PA-50 II Riddle - Got a minute or two?

After days of reading manuals and forms/posts I had a go at some of the fixes people suggest. The results seemed sucessful... for about 20min and until a big hill.

If you're willing and interested, here's what happened:

-Removed petcock to check fuel filter / screen

-Air filter seems ok

-Added some gas (32:1)

-Adjusted idle speed screws (to try to keep it from stalling)

-At this point the ped is running great (so I didn't check the spark plug)

-Took it out for a ride and it felt as if it were 'four stroking' (at least from the definitions I've read)

-Stopped for a coffee (and to watch people stare at my bike : )

-Hopped on again, started no problem, but still 'chugging' / four stroking

-Drove up a big hill (slow, but made it)

-Drove down the big hill, alll the while wondering what going so fast was doing to the engine?

-Slowed down, turned right and it stalled

-Started again (somewhat reluctantly) and went the restof the way down the hill

-Pulled into a parking lot and it stalled again

-On restarting is backfired a couple times, not a big bang, but definitely a backfire

-Checked the air filter again and tried riding without it (four stroking check)

-Engine was much worse without the air filter

-I let the moped sit for a couple hours, and when I tried to start it no luck. Would start to turn over but wouldn't continue

Being a newbie I have some ideas from readings posts etc. but at this point I probably know just enough to be dangerous. I'm going to clean the air filter, check the spark plug for signs of fouling and maybe try some carb cleaner (to see if that makes a difference before trying to take the carb apart).

Sorry for the long post, but I thougt I'd give as much info as I could.

Any help and suggestions are most appreciated.


Re: PA-50 II Riddle - Got a minute or two?

Jason Luther /

i bet with the 4 stroking it fouled the plug. my hobbit four strokes at top speed too and the only way to make it stop is to pull the air filter out about 1/2 inch. so get a new plug and try that (if the old plug is fouled)

Re: PA-50 II Riddle - Got a minute or two?

i've had similar symptoms a few times.. one time, the symptoms gradually worsened over a period of a couple days.. Amazingly, a brand new spark plug cured it completely..

However, the rest of the times (several) it was traced to dirt in the fuel system, specifically a partially clogged main jet. The reason in my case was short term storage and deteriorated fuel creating varnish deposits which peeled and flaked off, ending up in the float bowl..

If opening the airbox filter (allowing more air intake) worsened the problem, it says that there's already enough air getting in but not enough fuel. Opening up the air intake makes it even leaner..

Try choking the engine slightly.. If it runs a bit better its almost guaranteed there's a fuel restriction of some kind. (Choking allows less air and artificially richens the mixture)

First make sure fuel flows in a thick steady stream from the fuel line into a container, both in Main and Reserve petcock positions.. (did you clean the little screen filter screwed into the base of the petcock?)

The gas tank is vented, preventing a vacuum in the tank, which slows fuel flow.. If flow slows gradually, but suddenly increases when the gas cap is removed, it's vent is clogged..


If fuel flow into the carb is excellent, open the float drain screw 3 or so turns.. (accessed throught the special hole in the right side swingarm through the sprocket.. End of the drain hose is somewhere around or above the muffler... or on the left near the centerstand spring. ).

Drain the bowl into a clean clear glass container.. look for any little bits of junk in the fuel. If you see anything the bowl does have some junk floating around in it and the carb needs a cleaning.

All it takes is a tiny floating piece of crap in the bowl.. it swirls around, gets sucked into the mainjet and blocks fuel.. it may drop back into the bowl and only periodically block the jet.. or it may get stuck up in it...

An immaculate fuel system is #1 to good, reliable PA50 performance..

Re: PA-50 II Riddle - Got a minute or two?

couple other things..

4-stroking translates to misfiring every other revolution.. many things can cause it but on a 2-stroke it's common to refer to 4-stroking near idle and very low rpms.. The reason is regurgitated mixture at low RPM on a piston-ported intake engine.

This is due to symmetrical intake porting..

The intake port is actually open when the piston begins to decend. This can push some mixture backwards from the crankcase through the carburetor. The mixture picks up another load of fuel as it moves through the carb.. And, on the way back in, it picks up yet another load of fuel.. The triple-loaded mixture rich-fouls the plug.. result is a misfire .. The engine usualy coughs but continues to run as it is 4-stroking.

But the PA50 has reed valve intake direct into the crankcase and is immune to this particular form of misfire..


Carb cleaner is a longshot .. I did try it one time.. fed a 50/50 mix of cleaner and fuel directly into the carb through the fuel intake nipple (float bowl holds 25cc of liquid) .. left it overnight .. no luck.. whatever was in there was not dissolved by the cleaner. (rust or something). Anyway, all gasoline formulations now contain "fuel injector cleaner" as an additive...


Simple check to see if lack of fuel is the problem: Squirt a bit of Starter Fluid into the 3-holed rubber air intake tube. If it starts and runs, fuel delivery is restricted. If no-start, double check spark.. Remove the plug and ground it's base to the engine block.. crank it over and look for spark. Or, get a brand new sparkplug and try Starting Fluid again.

Re: PA-50 II Riddle - Got a minute or two?

25:1 is the fuel mix.

Re: PA-50 II Riddle - Got a minute or two?

John S.:

I would like to congratulate you on a good possting.

If everyone gave a detailed posting like you did it would make diagnosing problems a lot better. We get too manu postings like..."my ped quit running, what is wrong?"

Like joew says it sounds like fuel starvation to me. Engine dropping/carb cleaning time.

Re: PA-50 II Riddle - Got a minute or two?

Thanks for all the posts, they're extremely helpful.

To make sure I'm understanding: The PA50 can't four stroke, as joew explaied above? So I can scatch that off the list.

I'll check the spark plug today, and I guess prepare to clear the carb - this could be interesting! Hopefully this won't be anything like my plumbing experience - that would be very bad indeed.

Thanks again


Re: PA-50 II Riddle - Got a minute or two?

Patrick Mattison /

i don't think it can't fourstroke, just cannot 4stroke for that common reason

Re: PA-50 II Riddle - Got a minute or two?

Hobbits are famous for four stroking.

Re: PA-50 II Riddle - Got a minute or two?

you don't really want to put 25:1 mix in it, even though there is often a sticker that tells you to do so. put around 45:1 in it or so and it should run a lot better for you. i feel like the hobbits are kind of tolerant to shitty gas mixing but a good mix will definitely help performance. somewhere between 40:1 and 50:1 is good.

check your plug; it is probably kind of nasty from burning a bunch of 32:1 gas... might want to replace it

check for air leaks... head gasket, base gasket, exhaust. everything tightened down nicely?

perhaps an air issue? that three holed tube has a tendency to plug up, people say.. or the air filter.. is it clean.. carb... ??

fuel flow? the hobbit petcock is kind of nifty; it contains a built in filter and is fully disassemblable. might take a peek and see if the built-in filter or fuel lines are clogged with rust from the tank or dirt or what have you .. mine got clogged to shit with rust; i spent almost a half hour cleaning the thing out...

i got my pa50 (i) running about 25 but it would four stroke on the high end and it would four stroke always if it was just started and needed to warm up... never figured out exactly what the deal was, but these were some of the things that i thought about. i think ultimately there are some in-built issues with air supply and carburettor capability... and some of it was probably my ill-sealed proma circuit that i stuck onto it, but that's another story entirely.

just some suggestions from a slightly intoxicated fellow pa50 owner

Re: PA-50 II Riddle - Got a minute or two?

Where did tou get that Proma Circuit pipe?

Re: PA-50 II Riddle - Got a minute or two?

Leon Swarmer /

another option..backfiring and lack of power could be timing off.


Re: PA-50 II Riddle - Got a minute or two?

If I run mine with a 25:1 mix, it fourstrokes like crazy. I lean it out to 32:1.

I have been told that this is fine because the oil we have today is of better quality than the stuff made in the 80s.

Re: PA-50 II Riddle - Got a minute or two?

Mine four strokes no matter what the mix is. I was running 25:1 on Catrol 2T oil and am now running 40:1 on Redline and at top end it will four stroke either way.

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