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Discussion Starter · #1 ·
I have nearly finished the rebuild of my 450 and it now starts and runs but runs at about 7000 rpm. I can get it to idle at about 1000 by using lots of choke. I have tried swapping carbies but does not seem to make a difference.
Has anyone had this issue, suggestions would be great.

scott
 

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First, make sure the throttle cable has enough slack that the idle screws are actually in control. Check for binding in the throttle cable by pressing the throttles down against the screws after using the grip to open them; they should not move. Make sure the throttles are in the same relative position; if not, the splitter may be at fault, and one cable has jumped out of its holder. Next, make sure the carbs are locked into the grooves in the inside of the intake boots, and that the bolts holding those boots are tight. Check static timing, and make sure the springs are holding the weights against the inside stops; turn the cam with your fingers, and the weights should fully return. Then check timing with a light; this is less messy if you have a spare alternator cover you can punch a hold in over the timing marks. At that rpm, it should be fully advanced, but stable; not bouncing around or above the full advance marks.
 

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Discussion Starter · #3 ·
First, make sure the throttle cable has enough slack that the idle screws are actually in control. Check for binding in the throttle cable by pressing the throttles down against the screws after using the grip to open them; they should not move. Make sure the throttles are in the same relative position; if not, the splitter may be at fault, and one cable has jumped out of its holder. Next, make sure the carbs are locked into the grooves in the inside of the intake boots, and that the bolts holding those boots are tight. Check static timing, and make sure the springs are holding the weights against the inside stops; turn the cam with your fingers, and the weights should fully return. Then check timing with a light; this is less messy if you have a spare alternator cover you can punch a hold in over the timing marks. At that rpm, it should be fully advanced, but stable; not bouncing around or above the full advance marks.
Thanks, I will try all of that.
 

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Have you tried the straw test on the CV pistons? Use a bit of fuel line to direct air into the air vent, and the pistons should rise and fall smoothly and quickly.
Also, because you need choke to make it idle, the felt seals on the throttle could be failing; while it is idling, aim an unlit propane torch or spray some starter fluid at the throttle bearings. If they are leaking, you will know it.
 
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