I am stumped... Suzuki FA50 problems please help

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kingdele
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I am stumped... Suzuki FA50 problems please help

Post by kingdele » Thu May 10, 2018 9:09 pm

I recently acquired a Suzuki FA50 in decent shape and not running. Got it running within five minutes of getting it home. The problem is that it doesnÔÇÖt go past 18 mph. It will not rev high and stumbles between 3/4 and full throttle. Full throttle makes the revs actually lower from 3/4 throttle. It idles perfect btw. I have put a brand new carb in (cleaned the stock one but was still convinced it was a carb problem which it wasnÔÇÖt), ran full tank of gas with seafoam through it, opened up the head to check for score marks of possible piston ring damage and it was perfectly fine, checked fuel lines and the fuel cap to make sure there is no vapor lock or shortage of fuel, changed transmission oil, checked for air leaks anywhere and everywhere possible by spraying wd40 while it was running, and changed spark plug. I cannot figure this out and am reaching out to you guys as a last ditch effort before getting rid of her.

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Re: I am stumped... Suzuki FA50 problems please help

Post by Meatball » Thu May 10, 2018 10:15 pm

Sounds like its getting choked out somewhere since full throttle is where the issue occurs. Possible airbox restriction with a crappy filter cutting off airflow. Maybe a gummed up exhaust not allowing gases to escape at full bore. Possible fuel delivery restriction not allowing the needed fuel at wot...like petcock, fuel filter, fuel line, etc..

Im assuming that youve removed the airbox and looked into the carb venturi and confirmed the slide is fully open while you twist the throttle. Possible issue with the throttle cable being too long, stretched or simply needs an adjustment if possible.

Dont sell it...keep at it and youÔÇÖll find your gremlin eventually.
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Re: I am stumped... Suzuki FA50 problems please help

Post by kingdele » Thu May 10, 2018 11:07 pm

Thanks for the motivation I need it lol but I forgot to mention the previous owner did buy a new air filter but I might try my high flow air filter that I donÔÇÖt use for my elite and maybe try to tune that. I also checked the exhaust which the previous owner bought ÔÇ£newÔÇØ or in other words new to him but it was pretty dang spotless from just looking inside and ran the same with the exhaust off (just a slight bit louder). Has anyone heard of someone whoÔÇÖs had a petcock clog?

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Re: I am stumped... Suzuki FA50 problems please help

Post by Meatball » Fri May 11, 2018 12:24 am

Ive had a petcock go bad in couple different ways. No flow, constant flow and the ever frustrating (and toughest to diagnose) intermittent flow. Ive never had restricted or partial flow but its not impossible. A dirty fuel filter would create the situation you describe..also a gummed up (or kinked/damaged) fuel line.

How old is the fuel? Check compression?

YouÔÇÖll only fail if you stop trying. Keep going.
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Re: I am stumped... Suzuki FA50 problems please help

Post by noiseguy » Fri May 11, 2018 10:47 am

Fuel starvation, it will normally go to top speed immediately, then stumble down.

You're describing a lean carb at 3/4 to WOT. You need to check the condition of the main jet and emulsifier tube. I'm betting one or both are partially clogged, or main jet's not correct for the application.

Other things to check are clogged exhaust and over-oiled intake filter (wring it out with clean paper towel until you can't get any more oil out.)

Also check condition of plug cap. On most, you can unscrew the cap, trim 1/4" from end of wire, and screw back on. I've had this create goofy issues in past.
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Re: I am stumped... Suzuki FA50 problems please help

Post by kingdele » Fri May 11, 2018 12:39 pm

Meatball wrote:Ive had a petcock go bad in couple different ways. No flow, constant flow and the ever frustrating (and toughest to diagnose) intermittent flow. Ive never had restricted or partial flow but its not impossible. A dirty fuel filter would create the situation you describe..also a gummed up (or kinked/damaged) fuel line.

How old is the fuel? Check compression?

YouÔÇÖll only fail if you stop trying. Keep going.
I dumped the fuel when I got it and have ran about one and a half fresh tanks through it. I have heard that some gas tanks sometimes have a fuel filter at the very bottom of the tank have you heard of one of those being on a moped?

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Re: I am stumped... Suzuki FA50 problems please help

Post by kingdele » Fri May 11, 2018 12:53 pm

noiseguy wrote:Fuel starvation, it will normally go to top speed immediately, then stumble down.

You're describing a lean carb at 3/4 to WOT. You need to check the condition of the main jet and emulsifier tube. I'm betting one or both are partially clogged, or main jet's not correct for the application.

Other things to check are clogged exhaust and over-oiled intake filter (wring it out with clean paper towel until you can't get any more oil out.)

Also check condition of plug cap. On most, you can unscrew the cap, trim 1/4" from end of wire, and screw back on. I've had this create goofy issues in past.
The carburetor is new and acts the same exact as the stock one which I cleaned two times so I donÔÇÖt think itÔÇÖs clogging anywhere in there (I made sure the emulsifier tube was clean on the stock too). Otherwise the exhaust and intake filter are checked and fine. But my question is, what would be characteristic of if those plug cap wires were junky like you said?

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Re: I am stumped... Suzuki FA50 problems please help

Post by cancunia » Fri May 11, 2018 1:24 pm

If you're getting lower revs at full throttle than half throttle it's maybe a too rich, or too lean problem at WOT. Did you try to move the needle in the slide up or down? Personally, I'd see what happens without the air filter. Did you check the reed valves?

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Re: I am stumped... Suzuki FA50 problems please help

Post by noiseguy » Sun May 13, 2018 10:47 pm

kingdele wrote:The carburetor is new and acts the same exact as the stock one which I cleaned two times so I donÔÇÖt think itÔÇÖs clogging anywhere in there (I made sure the emulsifier tube was clean on the stock too). Otherwise the exhaust and intake filter are checked and fine. But my question is, what would be characteristic of if those plug cap wires were junky like you said?
Checking the wire would literally be faster than me explaining the possible running issues. Just do it.

"New" carb... new from Yamaha, new Chinese, new to you (used?) You checked the size of the main jet... right? B/c that's one of the things you check on a replacement carb...
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Re: I am stumped... Suzuki FA50 problems please help

Post by kingdele » Wed May 16, 2018 8:33 am

noiseguy wrote:
kingdele wrote:The carburetor is new and acts the same exact as the stock one which I cleaned two times so I donÔÇÖt think itÔÇÖs clogging anywhere in there (I made sure the emulsifier tube was clean on the stock too). Otherwise the exhaust and intake filter are checked and fine. But my question is, what would be characteristic of if those plug cap wires were junky like you said?
Checking the wire would literally be faster than me explaining the possible running issues. Just do it.

"New" carb... new from Yamaha, new Chinese, new to you (used?) You checked the size of the main jet... right? B/c that's one of the things you check on a replacement carb...
ItÔÇÖs a new carb exactly how I said and yes the main jet is the exact same. I think itÔÇÖs a Chinese but I looked it over and itÔÇÖs very well built and they included all the connections and assemblies to replace instead of use the old parts.

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Re: I am stumped... Suzuki FA50 problems please help

Post by noiseguy » Wed May 16, 2018 2:51 pm

Wait... issue followed from old carb to new carb? So that's not the issue then.

Did you check the electric / spark? New plug, etc? It has to be either the electrical system or the exhaust.
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Re: I am stumped... Suzuki FA50 problems please help

Post by kingdele » Sat May 19, 2018 8:41 pm

noiseguy wrote:Wait... issue followed from old carb to new carb? So that's not the issue then.

Did you check the electric / spark? New plug, etc? It has to be either the electrical system or the exhaust.
Yes, and I have put in a new plug.

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Re: I am stumped... Suzuki FA50 problems please help

Post by Wheelman-111 » Sun May 20, 2018 8:46 am

Greetings:

Coming late to this, sorry. I don't see that you have performed a compression check anywhere? The condition of the crank seals - one is hidden behind the flywheel, is open to question. If a little weak, it might idle just fine but leak as the pressures rise with higher output conditions.
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Re: I am stumped... Suzuki FA50 problems please help

Post by kingdele » Sun May 20, 2018 11:14 pm

Wheelman-111 wrote:Greetings:

Coming late to this, sorry. I don't see that you have performed a compression check anywhere? The condition of the crank seals - one is hidden behind the flywheel, is open to question. If a little weak, it might idle just fine but leak as the pressures rise with higher output conditions.
So by this theory the compression is low but the increased force at full throttle causes a more dramatic drop in power than when using 1/2 throttle in regard to rpms? And yes, I have been meaning to compression test it but I really didnÔÇÖt think it was that because it idles perfect so I guess I gotta go borrow one (I donÔÇÖt own a compression tester).

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Re: I am stumped... Suzuki FA50 problems please help

Post by noiseguy » Tue May 22, 2018 10:21 am

I always forget about the bottom end seals... yes those can definitely cause issues if they're worn out. You need to inspect them though... this is bottom end compression and so measuring top end (I don't think) will show the issue. Expect you'll be looking for evidence of oil leak around bottom end seals as the indicator of failure.
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