gio 250cc mx bike wont start

[shawnj]

just rebuilt the top end on my gio 250cc mx bike. put new piston and rings in it. now that i have it back together it won't start. Have spark on the plug but it won't start at all. When i put it back together i set the flywheel at tdc and put everything on. It is a pushrod motor. No timing chain or marks. Not sure if I set this up right. Anyone have any ideas of what I am doing wrong. I can kick it over , get spark everytime but no fire.

Please help if you have an idea>>

[Weldangrind]

No offence intended when I ask the following:

Are you sure you're getting fuel? When your mind is in overdrive after a rebuild, it's easy to forget to turn the fuel back on. If the valve is on, open the screw at the bottom of the carb and see if fuel comes out.

Have you installed a genuine NGK plug?

Do you have decent compression? Does your engine have an automatic decompression device? The old Honda XR200 engines (after which many of our engines are patterned) have a cable that connects the kicker mechanism to the exhaust valve. The concept is that the exhaust valve is slightly held open while kicking to relieve some pressure, which allows for easy starting. If the rocker at the exhaust isn't adjusted properly, the exhaust valve will hang open and compression won't be obtained. Does it feel like there is suitable compression when you kick it over?

[shawnj]

fuel is on and I do get fuel when I open the screw to drain the fuel out. I tried to flood it with fuel when starting but when I took the spark plug out it had no smell of fuel at all. Had the plug out and kicked it over and there is lots of spark. It is NGK plug. When kicking it over it seems to have good compression. I am wondering about when I set it at TDC, do you need to be on the air /fuel pull in stage or on the compression to spark stage? Not sure if this even matters.

[Cal25]

maybe a SMALL shot of starting fluid is in order? How long has it been since it ran? Any chance the carb is clogged or gummed up?

[shawnj]

cleaned the carb just before I tore the engine down but I ran it to make sure it was working good. Only been apart a couple of days.
I am stumped on what it might be but am still focasing on the timing.

[Weldangrind]

I think I understand your question, but please correct me if I'm wrong. Valves should be set when the engine is at TDC on the firing stroke, which means that both valves are fully closed, and the piston is at the top, as indicated by the pointer at the flywheel. When the valves are fully closed, there should be no spring pressure on them, meaning that the rockers should be able to wiggle a bit; this is where you would insert a feeler guage and check for proper clearance.

Make sense?

[shawnj]

yes I am understanding you. I set them up exactly the way you are saying. Set it at the "T" on the compression stroke when both valves are closed. I have the right clearence on them but I still get nothing when I kick it over. It doesn't even backfire. I even tried kicking it over with the throttle full open a bunch of times and still nothing. I thought after doing this the spark plug should be wet with gas but it isn't. I don't know if I set something up wrong installing the new piston or have some other issue..
Don't know what to try next.
Also live where nobody works on these types of bikes. They are like the outcast...

[Weldangrind]

That's why we all hang out here.

I'd recommend against starting fluid, but I'd certainly remove the plug and prime the cylinder with a little fuel. See if it wants to run. If it does, you have a fuel or air problem.

[shawnj]

I will try this out and will let you know.
scares me a little to put fuel in there though.
I'll try anything right now. Want to get back to riding.

[Cal25]

putting the gas directly in the cylinder, the engine should fire if even for a second or two. If it doesnt fire, compression should be checked. Then perhaps investigate the ignition timing.

[shawnj]

Thanks I will give it a try.
Will post after i do it.

[brentn]

Did you set your valves on the compression or exhaust stroke for TDC???

This is important, if you set them up on the exhaust stroke then the plug will fire at the wrong time.

Turn the flywheel over with your wrench and watch the valves, it should go like this

-Piston moves down
;Intake valve is open, exhaust valve is shut
-Piston at BDC
;Intake valve begins to shut exhaust valve is shut
-Piston moves up
;Intake valve is shut, exhuast valve is shut
-Piston at TDC ADJUST YOUR VALVES HERE
;Intake valve and exhaust vales still shut
-Piston moves down
;Intake valve and exhaust valves still shut
-Piston at BDC
;Exhaust valve begins to open, intake valve is shut
-Piston moves up
;Exhaust valve is open, intake valve is shut
-Piston is at TDC
Exhaust valve is begining to shut, intake valve is begining to open
-Piston moves down
Cycle repeats

Turn the engine over with the wrench and watch the rocker arm movement until you understand the pattern, then find TDC on the compression stroke mentioned above in bold.

This is where the feeler gauge comes in because you do not want the valves to be tight at this point. There must be clearance so that when the metals heat up the valves are then in spec. The gap between the lifter and valve with your shim is important. The valves basically are purposely set out of spec when cold, but when warm these tolerances close up and then the valves have zero clearance once the engine warms up.

Hope this helps.

if your getting spark and fuel, then this is another approach.

If your sure that you set this right, then check the carb out and make sure that there are no air leaks, that the pilot jet is not clogged and that the engine has good compression. If there is in-sufficient compression (cause you fucked up) then it will not start.

[shawnj]

thanks for the info.
tore down the motor again and found that my exhaust valve was bent and not closing all the way. This in turn bent one of the push rods. Have parts on order and hopefully this will correct my starting issue.