Bing Jetting advise

[schrader7032]

Pete -

Can you describe the steps you did for carb balancing?

[drpetemurray]

I use the Carbmate and Snowbums method #1 for idle adjustment, next Idle mixture adjustment I adjust the IMS for fastest running and then 1/8 turn out to avoid a lean slow circuit as per method #1. I then go back and verify idle RPM and balance with the carbmate. Going back and forth until balance is achieved. I have additionally used the plug shorting method to verify ticover speed individually between cylinders after using the carbmate. At this setting slow throttle roll-on has the hesitation. Both carbs are set individually and are both set at ABOUT 3/4 of a turn out. No rocking smooth as glass.

I was able to achieve proper stronger running without hesitation at an IMS setting of about 1/2 turn out both sides. Unfortunately at idle the engine rocks at idle. Also my spark plugs developed a tan color. Prior at 3/4 turns with the IMS the plugs were almost colorless.
The plug color becoming tan to brown with the leaner setting is the complete opposite of what I would have expected. This discover made me question what happens when the IMS is turned in, I would have thought turning the screw in richens the mixture (allowing more fuel than air)and would explain the darkening of the spark plug. Conversely, I understand turning the IMS in reduces fuel flow from the jet needle creating a lean mixture.

Next Tuesday the 24th will allow me time to test.

Thanks

[srankin]

The more you write the clearer things become.
I will admit I don't quite know how to explain carb workings as well as someone with a higher degree of learning or experience so I won't.

I do not have experience with any motorcycles other than BMW twins and each of the bikes I have worked on or restored have had individual quirks that sometime don't warrant overthinking or further effort to correct.

Example, my RT starts hard cold, my friend's RT starts fine cold, both of us have everything adjusted the best either we or my local airhead shop can do to ensure proper starting. What is the difference? I sure don't know neither does my mechanic friend.

After a while, I realized while these bikes were made well and of good quality, they are not precise instruments. I now use more choke and leave it on longer than my friend. Once warmed up both bike perform strong.

From my experience, I will go so far as to say; set it for performance and ride it. Maybe I am a jerk but smooth idle is a minor issue that should not be a huge problem as long as the bike is running properly while riding. Of course if you are going to enter the bike in a show, I bow to perhaps you are more concerned about the idle. I have never resorted or worked on a show bike.

Again not having your bike at hand, I cannot tell if the rocking you are getting at idle is abnormal and requires further fixing or is just the nature of that particular bike.

I think you have done all you can with the carbs and if you have further issues perhaps explore another avenue?

Again, due to limitations of writing, I cannot deduce directly subtle clues of your personality nor can you mine, LOL well I will admit to being a stubborn cuss. I JUST want to help you enjoy riding the bike. IF you feel a need for further contact I welcome you to send me a private message and I will be happy to give you a phone number. Stroudsberg is close but not too close to me in Rochester NY right now I am suffering from injuries due to an accident and while still riding, not as far. Good luck. St.

[schrader7032]

I'm pretty familiar with Snowbum's Method #1 and I use the TwinMax on my /7. Some other points and thoughts:

1- you must start out with 1-2mm of slack in the throttle cables where they run into the top of the carb.
2- I'm not familiar with the Carbmate but guess it gives you individual vacuum readings for each cylinder. So, you should get the vacuum's the same at the RPM you want, say 1100.
3- The mixture is set for each cylinder and it doesn't matter about the vacuum. You turn the mixture screw in until the engine begins to slow (the cylinder is lean), then out to where it begins to slow (the cylinder is too rich). Then at the point in the middle of those two screw positions, turn the screw slightly CCW or to the rich side.
4- repeat 2 and 3 until happy with speed and mixture.
5- set throttle cable tension. Snowbum says to roll on throttle to about 1500 RPM for this. I believe his point here is that at this RPM, you have tension in the cables and the carbs will be more susceptible to vacuum changes. Using your Carbmate, compare vacuum readings left vs right. If adjustments are made, slow down the faster cylinder. Do not try to speed up the slower cylinder. The reason is that if you increase tension in the cable, you will mess up the slack you have when you get back to idle.

I've done it this way many times. I have had no reason to go back into the carb and change jets or needles. And the bike has idled and accelerated fine for my tastes.

You seem to have a good running bike but it rocks at idle. I can see where if you didn't start with the proper cable slack or reduced it during cable synch, then one cylinder might not return to proper idle when the throttle is closed. You can gently pull up on the cable ends to see if you have the required slack the next time you have the bike running.

[Vega102]

I am new to airheads and rebuilt my carbs on my “new to me” 90/6 recently. Had the same issue at idle. Turned out the right side carb choke was not operating freely and not shutting off completely with the choke in the off position. It looked correct but when on the bike the spring wouldn’t close it quite completely. Took the carb back off, loosened the 4 screws holding the choke and rotated it slightly when tightening up the 4 screws, now operated correctly. Idle smoothed out right away.

[schrader7032]

Nice! Partial choke!

[srankin]

Yeah a hung up or misadjusted throttle cable can cause an issue. Nice bit of info on the choke issue.

I have been assuming those things were sorted. Maybe I am wrong? St.

[drpetemurray]

> IF you started out with dark plugs and poor performance at initial Bing recommendations, for needle settings, main jet settings, and idle screw mixture adjustment, and found by slightly leaning out the idle mixture, performance improved and plug color lightened.

Not correct, In other posts/responses I noted the plugs were neutral in color/lean. After Leaning the IMS adjustment the plugs developed a more acceptable tan color.

I am trying very hard to understand here. At this point, the bike runs fine with rock at idle?

Yes


Do I not make myself clear that perhaps minor tweaking of idle mixture not of both carbs at the same time but one carb at a time may smooth things out? Have you tried that?

Yes, it has been clearly stated in prior posts.

Setting the each carb exactly the same doesn't always work. Allowances have to be made for individual carb variances. So as I wrote, setting one carb to 1/2 may be spot on, the other carb may need to be 33/64 to get the same final performance, and running mixture.

I am well aware of this.

The idle system only works at a tiny fraction of throttle opening, at that point needle position takes over. And at that point, you are saying you have a good running bike with proper plug color or assumed fuel mixing. However in that fraction of a point in time between true idle and run, one carb may be a bit richer or leaner at total idle but that difference won't be noticed during riding or acceleration. It may however be noticeable at idle. St.

Partially correct, According to Kurt he referenced the Bing manual and the IMS /Jet needle influences 25-30 % of the throttle/throttle disc opening. To me, the 25-30 % is quite significant not tiny.

ST,
Thanks for the subject matter points. Sometimes folks read through posts too quickly me included and information is missed or misinterpreted.
Hence the theme of a prior motorcycle rally put on by rally master Rick Miller and the Mason Dixon 20/20 crew, Questionable Interpretation.

[drpetemurray]

Of course if you are going to enter the bike in a show, I bow to perhaps you are more concerned about the idle. I have never resorted or worked on a show bike.

The AMCA Judging events are not a show. The judging rules state motorcycles are evaluated for authenticity in the condition they would be found in the dealer showroom. The categories are unrestored original and restored motorcycles. There are 25 categories to be evaluated, all bikes start at 100 points and deductions are made for the final score. Awards are then presented based on score examples Junior First, Senior First and Winners Circle. My restoration is recognized as restored. Although my fuel tank, fenders, headlight bucket and ears are unrestored excellent examples.

Stroudsberg is close but not too close to me in Rochester NY right now I am suffering from injuries due to an accident and while still riding, not as far. Good luck. St.

ST thanks for your valued input. I wish you a speedy recovery.

[schrader7032]

Pete -

Just to be clear, I said that the idle circuit is in play or influences the first 25-30%, not just the 25-30% range. But while the idle circuit is playing a role up to say 30%, it's influence also is tapering off and the mid range circuit is beginning to work. There is an overlap of each of the three carb circuits.