1989 SA50 will idle but not rev after bearing replacement.

[mwistrom]

Well, as the title says, my scoot won't rev.

History: Found scooter in a garage. Hadn't been run in 20 years. Cleaned out the carb, put a bolt in place of the screwdriver that was holding the front suspension together. Put about 3,000 miles on it over the next two years. Even ran through the gas that was in the tank when I got it.

[mwistrom]

Started running LOUD and decrease in power. Let it sit for a year.

[mwistrom]

Can't get by the SPAM filter......

[mwistrom]

Pulled out the engine and tore it down. Used the kitchen table, which is one of the perks of not having a gf. Main bearing was shot; the cage in the bearing was only holding 2 of the 7 balls in place.

[mwistrom]

The other balls were running freely between the two races. Crank has play in it. Replaced only the bearing and reused everything else. Crank spun smoothly after the replacement.

Now, she won't rev up. Starting can be a little difficult, but once idling, it will sit and run forever. Open the throttle and the engine speeds up and then dies. Seems a little harder to get started after that. Sometimes it takes many, many kick starts to get it going again.

[mwistrom]

Here's what I've done:
Carb: I've cleaned it three times and everything seems in order.
Spark: pulled the plug and cranked it to see lots and lots of sparking.
Reed: reed seemed fine when I put it back together. I pull the reed again, and it still seems fine.
Compression: i put a tester on it to verify that I had compression. After 10 kicks, the tester indicated a pressure of 115 PSI.
Air filter: seems in order. No changes to that in a while.

Just got back from starting it up and letting it sit for 5 minutes at idle. Then it just died by itself. Kicked it for another 5 minutes, but only got like a couple of fires, and it wouldn't start again. <sigh>

Comments?

(Sorry about the format. Could not figure out how to get by the SPAM filter.)

[mwistrom]

No idea what to do.

It will start and run, rev up and then die.
I dumped some oil in through the plug hole and it started and reved high until the oil was burned out.
Pulled the vacuum line to the fuel tank and the engine speed up, but it died after and wouldn't run right.

It reved up before I replaced the bearing so I don't understand what is wrong now.

Compression is a bit low @ 115, but I think it should still run just a little worse than normal right? I measured the cylinder dimension at several places and it was between 1.611-1.614 which seems to be within spec.
The float measured at about 0.46" which means the float is a bit high, but does that mean it is too rich? How does the float height change when there are no adjustments?
Too much oil coming in from the oil pump? Preventing enough gas to mix in?

Choke or by-pass thingy on the carb extends with 12V applied to it after about 30 sec - 1 minute, so I guess that is fine.

Given the way that it dies, I don't think it is a spark issue.

I noticed that the spacer between the carb and the intake manifold is gone. I don't think it was ever there. Does that make a difference?

No idea what to do next.

[mwistrom]

Alright, lets go through the checklist:

1. Spark
   a. Pulled the plug and cranked the engine. Saw some sparking. See video.
   http://youtu.be/BoiKh_nkSUg
   b. See close up of the spark plug. Looks like it is a little rich?

   

   IMG_0803.JPG (44.32 KiB) Viewed 5722 times

2. Compression
   a. Put the compression tester on there and cranked with WOT. 115 PSI.
   b. See picture

   

   IMG_0806.JPG (68.36 KiB) Viewed 5722 times

3. Fuel supply
   a. Verified that fuel will flow when vacuum applied to the fuel valve
   b. Cleaned tank anyway and forced air through the fuel valve. Looks REAL clean in the tank.
4. Carb
   a. Cleaned about 4 times. Used carb cleaner and compressed air.
   b. Only thing is that the float is more like 47mm and not 48mm, but there is no way to adjust it.
5. Air cleaner
   a. Seems OK
6. Exhaust
   a. Seems OK. I see smoke come out of it like it always does.
7. Reed valve
   a. They look OK. I don't know what can go wrong with the reed valve. I suppose I should snap a pic of it too.
8. Crankcase pressure
   This is the area that I changed. I suspect that the problem lies in the reassembly of the crankcase and it related parts.
   a. I don't know how to test the crankcase pressure.
   b. When reassembling the engine, without a plug in it, I could spin the crankshaft and tell that there was pressure being built up in the crankcase. No idea how to test while the engine is running.
   c. I had to replace a bad main bearing. I reused the crankshaft seal on that side because it looked good. Maybe that seal is the one that is going bad and leaking? Would that make it run rich?

Well, a simple google search "how to check crankcase two stroke" brings up some ideas. This is my next avenue of attack.
I pressurized the crankcase. Put 20 PSI in it and sprayed all around with soapy water. Could not see any leaks except for the intake and exhaust ports which I couldn't get a super tight seal on. The spark plug leaked a bit when it was hand tight, but not after I used a wrench.

Anything else I'm missing?


Here is an example of it "running":
https://www.youtube.com/watch?v=FNY-dRm ... e=youtu.be


Oh, and here is what is left of the bearing.

IMG_0811.JPG (38.31 KiB) Viewed 5722 times

[mwistrom]

<sigh> I'm an idiot. I know.

I replaced the spark plug on a whim, and it runs fine now. I thought I had excellent spark, but no....

Hopefully someone else will be able to gain something and troubleshoot their scoot based on this thread.

[mwistrom]

I tried to compose a single comment, but it kept getting rejected by the spam filter.

What is "the facebook"?