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Discussion Starter · #1 · (Edited)
1979 CB400T II, Carb trouble, Revvs up to quickly???

Covering 2 items with one hot. The bike started stalling and would not idle. I went through several things mentally, dirty carbs, failing stator, dirty fuel, failing coils, the answer was too easy. The idle speed adjustment screw had backed out and closed the throttle. This bike is a rescue bike, $100.00 bike with a title. New tires and brakes, GM distributorless coil, clean carbs and so on. My question is, this bike, on the center stand, in neutral revs up so quick it is scary. A little blip of the throttle and she will go to 4000 or so, smoothly and willingly with no funny noises, she just buzzes. Is this normal??? We think the bike runs really well but we have no experience with CB400s. Also the bike has the stock air box and H box with some fairly open mufflers.
 

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When I had my CM400 it didn't rev that freely, even in neutral i had to really take a handful of throttle to rev to 4 grand. I'm not aware of anything like a carb slide that can be put in backwards causing such easy revving. Are your exhaust pipes the same temp or is one much hotter? I had an issue early on with mine that one carb needle had been replaced and one was horribly worn causing the right cylinder to run really hot and I couldn't calm it down, I swapped in the less worn pair of needles from some parts-only carbs and it smoothed right out and I could then work on syncing them.
 

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Does it return to idle normally when throttle is released?

Mine is definitely "responsive", but I can easily hold rpm wherever I want it.
 

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Discussion Starter · #4 ·
The bike starts easily, idles well and returns to idle after being reved up.
The bike revs up so easily it is scary but it does run very well.
If the weather permits I will ride it today and see what I can see.
My grandson rides the bike nearly every day as a dirt bike and he
runs it pretty hard. I can find no fault with the way the bike performs.
 

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Quick revving, in neutral or in gear on the center stand, sounds normal to me. Both of mine do but neither has stock exhaust.
You can adjust the throttle cable freeplay so there's more movement needed off idle
 
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