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Having a garage in hot, humid weather is a double edged sword. One one hand, if the garage door and all windows are kept closed, the inside of the garage stays about 5-15 degrees cooler than the outside air. But, once you open the garage door, all the humidity condenses on the already slippery slick floor and you get this:



It doesn't look that bad in the picture, but there is a coating of moisture all along the floor of the garage where the humid air condenses onto the comparatively cold concrete floor. It gets worse the more you walk along the floor as well.

I went out today and wanted to start by trying the engine with the same jets/tune/everything as yesterday when I stopped working on it so I could see if it ran the same or if there was something like a bubble in a fuel line or in one of the carb passages that could have worked it self out overnight.

I went to start the engine the same as I always do, but it just wouldn't start. I always twist the throttle 2-3 times before trying to start the engine; using the accelerator pump as a primer. I suspected the pump wasn't working right because when I manually pushed the pump's plunger down my hand, it didn't feel the same as it usually does. I took the air filter off and looked at the point the fuel is supposed to come out of the pump when you twist the throttle; nothing came out.

Now, yesterday during the carb cleaning, I did take the jet, spring, and ball out of the accelerator pump casting part to clean it. It appears that when I re-assembled those pieces, the ball (that acts as a one way valve) had too much pressure on it from the spring, causing it not to work right. I dis- and re-assembled those pieces, put the carb back together and put it back on the scoot. Before I tried starting the engine, I left the air filter off and twisted the throttle a few times; the accel. pump was working perfectly again.

The engine ran just like it did yesterday before I called it a day, so my hope that the problem was just a fluke was gone. I took the carb off yet again and inspected the idle jet. I mentioned in my last post the I had the feeling that i may have clogged it while trying to clean out the carb. I looked through it and could see a very small size-of-a-human-hair piece of something in the jet. I again cleaned it out with carb cleaner as best as I could and re-inspected it. This time I could see straight through it; no obstructions. I re-installed it in the carb and put the carb back on the scoot.

This time the engine ran just as it had been running during the first video I posted in this thread; it idled fine, but had the hesitation on acceleration. I took the scoot for a ride to fill up the gas tank and get the engine warmed up. When I came back, I tuned it with the mixture screw to get the highest idle, which turned out to be about 2 turns out. Here's a video of the engine running at that moment.

Next I did as alley suggested and start taping up the air filter bit by bit, reducing the air going into the engine. I started on the end of the filter furthest away from the carb, taping up the end and about 1 inch of the sides. The engine ran exactly as it did in the video I linked to in the previous paragraph. I took a video of it running; blipping the throttle and holding the throttle until the engine stopped hesitating, but no matter what I do, photobucket will not let me upload it.

Note that in all following videos with tape on the air filter, the tape was the only thing that changed. The mixture screw and idle screw were not touched.

I noticed something about this time; when I open the throttle and keep it open until the engine stops hesitating, for about 3-5 seconds after that if I blip the throttle very quickly, not waiting for the hesitation to stop, the engine won't hesitate or bog down, it just revs up and slowly settles down. The longer I wait after revving the engine to blip the throttle, the more it hesitates and bogs. If I open the the throttle, wait for the hesitation to end, let the engine settle back down to idle, wait about 20 seconds, and quickly blip the throttle open and closed, the engine will bog down and die or nearly die. Something similar happens if I wait about 20 seconds or more and then hold the throttle open until the hesitation stops; The engine will heavily bog and hesitate and black smoke will come out of the exhaust until the hesitation stops. I captured this happening on a few videos I'll link to below.

Since there was little-to-no difference with the first bit of the air filter taped off, I added another wrap of tape around the circumference of the filter and started the engine back up. Again there was almost no difference in the hesitation of the engine. Here is a video showing what I described above with holding the throttle open and quick blips.

I added another wrap of tape and repeated the process. This time I could notice that the hesitation was getting worse; lasting longer and bringing the engine closer to dieing. The first throttle opening in that video was after the engine had been idling for about 45 seconds. As you can hear, the hesitation and bogging was getting worse.

Again, I added another wrap of tape, this time there was only about a quarter-inch left for air to get in. As I thought might happen, the hesitation got even worse. The first throttle opening in that video was after the engine was idling for about 45 seconds.

By now I had been revving the scoot's engine for about 5 hours and I'm pretty sure my neighbors would like some quiet, so I stopped there for today.

I'm now starting to think that I might need to go the other way with fuel at and around idle - more lean. When there was that piece of debris obstructing the idle jet, the engine revved quickly without hesitation. When I removed the piece of debris, the engine hesitated and bogged once again. When I reduced the air going into the engine, making it run richer, the problem got worse. Tomorrow I think I'll try going down one size in idle jet to a #33. I sure do have enough different sizes to test them all:

I will try that today. Hopefully the near 100% humidity won't throw off the results too much. Should I be adjusting the mixture screw each time after I put on a piece of tape or just do it once at the beginning and leave it?

I went out and raised the needle/lowered the clip one notch (it was in the middle when I took the video I posted before):



The engine ran quite a bit worse. The hesitation on acceleration became much more pronounced and lasted longer. I adjusted the fuel mixture screw until I got the highest idle and here is the result.

Since the engine behaved worse when I raised the needle/lowered the clip one notch, I decided to try to lower the needle/raise the clip one notch so the clip would be one notch above the middle. Again, I adjusted the mixture screw until I got the highest idle, which was a bit more difficult this time. The hesitation got a little better, but now I am having trouble at idle. Before (with the engine tuned as it was when I posted the first video) I could sit at a stoplight for about 20 seconds with the engine idling and take off without the engine dieing or almost dieing. Now, if I let the engine idle for anymore than 10 seconds, when I go to accelerate it slows down, hesitates, and dies or very nearly dies. I can keep the engine from dieing while sitting at a light if I lightly rev the engine just to the point where the clutch starts to engage, let off the throttle, and repeat until the light is green.

Here and here are two videos showing what I mean.

    

I tried that, no luck. I'm using a #30 idle jet at the moment; I get the highest idle speed (with the hesitation) at about 2 1/8 turns out. If I turn the adj. screw more CCW the idle drops, but the hesitation remains, the same thing happens when I turn the adj. screw CW; the idle drops and the hesitation remains.

I have tried putting in a #32 idle jet, but that floods the engine even with the adj. screw all the way in.

I have thought about that quite some time ago, back when I didn't know too much about my scoot. I decided against it because it would make troubleshooting and asking for help difficult because I wouldn't be using the standard carburetor that comes with these engines.

However, having owned my scoot for about 5 years I think I might be able to do it. But for the immediate future, I'll stick with the CVK carb.



I tried tuning the carb by turning the fuel adj. screw CW and CCW with every idle jet including 30, 32, 33, 35, 38, and 40. The only idle jet that doesn't flood the engine at idle (out of the ones listed above) is the 30; it's the one I have in the carb now.



I have adjusted the spring that pushes the plunger. When the carb was new, the spring was about 1-2mm from the plunger when the throttle was at idle. I adjusted it so that there is just a hair's breadth between the spring and the plunger (I used a feeler gauge between the two, the same one that is used for adjusting the valves).

I would like to be able to completely (temporarily) remove or disable the accel. pump to see how the engine behaves without it. I know I could bend the spring all the way up, but I'm afraid if I do that too many times it will break.

When I twist open the throttle quickly from idle with the engine at normal operating temperature and the enricher fully extended, the engine will, for about 1/4 of a second, sound normal; as if it is going to accelerate as you would predict it would. After that the engine bogs for about 1/2 to 1 second, then the rpms climb and the scoot accelerates as you would expect.

I'll see if I can get a video demonstrating what I mean uploaded some time today if the weather cooperates.

I'm quite sure it isn't the variator weights, the engine bogs the same when it is on the center stand with and without weights installed.

Are there different sizes of accelerator pump jets out there? I have a feeling that the accel. pump/jet in the carb on my scoot isn't giving the engine enough gas when I snap the throttle open.