Engine dies when increasing throttle (movie)

[yatezy9]

 Hi Everyone,
Got a strange problem where i have no throttle advance, dies out as soon as i touch the throttle, can coax it up a little but still dies and then misfires on the way down revs, lean?
needle slide is moving, got vacuum, starts easily, idles well.
Anyone with suggestions on this?
see the vid:



cheers,
Yatezy

[tortoise]

needle slide is moving

Have you visually verified that main jet fuel is atomizing?

[yatezy9]

Hi tortoise, thanks for the movie, now i know what its suppose to look like. Heres what my carb atomisation looks like when i pump the throttle.



I back off when it looks like it will die. getting a bit of fuel mist coming out of the carb and into the air turbulence around the camera. not sure if that is suppose to happen.

Just read skishades carb problem http://www.kymcoforum.com/index.php?topic=6942.0, solved by changing the needle holder. I took apart the holder and the small spring, looked ok, reinstalled, still the same prob. but i might take a closer look after reading his post.

[yatezy9]

Anyone know what happens if the secondary filter is blocked, that little canister that feeds fresh air to the exhaust?

[tortoise]

getting a bit of fuel mist coming out of the carb

Have you checked for exhaust obstructions?

[yatezy9]

Took the muffler off today to see if any difference possibly due to something (carbon?) obstructing flow.
ran the engine without it, bit noisey, no combustion at higher revs a bit more noticable.
See vid:





Thinking of taking the carby apart again just to make sure.

The scoot is pretty much bare essentials at the moment:

[yatezy9]

and the other side, wanted to take the variator apart too while i'm at it.

[tortoise]

Thinking of taking the carby apart again

Really scrutinize the carb diaphragm for tears.  Might also check if the insulator spacer between the intake manifold and cylinder head is aligned properly and not cracked.

Sometimes the crankshaft flywheel woodruff key will shear, causing an ignition timing issue.  Poke something like a plastic straw into the spark plug hole to feel when the piston is at top dead center, then check if the flywheel timing mark is aligned.

Don't mean to insult your mechanical intelligence, but when troubleshooting one should never assume anything.  You have already performed the VERY BASIC maintenance procedures of checking intake and exhaust valve lash, and cylinder compression . . RIGHT!

[deaneop]

Most def a fuel issue i had a bike that done exactly this turned out to have a worn throttle needle and very very small hole in diaphram.

[yatezy9]

Most def a fuel issue i had a bike that done exactly this turned out to have a worn throttle needle and very very small hole in diaphram.

Really scrutinize the carb diaphragm for tears.

On the weekend I was able to find the time to really scrutinize the carb and a friend pointed out a very interesting area near the atmospheric vent that I had previously assumed to be surface roughness. But actually on close inspection, under good light, there seems to be a series of cracks (porosity) which may lead to the vacuum diaphragm chamber. Have a look at the pics.

[yatezy9]

Here's the inside of the vacuum diaphragm chamber showing a rough area which corresponds to the previous pic.
Any thoughts on this one?

[yatezy9]

Might also check if the insulator spacer between the intake manifold and cylinder head is aligned properly and not cracked.

aligned and no cracks. Note: viewed some carbon deposits on top of the intake valve.

[yatezy9]

Sometimes the crankshaft flywheel woodruff key will shear, causing an ignition timing issue.  Poke something like a plastic straw into the spark plug hole to feel when the piston is at top dead center, then check if the flywheel timing mark is aligned.

Already had the tappet cover off so checked TDC on cam chain and flywheel, both aligned.

[yatezy9]

Don't mean to insult your mechanical intelligence, but when troubleshooting one should never assume anything.  You have already performed the VERY BASIC maintenance procedures of checking intake and exhaust valve lash, and cylinder compression . . RIGHT!

No I didn't check the valve clearances, engine sounded ok so didn’t bother, (yes I agree assumptions are a big problem in trouble shooting and I'm guilty as charged) so after ur suggestion Tortoise I have now:
IN:      0.12mm or  0.0047244 in
EX:      0.11mm or 0.0043307 in
I figured they are pretty close to spec. 0.12mm and wouldn't be the source of the prob so I didn't change anything (correct me if I'm wrong).
I don’t have a pressure gauge so the compression test is a bit difficult for me. I imagine if the pressure is too high there would most likely be too much carbon build up around the combustion chamber. I'll see if I can buy/borrow a gauge.

The reason I'm here is firstly to learn more about engines/scooters because I enjoy it and secondly to fix the scooter. So don't be worried about insulting intelligences, that’s just a roadblock to learning. The best way to solve these problems is for me to give the right info (and not to make assumptions) and get the right advice.  (even if it is hard to take, at least we get to the heart of the problem).  My mechanical ability is ok, I've been through a few bikes in my time and did a lot of maintenance and repairs on them, but I still have a lot to learn and hope I'm in the right place to learn it.
I'm enjoying working on this scooter and hope that what I've learnt (which might be rather basic) will help other people in similar situations.

[yatezy9]

Heres another pic of the carb cracks, scratched the surface a bit to see the extent of the cracks. Apparently in production there are ways of making the higher porosity metal occur around the least important area of the casting. I imagine the atmospheric vent would be that area. Since small cracks only get bigger over time its possible this is the prob.

Possible solution:
Found a 24mm GY6 carb on Ebay for around $40, so might give that a go, usually stuff out of China takes forever to get here though.

Also thinking of just glueing it up just to test if it really is the prob.