[Dave]

Originally Posted by No Worries

Reminds me of a time in the 80's when I was visiting a mechanic friend of mine who worked at a Yamaha dealer. A kid brings in an RD350 and says it won't go over 30mph. Greg lifts the seat and sees a beach towel folded neatly on top of the intake snorkel.

When I see something like this, I check the ignition first. You can fiddle with the carbs until the world ends, but if the ignition ain't working right, it won't run right. Spark to both plugs and check the timing. Then I check the fuel petcock, related hoses including the vacuum and fuel line, change the filter, and check the choke.

As for the carbs, the engine runs on the idle jets until about 30mph, then the needles lift out of the main jets. If the piston/needles are stuck in their bore, the bike will only run on idle jets. And I believe that they are very lean on the big Vulcan. You can run an ocean of Sea Foam through the carbs and it won't clean the pistons or bores. The tops of the carbs have to come off to clean them.

On my 79 Suzuki, the piston needles are connected directly to the throttle cable. They never stick. I think all carbs after 79 used Constant-Velocity (CV) carbs. The piston/needles rise by the vacuum of the engine, and the piston and bore has to be squeaky clean for them to operate correctly.

That was my issue when trying out my friend's gs750 bobber. Id never ridden a bike with the old style carbs and with four of em to pull that throttle was HEAVY