More strange behavior
 

Well, I had the scoot running well and made some more adjustments. I thought the plug seemed a bit light (not blistered) and thought it might be good to up-jet. I opened up the stock air box a little more and stepped up to a 115 main and 38 idle jets.
On test ride it seemed to surge at speed and would stumble off idle . I swapped back the 35 idle jet and since then have been having issues. I seems like I have a vacuum leak, but I have tried all I can think of.
What it's doing ... with the opened airbox, accelerating you hear "Bwaaaaaaaa", at certain speeds and even hard acceleration from stop it will change, more like "BwaaaaaAAAAAAAA" along with what sounds like a hissing noise and power loss.
So far I have reduced the main jet back to a 110 and taped up some of the airbox holes. Swapped out the carb with a spare, same size, same size jets. Vacuum line, verified/adjusted the valves, removed and inspected the intake (ordered a new one and gasket). I'm going to swap back the original carb once I get the new intake as the replacement seems more difficult to set the idle mixture.

I'm sorry for the long post, but I'm getting frustrated. I was wondering if the CDI could cause this, but it would be intermittent as at moderate throttle it runs ok. Spark was good when tested today.
Any ideas would be much appreciated.

Thanks, Gene

Sounds to me like your problem lies in the modifications you've made. I would suggest making only one change at a time.....then if the performance degrades, you know exactly what caused it. Maybe you can go back to the original setup (you said the scoot was running well), and start over...doing one thing at time. If you think it's a bit lean, go up a step in main jet size, don't over do it by going 2 or 3 sizes bigger all at once, and don't change both jets at the same time. You might try just raising the needle a little (by lowering it's retaining clip a notch), but again, not at the same time as a jet change.

Most of us shade tree mechanics, trash the airbox in favor of an aftermarket airfilter. I didn't want more speed or power when mine was replaced.....just an engine that wasn't struggling to breathe. That was more than 3.5 years ago....all I've done since is an annual filter cleaning....no carb adjusting, or cleanings......scoot runs better than ever.

You said that you're ride was running good to start with except for a "slight" discoloration of the plugs but not "bad"!
My solution---- Put it back the way that it was & if it ain't broke , don't fix it!:shrug::hmm: Irish:scoot::nuts:
P.S. My $.02. I used to enjoy working on bikes. After so many yrs. of working on them , I avoid anything that is unnessessary on them! The worst that my (street , Drag )motorcycle ever ran , was when I had my shops. It still ran great but after working on other bikes all day , who feels like working on your own!

rks,
I agree with what you're saying, I just got caught up in the excitement and thought I'd make a couple tweaks while I was in it.
The airbox mods I made weren't too drastic (from 2.5 holes in the box ... opened to 4); this done in hopes to allow easier breathing. It seemed to work well until lately.
Something else I failed to mention, after the the upjet, I noticed a vacuum leak from the manual choke set-up. I have since switched back to an enricher which seems to be working ok.
I have everything back to almost stock configurations with the exception of the 110 main jet (105 stock). When I receive the new intake, I'll put the original carb back on at stock spec and see where I stand.
What has me baffled is what I tried to describe about accelerating. The noise from the airbox gets significantly louder and instantly looses power. Easy on the throttle, or lower RPMs, and it will run pretty well. I thought maybe a tight valve would allow exhaust noise to backfeed through the intake ... adjusted, doesn't seem to be the case. Then I was thinking about the CDI or coil; if failing, causing the loss of power, maybe the noise is a side affect.
Frustrating... any other ideas ... anyone?

A cracked intake manifold and still check both your valve clearances again.

Thanks KZ, will do. I was hoping to receive the new intake today, but not.

Irish, You're right, but I guess greed got the better of me. I saw some minor improvements, prior, and was hoping for more.

Any engine will be noticeably louder at wider throttle settings, with air filter mods that increase flow. Even a K&N type filter, will raise noise levels, over an OEM setup, when throttle is opened to pull a hill and such. This is normal......the drop in power is not, and I don't know what would cause a hissing....seems like something would have to be pressurized and leaking a bit to cause that.

Runs alright at moderate throttle, spark plug shows no color, looses power at wider throttle settings....all adds up to lean....too much air for available fuel. Don't fiddle with ignition system.

One question, have you done anything to the emmissions system on this scoot?

I'm aware that it is louder with the modified filter box; that was part of the allure ... it sounded much better than stock. My issue is beyond that, almost annoyingly loud.
As to the emissions gear, the evap canister was removed during my PDI and the PAIR system a while later.

Update: I have discovered that it is the muffler causing my problems. I re-adjusted the valves, played with the idle mixture, and took her for a test ride. This time I was wearing my half helmet and I could hear the hissing from the exhaust. As i would get on the throttle and build speed, I would hear the exhaust release pressure, like a tea kettle. I could ride that as well ... meaning I could sustain that pressure, but once I let off the throttle, it would dissipate, like taking a kettle off heat.
I returned home and a short while later, removed the muffler and went back out for a short ride. Although loud as heck, it seemed to run well.
Does anyone have a recommendation for a replacement muffler?

It's been a while and I have made some improvements.
I have a new performance muffler installed. I didn't necessarily want loud, just to avoid the factory, catalytic internals. I even tried a cheap alternative, that I saw on Youtube; although fun playing, it's not what I was going to stay with.

Since the replacement, I'm slowly tuning the carb ... one step at a time. I have noticed the incremental changes while working up from idle, needle position, and now the main jet. The weather currently has me grounded as Winter has finally arrived.

I have another write-up and video links in the forum linked below.

http://49ccscoot.proboards.com/threa...cer-150-tuning

Glad to hear things are improving...it can take some experimenting, and time to get things right, but it's well worth it.

Keep up the good work.

I don't know if anyone has ever publicly stated the size (number) of the jet can not be trusted.

Even if the jet is stamped on it or a marketer tells you it is such and such, don't trust it. I have checked main jets from several suppliers and NONE were on specification.

These are Chinese parts, made by a very low paid worker whose pay is based on production NOT accuracy. I am not bashing China, it is just a fact of business in low price goods manufactured there.

I got the scoot out for a ride yesterday; a beautiful day, but quite cold.
For the first time in a while, I've actually been able to get up to full speed. With all the issues, I had been topping out at around 45 - 50; this ride I was getting up to 55 easily and hit 60 on a downhill.
I haven't read the plug yet, but I have noticed 2 things while riding.
1) I get some popping from the exhaust. It seemed to be mostly at lower speeds (like coming to a stop) and maybe worse when the engine was cold.
2) When accelerating from idle, or rolling on throttle (like when rounding a corner), it will stumble a bit; it didn't stall at all, just the stumble when giving gas.

I always thought the popping was from lean conditions and not sure what to think about the stumbling. I will ride it more when the weather permits and keep an eye on the plug condition before making any more changes.

It's been a while, so here's an update.
I have made some minor carb adjustments and come to a point where I'm satisfied for now.
I borrowed an idea from member, rks, and installed a cone filter on a radiator hose, inlet tube.
I also painted my side panels where the stickers were removed; I had some minor complications, but they turned out ok. I installed a set of ebay, cheap, bar end mirrors. I had long stem mirrors prior to these, but they shook terribly at idle. These new ones are very stable and look better, IMO.
I have a similar write-up with pictures attached in another thread ... link in post #9.