Brand new engine low compression (50 psi)

[Daveinfl33777]

I got some conventional oil at autozone...mixed it down to 16 to 1....it actually starts now a little easier and I had it running and surprisingly it did idle for about 20 to 30 seconds after I warmed it up....really only wants to run at full throttle though...

So my theory right now is it probably increased the compression enough to get it to start a lot better than before because of the extra oil....even if it just bumped it up 5 or 10 psi it's enough to actually get it to run better than before...before it wasn't even starting at all...if this is the case then I need a rebuild I probably egg shaped the cylinder by maybe going a little too hard in beginning...

Now the other possibility (and I'm hopeful) is it is running very rich either from lack of spark (weak spark) or a carburetor jetting issue....the 16:1 leaned things out (because less fuel of course is available compared to the previous 40:1 I was using)

So at this point I'm leaning towards low compression but I remain hopeful that maybe an ngk spark plug and new cdi gives it a stronger spark and that's all it was or there is a carburetor issue....reason I think it would be running rich versus lean is because it just never starts on choke I can only start it off choke....I guess all that's left to do is put the ngk in and new cdi....then try to mess with carb maybe try some smaller jets...but most likely I'm counting on needing a new engine or top end rebuild

 

[Johnny_]

but most likely I'm counting on needing a new engine or top end rebuild

No.

rebuild I probably egg shaped the cylinder by maybe going a little too hard in beginning...

No. The worst you could have done is scuffed/scratched the cylinder or damaged or removed the plating. You did not run it long enough to actually change the shape of the cylinder walls. And from the pictures you posted, as far as I can see your cylinder is fine.
Idk what engine you have, but I'm gonna guess you have the standard Bofeng carb like is in the picture I'll post. It sounds like you need to lean up the idle. It's easy and fast, and might fix all your problems. If you don't know how to do that we can help. @DAMIEN1307 has a picture that shows the direction you need to go to make it richer/leaner. I'll see if I can find it.
Bofeng carb looks about like this.

Definitely wait until after you tune the carb and install the NGK plug before drawing any conclusions on whether the engine is wrecked or not.

 

[Johnny_]

Here is the reference. Sounds like you need to go up on the needle to make it leaner.

Here is the order it goes together in.

Here's a video showing how it's done. The cap just screws off the carburetor.

View: https://www.youtube.com/watch?v=4KNISUKuQwY

One more thing, there's a possiblity you won't have to change the actual jet size. It may just need adjustment of the needle. The main jet controls high speed, and you mentioned it does run at higher rpm's.

ALSO you may need to set your idle speed higher to keep it running. It's that flathead screw near the center of the carb by that brass thing in the picture I posted earlier.

 

[Daveinfl33777]

No.

No. The worst you could have done is scuffed/scratched the cylinder or damaged or removed the plating. You did not run it long enough to actually change the shape of the cylinder walls. And from the pictures you posted, as far as I can see your cylinder is fine.
Idk what engine you have, but I'm gonna guess you have the standard Bofeng carb like is in the picture I'll post. It sounds like you need to lean up the idle. It's easy and fast, and might fix all your problems. If you don't know how to do that we can help. @DAMIEN1307 has a picture that shows the direction you need to go to make it richer/leaner. I'll see if I can find it.
Bofeng carb looks about like this.
View attachment 222468 View attachment 222472

Definitely wait until after you tune the carb and install the NGK plug before drawing any 7gg%

Here is the reference. Sounds like you need to go up on the needle to make it leaner.
View attachment 222470

Here is the order it goes together in.
View attachment 222471

Here's a video showing how it's done. The cap just screws off the carburetor.

View: https://www.youtube.com/watch?v=4KNISUKuQwY

One more thing, there's a possiblity you won't have to change the actual jet size. It may just need adjustment of the needle. The main jet controls high speed, and you mentioned it does run at higher rpm's.

ALSO you may need to set your idle speed higher to keep it running. It's that flathead screw near the center of the carb by that brass thing in the picture I posted earlier.

I actually have the needle clip in the leanest position. I have 4 positions on mine. I tried on every setting except the very bottom which is of course the richest mixture..

I also already turned idle screw all the way in as well......I just fear the 50 psi that I got when I compression tested it is telling me I may have done damage...or got a dud engine

 

[Daveinfl33777]

Maybe i get lucky and my spark is just simply weak...New cdi and spark plug will tell me that...I have no clue what jet is in there now...I bought this secondhand so who knows what jet they had in there...I bought a pack though...going to try 65 or 60 size jet and see if anything changes

 

[ImpulseRocket]

Maybe i get lucky and my spark is just simply weak...New cdi and spark plug will tell me that...I have no clue what jet is in there now...I bought this secondhand so who knows what jet they had in there...I bought a pack though...going to try 65 or 60 size jet and see if anything changes

I've noticed that many people tend to find the 65 works well on the standard 66cc engines. Keep in mind that the heavier oil mix ratio does lean out the fuel mixture some too, so don't change the jet just yet. Also, you will find 16:1 is going to foul everything up pretty good. Might want to go a tad thinner at 20:1 or even 25:1 after this next tank. Once out of break-in I wouldn't go thinner than 36:1 in hot weather. In cool temps 40:1 can work ok as that was what I used to run in the spring and fall without issue. Summer time I always went heavier on the oil.

 

[Daveinfl33777]

I've noticed that many people tend to find the 65 works well on the standard 66cc engines. Keep in mind that the heavier oil mix ratio does lean out the fuel mixture some too, so don't change the jet just yet. Also, you will find 16:1 is going to foul everything up pretty good. Might want to go a tad thinner at 20:1 or even 25:1 after this next tank. Once out of break-in I wouldn't go thinner than 36:1 in hot weather. In cool temps 40:1 can work ok as that was what I used to run in the spring and fall without issue. Summer time I always went heavier on the oil.

Good to know...yeah that was part of my theory as to why it's running a touch better with the 16:1 versus 40:1 because I'm leaning things out...but also my theory is that I have low compression and the added oil is aiding in a touch more compression...kind of like you see when you do a wet compression test compared to a dry one...

I live in Florida. It is mid 70s now on average and a cold day is mid 60s...we get down to low 50s mainly in winter...occasionally see 40s too....and then of course after the winter it's warm year round...what do you recommend? 40:1 synthetic mix year round? Or maybe 32:1 in winter 40:1 summer?

 

[Daveinfl33777]

Update guys! I'm in ABSOLUTE shock...I got new cdi in mail as well as new jet sizes and ngk spark plug too...I decided to just simply try the ngk...I was going to put the new cdi in too because spark plug boot is way better but I said no I want to find out what this issue is if in fact something else fixes it...had I put new spark plug and cdi in I wouldn't have known if it was the cdi or the spark plug...

I wasn't even thinking anything would be remotely better but i put the new ngk spark plug in and took it for a ride......I'm in shock the engine started right away and it idled!! It stayed running too...that's the most enjoyment and longest ride I got out of it yet!! All those pedaling as fast as I can to get it to start and all those times of pulling the clutch in to let it idle and it dies IMMEDIATLEY....I can't believe it is fixed...in absolute shock...never thought one time that it was spark because the spark plug did fire up when I tested it outside the cylinder against the block...well I should've known this wasn't fuel related (I kept thinking it was running rich)...I should've known it wasn't fuel related because it died ABRUPTLY and when engines shut off that abruptly they tend to not be fuel related...fuel issues usually cause some sputtering and then it stalls...

I'm just so happy I'm finally able to use this bike...now a followup question is what color loctite do you guys recommend for motor mounts...I dont want them loosening up on me

 

[weefek]

I've never used loctite on anything for these bikes. As long as you're using the proper lock washers and checking the hardware every so often you shouldn't have a problem.

Don't forget to retorque the head nuts to 12-14ft-lb (after engine has cooled) for the first few rides, and then periodically recheck after that.

 

[Daveinfl33777]

I've never used loctite on anything for these bikes. As long as you're using the proper lock washers and checking the hardware every so often you shouldn't have a problem.

Don't forget to retorque the head nuts to 12-14ft-lb (after engine has cooled) for the first few rides, and then periodically recheck after that.

Yeah I'll definitley keep an eye on these head nuts...

Reason I mentioned the loctite is because I actually noticed the nut and washer were actually 100% missing one day...3 out of 4 were still on

Also any idea why an ngk fixed my issue? I'm just curious...it's so odd to me that a brand new spark plug still produced my symptoms of hard starting and only running on full throttle but getting the ngk one fixed all those issues....I'm genuinely curious