Diagnosing fuel and vacuum problems. By scooter2 (Read 731 times)

[scooter2]

I took some vacuum and fuel pressure readings, from a 2008 Qlink Commuter 250 Helix clone, and the results are interesting because this bike runs like crap at WOT. I will post videos and/or pictures when I can, but for now here is a list of vacuum and fuel pressure readings.



These readings are on the stand.

Fuel Pressure:

1.2 PSIG @ 2000 RPM

1.6 PSIG @ 3000 RPM

1.7 PSIG @ 4000 RPM

1.7 PSIG @ 5000 RPM

1.6 PSIG @ 6000 RPM

1.4 PSIG @ 7000 RPM

1.5 PSIG @ 8000 RPM

When I open the throttle any more, the readings drop drastically until I let of the gas some and let it back down in RPMS, then it recovers and goes back up.



Vacuum:

1 -5 INCHES Hg @ 1800 RPM Idling. Steady oscillation.

3 INCHES Hg @ 3000 RPM

3 INCHES Hg @ 4000 RPM

3 INCHES Hg @ 5000 RPM

3 INCHES Hg @ 6000 RPM

2.9 INCHES Hg @ 7000 RPM

2.9 INCHES Hg @ 8000 RPM

1-5 oscillating to 10 INCHES Hg and back, Goosing from idle to full throttle



After hitting 8000 RPM on the stand, when I open the throttle any more the readings go to about 1 INCH Hg and the "jerking" begins with RPMS jumping up and down, as though the gas is coming on and off rapidly.



I will note that I have not yet done a valve adjustment on this bike. I will also note that I seem to be getting poor gas mileage, about 45-50 mpg. I do not know what is standard for this fat and heavy 250 scooter.

A cursory propane vacuum leak test revealed no leaks, however I was not thorough in testing.


Anyone want to take a stab at what these readings mean?  I don't have any baseline data for this engine yet to compare to.

I'm guessing a vacuum leak somewhere.
Read more: itistheride.boards.net/thread/6945/using-gauges-guessing?page=3#ixzz3OptqwrZU

Here's a video of the tests:

[ellpee]

My 2011 Roketa, same engine, weighs in somewhere in the 350-375 range, and gets 70-75 mpg, if that's any help. (I myself am around 205.)

[scooter2]

Jan 15, 2015 8:28:37 GMT -6 ellpee said:

My 2011 Roketa, same engine, weighs in somewhere in the 350-375 range, and gets 70-75 mpg, if that's any help. (I myself am around 205.)

Thank you.  I have seen gas in the intake.  I don't know what to make of it.  I have good power until I open the throttle too far, especially when I reach 40-45 mph.  It looks like I have a vacuum leak but I'm also drowning in fuel?  I think the main jet on this is a 120 or 125, but I didn't write that information down when I had it out.

[rks]

If your scooter is bogging at higher throttle settings, then my guess would be it's running too rich. (Main jet too large) Your fuel mileage points to the same rich condition. (I average 46+ mpg, riding 2 up, on my 1200cc bikes) A quick check of the spark plug would verify this.....bet ya it's black with carbon

Is this a stock or modified intake system? (carb, jetting, air cleaner)
It is always a good idea to adjust the valves, even on a new scooter, before it's started for the first time.

[ellpee]

If it's indeed running rich, tweaking the mixture might be all that's needed -- simple enough other than getting at the darn screw, which they tend to put in very inconvenient places. Don't see anything in your posts about mixture ....

[scooter2]

Jan 17, 2015 9:18:49 GMT -6 ellpee said:

If it's indeed running rich, tweaking the mixture might be all that's needed -- simple enough other than getting at the darn screw, which they tend to put in very inconvenient places. Don't see anything in your posts about mixture ....

I started with the screw at 1-1/2 turns out, the 1 out, then 3 out, none of which seemed to make a difference.

I wouldn't call it bogging, I'd call it cutting out, whether from fuel starvation, some sort of electronic cut off, or due to something I don't know about yet. I have a very similar scooter here I can take some more vacuum readings on, to compare to these, but I don't know how well it runs yet. Seems peppy on the stand. I have to make a few repairs on it before I can ride it.

I just put a new variator on it and now it's running better, I assume because it's keeping the RPMs low. I have a post about it here thescooterprofessor.proboards.com/thread/4118/engine-runs-new-belt-variator


Maybe this can shed some light on the problem.

[scooter2]

Jan 17, 2015 3:32:13 GMT -6 rks said:

If your scooter is bogging at higher throttle settings, then my guess would be it's running too rich. (Main jet too large) Your fuel mileage points to the same rich condition. (I average 46+ mpg, riding 2 up, on my 1200cc bikes) A quick check of the spark plug would verify this.....bet ya it's black with carbon

Is this a stock or modified intake system? (carb, jetting, air cleaner)
It is always a good idea to adjust the valves, even on a new scooter, before it's started for the first time.

It's a stock system. I'll have to check the plug later as my standard sized plug wrench isn't big enough to fit on it. I gave it a quickie valve adjustment while it was running. I'll do it "the right way" later.
Please see my new post here for some more details and thank you for your help.

thescooterprofessor.proboards.com/thread/4118/engine-runs-new-belt-variator