When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So it doesn't seem to be an ignition problem since it can rev to redline in 1st and 2nd. Then 3rd, 4th, 5th, and 6th have problems at velocities above 115mph. Seems like an airflow issue. Vacuum slides not opening all the way, or vacuum leak somewhere. During the rebuild of the carbs, "all" O rings were replaced? Have you pulled the tops of the carburetors to verify the vacuum slide skirts are seated properly and not leaking?
Dug back into it today and #1 carb slide has a resistance and the other 3 do not have any resistance. Pulled the tops to check the diaphragm and could not find any type of crack or pin holes anywhere.
When you push up on the slide there should be an even pressure against your finger. When you release there should be a cool sounding sucking/swooshing sound.
There are two springs per diaphragm assembly. One is the big one that goes directly under the cap. The second one goes under the black stem thing. Do you have all those?
Along with what hamlin6 said, when testing the slide operation with your hand, look closely at the bottom of the slide close to where the main jet needle sticks out the bottom. There is a small hole drilled through the plastic. If you can cover this hole with your finger as you are attempting to move the slide upwards, you should feel greater resistance as air pressure builds up inside the upper chamber of the slide. It will feel like you're pumping a bellows if you know what that is. Doing that to each one, they should feel the same between each carburetor.
During normal operation at higher RPM's, this hole is what allows the vacuum (low pressure) to be sensed in the upper portion of the vacuum slide chamber. The vacuum overcomes the spring pressure holding the slide down and the slide moves up. As it moves up, the main jet needle is pulled out of the main jet and more fuel is added to the additional air that is being allowed in due to the larger opening in the carburetor throat.
Last edited by IDoDirt; Jun 11, 2021 at 03:11 PM.
Reason: Spelling
Ok I’m currently 8,000 miles from my bike on a phone that is slow to download my SM for pictures, so apologies if this comes across short or incomplete in information.
Are your throttle cables hooked up correctly at the carb bracket/plate (item #7)
Cable A has two nuts on the thread screw and Cable B only has one.
Make sure the two nuts split the top ‘hook’ of the bracket and adjust accordingly. The first time I hooked the cable back up on my bike I ended up putting both nuts on top of the ‘hook’ and was unable to get proper adjustment causing me to have what I remember to be a governed like effect. My memory may have failed me on this as it was 7 years ago now but that is what came to my mind first reading your issue. Just another suggestion to ponder.
