Repair and troubleshooting information for the Suzuki FA50 Moped.

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Stuck Throttle Cable

I have a 1984 Suzuki FA50 moped that ran fine until about six months ago. One day I tried to start it, and the throttle got stuck while trying to rev the engine. It would not budge from idle. I unstuck the throttle by twisting it as hard as I could (who says brute force doesn't work?). The throttle remained "unstuck," but the moped just wasn't the same -- it would immediately shut off as soon as I applied the throttle. I let it be and saved the repair for another day.

Fast-forward four months. I decided it would be a stellar idea to create a teardown for the moped, clean the carburetor, and figure out the throttle problem. I managed two of the three (teardown is almost done, and the carb is clean), but to this day I cannot figure out what the heck is wrong with the throttle. Since it's a pretty involved piece of machinery, I created another teardown that described the stuck cable problem in greater detail. Please take a look at it here:

Suzuki FA50 Moped Throttle Cable Teardown

I would love to hear any suggestions you have on how I can fix my Suzie's throttle. I miss riding it.

Update

I have since resolved the stuck throttle problem. After screwing with the throttle for hours, I figured out I've been inserting the cylinder off by 180 degrees.

I was actually about to order another throttle cable online, when I came across a schematic (which I already had in my manual). I glanced at it, and noticed the position of the cylinder in relation to the carburetor. What I found odd was that the notch (which I've seen dozens of times before) was 180 degrees rotated from how I was inserting it...

So I went outside, rotated the cylinder 180 degrees, and presto-blamo the entire cylinder assembly went into the carb about twice as deep as before!

What sucks is that I've tried the cylinder in that position before, but it didn't want to enter the carb in my previous try. I had actually rotated the cylinder multiple times, trying to insert it into the carb, and the only position that I thought worked was the one I was trying all along.

Finally after inserting it correctly, reassembling the throttle handle (I took it apart out of desperation), trying to get the thing started and fine-tuning it for three hours, I managed to go for a ride down the street!

...And then the weather turned inclement and poured rain for a week straight, rendering the moped useless for a while longer...

Answered! View the answer I have this problem too

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After looking at the teardown,can you confirm that when you twist the throttle the 'cylinder' (slide) with the needle moves inside the carburetor? The throttle action is to lift the slide to allow more air in, and to lift the needle in unison with the slide to allow more fuel in (bigger opening = less pressure drop, so we need larger fuel opening etc).

You state that the moped engine idles, but dies on opening the throttle - I could only imagine the needle stays down when the slide opens, and -like on idle - only just the idle circuitry supplies the engine with fuel.

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I think I figured out the problem, after talking to another iFixitian and reading your answer above. Thank you for confirming that the entire cylinder (slide) should move up and down. That was the flaw in my reasoning -- I thought only the needle should move up and down, not the entire slide. In hindsight, that makes sense.

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So the real problem is that I overextended the throttle cable when I "unstuck" it. Now it's too long, so it never pulls the slide upwards, but more fuel comes in and kills the engine. I will have to replace the throttle cable with a new one, and I'm pretty sure that will solve the problem.

Thanks a lot!

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Control cables on bicycles, motorcycles, mopeds and motor scooters are subject to wicking rain water if the machines are left outside in the weather or operated in the rain. This can promote rusting of the cable and the outer spiral-wound housing. If the temperatures drop below freezing, this can also cause ice formation in the sleeve and will make the cable stick, a potentially hazardous situation if discovered while riding. If one is unable to keep the machine out of the rain, the next best thing is to periodically disassemble the cable for maintenance, if possible. If you have access to an air compressor, blow out the housing with a rubber-tipped blow gun. Wipe off any moisture from the cable, lubricate it with a light coating of approved grease and re-thread the cable into the housing. It may also be helpful to inject a generous amount of light penetrating oil, such as WD-40, to displace moisture from the housing.

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Hi, Here is a URL for the owners manual that you can download. Ralph

http://www.scribd.com/doc/3829218/1986-S...

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Thanks for the Owners Manual link. However, it doesn't answer my question. I actually have the Service Manual, which I used to take apart the FA50. It mentions the throttle in somewhat greater detail than the Owners Manual, but still doesn't offer any pertinent troubleshooting information.

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Thanks rj713, I have Same problem

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This used to happen a lot with the speedometers in old cars.

I would say some 3-in-1 oil, liquid wrench (or other rust buster) inside the cable sleeve, where IMnsHO, your problem is.

Though it might be cheaper and faster in the long run to just replace the cabling.

N.

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did you put it together right?

and what do you mean by 'immedialtely shutoff as soon as I apply the throttle?"

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yes that sounds like what was required.

for anyone else with the same problem of a stuck throttle. (it is a common problem too)

the little brass cyclinder should be installed with the biggest,longest gap that runs from the top of the cyclinder to the bottom of the cyclinder- facing the right hand side of the bike.

that is to say that the sleeve can fit into the carby two different ways, however only one of those two ways will correct the stuck throttle problem. easy once you know how :-)

Update

oh and by the way the needle has 6 little notches on it.

the single C clip holds the needle at a required position, which can be adjusted as required. ie. lift the needle up and it will make the engine run richer (more fuel goes into the combustion chamber). drop the needle down a few notches andnit will run leaner.

this helps the motor perform to its best ability in various heights above sea level.

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Looking at at exploded view of the carburator on suzukiparts.com it appears that the "SEAT, THROTTLE VALVE SPRING" (the M shaped clip) should lift the throttle needle/ needle clip with the stop at the end of the throttle cable lifting the whole needle assembly. The setup looks similar to other slide carburators I've seen on the larger honda keihin scooter carbs

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Miroslav Djuric will be eternally grateful.
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