Bonneville America Forums Forums Technical Forums Performance Mods Carb balance varies ( Help)

Hi all
When I am balancing the carbs, I set the idle to about 1200 rpm. I balance the carbs and it sits even but then when I give it some revving it starts to drift again. When I release the throttle it heads back in the opposite direction. Whilst on a ride today I have a bad vibration from about a third throttle onwards which I think is my carbs out of balance. I may be wrong as Im fairly new to bikes.
I removed 2 baffles from each exhaust, added a Uni filter, rejetted with 130 mains, removed top snorkel and AI removed in the last week or so.
I removed the plugs when I got home from the ride and they look good, both of them. Very clean and a slight tan colour.
Would I be right in thinking that my carbs are just not balanced ?
Am I balancing them at the right throttle range ?
Help

Regards
Derek

Look for vaccuum leaks, try raising the RPMs some. After removing baffles, I could feel some vibration, not bad, though.

Balance the carbs and blip the throttle. Repeat. Repeat. Switch the lines of the balancer on the carbs. Balance the carbs and blip the throttle. Repeat. Go ride....

Derek,

No, you are not balancing them correctly.

I have your setup and balance with a good quality Morgan Carbtune II. First, balance carbs at the normal idle, about 1,000 RPM, using only the idle air adjustment screw under each carb.

Next,do not change those screws or the idle speed screw. Hold throttle open, with your hand, to about 2,000 RPM and adjust the balance screw. I don't have a tach, just "ear" it. The balance screw is between the carbs, and is a phillips head screw, accessible from the top. It helps to loosen the rear fuel tank bolt and to lift the aft end of the tank a couple of inches.

After adjusting the balance, recheck the idle balance to see if it is still ok. If so, quit. If not, repeat.

To keep the motor and exhaust cool, it is a good idea to place a big fan in front of the motor.

Bike should run and pull strong from any speed or RPM until you top-out, with no hesitation. You have a good setup. (PS, you can also pull the inner two snorkels if your model has them-some don't.)

cowboy, if he is using the homemade balancer there is no need to switch lines on the carbs

tomv. you say adjust each idle air adjustment screw under each carb. You mean the air mixture screws (D tool) ?
Next I can balance the carbs at idle and they sit perfectly but when I open the throttle as you say then it starts to climb on one side of the home made carb balancer. When I release the throttle back to idle it reverts back the other way. I feel this is what is causing my vibration when I ride.
Now I also think I notice that the bike vibrates more as the engine get warmer. Hmmm maybe its my imagination. (Believe me I have a good imagination after I left my tobacco patches on overnight once, different story).
Im sure all my vacuum ports are sealed well, I checked.
There was only one snorkel that extended down into the air filter that I removed. Now it is just a box with two golf ball size holes in the front top corners to allow air to the carby

Quote:

---

tomv. you say adjust each idle air adjustment screw under each carb. You mean the air mixture screws (D tool) ?
Next I can balance the carbs at idle and they sit perfectly but when I open the throttle as you say then it starts to climb on one side of the home made carb balancer. When I release the throttle back to idle it reverts back the other way. I feel this is what is causing my vibration when I ride.

---

For the idle: D tool--yes.
For the higher RPM balance: As long as they track close, e.g. 2 to 4 cm up to the 2,000 RPM and then hold within the 2 cm. Mine does like yours, but the better the balance on accel and decel the better. The balance at the higher (e.g. 2000 RPM) is set by the carb balancer screw between the carbs. If this still does not work, you may need to check the float heights, and that the main jet inside each carb (above the float bowl) is not loose. Check manual for details.