More speed; can't I just get 8k? By wutzthedeal (Read 1,162 times)

[wutzthedeal]

On my cy50a, since my most recent problem, I've lost top end speed. It wasn't great before that, but something I've done has made it worse.

Shouldn't I be able to get at least 8k rpm on the Chinameter? I'm only getting to about 6100. I know in general what types of things can improve top speed, but I don't know what I've done to slow it. It's possible that the nuts holding the throttle cable in place at the carb are not in the same position along the threads as they were; would that affect it? Or should I really super-tighten the clamps around the hoses for intake manifold and air intake? I also adjusted valves and now have a slight tick which is ok from what I've read.

I have no restrictions that I know of (CDI isn't restricted, no washer in variator area) except maybe a tight exhaust. I don't wanna be too greedy; just happy the thing is running, but with my CDI, high quality oil, 93-only fuel and religious use of Seafoam, along with my Dr. P sliders (6g), shouldn't I be able to get 35-40 mph gps out of this scooter? Tonight I got to 35 with a strong wind at my back; average was 30. Used to be 34 at least average.

[Alleyoop]

Well have to ask WHAT DID YOU DO that now you believe is slower? Now if it is a stock 50cc 4 stroke they are only good for little over 30mph some won't even hit 30. To get in the upper range of the 30s you need some mods on it. To get it to near 40 or 40 you will need to put in BIG BORE KIT like a 72cc version.
Alleyoop

[wutzthedeal]

Ok. I just thought 6k rpm was awful low Chinameter. I don't know what I did except what I mentioned (removed and lightly cleaned carb; may have reconnected hoses too loose or too tight, throttle cable slightly off). Whatever I did cost me 4mph top end I guess those warm months will be bbk time; I'll watch 20 videos before i ever even order one because I can't stand to be down for long! Thanks Alleyoop.

EDIT: Hope I understood you right and you weren't asking how I measured speed. If you were, I only use Ulysses GPS (I've tested with others to ensure Ulysses works accurately, then just stuck with it on my Android phone).

[Alleyoop]

OK, you took the carb off and YOU MAY have the throttle connected on the bracket not adjusted right. If so you may not be letting the Butterfly open all the way and therefore that will cause low rpms and lower speed.

As you look down on the cable LOOK AT THE ACTUAL WIRE, DOES THE WIRE HOOKING onto the CONTROL WHEELL have a lot of SLACK if so that is your problem. You can also tell with your throttle grip if you just turn it easy you can feel WHEN IT ACTUALLY PULLS on the CONTROL WHEEL, If it twist more than OH 1/2 inch or so that is your problem.
You should only have about 1/4 of an inch of PLAY before it pulls on the CONTROL WHEEL and starts to open the BUTTERFLY.
Alleyoop

[wutzthedeal]

Ok thank you, checking that now. I had my idle set awfully low, too; probably unrelated but you know the standard thing of getting the rear wheel turning and then backing it down just til it stops? That puts me up at like 3k rpm chinameter, probably 2.5k actual vs. the advised 1.9k. Ok just got back; no slack in the throttle. Motion of less than 1/8th inch moves it so the cable is tight.

[Alleyoop]

BUMMER!! I was hoping that was it. Ok, did you by any chance take the GOLD OR BLACK top off the carb and took out the Diapghram and needle. If the Rubber Diapghram is not in the groves that it fits in it will not seal good and your Diaphgram will not raise the Needle out all the way.
Let me know If not we can go through adjusting the carb.
Alleyoop

[wutzthedeal]

I did have that out during that big problem and I had put it back on wrong; bent the needle plus this one has a little tab on the diaphragm that lines up with a little recessed area. I double-checked with the carb out for freedom of movement after straightening the needle and that was good, but I could have the diaphragm (tab notwithstanding) slightly off so I'll check that tomorrow. I was excited; went out for a 1:30 am ride and hit a max 37 gps; didn't realize it was the wind getting me there; max coming back was 29, into the wind. But I'm 6'5 250 with no windshield so that doesn't help top end, either on a 49cc.

[Alleyoop]

Well it appears to be running good, did you by chance put in heavier rollers or sliders. That will drop your rpms as well.
Here is how 1 GRAM up or down effect the RPMS:
Rollers 1 gram up or down will change your rpms by 500-600.
Sliders 1 gram up or down will change your rpms by 200-350.
EXAMPLE:
If you have 8 gram rollers and your rpms were 7000 at Wide Open Throttle and you changed the rollers to 7 grams your rpms would GO UP BY 500-600 rpms and then your WOT would be at around 7500rpms.
Alleyoop

[wutzthedeal]

My factory rollers were 8g, I put in Dr. Pulley sliders 6g. There was no change in top end speed (I didn't pay attention to RPM) but my speed off of the line made a major leap. It's still impressive to be honest. Just the top end I've messed up somehow, and I've tinkered back and forth with idle and a/f adjustments trying to find sweet spots. I used the pepsi can method for adjusting valves but I don't think that would affect it; I will be re-adjusting when I get some real feeler gauges. That spark plug may have something to do with it; dropped it and bent it, had to bend it back so had to re-gap it and only used a dime and my eye to measure the gap/adjust it to half the width of the dime or about .75mm.

[Alleyoop]

No going down on the weights will require higher rpms to get top end speed and if you don't have the rpms you will loose top end. Well check the seal on the rubber diapghram because if that is leaking it will not raise your needle out and will cause your low rpms.
Alleyoop

[terrilee]

i havent had enough coffee yet to make any decent comments, but i will say this. China rpm meters are as bad as china speedos most are way off i look at mine, but dont trust it
i use the sound of the engine, if i had to be perfect on it, id put on a good tiny tach