Columbia commuter throttle

Wes Lindquist /

My 1978 Columbia Commuter with a Sachs engine and a Bing carburetor has this characteristic: once up to full speed (currently 24-25 mph), laying off the throttle does not slow it down at all. Only the brakes slow it down.

As it slows down(by braking), the 2 speed automatic transmission does downshift to first, but I can't take either brake off or it will shoot forward.

Is there supposed to be some linkage between the throttle and the butterfly valve? Or does the trottle cable only control the carburetor jet?

I can add that it gets pretty poor mileage for a moped-probably only 20 to 25 mpg.

Thanks for your suggestions.

Wes

Re: Columbia commuter throttle

It sounds like the throttle remains open even though you twist the throttle closed.

Lubricate the entire length of throttle cable in it's sheath as well as the handle bar's end inside the throttle twist handle. If the cable binds anywhere the engine will not react to throttle grip position...

Just the spring inside the top of the carburetor is expected to close the carb-slide and pull the entire length of cable while it also returns the throttle grip to the closed position when you release it. The cable must easily move in and out inside it's sheath.

I had a Bing but no butterfly valve. It had a "slide" and a slide needle attached. These two elements control how much fuel/air flows. The tapered needle goes into a "needle jet" and regulates how much gasoline flows up through the main jet passage.. while air is allowed to pass under the slide.

Instead of a butterfly you might be speaking of the choke which is a guillotine type restriction (hand operated choke on my bike). So, on my carb there was only one cable. It went directly into the center of the top of the carb and attached to the slide..

The bike shifts to 1st gear when it slows because 2nd gear engagement and disengagement is a matter of road speed..

Re: Columbia commuter throttle

Wes Lindquist /

I recently put in a brand new throttle cable and that didn't seem to have any effect. Perhaps the spring in the carb has lost its strength.

The air valve that I was guessing might be in play here is the one valve between the airbox and the carb. It has a separate connection on the right side of the handlebars that can be used to close the valve and stall out the engine as opposed to using the electric kill switch.

Re: Columbia commuter throttle

Perhaps the spring.. or perhaps the carb's slide is binding (or some other malfunction in that area)

Remove the end of the cable at the carburetor. Push and pull the cable end and see if it easily moves the throttle grip on the bars.. If it does, the trouble is likely to be inside the carb. If it doesn't, investigate the throttle grip internals and the cable routing (no kinks allowed)

That valve between the carb and airbox is most likely the choke.. it is not meant to kill the engine, rather to restrict air when starting a cold engine and so provide the needed very rich fuel/air mixture.

I wouldn't advise killing the engine with the choke since a rich mix will be delivered as the engine dies by fouling the sparkplug.. and restarting it could be more difficult.

Re: Columbia commuter throttle

Jason Luther /

springs dont just loose their strength, so i doubt its that. does the throttle grip return when you let go of it? maybe there is an airleak in that valve, but even that wouldnt matter that much if the carb slide closes normaly. try cleaning the slide in the carb off with some wd-40 and lubricate it a little, any little crap in there will hinder its sliding ability.-jason

Re: Columbia commuter throttle

Wes Lindquist /

Is the slide the tube that the carb jet slides in? I've had the carburetor apart twice but can't remember clearly.

Re: Columbia commuter throttle

Ben Van Zoest /

The cable may have frayed in the grip spiral wind up groove, nasty problem.

Re: Columbia commuter throttle

Guys,

I have a Columbia Commuter, and I have a common problem: My left black lever (not brake lever for sure) (maybe clutch lever?) is loose, and I don't know how to tighten it up. How do I do this?

Thanks

Re: Columbia commuter throttle

The slide is the round aluminium piece that the throttle cable attaches to. It has a needlejet with a clip on it, then a disc and the spring. Be sure that you put the throttle slide in the correct way.

There is a pin on one side of the slide bore. There is a notch the complete length of the slide that keeps th slide from turning. This goes over the pin.

On the top of the slide there is a cut out, about a quarter inch deep. This opens the choke up when you turn the throttle.

If you put the slide in wrong the spring may push it closed but when you turn the throttle it may be jamming and hanging open..

Re: Columbia commuter throttle

Wes Lindquist /

The other lever on the left side of the handlebar (not the brake) could be considered the clutch or more properly the starter. When you pedal to start and get some momentum up, you engage that lever and it starts the engine. You let go as the engine starts. If you already know this--sorry for being so elementary.

If it's loose, the only thing I could think of is to repair or replace the cable that goes from the lever to the little switch on the side of the engine. Perhaps the connection to the engine has become loose and allowed some slack in the cable.

Wes

Re: Columbia commuter throttle

Wes Lindquist /

Thanks for the reply. I learned most of what you described by taking the carb apart and cleaning it. I'm experimenting with the position of the lock washer on the jet. I have placed it in the closest to the end of the jet (ther are 4 positions) and I'm waiting for nicer weather to test it.

I did do a visually test of the slide operation as I was re-installing the carb and it looked pretty good. It does not appear to stick at the open position.

The proof will be in the pudding and Spring is just around the corner.

Re: Columbia commuter throttle

Wes,

Thank you so much for the info. Until last week, I've been strictly a scooter operator (I have owned mopeds but they all were dead) Now I have a nice one that is in good condition and I think it runs. Just needed to know how to do it. :o)

It does make my life easier. Thanks, wes. :o)

EK

Re: Columbia commuter throttle

I second that! I can't wait to ride/start my Columbia for the first time! These mopeds are awesome... Nice big size and very comfortable. Can't wait to ride it... Danged winter.

Re: Columbia commuter throttle

Wes Lindquist /

ten months later, and 3 more 2-wheelers in the garage and I finally figured it out. The throttle cable was short and the carburetor slide was nearly full open all the time. Because I had two throttle cables, I felt free to experiment with one. I used a hacksaw to cut about a 1/4 inch off the metal tip of the outer cable. This allowed the slide position to be pushed lower down in the carb--(by the spring) and gave much better results. I still may need to find another 1/8 of an inch to get it perfect---maybe on the end of the cable that goes to the handlebars. The inner part of the throttle cable remains the same length.

Re: Columbia commuter throttle

Leon Swarmer /

Glad you got it.. they are amazing little puzzzles aren't they?

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