CB125S with new rings, doesn't want to start...

[nrcb125]

Put new rings in my CB125S and was all excited to ride today, but nothing went to plan.

At first, there were fuel problems. I hate these fucking brass floats. Got it fixed.

Then there were electrical problems. Going to solving this with a new wiring harness in the next couple of weeks.

Decided to bypass is for today... Hooked up my car battery (it's been running on a 12V system for over a year now so 12V is not an issue).

I kept it simple. No wiring harness, only the +12V (there's a 2 Ohm 20 Watt resistor to make this work with the original coil) and ground. Battery grounded to the frame, and the +12V hooked to the resistors which are hooked up to the coil. Attached is a wiring diagram showing how I had everything connected.

Cue me kicking the thing over like a jackass for quite some time, flooding the cylinder a couple times, airing it out, flooding it, and repeat (good entertainment for the neighbors!) and the little bastard doesn't want to run.

As best I can tell it's not the fueling and it's not the electrics. I'm thinking it might be the points timing or it might be the compression. The plan is to grab a compression tester on the way home tomorrow and double check the points tomorrow.

From doing some basic calculations (PV = nRT strikes again!) I think the pressure should read around 135 - 140 psi. Below is the math. Does that seem reasonable?

Using:
P1*V1 = P2*V2
9.4:1 compression ratio -> V2 = (1/9.4)*V1
Air pressure at sea level is ~14.7 psi

14.7psi * 1 = P2*(1/9.4) -> P2 = ~138 psi

Any other ideas or thoughts? Maybe something I missed?

 

[CALfeRacer]

135-140 sounds reasonable. Definitely check the points timing. Did the same thing with mine after the engine rebuild, refused to start. Cleaned and set points, and she started up.

 

[nrcb125]

Thanks! I'll be checking everything once I get home from work.

 

[Tune-A-Fish]

Thanks! I'll be checking everything once I get home from work.

You won't get a solid compression read until the rings seat. break out the meter look for the obvious.

 

[surffly]

Got a pod?
Sure fire way to get a Honda single to not run..

 

[nrcb125]

Got a pod?
Sure fire way to get a Honda single to not run..

I do... It was running with the pod for about about a year before replacing the rings. Not sure the pod is the problem, but I'll put it on the list of things to check!

 

[Tune-A-Fish]

Thats pure BS... if you have a plugged pod yeah, it may run like shit, but a pod wont kill it all together.

 

[surffly]

Just telling you what I have seen with my own bikes.
Owned a few 100/125s

None would run right with a pod. And open box or pod made them hard to start and such.

But the basics need to be checked.
Have you confirmed that the plug is sparking?
reset the timing.
Confirm the valves are adjusted.
ect
ect

 

[nrcb125]

Quick update...

Timing is spot on. I spent a bit of time with a multimeter turning then engine and adjusting the points until the points were open (no beep) at F. Set the gap as well.

Confirmed it was sparking by pulling the plug and kicking it over. Lots of sparks.

It might be a fueling problem now... Going to try a different air filter/carb combo.

Still unsure of the problem.