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Here's what Black Magic boys have to say,


Lacking Some Speed on That Exhaust Valved Twin???

During the past couple of weeks we have had a number of callers expressing that their Twin just is not performing up to expectations. They are complaining of lack of peak RPM and top speed. Some of these fellows have explained that their respective sleds have acted this way since they were purchased new.

After conversing with them, for a fair length of time, it was suggested that they check the actions of the exhaust valves to insure they were operating properly. Virtually everyone has called back and indicated that this was the problem, the cables at the servo were unhooked, causing the exhaust valves to only operate slightly from the actual exhaust pressure. What does this mean in layman's terms?? Low RPM @ peak, virtually no top speed and a sled that is only performing at 80% of it's full capability.

There is a test or two that you can do yourself to see if your valves are working correctly.

You should be able to "hear" your valves open when the engine is idling. The sled is doing its "cleaning" while it sits there and idles. You will hear the engine tone change when the valves cycle. However, this does not necessarily mean both valves are opening.
Remove the servo cover and remove the cables from the servo. By pulling the cable on each individual valve and releasing it quickly, you will hear the valve bottom out on the valve stopper. This is also a way to see if your valves are sticky or not. Any resistance while pulling on the cable will indicate a valve cleaning is in order.
If you happen to have a slug compared to your buddies sled, this is the first thing we would look for. A valved sled with the valves not working is a pooch to say the least.
 

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Well..you've hit that one right on the nail..seems everyones problem as far as speed is concerned is 1 way or another to do with these power valves (including myself ) 300 miles and i finally got it on a lake just to be embarrased at the speedo reading 80mph while a zl600ss went by... :angry: i've gone thru it all and now determined there stuck closed..or bairly opening...Going to the shop on monday for a fixin and some 350 main jets..then i'll find that silly zl and see what hes got :p
 
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