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Old 12-17-2013, 06:53 PM   #61
Dabears
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Is there any possibility that you have over tightened either the manifold clamp or anything on the carb itself that could have torqued the carb body slightly?

This happened on my Vespa once (granted- it's a flat slide carb, so very different design) but I'd slightly over tightened one of the carb to manifold bolts and it was enough to hang the slide. I backed it off slightly and it's been fine ever since.

Only other thought (back to my Mikuni days) is if the spring was jumbled up it could be putting uneven pressure on the slide forcing one side to be jamming into the carb walls. Sorry, that's all I got.

I sure feel for you though after all the work you put into that little Fly. Hope you can get it corrected soon!
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Old 12-19-2013, 08:01 PM   #62
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Wow, what a pain!! But I think now I might have a handle on the problem. I would be embarrassed to reveal how many hours Driller and I have put in on that stupid carb over the last couple days. The cap on the vacuum chamber is poorly designed. Instead of sitting down on the diaphragm the cap just barely catches the very outside edge of that diaphragm. The diaphragm comes out of the little groove on the top of the carb and there goes your seal. Who would think you could put that cap on 15-20 times and never once get it on right. If the diaphragm comes out of the groove the cap still fits down normally, you can't tell that the dia. isn't seated correctly. Finally after connecting the carb to my shop vac to test the slide, it worked just like it should. I've worked of dozens of this type carb but never had this kind of problems. Once in a while while working too fast I have pinched a dia. Usually just looking how the cap sits on the carb body will tell you what is wrong.
So, tomorrow we should have decent weather so I'm off to my test location with high hopes for some very positive results.
On a side note, Driller also has a Vespa 200 with nearly the same motor as the Fly, just more CC's. The bike had a very rough idle ever since he owned it. He left it here with me to see if I could find the problem. After fooling with it, I finally found an air leak where the intake manifold mounts to the head. Problem solved!! Idles fine, but now it seems to be down on power. I'm guessing that diaphragm may also be a problem. We did take the diaphragm out yesterday because I wanted to look at the spring. This time I may have done a better job on reassembly because he called me today to say it seemed to run better on his way home.
That's all for now, wish me luck tomorrow. Hope I don't get hurt if it wheelie's over backwards.
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Old 12-20-2013, 04:50 AM   #63
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Quote:
Originally Posted by brianwheelies View Post
If it was fine before removal and now it isn't, look to what you have changed and reverse it.
Sounds like this quote kind of summed it up! Glad to hear you got it sorted- please let us know how with runs on your test ride!. Also good to hear that you found a carb leak on your buddies Vespa. That kind of thing only seems obvious AFTER you find them. So many variables can cause running issues.

Funny side story- years ago I had a friend who's brother was selling a very nice Kawasaki Z1 900 (back when you could pick them up all day for under a grand- sigh). Anyway, he had parked it for the winter and couldn't get it to run right to show it to sell, and he was panicked. So you can imagine all of the obvious things we looked it. I decided to pull the aircleaner apart. Sure enough, he kept a shop rag under the seat and it had gotten completely sucked into the air horn into the filter assembly. Pulled it back out- bike ran like a charm and sold that afternoon. Sometimes it is the obvious thing....
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Old 12-20-2013, 06:51 AM   #64
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Starting to warm up here in the moutains of North Carolina so I'll get out later today on the BlowFly.
I like your little story abut the rag in the air filter. Similar story. I went to look at a bike that was for sale. Ad says it starts and runs but wouldn't take throttle. I got the bike for $400. Found a mouse nest in the air box. Sold it a month later for $1200.
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Old 12-20-2013, 08:04 PM   #65
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As promised, the test results are in. Acceleration was 9.77 sec, averaged of 8 runs. The stock, baseline time was 10.51. Almost 3/4 second improvement. I was a little disappointed, hoping for a little better than that, but I may have had hopes that were a bit out of line with reality. That 9.77 sec. is almost identical to what I got with Drillers own 200 Vespa.
Top speed results were more disappointing, 56.5 mph two way average using GPS. Speedo was indicating 61. This is right where we started with the stock bike. Many modern bike do have a rev limiter built into the ignition system. Don't know if the Fly has that or not. I did run the bike on a long downhill and got it to indicate 69MPH. This would seem to rule out a rev limiter, but, most bike use a "soft" rev limit. This retards the ignition to reduce power, not cut the ignition off. So, it may be the bike does have a rev limiter, but will still run higher rev's on a downhill. Does anyone have any knowledge on this? Really would like to know.
I'm now getting even more backfire on deceleration than ever, it's really bad. Bike idles a bit rough and will not start when hot unless the throttle is opened. I did try to adjust the idle mixture but didn't seem to make much difference. Screw was out 2 turns to start with. Driller has the tool to do the adjustment, but it isn't very easy to get to so don't know exactly where it is now.
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Old 12-20-2013, 08:12 PM   #66
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Sounds like you need richer jetting. Don't burn up the the engine with a downhill run on a cylinder that is not broken in and running lean.

Are there any threads on Modern Vespa that have used the same kit that you can get a litmus test?


How does the plug look after a wot chop?
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Old 12-20-2013, 08:15 PM   #67
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Driller also has a Honda PCH 125. At some point in time we will do a set of tests on it to compare. This bike has what seems to be typical Honda off line acceleration, ie, very good. It will be interesting to see what such a small bike can do. Wish I had done a set of tests on my old '87 Honda 150 Elite before I sold it.
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Old 12-20-2013, 09:22 PM   #68
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Most of these Piaggio things seem to have a 2-stage limiter. The first is a soft limit that reduces advnace, then a full limit where it starts missing firing points to stop it.
Plenty of info on advance curves on MV in the "hotrod" section, my own SC One 125 did it, as did a friends LX150, as does my X8 now.

I know when these Liberty 200s came out they didn't have any more speed than a 125/150, just got there a bit quicker. The stock set up used low compression and was under carbed to reduce high rpm output (think VW Beetle). Lots of low and mid grunt.
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Old 12-21-2013, 05:48 AM   #69
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I thought from all of the stuff I read on MV that the GT200 was good for 75-80 mph? Why would your Fly be limited to 60 or less with the upgrade?

http://modernvespa.com/forum/topic99595

Is it an appropriate comparison? A SYM HD200 will do 72 with 171cc....

Edit: just read this about the Liberty 200- says top speed is 62..Not much more than you were able to get, so sounds like the GT200 is in a different league. 62 is about what my P200e gets....
http://www.moto-choice.com/en/Bike-R...he-narrow.html
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Old 12-21-2013, 08:45 AM   #70
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I should have mentioned that in checking fuel milage, since the 200 top end job mileage is only 45MPG. I never did check milage before the change. Also, I've kept a log of any reliable performance data I can find on scooters. In Feb. '06, Cycle World did a full road test on a Vespa LX 150, which I believe is the same motor as the Fly. Bike dyno'ed at 8.7HP, top speed was 66MPH, and weighted 247# dry. That is over 10 MPH faster than the Fly. That and the 45 MPG makes me think all is not well with that motor. When time allows, I'll check ig. timing, making sure the advance is working, cam timing, although Driller and I checked cam timing at least 3 times. I'l take a look at the plug although I'm certain it will be very rich and I've never really mastered the art of reading plugs.
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Old 12-22-2013, 12:31 PM   #71
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If we had known...

Quote:
Originally Posted by Yellow Jacket View Post
Wow, what a pain!! But I think now I might have a handle on the problem. I would be embarrassed to reveal how many hours Driller and I have put in on that stupid carb over the last couple days. The cap on the vacuum chamber is poorly designed. Instead of sitting down on the diaphragm the cap just barely catches the very outside edge of that diaphragm. The diaphragm comes out of the little groove on the top of the carb and there goes your seal. Who would think you could put that cap on 15-20 times and never once get it on right. If the diaphragm comes out of the groove the cap still fits down normally, you can't tell that the dia. isn't seated correctly. Finally after connecting the carb to my shop vac to test the slide, it worked just like it should. I've worked of dozens of this type carb but never had this kind of problems. Once in a while while working too fast I have pinched a dia. Usually just looking how the cap sits on the carb body will tell you what is wrong.
So, tomorrow we should have decent weather so I'm off to my test location with high hopes for some very positive results.
On a side note, Driller also has a Vespa 200 with nearly the same motor as the Fly, just more CC's. The bike had a very rough idle ever since he owned it. He left it here with me to see if I could find the problem. After fooling with it, I finally found an air leak where the intake manifold mounts to the head. Problem solved!! Idles fine, but now it seems to be down on power. I'm guessing that diaphragm may also be a problem. We did take the diaphragm out yesterday because I wanted to look at the spring. This time I may have done a better job on reassembly because he called me today to say it seemed to run better on his way home.
That's all for now, wish me luck tomorrow. Hope I don't get hurt if it wheelie's over backwards.
Yep,that was the problem. Wish this had surfaced earlier.
http://modernvespa.com/forum/topic123697
Good to know it was not just us!

Actually, the GT200 is rated at about 72-74mph by Vespa. Using the 10% optimistic rule of thumb, that seems about right according to the speedo.
The older Fly 150's are rated at 61-62mph top. The newest model with the 3valve head and more power is rated lower at 59mph. Don't know how the ET4's andLX150 are getting more claimed top end with essentially the same engine.
Some who have done150 Leader conversions have opted for an upgear change in the tranny for more top speed (65-66mph) to go with the increased power. Most have done this because they prefer the small frame scooter for light highway/touring as opposed to the large frame GT series.

We will be removing the evap system to see if that has any effect on the pop/backfire issue. Also, still need to check the plug and maybe change the jetting.
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Old 12-22-2013, 12:44 PM   #72
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Quote:
Originally Posted by MODNROD View Post
Most of these Piaggio things seem to have a 2-stage limiter. The first is a soft limit that reduces advnace, then a full limit where it starts missing firing points to stop it.
Plenty of info on advance curves on MV in the "hotrod" section, my own SC One 125 did it, as did a friends LX150, as does my X8 now.

I know when these Liberty 200s came out they didn't have any more speed than a 125/150, just got there a bit quicker. The stock set up used low compression and was under carbed to reduce high rpm output (think VW Beetle). Lots of low and mid grunt.
What MODNROD says fits into my expectations. Not looking for much if any increase in speed. Just get there a bit quicker.
Disregarding rev limits, it appears the only reliable way to increase top speed is by changing gearing in the final drive providing you have the increased power to pull the higher ratio..
I'm still wondering why the mileage seems so poor.
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Old 12-30-2013, 07:46 PM   #73
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I've spent my free time for the last several days trying to find what's wrong with the Fly. Here is a list of what I've checked. If anyone has any suggestions for anything else I could look into I'd like to hear them.
Rechecked cam timing.
Checked ignition timing. It is running maybe 6 degrees advanced but there is no way to change it. Advance works but there are no marks for advance so don't know it full advance is correct.
Checked gap between flywheel and pulse coil. Gap was only .006, spec's call for 14- 35 thousands. Set gap at .018. Not sure but doing this may change timing a small amount. Will check it when I get Fly running again.
Valves set.
Checked to make sure no obstructions in the intake, i.e., no shop towels, rats nests, etc. We did install a new air filter.
Been through everything on the carb several times. Jets are all stock size and have not been drilled out. No blockage of either idle or main air bleed jets. Set carb up on bench with a test fuel supply to check float valve for leakage. Adjusted float height.
Spark plug was sooty black and bike is only getting 45MPG.

As of now, I'm trying to locate a 72 main jet which is the smallest available in this series. Once I have that installed will see how it runs. I have the tools to enlarge the jet in very small increments so will work on jetting trying to improve performance.
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Old 12-31-2013, 03:04 PM   #74
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The backfiring could be the SAS. 6 degrees of advance isn't a lot, and with a stock jet, the bike should be a little lean, and not overly rich, which the spark plug indicates. What you describe sounds like a bike that is bogging. Have you tried running it without the airbox? That will tell you if you're overjetted or not. And of course, you can use a ziptie to cut off some of the air getting in and see if that makes it run better too.
My ET4 got about 49mpg with a big bore kit, so that's not too surprising, but it ran out well.
How does the motor do when you are revving it up on the centerstand? Does it hit a rev limiter? Is it blowing smoke? You might need lighter rollers so it runs up into the powerband, but this does sound like it's in the top end. Are you getting a lot of blowby or oil in the airbox? On some of their air cooled engines, Piaggio says to set the valves at .15 and .25mm, which seems incredibly loose, but you might try that.
if either of you are coming this way before March, bring it in and we'll throw a couple of hours at it on the house, to see if we can't figure out what's going on. Thing I hate about Flys is what it takes to get to the engine,
Last but not least, are you using an e plug and not an h?
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Old 01-03-2014, 11:46 AM   #75
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Baby its cold outside...

Thanks, George. The SAS filter foam was falling apart when we pulled the fan shroud off. We replaced it with some foam we had that is coarser than the OEM stuff. Just wondering if that is more free flowing would the backfire/pop be related. Or, could some of the broken down foam filter have gotten in the SAS and be partially blocking it? Did you get the rubber variator ring in for the GT200?

Cold, cold cold. No testing right now.
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