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'77 CB750a

Perlmutter

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1977 Honda CB750 Hondamatic

Okay, so I'm having a problem.
For some reason, the throttle on my bike has a tendency of opening itself. And by tendency, I mean it does every time. Let me explain.

I've had this bike for less than a month. I bought it with this issue. I took it in to the shop to get looked at and have some basic maintenance done. I mentioned the issue of the throttle. When I picked the bike back up, the mechanic told me he didn't notice it and when I rode the bike it wasn't happening anymore.

Anyways, after riding fine for a few weeks, the problem presented itself. Here's what happens. I've got the '77 CB750 Hondamatic. It's got neutral, L, and D. It idles fine in N, but as soon as I kick it into L, the throttle opens itself and the bikes wants to take off, and pretty quickly. Once it gets up to around 15~20mph it'll close itself and decelerate. Once I'm cruising, no problems at all. The even weirder part is when I'm braking. Wether I'm in L or D and I start to brake and get around 10mph the throttle will again start to open itself. At this point I need to either brake heavily or throw it into N. Once it's in neutral, no problems.

It does this without fail every time now. I'm reaching out to you guys for some help. I'd rather try and figure this out and repair it myself.

Could it be my push/pull cables? I don't know much. Any help is greatly appreciated! Thanks!
 
There is a vacuum motor on the carb that is used to open the throttle just a little bit when put into gear to keep it from stalling. Sounds like it is either hooked up wrong or adjusted wrong or something. It should only open the throttle enough to bump the rpm a couple hundred rpm...its just used to keep the motor from bogging down and stalling when you put it into gear and a stop.
 
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