PA50 II--Trouble running and what is DECOMP?

Hi All

New moped owner-Bear with my stupidity.

Im trying to figure this thing out. I dont have a manual. No one around here seems to be able to answer me. So Im coming to you all.

The bike is a Honda PA50 II (marked 1981 on the steering column). It has sat for quite some time but only has 100 or so miles on it and is in pretty good shape. I got it running tonight....ran real choppy--then REAL well (over 30MPH) then real choppy-then died. (over 15 minute period). When it ran well, I thought I had just blown the cob webs out of it. Then it got choppy again (running 10 mph or so and puttin along). Is there an air filter on these? If so-I cant find it. A fuel filter? If so-I cant find it--I want to explore ALL of my options BEFORE having to deal with the carburator. I did replace the spark plug.

There is a small throttle like switch under my throttle handle that says decomp on it. What is that? It seemed to do something when I pushed it.

Please help. Anyone with ANY help I welcome.

Re: PA50 II--Trouble running and what is DECOMP?

I can't say what's wrond with the running... Min currently isn't running (I'm almost ready to scrap it).


The decomp lever...

You use it to start it.

I have a 79 PA50, so I'm gonna imagine it's not too different....

Make sure you're running on engine power. I think you kick the lever up. Be sure the fuel valve at the front of the bike is pointing down. You may be pointing it up which is the reserve and could be causing the problem. Switch the engine to "run" and turn the key. Point the choke lever forward, press in the decomp lever, and give the pedals a go. When you hear/feel it kick over, let go of the decomp and slowly and lightly open the throttle. When your bike is all warmed up, you don't need to use close the choke.


Re: PA50 II--Trouble running and what is DECOMP?

the DECOMP is a is a small vaulve on the cylender of head that opens up to lower the compression and make the engine easier to start...........when its running opening the decompresser will take away some power.....only use it to start the bike ...when it starts let go

Re: PA50 II--Trouble running and what is DECOMP?

Here is an owner's manual:

A shop manual:

And Fred's Guide:

If the bike has been sitting for a long time, I would definitely drain the ols gas and refill the tank with fresh gas and 2-cycle oil. (You might want to start with 40:1 if it hasnt been run in a long time).

You may still have to clean the carb, which is a bit of a pain in the ass.

Re: PA50 II--Trouble running and what is DECOMP?

Holy smokes you guys

Thank you for the quick responses and help--I wasnt using the choke-so that could be part of it too--it might have been choked the whole time--or not choked at all.

I will probably end up having to do this carb cleaning thing. I, at first, was wondering if I would have to (after all-it only has 100+ miles on it really--I didnt think it had been run enough to gum up).....but Ill try every option first. I know Ill replace the gasline--its a little leaky.

Im printing the manuals and gonna study up real good.

Any input you all have-Ill continue to receive it! :)

Thanks for the manuals!

Re: PA50 II--Trouble running and what is DECOMP?


There are two fuel filters on the bike.

On the bottom of the on-off-reserve tap is a hex headed cap. Unscrew it to clean one of the filters. The other is a screen over the fuel/reserve piped up inside the tank. To get to them you have to remove the fuel hose and unscres the whole thing out of the bottom of the tank.

The carb is probably plugged up with hard gas residue from sitting so long. When the gas evaporates it leaves behind a varnish like substance that gums up the jets.

There is a possibility that the vent hole in the gas cap is plugged. Try running it with the gas cap loosely attached.

What gas/oil mix did you use? Did you mix it properly before you put it in the tank? What does the plug look like?

Do a search on recent postings about the Hobbit. Joew has posted an explanation about how to get to the carb easily.

These are good solid bikes and with the variator it even goes up hills. Do what you have to do to get it running properly.

Good Luck

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