1979 PA50 II Engine Cleaning

I recently bought a used PA50 (fourth-hand, no less) in very good condition. Starts on the first kick, and runs fine. However, it wouldn't ever stay idling. After messing with the idle screw, we determined the issue was a dirty carb. Last night, we finally got around to taking the engine apart (thanks a lot Honda) to get to the carb to clean it.

However, we then realized that neither of us really knew what to do exactly (it didn't look like I had imagined it would). I've done some research, and I basically determined that I should just spray carb cleaner anywhere that looks gross (not on rubber of plastic) and then shoot some canned air in the same spots. I'm going to do that, but I have two questions -- am I right in doing that, _and_ is there anything else I should do before putting everything back together? It's quite a production to take everything off/put everything back together on a PA50, and I don't want to have to do this all over again. Thanks a lot, you guys have helped me a lot already.

Re: 1979 PA50 II Engine Cleaning

the carb is accessed by separating the frame from the swingarm.

The swingarm/engine assembly can drop to the floor if the main pivot bolt in front is removed.

Another way is to suspend the frame from overhead. Then remove that pivot bolt as well as the rear shock lower attachments and raise the frame.

Both methods require the disconnection of various cables and wires and both method details can be "Searched" out in this forum.


As far as cleaning the carb, i recommend you do a lot more than spray cleaner on whatever looks gross .. the penalty for a botched job is dropping the engine again.. and again.

Search this forum for general carb-cleaning tips and techniques

The carb should be completely disassembled, carefully cleaned and examined (this cleaning includes removing the emulsion tube and it's cavity, found above the main jet). Detailed instructions on cleaning this carb can also be Searched if you can't figure it out.. Here is one thread break>


Make sure there are no vacuum leaks in the carb / reed valve area. Seal gasket surfaces on the intake manifold-engine-carb with Permatex 2 (non-hardening gasket sealant).


Assuming the carb is truely clean and there are no air or fuel leaks anywhere, reinstall it, reattach all cables, wires, etc and adjust idle.

The idle air and speed screws are used together to set idle. First the engine MUST be really warmed up or it wont idle when it's hot.

On the warm engine, lower idle speed (with the idle speed screw) until the engine threatens to die. Then, slowly play with the air screw, in and out, until RPM increases. Then lower idle speed with the speed screw. Then play with the air screw again so idle speed increases.

At some point, the air-mixture screw will no longer be able to increase idle RPM. At this point the idle air:fuel mixture is correct and you're done.


Grab both PA50 Hobbit Manuals on THIS PAGE break>

if you get stuck or can't find some specific info, ask..

Re: 1979 PA50 II Engine Cleaning

"This should be the correct Wiring Diagram":http://www.mopedarmy.com/forums/discuss/download.php?f=6&file=1082480832_honda_pa50_1978_wiring_diagram.jpg since the '78-79-'80 PA50s have no battery.

There's nothing special about reasembly beyond being careful and thorough .. shortcuts turn into longcuts.

It might be wise to put a drop of blue (removable) LocTite on the engine block-to-swingarm mounting nuts/bolts (if you actually removed the engine from the swingarm) since they tend to loosen and fall off and get lost.

I'd caution again about getting and keeping the carb and fuel system absolutely clean.. once that's done the bike will run strong and trouble free. Use fresh gasoline and run the engine at least once every few weeks.. Leave it sitting for a couple months and you'll probably end up dropping the enging and cleaning he carb again.

Re: 1979 PA50 II Engine Cleaning

Make sure when you re-install the carb float bowl, it is in the proper orientation(position). There are two ways it can go on, one is 180deg out and incorrect. The key is the drain on the exterior bottom of the float bowl should be pointing to the RIGHT. This is the correct position. Take a look at it and you will see what I mean. This is a very simple thing, but critical! (and not mentioned in the manual!)

Getting to the carb is talked about alot in these forums. Once you do it a few times using the recommended methods, you will see that it truly is no big deal.

Good luck!

Re: 1979 PA50 II Engine Cleaning

Be sure to remove all jets from the carb. After removing the main jet, smack the carb against a block of wood to remove the emulsion tube, or you can reach into the throat to see if it will come loose. Clean every port and orifice thoroughly.

While you are at it, remove the fuel shut off valve and clean the screens on it also.

Re: 1979 PA50 II Engine Cleaning

Awesome, thanks a lot guys. I think the carb is clean now, sprayed out all the holes and stuff, made sure air could go through all of them. We're going to start reassembling it now, if I can get a new tire for the back. It's the original tire, it looks like, from 1979. Probably not very safe. Thanks again!

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account