Suzuki fa50 low top speed need help, tried everything.

Hi guys, I have a problem. I have a 1981 suzuki fa50, it starts on the first kick every time runs flawless. But it only goes 17 or 18 mph when it hits that speed it changes the sound it makes from a smooth running engine to somewhat of a farting sound. It acts like it's not running as good as it should be and occasionally it will surge for a second or two. So things that I have done to it. Everything. I've done literally everything. Changed every parts and no new part makes a difference in the way it runs. At this point I am questioning if the motor is bad except that it runs and starts so good. I bought a parts fa50 and just started changing parts. Things I've changed so far. Muffler, airbox, both changed and also ran without them on the fa50 no difference. New carburetor, (chinese I assume), changed the 2 jet screws on the side as well from new to old, no change in it running. I've changed the coil, checked the magneto, changed the regulator, the petcock, I've mixed the gas with oil and drained the oil pump to see if it was putting in too much oil, still no change in it running. It also puts oil out the tail pipe not a ton but definitely noticable. Only things I haven't done is change the chain oil and replace the bad battery. It also has a light electrical issue, I think the battery is bad and a couple bulbs are blown. Anyway that's it. Any ideas as to what is wrong? I really like the fa50 but its driving me crazy.(edited)

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Re: Suzuki fa50 low top speed need help, tried everything.

Have you done a plug chop from 18 MPH ? What does the plug look like ?

What main jet are you running ?

Have you tried applying the choke when running at 18 MPH ?

If it runs better , you might try lowering the needle clip .

Re: Suzuki fa50 low top speed need help, tried everything.

You have probably checked these, but it may be worth confirming or revisiting:

Are you sure the exhaust pipe is clear? I routed out mine to increase flow.

The original air box is limiting. I replaced mine with a cone shaped filter and it helped.

Are you premixing gas 50:1? I would always premix and not use the oil pump. The pump is not always dependable, and adds more oil than needed (forgot the ratio it produces) causing it to be less rich.

Are you sure you are mixing gas-oil correct? I was refilling the little 2-stroke containers from a quart and later realized I was using too much oil. That will clog things and slow it down.

Re: Suzuki fa50 low top speed need help, tried everything.

If you happen to have a bad oil pump , it would be a very rare occurrence .

And , the OEM air box suits me just fine . But , if you like a lot of noise ...

My FA50 runs 30+MPH all day long and has been for more than 10 years , without fail , other than once , which was my own fault .

Re: Suzuki fa50 low top speed need help, tried everything.

What's a plug chop exactly? I will post pics of the spark plug. I have no idea what jets are in the carb, it's supposed to have normal factory ones in it. I put the original ones in it from the original carb. Running it on choke kills the motor or if driving slows it down at least.

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Re: Suzuki fa50 low top speed need help, tried everything.

Hey there, yes I am pre mixing 50.1. I drained the oil tank last night amd premixed gas and ran it without oil in the tank. No change. I've ran the moped without an airbox and and muffler attached to it. No change. I've got a parts moped and have changed basically the entire machine and no change lol. Its frustrating.

Re: Suzuki fa50 low top speed need help, tried everything.

Everything is stock. No mods have been done. I should take it for a spin today amd take a video and post for everyone to see how it's running. It's somewhat torn apart because I've been changing parts all week on it. I will take a video and post it today.

Re: Suzuki fa50 low top speed need help, tried everything.

Here's another thought. Are you sure the foam air filter inside the air box is in correct? Seems to me that there was a recent post where someone had the foam filter on the wrong side of the plastic support piece and it caused it to run slow.

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Re: Suzuki fa50 low top speed need help, tried everything.

Re: Suzuki fa50 low top speed need help, tried everything.

Hey there here is a picture if what I have.

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Re: Suzuki fa50 low top speed need help, tried everything.

looks right.

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Re: Suzuki fa50 low top speed need help, tried everything.

You need to find out which jets are in your carb .

Re: Suzuki fa50 low top speed need help, tried everything.

How do I find that out?

Re: Suzuki fa50 low top speed need help, tried everything.

Remove them and look at the stamped #s on them .

Re: Suzuki fa50 low top speed need help, tried everything.

Okay so I dont see anything stamped on them.

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Re: Suzuki fa50 low top speed need help, tried everything.

I think you better download and read the manuals ( free ) :

https://drive.google.com/drive/folders/1raDJJQ2M_A8v9lFIxSyYpzRKIRMQ4a1f

Re: Suzuki fa50 low top speed need help, tried everything.

I already have the manuals in person and have read them cover to cover many times. I have done everything in them and nothing fixes this thing. Did you see the video I posted? Why when it reaches max speed of 17 mph does it have like a farting sound? And only go 17 mph?

Re: Suzuki fa50 low top speed need help, tried everything.

Jack Rutherford /

You didn’t pull out the main jet.

Re: Suzuki fa50 low top speed need help, tried everything.

Then you better work hard on your comprehension skills because you obviously don't know what a is main jet is or where it is located in the carb .

Neither of what you have in that bag are main jets .

Re: Suzuki fa50 low top speed need help, tried everything.

Dr. Mantis Toboggan M.D. /

You more than likely need to upjet you main jet. Looks like the stock jet is #77.5 but it's probably not stamped on your main jet with the clone carb you are using, see carb diagram. Buy a range of different sized main jets (maybe like an 80, 82, 85, 87 & 90) and switch them out until you get the best result. I would start working your way down from the largest jet size.

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Re: Suzuki fa50 low top speed need help, tried everything.

That is not the original foam element. Looks to be aftermarket or homemade. Any variance in density or thickness will have a dramatic effect on how the motor runs in otherwise stock configuration. Also there is closed cell and open cell foam. You need the later.

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Re: Suzuki fa50 low top speed need help, tried everything.

My reading comprehension is fine lol my understanding of carberators is what's lacking lol. Hence why I bought a new carburetor. I will probably end up trying the new jets and see if it makes a difference.

Re: Suzuki fa50 low top speed need help, tried everything.

I removed the air filter completely it didnt make a difference.

Re: Suzuki fa50 low top speed need help, tried everything.

Okay guys, so I changed the jets from my original carburetor to my new carburetor. No change at all. And I've removed the air filter from the box and run it, still no change. Any other ideas? Also the original jet was 77.5

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Re: Suzuki fa50 low top speed need help, tried everything.

That sound you keep refrencing is called four-stroking. Its doing that up top becuase it is too rich on the main jet. Get the main right an it will run clean in the higher rpms and youll be going faster. Read up on simple carb tuning and rejet accordingly.

The problem with swapping og parts to the chinese clone is that the two units are not going to be manufactured to the same specs and its basically a craps shoot whether any swapped parts will actually work. Youre much better off finding an original carb.

And stop saying you've done "everything" because you obviously haven't.

Re: Suzuki fa50 low top speed need help, tried everything.

> live ɘvil Wrote:

> -------------------------------------------------------

> That is not the original foam element. Looks to be aftermarket or

> homemade. Any variance in density or thickness will have a dramatic

> effect on how the motor runs in otherwise stock configuration. Also

> there is closed cell and open cell foam. You need the later.

> >

This, removeing the filter entirely will make it worse, you need some restriction the amount provided by the stock element, throwing a clone in adds tons more variables, stick with stock.

Re: Suzuki fa50 low top speed need help, tried everything.

Clean the original carb and reinstall!!! No Chinese junk! The original carb is jetted for that engine.

On to your video. When you open it up u can hear the carburetor you shouldn't hear it like that. Replace original foam filter. Check for air leaks? Carburetor gasket, reed valve gasket, base gasket, case gasket, and exhaust. I remember my 1st fa drove me nuts doing the same thing! This is what mine was check all your vacuum lines. I had little cracks in mine just enough to be way lean. Your engine is lean not rich!

Re: Suzuki fa50 low top speed need help, tried everything.

> Cameron Cate Wrote:

> -------------------------------------------------------

> That sound you keep refrencing is called four-stroking. Its doing that

> up top becuase it is too rich on the main jet. Get the main right an it

> will run clean in the higher rpms and youll be going faster. Read up on

> simple carb tuning and rejet accordingly.

>

> The problem with swapping og parts to the chinese clone is that the two

> units are not going to be manufactured to the same specs and its

> basically a craps shoot whether any swapped parts will actually work.

> Youre much better off finding an original carb.

>

> And stop saying you've done "everything" because you obviously haven't.

I agree but failed to touch on the four stroke sound hes hearing. If someone else had that carb apart to "clean" they may very well have enlarged the original main jet with a wire or jet drill.

Re: Suzuki fa50 low top speed need help, tried everything.

If they opened up the jet it would run better with out the air filter but since its running the same I'm betting there's an air leak somewhere!

Re: Suzuki fa50 low top speed need help, tried everything.

Pushrod Fifty /

If you didn't block the oil inject system youre pulling air into the crankcase. That foam is upholstery closed cell foam. Best to put everything back to stock and work with one variable at a time.

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