reduced top speed after carb rebuild

[rob650]

what should i be looking at to resolve this?

carbs have been syncronized, starts and idles well. Accelerates smoothly although not as much of a "punch" as i remember pre-rebuild.  Once up to about 50MPH it just seems to run out of breath...not like its starving for gas, more like it just ran out of horsepower.

Thanks for any advice

[Bob_Roller]

Did you replace the diaphragms
Are they OEM Bing parts, or aftermarket  pattern  parts ??
Float levels adjusted correctly ??

[nhmaf]

And, there are little tabs on the edge of the diaphragm that have to go into a little slot when they are in the proper position.   Otherwise you will have an air leak, and won't get above 50-60 MPH, typically.

[thrang]

If you've not replaced the diaphragms, look for a hole in them. If you have replaced them, are they seated correctly?

[rob650]

replaced diaphragm with BMW parts.  checked, they are in good condition with no holes, but one was out of it's "tooth" mark.  Reset, a little more top end acheived but not much better.  Will go over the valve adjustment settings again.  

[Mike V]

Rob,

If you're confident both your new diaphragms are correctly positioned, and installed ...

Are your throttle cable settings correct?  Are your butterflies fully open when you twist the throttle grip fully open? Make sure the vacuum take-off ports at the bottom of the carbs are secured with good vacuum lines or if you have the AIR equipment removed make sure the take-off nipples are secured with fiber washers and screws and you have good air-tight connections at the rubber carb collars and intake horns.

After your valve adjustment check your timing with a timing light.  You should be at full advance at approximately 2500 to 2800 RPM.  Locate your timing marks on your flywheel through the inspection window and clean off any clutch dust or smoodge.  I prefer to set my timing at full advance - the "F" or "Z" mark should align with the casing hatch mark at 2500 to 2800 RPM.

-Mike V.

[Bob_Roller]

Did you disassemble one carb at a time and then reassemble it before going to the other one ??
The ' choke ' / enrichment assemblies are side specific, if you get them swapped, the ' choke ' is on all the time .
Also after you get the carbs synchronized, after you tighten the throttle cables, bring the engine up to 3500 rpm and check the balance, you may have to adjust the cable(s) to get the carbs synchronized when above idle speeds .

[rob650]

im going to sit in the corner with a dunce cap...

popped off the valve covers.  One of the exhaust adjuster locknuts had come off, and was bouncing around like a popcorn kernel.  valve adjustment loosed up to about a country mile wide.  re-adjusted valves again, runs better, quieter, and (most of) my top end is back.

ill do another carb/cable re-balance.

[nhmaf]

At least you found it - so that is a good thing!

[rob650]

To close this out, my mis-adjusted valves was the cause.  Have taken a couple of rides, checking the adjustments after each one and tweaking them, as well as carb balancing.  Performance is back to normal, noise levels (post-rebuilt heads) have dropped a bit so thats a nice bonus.  Hoping my MPG will also increase some with the new head work.  

Thanks everyone for the advice.