SOHC.co.uk Forums > SOHC Singles & Twins
High revs won’t drop back down
Craizeehair:
I picked up a new project bike last week, a CB350 K2 as I fancied something different to play with.
I knew it had a few things to sort, one of which is when the bike is running it ticks over fine and will rev fine and go back to tick over but it will at some point hit 4-5k revs and just stay there, it won’t drop back down, you can’t twist the throttle forward to bring it back down. If you kill the engine and start it again it will tick over fine but will stick at high revs again when revved up.
I haven’t had it long enough to really do much and was hoping I could get some pointers before I go tearing in and set off down the wrong path. I have had a quick look in the carbs and everything seems ok at first glance, diaphragm, jets etc all seem ok.
Any pointers as to where I might start?
Athame57:
--- Quote from: Craizeehair on June 07, 2025, 11:20:01 AM ---Any pointers as to where I might start?
--- End quote ---
I would be getting new throttle cables myself. Also I would check the movement of the throttle arm, maybe the shaft that is holding it and the 'butterfly' et al is sticking and slow to close again because it needs cleaning and greasing.
Craizeehair:
Thanks, I will check all that but everything seems to snap back closed but the high revs maintain, I haven’t left it too long but it will stay there for a good 30 seconds to a minute before I kill the engine.
I haven’t done enough testing to be sure but it may be the new it warms up rather then from cold. My initial thoughts are an air leak, carb issue or spark advance, just wondering if they are reasonable assumptions and places to start?
McCabe-Thiele (Ted):
This reads like typical so called "Hanging throttle" problems.
If you use the site search facility this subject has come up frequently.
Ths is one of many posts on the subject.https://www.sohc.co.uk/index.php/topic,31510.0.html
SteveW:
Air leak on inlet rubbers?
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