Jet Needle Story

[bostonmish]

I was addressing a leaky carb and used the occasion to check the jetting and other settings as well as the PO's relatively recent rebuild.

I discovered less than stellar previous work:

- Missalligned throttle plate
- Poorly peened throttle shaft screws
- Incorrectly set float
- Plugged overflow tube
- Incorrectly set Jet Needle

The carb itself was full of new components (O-rings, Jet Needle, throttle shaft, diaphragm, etc.), but the assembly was careless.

I wonder if this is the fate of EVERY PO out there - to be perpetually derided for the sins they left behind. Seems to be such a common occurance, ...but I digress into philosophy. Sorry.

The most important event that took place and one I want to share with others involves the Jet Needles in my carb.

The clip was set one notch too low (position 3, instead of 2). It just so happens that my motor is a dual plugged R90 which could be set leaner than stock on account of its more robust ignition. Instead, as purchased, it was set too rich.

The stock Jet Needle position for this motor is the 2nd notch. To go leaner, one would go up to notch number 1 (although that is a lot of leaning out all at once) or, preferably, would go more granular with smaller midrange jets (like from 2.68 to 2.66, etc.)

The PO, at the time of the carb rebuild went completely the other way. He went down by a notch, to position #3 which enrichens the mixture way beyond even the stock (single plug) settings. Why did he do this? I think it was mistake. I think he misread the manuals (he gave me copies, including the Tom CutterÔÇÖs dual plug opus) and intended to go leaner, but went the other way.

It seems that I have found at least one cause for the bike being such a P. I. G. pig on gas. Add to that the incorrect float height (too much gas in the bowl) and there you are.

But the story gets better. When putting the carb back together, I decided to take Robert FleischerÔÇÖs advice and actually measure the protruding needle, just for reference. Set on the second notch, its visible portion measured 40mm. Fine. I finished the carb (right side) and put it back on the bike. Buttoned everything up.

Now, the left side needed a needle adjustment. My assumption was that it was also still in #3 position. However, when I removed the slide and measured the needle, to my surprise I discovered it too was measuring 40mm.

One of several possibilities was on hand:

a. The PO set the left side Jet Needle on notch #2 and right side to #3 by mistake or
b. The needle was NOT seated correctly in one of the slides, causing one to sit higher or
c. Perhaps I made a mistake myself and set the left side to #3 and the right was still at #3 from the POÔÇÖs work.

It turned out to be (c.) !

Had I not gone the extra step and measured the Jet Needle height in the right carb, I would have reset the left side to notch #2 (the right would have remained at #3, although I would not have known it, thinking I had correctly set it at #2) and rode off to a future of never being able to properly tune the motor.

Hope this is not too boring for the casual browser. For all you Jet Needle changers out there, however, take note. ItÔÇÖs gotta be belt and suspenders with those needles!

--
Michael Stoic

 

[boxerkuh]

I hear you, I have been there... however, when I check the spark plugs I have been known to read them individual, rather than together. That way I can adjust it specifically. I have run different settings in the carbs on purpose. So the previous owner may have done that too.... I have changed the needle positions and changed jet sizes, but always remember, only ONE change at a time...

 

[Bill Burke]

Great catch on the misaligned throttle plate. You would've driven yourself crazy trying to figure out why you had no real ability to adjust and sync that carb with the other one.

 

[pmdave]

It's very easy to set the needles wrong, since you have to carefully feel each click as you rotate the needle 90 degrees. That's why measuring the protruding needle is a wise check on your work.

My gut feel is to avoid going too lean, even with dual plugs. I suspect a lean mixture would burn hotter, risking valve problems. I don't know this for sure, but I also suspect that a too-rich mixture burns cooler.

I also believe that setting the carbs differently is a bodge to cover a symptom of a problem. The two sides should burn about the same, and if a carb seems to be demanding a completely different needle or jet, I'd start tearing it down and looking for the real problem. (as you've been doing)

Yes, it usually takes some work to correct the average PO's errors--and sometimes your own errors. But as you gradually get things sorted out, the motor will work and sound sweet, and you can take some pride in figuring it all out.

pmdave

 

[bostonmish]

... My gut feel is to avoid going too lean, even with dual plugs. I suspect a lean mixture would burn hotter, risking valve problems. I don't know this for sure, but I also suspect that a too-rich mixture burns cooler.pmdave

Dave, Your gut is so right!

I went for a ride with my now leaner settings (notch #2, up from #3) and it was immediately apparent that the settings were too lean. surging as soon as the midrange jets come into play. this condition could be alleviated by activating the enricheners. In other words  too lean.

I have now changed the needles back to #3 (have yet to make a testrun), but now have to rework the theory.

First, the PO is absolved, at least on the Jet Needle settings, however, two things are bothering me (again, on the theoretical level):

1) Bing says that R90/6 carbs get their needles set in position #2, not #3
2) I happen to have the original needles (pre PO rebuild) and they clearly show the wear to be on the #2 notch

Another area of potential concern is the correct position of the enricheners and their components. Ive heard it mentioned that a reversed (or incorrectly assembled) set of enricheners will cause a lean condition. This could conceivably be the reason that pre-PO-rebuild, the needles were in #2 position Just a thought.

I am off to research the absolutely correct way to KNOW that the enricheners are assembled correctly and placed on the correct side

--
Michael Stoic


PS Does anyone have a set of 2.66 (or lower) needle jets that they would trade for an extra set of 2.68 that I have ?

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[pmdave]

Like yourself, I played around with the needles for a while on my R100s, trying to get good mix at all rev ranges. Then I bumped into the Bing man at a rally. I mentioned that with the needles in the standard positions I had lean surging at wide open. When I explained that I was pulling a sidecar, he nodded sagely, and suggested upping the pilot jets a step or two, and dropping the needles down to the original positions. It only took a few minutes to pop off the float bowls and swap the pilot jets.

On the trip home, the fix was obvious. Better (leaner) mixture throughout the mid range, but rich enough for WFO on the top end. To boot, my mileage was increased and the valves held clearance longer.

So, check your pilot jet sizes, then talk to the Bing man.

pmdave

 

[bostonmish]

>>> Then I bumped into the Bing man at a rally. I mentioned that with the needles in the standard positions I had lean surging at wide open. When I explained that I was pulling a sidecar, he nodded sagely, and suggested upping the pilot jets a step or two, and dropping the needles down to the original positions. It only took a few minutes to pop off the float bowls and swap the pilot jets.

Trying to understand the scope of changes: at the beginning of the rally were your Jet Needles already set one notch lower (position #3 instead of #2)? to get a richer midrange and you had stock pilots, say #45 and you had the stock Needle Jets, 2.68?

[ That, BTW is exactly what I now have in my R90 Rig ]

And then, to implement the Bing man suggestion did you only install larger Pilots (#50 or bigger)? at the rally or did you also drop the Jet Needles back to the factory position (I am assuming it would have been position #2, down from #3) ?

........Pilot...JN...NJ...HS

1. ...45...3...2.68...145
   
2. ...50...3...2.68...145
   
3. ...50...2...2.68...145

Effectively, the Bing man suggestion (which apparently worked) was to supply the extra fuel through the Pilot circuit ?

ItÔÇÖs an interesting reminder that there is an obvious circuit overlap and that the Pilot Jets are still online when the Jet Needles and Needle Jets are in control. ÔǪthis would account for the extra enrichment available from the (now larger) Pilot Jets at ?? to ?¥ throttle.

>>> So, check your pilot jet sizes, then talk to the Bing man.

I wish I could. I might bump into the Bing man while out getting milk , but itÔÇÖs not something I can count on.

I am going to do some more thinking out loud on this forum, in hope of getting feedback and fine tuning the logic.

Thank you again for sharing the great info!

--
Michael Stoic

 

[awshucks]

What is the proper way to 'peen' butterfly screws in throttle shaft, and more importantly, how does one then remove said screws if needed? Thanks!

 

[pmdave]

Michael,

I don't remember exactly the pilot jet size. It's only been about 30 years. As I recall, I had done a dyno run at a rally the week prior, and they determined that one carb had a needle one notch too high. So, they dropped both to the stock position.

Then at the next rally I installed the larger pilot jets.

The "Bing Man" is at Bing Agency International, Council Grove, KS.
technical questions: 620 767-7844 (8:30 - 4:30 central time), or bing@bingcarburetor.com.

orders only 800 309-2464. They have all the parts for Bings and Delortos. Tell them you're pulling a hack.

While we're on the subject, I had installed the alcohol-proof float bowl kits. Pricey, but ensures the floats don't absorb alcohol and sink--causing a change in mixture. I've also heard that BMW has "alcohol-proofed" the latest foam floats, but I haven't bought any foam floats for years so I can't vouch for them.

I also suggest replacing any old fuel line. Scuttlebutt is that the braided stuff tends to disintegrate on the inside after a few years. New braided/rubber fuel hose is cheap enough, but I'm now using snowmobile fuel line (urethane or something) from my local dirt bike shop.

On my 1980 R100, I've had a problem with the carbs stumbling just off idle. After a few rebuilds, I removed the butterflies and replaced the o-rings on the throttle shaft, then did some careful filing of the edges of the butterflies to get the least clearance in the bores. I "peened" the screws with vice grips once I had them centered. I still have the stumbling problem, but not quite as bad, so I'm living with it.

A fellow sidecarist snidely suggested that after 30 years of hard use, maybe it's time to buy new carbs. Ha!

pmdave

 

[bostonmish]

I don't remember exactly the pilot jet size. It's only been about 30 years. As I recall, I had done a dyno run at a rally the week prior, and they determined that one carb had a needle one notch too high. So, they dropped both to the stock position.

which made the fuel supply lean until

Then at the next rally I installed the larger pilot jets.

makes perfect sense.

I found this article, distributed by Butler & Smith which gives a pretty good explanation to why Pilot jets can cure a mid-throttle lean running condition. because the pilot jets dont just drop out after you exceed ?? throttle

Here is the link: http://www.omnilex.com/public/bmw78/cvcarb.pdf

I've also heard that BMW has "alcohol-proofed" the latest foam floats, but I haven't bought any foam floats for years so I can't vouch for them.

That would be very nice, since BMW is about 50% less expensive than Bing on most items I checked.

I am off to get myself a selection of jets. I will try to examine two scenarios:

a) Leave the needle position enriched (#3 notch; sitting higher than stock, for the given carb) and reduce the Needle Jet (from 2.68 to 2.66 or 2.64) and

b) Drop the needles down to stock (#2 notch) and install a larger Pilot Jet (#50).

Ill update this thread once I have any news unless I run out of weather and bike time.

--
Michael Stoic

 

[30064]

Wanted to share this chart with everyone. Can't comment on the accuracy, or even the author. I believe this came from the R65 Forum. I found it very interesting and if correct; very comprehensive.

 

[bostonmish]

ThatÔÇÖs a very nice chart. Offers a great insight indeed!

I would add that the graph labeled in this chart as Needle Diameter likely also correlates to the Needle Jet function itself. we dont get choices of needle diameters (maybe tapers), but do have a selection of Needle Jets.

At the risk of hogging all this discussion for my own tests, IÔÇÖll add that based on this chart, I will expect my ÔÇ£scenario (a)ÔÇØ to offer movement in the right direction.

The Bing manual just arrived too. I am in total and uncompromising carburetion immersion!

--
Michael Stoic

 

[radar41]

Old Fuel Line

I also suggest replacing any old fuel line. Scuttlebutt is that the braided stuff tends to disintegrate on the inside after a few years. New braided/rubber fuel hose is cheap enough, but I'm now using snowmobile fuel line (urethane or something) from my local dirt bike shop.
pmdave

Dave,

You are correct as usual!! The alcohol in fuel these days will cause fuel lines to break down and clog the "works".

I switched to this stuff about 4 years ago, and put it back on the RS after the rebuild .

http://www.tygon.com/tygon-lp-1100-tubing.aspx

Some local suppliers have it, or it can be ordered on line.

Yes, the purist mention my fuel line isn't stock. Oops!

 

[skiteach]

"Yes, the purist mention my fuel line isn't stock"

What color spark plug wires are you using? Dual plug, you could have 4 different!

 

[radar41]

Tygon Fuel lines

"Yes, the purist mention my fuel line isn't stock"

What color spark plug wires are you using? Dual plug, you could have 4 different!

The plug wires are black and the engine is bone stock! But if I had thought of it . . . . .