage in our fuel from the present maximum of 10% by volume to 15% by volume.   This will likely increase the rate of deterioration of non-alcohol rated rubber fuel system parts.  The bill aims to change the amount to 15% starting mid-summer 2009.

[Bob_Roller]

Has anyone contacted Motobins about this issue with their non-OEM diaphragms ?

[montmil]

Seems like a reasonable deduction to me, Mr. Holmes!   Do chart your fuel mileage over the next tank of gas or two, as I suspect more of us will be replacing rubber bits in the carbs in the coming year or so.

I'll see what I can do, Mike. I'm kinda wondering if I may have improved my fuel mileage as I'm no longer running around town with the choke half-on.


Monte

[Barry]

Interesting theory.  

I've always wondered about balancing CV carbs. You can make sure the butterflies open at exactly the same time but how do you know that translates to the pistons/needles rising by exactly equal amounts ?

I have found by experiment that my bike runs best with the carbs on two different needle positions.  Stock 2nd slot both sides gives me a flat spot at 3000 RPM which gets better with a hot engine but never completely goes away.

3rd  slot both sides makes the left  side too rich so I run the left on 2 and right on 3. It runs well with no flat spot, is very smooth and I get 60+ MPG.

I thought that there must be an underlying cause for this and had put it down to the silencers not being a match pair. Maybe it's the diaphragms that are not a matched pair although there could be other causes like one of the diaphragms not sealing correctly.

Thanks Monte

I would never have owned up to this without your post.

[Lucky_Lou]

Glad my 2 blazing 6 shooter train stopping repositioning worked for you too, ive now developed a problem with the revs not shutting down with ther throttle off. They seem to be sticking at about 3000rpm.
My brother has a 81 r65 and has just fitted new diaphragms and has the same problem anyone got a clue/? i was going to start a new thread but ill tag the question on this one his carbs are the ones with the springs inside  mine are the flat top bings with no springs.
Lou

[montmil]

I'm not that familiar with the flat tops, but I believe you may be able to retrofit springs in your carbs. Any other flat top knowledge about? I do know your brother's carbs should have the springs.

Also, suggest you two bro's check the throttle cable routing for any binding that might impact smooth operation and throttle closure. I had a too slack throttle cable that popped up and hung on the carb top's threaded adjuster and kept the revs up pretty high.

Monte

[bruce_launceston]

If you put a kit through your carbs, as I did, and pulled the butterfly shaft to replace the 'o' ring go back and check to make sure that the butterflys close the carb throat absolutely.
When I checked mine with a torch I found they weren't seating 100%. A slight adjustment and I was then able to balance both carbs AND get it to idle slow when hot without running out of adjustment on the throttle stop screws.

[montmil]

I'm wondering if your fuel mileage will decrease any noticeable amount with the needles raised one notch ?

...Do chart your fuel mileage over the next tank of gas or two.

Since you asked... A Friday afternoon ride outta town on state highways, then a superslab run to Texas Motor Speedway on Saturday, some in-town piddlin' over Sunday and a few Monday morning errands. Refilled to the bottom of the fuel filler pipe; same as previous fill up.

Drum roll, please. BaDaBing... 41 MPG.

Raising the needles most likely offset the need to drive about with the enrichener lever half-cocked. The adjustment made a great difference in overall s-m-o-o-t-h engine ops. That and a slight tweak of the throttle cables. Believe the mileage is right in there with most tuned R65s.

Still suspect stiffer diaphragms. Mine came from ChiTown BMW.

[smiley=beer.gif]Monte
 

[Bob_Roller]

Monte,

I assume that your fuel supply has 10% ethanol, 41 mpg average is in the average range, from what I've seen .

[montmil]

...I assume that your fuel supply has 10% ethanol, 41 mpg average is in the average range, from what I've seen.

In the Fort Worth/Dallas megopolis, we are now having to buy what the refiners refer to as a "summer blend" of gasoline. Lord only knows what's in it. Only difference I can see is that it costs more.  

[steve hawkins]

You could get 51 mpg (US) if you rode at a constant 56mph according to the book.

But who rides at a constant 56?

I would be happy with 41 for general hooning around

[montmil]

...I would be happy with 41 for general hooning around

My 1986 Cabriolet gets 28-29 on a truly good day-difficult to keep my foot outta it. My F150 Ford scores only 13 on the highway-Ugh. Wife's new Northstar-powered Cadillac Deville showed 27.2 on a 600+ mile highway run.   I'm really pleased to run around getting 41 on the R65.  [smiley=thumbup.gif]  And the 50cc Chinese Vespa-wannabe gets 80+ but is so s-l-o-w.

$2.48USD for a gallon of regular today.

Monte