Loss of power, compression loss or carb?

[robmsz]

Had my beloved totally stock zx50 over 10 years now (I think it’s a ‘04), hasn’t given me many problems. The biggest things that hold me up are things failing #1 are the CDI boxes. I was lucky to figure out (with the help of this forum) how to use $7 CDI’s from ebay, have a couple spares lying around. #2 was my oil line. Think my passenger was a little to heavy and helped the oil line off which resulted in it blowing up.

Now I have a never seen before problem (at least by me). I don’t drive it often unless my 90 yo dad sneaks it around the block. On one of my “test rides” around the block it ran ok once around and on my second pass it lost power and seemed to bog instead of the high pitched pinging 2 stoke noise. Things I have done.....checked my oil, enough oil, changed CDI, ran the same either way, changed the plug, no difference, drained the bowl, gas was running freely.

So I’m guessing either compression or carb? I don’t have much time on my $40 replacement head from eBay, although I did reuse a old ring after I cracked a new one installing the piston. It’s a pain taking all the plastics off so my next step....when I get around to it will be a compression test.

Any thoughts, advice?

Maybe someone else had the same problem?

[Tiny]

if it's 10 years old it may be time to rebuild the top end.  to keep it going strong 2T's need a top end build every few years/10Miles. so all you need is a new 50cc kit or upgrade to a 70cc but then that would necessitate a larger carb.

[robmsz]

I find that hard to believe. I had 16km on when I had to replace the head and that was only because my oil feed fell off. I have no where near the mileage on with the second jug & piston. That being said, I have yet to get off my a** to do a compression check. You do have a point by killing two birds with one stone with bigger head, bigger carb. I wouldn’t need to clean the carb if it was bad. Wouldn’t that necisitate A bigger exhaust to get the power out of the two other upgrades?

I guess that’s neither here nor there until I get a compression check. It’s been rather trouble free and I’d like to keep it that way. I’m dragging my feet because whatever I find I’m going to have to remove the plastics and they’re hanging precariously as it is.

[TBR125]

In general a higher flow exhaust isn't necessary unless a much less restrictive intake and filter are used. If you do get a higher flow exhaust it needs to maintain the current engineered exhaust velocity. If you lower the gas velocity until pulse draft is lost your low end torque will suffer which is not a great thing on a little engine.

[robmsz]

Way over my head except for the part that said “not necessary”. That is good news for me! So your saying I’ll benifit more power with a 70cc head & carb WITHOUT having to upgrade my exhaust? What size carb should be fitted to a 70cc head?

[TBR125]

70cc from 50 is about enough additional displacement to warrant a larger exhaust. I was thinking about air flow increase like air filter and missed the big block post. I do not know the best carb size for that bike.

[robmsz]

I finally got around to test the compression, 125psi so we can nix a jug change. I checked that first because that’s what it sounds and feels like.

I’m leaning to something Murphy law like, it’s something simple and stupid. Could any hoses or automatic choke have to do with anything? Tried starting it today and would even pop. I cranked it full throttle like I do with my chainsaws when the flood, still nothing. The plug is wet.

[robmsz]

Dragging my feet not wanting to rip this thing apart seems to have paid off for me. I did end up pulling the carbatooter and cleaning it. But like I said before, it’s usually pretty dependable unless something unforeseen (ex. Oil line falling off) happens. While I was stalling putting the carb back on and looking over stupid sh** on the scooter, I noticed the outlet tip on the exhaust looked a little small. I stuck a screwdriver in there and started breaking apart what looked like a mud plug. Apon further cleaning a couple BBQ’d wasps came out. Not saying that was the problem because I haven’t replaced the carb yet but talk about some stupid sh**?......

Now that I have a positive thing happen I’m about to re-install the carb....so update coming soon!

[robmsz]

Got it all back together and no spark, I mean what are the chances. I keep a spare CDI in the glovebox so I popped than in and it started right up and ran smooth as silk. The only thing I needed to do was unplug the damn exhaust    who woulda thunk it?

[TBR125]

We are usually stumped by the simplest of the problems. I have torn the bike down only to find the spark plug was left disconnected.

Glad you found it! dirt dobbers are bad at filling all holes.

[robmsz]

When I was younger I would have been elbow deep into pieces of this scooter. As I’ve gotten older, smarter and lazier I’ve learned to be more patient & methodical in my diagnosis. I’ll check, dbl check and check again if something doesn’t run right. It saves me a lot of un necessary work over a problem that was something simple to begin with. It helps to move from one project to another instead of the mindset MUST FIX NOW attitude.

[robmsz]

Had to walk the scooter home yesterday. Pulled the seat out to get to the muffler and had to remove it COMPLETELY to get it to run.. Does anyone have a original muffler laying around for cheap? Maybe upgraded to a high performance one. I’m not looking for performance, I’m looking for reliability, I have a motorcycle for performance.

Does anyone know where to get a decent CDI replacement for cheap? The last 3 I bought were duds. I had two spares for a few years. One hanging in the garage, the other in the glove box on the scooter. The one in the glove box is working ok. Then I wired up the second one and it doesn’t work. In the mean time I ordered two more. One will light up but won’t start, the other one won’t even light.

[robmsz]

We can nix the replacement muffler, I’m going to throw it in a campfire and hope for the best. I’m not sure if it’s wasps or oil buildup but I’ll let you know after it comes out of the fire.

[TBR125]

If you mean that in a literal sense kudos for creativity. May need a new coat of hi heat paint. Might also need some bending to get back on the scoot as the heat will warp the can.

[robmsz]

Yes, literally throw in the fire. Paint is no problem, it’s been painted before. I’m trying to get enough oil residue out to function semi normal. I don’t want it to turn cherry red, then I can take it for a couple hour ride to heat it up enough to clean out the rest.

I think my problem started when I start it, take it around the block (less than a quarter mile) and park it. I don’t give it a chance to heat up enough to keep it clean.

Do you think I’ll warp it if it’s done to medium?