Bing Jetting advise

[drpetemurray]

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.

Thanks for the input. Agree throttle cable play at the carb is vital. More tinkering to follow.

[drpetemurray]

I totally follow you and understand the individuality, overlap and influence of the Idle mixture screw, jet needle, needle jet and main jet.

Thank You

[srankin]

Despite the limitations of forum communications have we reached an answer? No hard feelings?

I learned a lot, and Pete, maybe next summer I will pay you a visit. I still have some short rides to do before the salt trucks start rolling but not that far. St.

[drpetemurray]

Srankan, No hard feelings at all. Tomorrow I will have time to do some tuning in between my pet's surgery. I will start with confirming carb balance with Snowbums method # 1. Next, as you noted at that point individual deviation of an idle screw or idle mixture screw could give the correction. We will see, I will provide the results. Thanks again for the help and enjoy the remainder of the riding season.
Pete

[drpetemurray]

After much great information and discussion provided, I started some testing on Sunday 10-22.

After a 10-mile warm-up ride on Sunday I attempted to eliminate the rocking at idle. Started by checking the balance between cylinders tick over speed at idle. The method simply pull up on throttle cable at the carb, I identifyied the R cylinder cable when lifted helped smooth the engine. Adjusted the throttle idel screw for balance and proper tick over and the rocking was gone... Quick test ride and the bike performed acceptable.

On Tuesday I had a little more time for testing. After warm up fans in place carb mate attached for sync analysis. Finding R cylinder pulling at a 4 bar stronger imbalance. I readjusted for balance and was able to set with less rocking.

Not being satisfied I decided to inspect the Idle mixture screw on both carbs. The screw was fine, I just received new O-rings for the MJ, Throttle shaft, Idel jet and IMS. Findings the IMS o-ring compared to the new IMS o-rings appeared to be a loose fit in the sealing groove. These o-rings are difficult to stretch over the IMS however job is completed.

Quick test ride, the motor was not at operating temp. Once at operating temp, the idle had increased by about 500 rpms.
This may have been the issue all along. Thursday I will reset the carb sync as per Snowbum method 1 and report back.

[srankin]

Thanks for the follow up.

Just for my information, where did the carb rebuild parts come from originally and where did you get the proper replacement parts from? St.