A A A A Author Topic: Choke & throttle linkage questions  (Read 118 times)


Choke & throttle linkage questions
« Started on: 25-May-21, 21:01 »
I am putting my 78 CX500 back together after a long hibernation in the shed, engine rebuilt now working on the carbs but a couple of things puzzling me and I would really appreciate some advice. Sorry no photos, but will try to get some close ups if I can, meanwhile I will try to explain. Looking at the LH carb where the linkages are, working in from the rear/airbox end, there is the linkage for the choke cable attachment on the rod that operates the choke butterfly valve. Next is the rocker arm as I call it, then at the front the throttle drum to which the throttle buttefly is attached. Between the drum and the carb is a plate that holds the push and pull throttle cables and a projecting tab that acts as a stop for the throttle drum. Below the drum is the idle adjuster screw that if wound in pushes on the drum. Looking in to the opening of the carb from the front, at the bottom are three small holes, the first close to the front of the chamber and two quite close together but further back in the area of the butterfly valve.

So, long winded description, but here is what I am puzzled about. At the moment, the idle adjuster screw is backed off and not touching the throttle drum. The throttle drum is against the stop plate. What is puzzling me is that looking into the carb, the butterfly is not fully closed, probably a milimeter gap at the top and bottom and the bottom of it being between the two rearmost holes in the bottom of the chamber. If I take off the cable connector/throttle stop plate, the butterfly closes fully and hides both the holes. I am sure the butterfly should fully close, but the plate is original so I guess has always held the valve slightly open, so maybe it is meant to be ?.

With the choke, when I rotate the linkage to close the choke butterfly, it has a cam on it that moves the little rocker and I think that should push on the throttle drum to open the throttle butterfly a tad. On my carb though, when the linkage is operated and the choke butterfly closed, the end of the rocker is about 1/8" clear of the throttle drum so does`nt move it at all. Again though, if the throttle cable/stop plate is removed, the rocker does move the throttle drum but only very slightly.

I know something is not right here, crazy thing is that I have never touched the carbs and ran the bike as everyday transport for a good ten years or so without any issues. I can`t decide whether I need to file off a bit from the throttle stop plate so that the throttle butterfly fully closes and the choke rocker contacts the body, or to just leave well alone. Any advice would be very much appreciated. Apologies for the long winded explanation  2smiley.


Re: Choke & throttle linkage questions
« Reply #1 on: 26-May-21, 00:11 »
Managed to get some photos, sorry they are a bit out of focus. Have`nt started cleaning the carbs yet either, so a bit grotty !. First pic of the mechanisms, as you can see the idle screw is not contacting the throttle drum, and the choke rocker nowhere near. The second is looking from the front/engine side, you can see the throttle drum is against the stop plate, also that the butterfly is not fully closed so the second hole in is just visible at the bottom of the chamber.   [ You are not allowed to view this attachment ]  


Re: Choke & throttle linkage questions
« Reply #2 on: 26-May-21, 00:13 »
Could`nt get the other pic to work, so trying again !. I`m not very good with computers  rolleye0012  [ You are not allowed to view this attachment ]  


Re: Choke & throttle linkage questions
« Reply #3 on: 26-May-21, 08:01 »
CX Phreak is probably the forum member that would be able to offer some advice as he has fully rebuilt a few sets of carbies.



Re: Choke & throttle linkage questions
« Reply #4 on: 26-May-21, 09:33 »
Don't forget Larry's book.


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