gx240 issue

[zero1dhd]

So I got a kart from some kid who didn't take care of it at all. The engine is a honda gx240 with a "bent valve" which apparaently happened from an overrev while "drifitng" it. I cracked it open and it's not a bend valve, the rocker on the intake was broken. The rocker was welded back together, but not great work at all. I re-welded it and ordered a new set of rockers.

I also ordered the full tune up kit you can get on amazon. The one with a new carb, ingnition magneto, pull start, spark plug, etc. I haven't put the new rockers in (haven't arrived yet), but I installed all the other parts.

The motor is getting fuel, air, and spark, but doesn't want to start up. It kinda seems like it wants to, then backfires a little.

Any ideas as to what could possibly be causing the motor to not want to start?

The kart is a project for me and my daughter, and I'd really like to get it going.

 

[qtband]

Take off the valve cover and observe the valves as you pull the rope. Are both valves moving like they should? I had an issue like that and the exhaust valve was sticking.

 

[itsid]

first:
check the cam and crank are lined up (dot needs to face on TDC in compression stroke)
the problem here: compression stroke... you need valves to see that properly
(a good time to verify the lifters are seated well on the camshaft and into the pushrod paths )
Talking about pushrods.. make sure those are both still nice and straight;
a bent one will not operate properly of course and you might set your valve lash incorrectly because of it.
remove them from the head to not upset the lifters or you'll start all over again

then, make sure the valves are currently in working condition at least (make sure they fully close and that your valve lash is set correctly)

if that is all taken care of properly
the next thing to check will be the carb..
preset the idle (all closed 2.5 revolutions back out again) as long as you cannot set it with a running engine.

check your carb gaskets are all sealing properly;
some painters tape wrapped around the manifolds .. if it's better than without they're not

lastly
try some starter fluid just to make sure it's not a fuel issue and report your findings

'sid

 

[zero1dhd]

I was thinking it was something timing related esp due to the bit of backfire here and there.

I assumed the carb was preset, but I'll check that as well.

As for the valves and whatnot. I pulled the head to confirm the valves are seating properly. Cleaned all the carbon buildup while I was in there. I don't know what the valve lash should be set to, if someone knows off hand ..... thanks, if not I'll do a search and am sure I can find it.

I haven't put the new valves in yet, but I got the broken one welded back together better and it was solid and moved properly just like the exhaust.

The motor will flood very easily, which I've read is common of these motors. I can try and adjust the carb, but if it's something else I'd rather not fiddle with it just yet. Unless of course someone knows I need to (like I said it was out of the box and on the engine)

The push rods are straight and function properly. I will note there was some sort of disc with a pocket sitting in the oil return. I don't know what it is (maybe 1/4" dia and about 3/16" thick, shiny with a pocket on one side only) but maybe it's important? Like I said everything rotates around as it should, there's fuel, air, and spark, BUT it just won't fire up.

Which leads me back to the possiblity of timing. I thought all of that was pretty fixed due to the fact that it's single cylinder.

One other final thing to note, on all the pulls I've done on this motor I've never got any oil up into the valve cover. Is there a possibility it's not getting oil pressure and that is messing something up? I don't have the oil pressure sensor connected to anything if that matters.

 

[Ebrownie]

Maybe check and see if the carb float is working because it could be overflowing in the bowl and flooding it. Probably not the problem, but maybe worth it to check.

 

[OzFab]

I was thinking it was something timing related esp due to the bit of backfire here and there...

I thought all of that was pretty fixed due to the fact that it's single cylinder.

Regardless of how many cylinders, if the balancer or flywheel on any engine is not aligned correctly, the engine may not run; ie: check that the flywheel key isn't sheared...

One other final thing to note, on all the pulls I've done on this motor I've never got any oil up into the valve cover. Is there a possibility it's not getting oil pressure and that is messing something up? I don't have the oil pressure sensor connected to anything if that matters.

As these engines work on a splash lubrication system, there's no such thing as "oil pressure"; oil will reach the rockers once the engine is running...

 

[zero1dhd]

Will do. I'll crack open the motor and check the timing. That's honestly what it seems like it might be, but I wasn't sure it could be an issue. I'm used to working on cars with timing chains etc.

The motor spins as it should and the valves open and close as they should. The push rods are straight. I'll try and get a pic of the little metal disc thing to see if that's an issue of some sort.

I wasn't sure if there was any oil pressure as oil "pumps" are such a simple gear in gear system that it wouldn't be hard to add one on a small engine.

Thanks for all the advice thus far fellas