150cc gy6 won’t rev like it should By javid234 (Read 5,147 times)

[javid234]

Hi guys first post here. I’m a decent mechanic and have worked on motorcycle for years, but can’t seem to figure out this simple scooter. I bought it for my wife years ago and it allways started hard. But once it was running ran great! Sadly we didn’t use it much and it was stashed in a backyard shed for probably the last 4 years, without being run. The shed was damp, and unfortunately the kill switch/starter button and blinker relay no longer work... I cleaned the carb very well and started it by crossing the starter solenoid .. and the scooter starts much easier than it used to oddly. But now if I twist past 1/2 to3/4 throttle it Boggs and stumbles like crazy, if I roll on easy it will rev much higher but if I roll on fast it stumbles almost right away..it used to carry me 50mph no problem not 30-35 is about max.. I thought maybe it was the carb running to lean or rich so I pulled the air filter off and it barley made a difference, so I tried covering up the filter a little and it again Made little difference. (Just trying to tell if it’s mix related or not) I’ve always been pretty good at playing with carbs and I feel like it’s not carb related anymore.... any ideas what would cause this ? This is a video link of the scooter revving on a stand.

[cyborg]

Pull the diaphragm cap,, check to see if the diaphragm has a crack in one of the pleats or a hole,,, also see if the slide works easily in its track,,,

[kz1000st]

Check all the vacuum lines and see if the intake manifold is cracked. Also have the valve clearances been checked. .004 intake, .005 inch exhaust.

[javid234]

I looked them over when I removed the carb. I didn’t see any issues in the diaphragm or intake... I set both valves to about .004 but no changes.. the slide was pretty corroded but I cleaned it very well, until it would move freely ... it barley makes a difference weather you have the air filter on or off... I can see the slide move clearly when I rev it, but as soon as the vacuum slide opens wide it Boggs...it Seems to rev a little higher with the filter off, but I don’t know why that would be... because it still pops when you roll off the throttle like it’s running lean. But if I restrict airflow it runs even worse ...

[zaphod]

Almost sounds like a clogged main jet... I assume you checked and cleaned it? Maybe try swapping to a new one? At full throttle its running almost completely on the main jet, so that may be it.

[javid234]

Yea I checked the jets .. clean as a whistle, i even tried drilling it out a little...still didn’t change a thing. It’s very odd... it never ran like this before storage ... cleaned it all up and set everything the same as it was. And now this... I can’t find any air leaks or pin holes in diaphragms, vacuum lines are still soft and pliable, valves are good compression is good.... I’m stumped

[zaphod]

Yeah, that's odd. You didn't change anything with the air filter or exhaust, did you? Sounds like you didn't. Did you check the slide needle on the diaphragm, the one that opens the main jet? Some of those are adjustable with a little C clip at the top. Maybe that clip came off or got adjusted to the wrong slot and the needle is not pulling all the way out of the main jet at full throttle.

[javid234]

Yea the needle is good, it’s only the single position type... and it’s all clean ... I’m wondering since it was stored in a fairly damp location, if the moisture did something to the electrics In the ignition system..... could it be ? The only other time a had a motor act similarly, was an exhaust restriction... but I pulled the pipe and it seems clear. This motor did run a tad lean before ...”pod filter” but never popped or or did this ... it was just hard to start

[zaphod]

Really sounds like it might be a main jet issue, because it really only seems to happen when you are near or at full throttle. What's odd though is if you didn't change anything and it did this just after sitting. I would say if you had upsized your main jet and then this started happening, it could be that you went too large and the engine is just getting flooded with too much fuel and bogging down at full throttle. You said you checked it for corrosion, because that might be one other issue if it was sitting for a long time with regular gas in it instead of ethanol-free gas. The ethanol over time can attract moisture from the air and cause corrosion of some internal parts. What I can't really tell from your video is weather it seems to be running too lean or too rich when the throttle is wide-open. That would make a difference as to what to do to correct it.

[boydiz]

I’m having the same issue with my scooter. Did you figure out the problem?

[biscuit2020]

Take a hose put on the other nipple on the carb intake and put a screw in it. The intake getting to much air which makes it bog like it doing!