Help! Compression on my 2 stroke way low. No start!

[hendo]

Hey all. 
I have been repairing an Oliver City CPI 2011. This scooter has a 1E40QMB engine in it (a 49.2cc 2 Stroke engine). I removed the oil pump after it failed. The scooter seems to be getting enough fuel and it has a pretty healthy spark. I ran to harbor freight and purchased an inexpensive compression tester to try to rule out compression as a reason for the no-start. Turns out that the compression in my engine is terrible. 
I saw a thread about what one can do if the compression is low for a 4 stroke but wanted to inquire about what I should/do now. Included below is a picture of my compression meter after doing a couple of strokes with the kick starter. 
Any suggestions about what I should do now? do I have to replace the cylinder and piston? Is this time to put a big bore kit in? Any suggestions would be more than appreciated. Thanks. 

[Happypancake!]

HF gauge isn’t the best. Did you open the throttle while testing ?

[pinkscoot]

I have a HF tester that reads 30psi no matter what the real compression is. They are for larger cylinders is what I have heard.

[maddevill]

Throttle has to be wide open. 2 stroke top ends are easy to fix. First thing, remove your reed block and see if you have a broken reed. If the reeds are metal and broke, you probably have cylinder damage. If everything looks good, just remove exhaust and intake and unbolt the head and cylinder. Boom you're 90% done. Measure cylinder bore or at least check ring end gaps. Refresh as necessary.

Mad

[pinkscoot]

Dec 9, 2020 16:06:42 GMT -5 maddevill said:

Throttle has to be wide open. 2 stroke top ends are easy to fix. First thing, remove your reed block and see if you have a broken reed. If the reeds are metal and broke, you probably have cylinder damage. If everything looks good, just remove exhaust and intake and unbolt the head and cylinder. Boom you're 90% done. Measure cylinder bore or at least check ring end gaps. Refresh as necessary.

Mad

But before you do that check your compression with another gauge.

[wiscootsin]

if you want to go the "right way to do it" route then yeah, do as pinkscoot says and get a better gauge.

If you want to go the "i'd rather not spend money" route then just take the thing apart and see if your reeds or cylinder and piston are bad.

if the oil pump failed while riding then under-oiling can blow the piston pretty quickly.

[repherence2]

I suspect your cylinder experienced a soft seize at some point.

You mentioned that you removed the oil pump after it failed. ...and now you have low compression.

I suspect that your piston rings are not seating properly on the bore wall. A condition like this happens after a seize and the piston rings end up trapped in the piston grooves, thus the rings are unable to properly seal against the cylinder wall. ...in turn, low compression.

[ThaiGyro]

Bottom line hendo...is open up your top end and check the pieces/parts.

The cylinder walls smooth? The piston "appears" ok? (check it for dimensions...diameter compared to what it should be, round? Not a dumb question)

The rings...easier to see. Are they flat on the contact surfaces? Magnify! If they look like my noggin, you need to replace them. They need a decent 45 degree shoulder from face to groove surface.

Last 2 penny's: If you are going to get a good compression gage... Find one that holds peak pressure, with a let off valve. That way you have a bit of time to see what you really have. If yours is a simple "Bourdon Tube" with no stop/check, then you must visualize the "apparent result". Not a big thing, however, but nice to have. (Trick: warm it up to ~70F/21C.)

[captincvmn]

If you do replace the cylinder check your wrist pin diameter. My Keeway has a 12mm. I ordered a Naraku 70cc kit fairly cheap and slapped that in after I roached my stock 50cc. Upjet carb slightly after cylinder swap.