FA50 Tuning Help

mishan /
mishan
Nov 27, 2007 04:22AM

I mentioned this in another thread from general discussion but this really deserves a thread of its own..

So I have an '82 Suzuki FA50 that I bought a while back. It was leaking oil from the base gasket and only lasted a couple of days before the engine seized on me and I could not get it started anymore. On disassembly I found that the first piston ring was seized.

Anyway, I had the cylinder bored/honed to first oversize, ports expanded, and head milled down. Before the engine seized I was able to pull almost 30mph out of it. After this build I can only get it to go about 25mph tops and I was hoping the build would give me more top-end rather than just extra torque.

What’s weird is it seemed to be running rich straight-out after the build with stock carb jetting. It responded negatively to any up-jetting and actually worked better when I kept the stock jetting and replaced the airbox with a high-flow air filter.

I'm wondering if anyone has any experience tuning these bikes and knows how to get more top speed out of it. Are there any larger carburetors that are compatible with it?

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Re: FA50 Tuning Help

jon /
jonko
Nov 27, 2007 06:43PM

you say that it was running rich and you upjetted? did you mean to say you downjetted?

if not, it sounds like downjetting or adding more air(like your high flow air filter) are the way to go.

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Re: FA50 Tuning Help

mishan /
mishan OP
Nov 27, 2007 07:19PM

I determined it was running rich by upjetting (I'm assuming this means increasing the jet size) and noticing that my performance and top-speed went way down as a result. I was thinking downjetting might be the way to go as well. Is the increased compression of the engine increasing the vacuum and thus fuel pressure?

Anyone know where to buy jets for the stock FA50 carb? There's a possibility that Dellorto jets may fit in there but last time I tried it seemed just slightly too long.. I'll re-try and report on it.

Does exhaust make a huge difference in performance? When I first put the stock exhaust on, it seemed like I could feel the exhaust pulses right by the cylinder. It was also loud as hell compared to the stock engine configuration. Unfortunately I tried to then tighten the exhaust more which ended up snapping one of the bolt studs into the cylinder.. I still have to drill out the stud and find a new bolt.

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Re: FA50 Tuning Help

Eric P /
neutral4x4
Nov 27, 2007 10:42PM

I have a stock FA50. It goes exactly 20 mph. You are really well off if you can make it go over 20mph. the exhaust makes a major difference. DO NOT RUN THE BIKE WITHOUT THE EXHAUST! Running the bike without the exhaust will make the excess gas dissipate into the air. the excess gas should be going back into the cylinder to cool the piston and add more power to the engine. If you can, ditch the old exhaust and make an expansion chamber exhaust. the stock exhaust might be restricted(no idea but probably) and doesn't have an expansion chamber to help the fuel return to the engine. Do a plug chop. there is an oil adjustment screw on the carb. The front screw is the idle screw the back screw is the oil mixture screw.

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Re: FA50 Tuning Help

greybeard /
greybeard
Nov 28, 2007 10:04AM

Check your vacuum operated petcock, the diaphragm may be leaking fuel causing your rich condition.

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Re: FA50 Tuning Help

william /
william42420
Nov 29, 2007 01:50AM

hey A MY FA DOES ABOUT 28 30 MPH DAMM NEAR STOCK ALL IVE DONE IS GUT THE MUFFLER

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Re: FA50 Tuning Help

greybeard /
greybeard
Nov 29, 2007 10:50AM

Mine does 27 totally stock and legal.

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Re: FA50 Tuning Help

CJ /
jcktm
Nov 29, 2007 01:03PM

I have one that wont exceed 20 mph, one that will do 27, and one that tops out at 23. They are all bone stock, and Ijust roasted all of the mufflers.

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Re: FA50 Tuning Help

mishan /
mishan OP
Nov 29, 2007 01:58PM

Frustratingly inconsistent nopeds aye?

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Re: FA50 Tuning Help

mishan /
mishan OP
Dec 10, 2007 06:26AM

I still haven't fixed the exhaust issue yet but I made some progress on this bike..

I flushed the transmission oil out (I had it overfilled) and refilled it with exactly 500mL of some good 10W-30 I had and now I can almost hit 30mph flat out.

I bet a performance pipe could get some good gains for it.. If I could find someone who could make one for me.

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Re: FA50 Tuning Help

william /
william42420
Dec 15, 2007 01:30AM

did the jets wprk out for you

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Re: FA50 Tuning Help

Graham Motzing /
grahammotzing
Dec 15, 2007 02:20PM

maybe suzukis are shit, but i've worked on a lot of expresses and they all do 27 stock, 30 without the airbox (which will sieze them). I am interested in this 'porting.' Did you do it, or did somebody else do it, did whoever did it know what they were doing? How did you break-in? Usually when you do something to a bike and it starts running rich, it means you fucked something up to retrict air more. I'd look at porting, and break-in procedure.

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Re: FA50 Tuning Help

mishan /
mishan OP
Dec 16, 2007 08:08PM

The engine was previously seized so I brought it to a machine shop. The guy said he specialized in 2-stroke engine building, so he bored and honed the cylinder, widened some ports and polished everything. I had him mill down the head a little bit for extra compression. He also milled the cylinder down around the transfers to remove obstruction -- he flattened the circular parts that were sticking out.

He said it would need jetting to get it to work right and it did run rich straight off so he was right. After some experimenting I found it worked well with a high-flow filter with stock jetting. What it really needs is a bigger carburetor I think..

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Re: FA50 Tuning Help

Eric P /
neutral4x4
Dec 17, 2007 10:14PM

Is the FA50 cylinder aluminum? I havn't needed to even look at my FA50 because it is so reliable. If the cylinder is aluminum, it probably had a nicasil coating so the cylinder will probably wear faster without it. Maybe not. The boost ports shouldn't be polished. That stops atonomization. what ports did he widen? What "circular parts that were sticking out" did he flatten?

Eric

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Re: FA50 Tuning Help

mishan /
mishan OP
Dec 17, 2007 11:21PM

It's a cast-iron cylinder. He polished the transfer ports, widened the exhaust, he milled down the outside perimeter of the portion of the cylinder that goes into the engine base. There are ports on opposing sides of the cylinder that were very slightly obscured by the curvature of the cylinder at the extremities.

Not sure how he modified the intake port as I didn't look at that closely enough.. This was an older man with a lot of racing engine trophies under his belt, so I believe he must've known what he was doing.

CW Racing Engines in Campbell, California

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