Greetings!
New member here with a first post and a problem.
I recently inherited
* a 2008 Roketa MC-04-150Y (150cc GY-6, Etc.) and it's having some 'issues' (big surprise, eh?). I found this place via the 'old board' (scootdawg) and
this post in particular. (very helpful BTW...might want to consider making it a sticky here too!)
I've tried the search function on both the old and new boards for answers, but my primary issue is RPM related and the search function drops 'RPM' from the search for being 'three letters or less'. My Google-Fu is lacking so I bit the bullet and registered here in order to pick some brains.
First the basics...Several months ago I did the following for the previous owner (PO):
New CDI (don't know brand. It has a blue anodized finned aluminum housing, and oriental writing. It claims to be non-rev-limiting)
New coil/plug-wire assy. (again, forget the brand, but it's bright orange, and is supposedly 'performance')
New NGK spark plug (stock spec)
New intake manifold (typical rubber cracks on old one)
New *quality* replacement fuel and vacuum lines...ALL of them.
New fuel filter
New air filter
Set valve lash (.004 on both, cold)
This all *seemed* to fix PO's issues...for a short time. He had his power back (and more than before, or so he claimed) but his mileage was significantly less...like down into the 30's/40's-ish. Then it began running rough at idle when warm. Then it began dying on him at stoplights. That's when he said 'stuff it!' and stopped riding. A month or so ago he decided he didn't want to mess with it any more and since I seemed to know how to wrench on things he asked if I wanted it...no charge, "just get it out of my hair".
Thing is...it wouldn't start. It would kick over on starting fluid, but not stay running (so I knew I had spark and compression). Got it home, tore into the carburetor and gave it a good, thorough cleaning (and it needed it!). The float bowl looked pretty good, with just some minor shellac deposits in the lowest nooks, but the jets were pretty plugged up with what looked like rust chunkies. Some time with a stiff wire twist tie, a can of carb cleaner and some compressed air and I got it all cleaned up and back together. (Hey..lookit that! No extra screws!
)
I put the freshly cleaned carb on the scoot, primed the bowl and she fired right up, and settled into a stable 1500 RPM purr after the auto-choke thingummy kicked off. Just for kicks I decided to see how low I could take the idle... it got down to just about 1000 RPM before becoming untenable. I took that as a good sign for no vacuum leaks, reset the idle for 1400 and did the starting fluid check on all the hoses and intake junctions. I got no changes in RPM, so I'm accepting that as further evidence of no vacuum leaks. Now for the test ride. ;D
PO reports that, when new, the scoot would pull nicely up to about 45-50 then taper off on acceleration, topping out at around 60-ish MPH and maxing out around 8500(ish) RPM. (faster than *I'll* ever run it). I took it out on a neighborhood side street and ran several passes at various throttle settings. It seemed pretty responsive at first during lower speed tests, but as I tried to go faster I noticed that it didn't want to seem to exceed roughly 5000RPM.
So I tried a WOT run from a dead-crawl. It took about 1.5-2 seconds to reach 6000 RPM with a nice smooth pull, but then it picked up this 'hollow' sound, and the revs dropped back down to 5000 (+/- 200 on different test runs) and refused to go any higher, though speed was still increasing, albeit slower than before (all this time it's still at WOT). The 'hollow' sound is best described as being similar to the 'bog' you'd hear going from part throttle to WOT on a car without the benefit of an accelerator pump (and without the RPM coming back as fuel finally reaches the pistons).
I thought on it some, and concluded that it may be the mixture screw being a bit wonky as that was something I was messing with previously (before finding the cracked manifold) trying to get it to run right. My thought was that it was going too rich and lugging the engine when the main jet kicked in since I had been adjusting it rich trying to compensate for the cracked manifold leaking in air. So I managed to find an extra long screwdriver with a flat-head small enough to engage the mixture screw from the side without removing any body panels and did a little screwdriver dance with the mixture and idle speed screws while the engine was running to get it to were it should be (based on several tuning threads I *did* find through searching here). No joy.
Still starts like brand new (three cranks...maybe four if it's cold), and settles into a nice rock-solid idle. Throttle response seems to be snappy enough for something that has no accelerator pump, and on the stand it'll pull all the way to 8000 RPM without a hiccup. But if I get it on the road under a load, it does the same thing; pull hard to 6000RPM, then go 'hollow' and drop down to 5000RPM. The one thing I *haven't* done as far as testing is see where it absolutely tops out. I'll confess to being a
VERY new rider (I've had my endorsement less than a month, and this 'inherited' scooter is the reason I went for it), and I'm still getting comfortable with this bike, not to mention being on the road with all those cages. Being on a scoot that I don't trust 100% makes it hard to get out on some of the larger arterial roads (with higher speed limits) to see where she tops out, and I've just about hit my 'don't piss off the neighbors' comfort limit by getting up to about 35 MPH in the neighborhood. At 35, the scoot was still accelerating, but at a slower rate than it does before the 'hollow' sound hits.
So...here I am, with a 'new' to me scoot that has just over 2700 miles on it, lots of replaced parts, a freshly cleaned carb, and it's pretty much unusable at the moment because I don't trust it *not* to leave me stranded somewhere. I'm open to any and all suggestions. I'm a bit of a gear-head by nature so don't worry about going 'over my head' with mechanic-talk. I've got three engines, two transmissions, and a front suspension rebuild under my belt already, and I've been 'blessed' with the opportunities of changing an oil-pump in a parking lot, and a starter on the side of a busy freeway.
So I think it's fair to say I'm pretty comfortable with a wrench in my hand!
On a wholly unrelated note, I'd like to yard off all the emissions garbage, including the EGR tube, but to be honest that's a subject I haven't researched yet. It would be wonderful if someone could point me to a relevant post or two on that subject.
Thanks in advance for any and all help.
*where 'inherit' = previous non-wrenching owner gave me a scoot he was tired of futzing with... no deaths were involved.
