Dies when starting at red light By prvrbs35 (Read 2,782 times)

[prvrbs35]

Just the other night coming home from work about 6 miles into ride my scoot died upon acceleration at a red light. As soon as I started to give it gas it would start to jerk and then cut out completely. When trying to start the engine back up I would have difficulty getting it started.

I checked the valve adjustment today since it has been about 2000 miles since upgrade and adjustment. I upgraded to new OEM style head (crack=oil leak), 59mm cylinder/piston and A14 cam. Everything else stayed stock. I have been running well except I notice at low end it is like starting in 2nd gear. Once I overcome that, mid to high range is very responsive. The valves were not out of adjustment. The spark plug is a light brown in color.

I have not played with air/fuel mixture setting. However, just before this post I did play with it a bit. I will go out for a test drive to the post office shortly after this posting.
I am just a little baffled at to why all of a sudden I am getting the jerking at acceleration from a stop where it kills the engine. I use this scooter as my daily commuter and have just over 8000 miles logged. Sorry for being wordy.

[prvrbs35]

No change during test drive. At stop I pulled throttle to wide open and the engine just dies. Easing the throttle slowly I get jerky hesitation and near stalls.

I forgot to mention that on the night that the engine stalled I noticed some high end hesitation/jerking as well.

I am going to pull the carb off and check for any cracks or leaks.

[Bashan]

Yes, pull the carb and check for vac leaks. Also, that's a 2008 Znen, see if you have a canister on the left side with a hose running from your gas tank to it through a check valve. Also, are you sure it's the engine and not the CVT? That's a lot of miles and the clutch could be grabbing if a spring broke. If it was me me I'd pull the cover and check the belt, variator, and clutch just to rule those out. Rich

[prvrbs35]

Thanks Rich, I will look into the CVT/clutch as well. What should I look into regarding the check valve from the gas tank? I have the hose from gas tank to PVC canister and then to intake manifold. I disconnected the line from the PVC port to the carburetor vacuum some time ago with increased performance. I left the PVC port open on the canister.
I am wondering. Is it possible to install the camshaft 180° out of phase and still run? Like I mentioned I upgraded about 2000 miles ago and something tells me that I may have done such a feat. When I looked into the intake port, I noticed deposits on the valve. The camshaft has A14 on one side and a smaller hole on the opposite. Which mark should be up at TDC?
Anyway, I live in SoCal and it is way too hot to be working on this scooter right now. May have to wait until tomorrow morning.

[prvrbs35]

The CVT/Clutch seems to be working correctly.

I did remove this device from the intake manifold for possible leak.
What is this used for?

(photo taken by dannicus)

However, I do think it has to do with heat. Went out for a test drive tonight after removing the device on the intake manifold and noted that as the scooter heated up that there was considerable hesitation and jerking as I continued to drive around. I was not able to make the scooter stall but it seemed to try.

I am considering to replace the fuel and vacuum hoses since these are original. The hoses looked to be good quality. Also, in mind is to replace the fuel filter. I do not know what else to try.

[Bashan]

If you put your cam in upside down you wouldn't go two feet let alone 2000 miles, so don't worry about that. It was running OK and then it wasn't right? So something changed dramatically. As an aside, you did plug the hole where the PVC canister dumped into the intake manifold right? Here's a diagram of how my Znen started to start hard and run like crap. This can maifest quickly when the check valve fails:

Juat to rule that out, take the line off of the check valve, and tie it off up on your filler neck. Or just loosen your cap, but I've seen those unvented caps get sucked bacK down on the rubbur and form a seal!

Your A/F Screw would not cause your problems, turn it in until it gently stops and then 2 1/2 turns out. That might not be exact for your bike but it's close. The A/F affects low speed performance and some on the overall mixture, it won't cause those problems.

Again, your problems started all of a sudden, it wouldn't be the hoses you took off and plugged, they would have caused immediate trouble. Now, the picture of the mystery device, I have no idea what that is. The Sinos create them quicker than I can keep up. That screwed into the intake manifold? It looks like it has a nipple for a vac line, where did that go?

Your problems started suddenly so I'm thinking maybe a bad coil. It can cause erratic running, jerking, etc. You can multimeter test, there's a couple articles in Electrical Tech, or my fav, just swap it out as a test. Swap your plug too.

Good luck, let me know what happens, Rich

[prvrbs35]

Went out yesterday trying to make my scooter fail. When the hesitation and jerking started I pulled over and check the fuel filter. The filter looked dry. I have a salvaged scooter and I replaced the fuel pump and hoses. Upon firing up the scooter I noticed the filter fill up with gas. Took a short test drive and ran well. However, I did get some jerkiness. The next two days will be the test. I will be driving to work and see how it performs. I will most likely put a new filter in also.
I have a coil as well to swap out but I want to do one thing at a time. If I still have problems, I will change the spark plug, then coil.

[Bashan]

Fuel pump! Dang, I never think of that because all of mine are gravity feed. I bet that's it, you were being intermittantly starved for gas as the pump cut in and out. Anyway, you're taking the right approach, one thing at a time so you know what does what. So many times folks start tearing things off and plugging lines and then you've got a confused mess. Oddly, my Znen has the mountings for a tank under the floorboards and a filler door with a lock! Yet they chose to put that ridiculous gravity feed tank in, go figure. I still haven't figured out your mystery widget. Rich

[valentino2003]

i had a very similar issue come up with my scoot, after a new fuel filter and cleaning the carb jets (there was a small bit of something in my main jet, violin string got it out) i'm over the sputtering/hesitation and going dead.

best of luck! i hope its something simple!

[prvrbs35]

Really strange but #1 and #2 are connected on each side of the intake manifold. Like at 10 o'clock and 2 o'clock. I had hesitation and sputtering again tonight but not enough to kill the engine. It usually does not act up until I have driven about 6 to 7 miles. I will be sitting at a red light idling fine, but as soon as I start to go the sputtering begins.
I work 12 hour days. I will be changing the fuel filter this Friday. Is there a way to clean the carb w/o taking it apart?
What about using an electric fuel pump? Pros and Cons?
I will take apart the mystery device Friday just to see what is inside.


Here is an old photo kind of showing the location of the mystery device.

[ootscoot]

That mystery thing is a supplementary air intake - part of the smog junk . We always removed them (sshhh) and plugged the vacuum intake port where they were plugged in - bikes ran much better without.
Your stalling and shuddering at start could be a jammed roller weight in the variator...

[Bashan]

Thanks Oot, I was going to bug you about that and I knew you'd know, but I figured you were busy. Also I knew you'd eventually see it and clue us in ;D. Rich

[ootscoot]

Right about busy - this is scooter season here in Santa Barbara - finally got the SYMBA and Fiddle ll CARB certified, so they are selling like crazy!

[prvrbs35]

ootscoot, I read your message last night b4 going to bed and it makes some sense to me. If it is truly a fuel starvation issue, I would see hesitation at WOT. The other thought is that it seems like I am starting in 2nd gear well b4 this stalling issue arose. That leads me to believe that I may have had a stuck roller for some time now. After I did my engine upgrade I had more response off the line and that slowly went away. I have been considering a variator upgrade but have been putting it off. My stock configuration has 17g rollers and I was thinking about 13g or 15g slider style upgrade. I do not want to go too light and over rev my engine.
Thanks for the insight.
Ed

[ootscoot]

Ed, 13g works great with the Milan - the sliders even better.
On that supplemental air intake - we just use the bottom section of tubing to jump from one vacuum port to the other, effectively just sealing it off - may have to lower and lean the idle to compensate...
Don't forget to constantly check the muffler mount/rear swingarm bolts - they like to loosen up. I even lost my rear axle nut once...