Engine cutting out at high rpm By dozer187 (Read 7,863 times)

[dozer187]

I have a taotao cy50a scooter with a 50mm bbk installed on it, it runs great except for when my rpms hit around 8k it starts stuttering. i have a no rev limit cdi installed so not really sure what the problem is, i also have a 90 and 95 main jet ive tried both and it does it with either one. any help would be appreciated

[Alleyoop]

Run it up at WOT and when it starts to stuttering BACK OFF THE THROTTLE 1/8-1/4 of an INCH AND HOLD IT THERE.
Now pay Close Attention to what the motor does:
A. Does it speed up?
B. Does it stop the stuttering and settles down?
Alleyoop

[dozer187]

once i back it off a bit it stays just below 8k rpm and stays steady at speed.

[jerryscript]

8k rpm is redlining it.

[tvnacman]

what he calls stuttering could be he is flattening the valves.
I do remember guys talking about 9500 rpm but not often.

John

[Alleyoop]

Nov 12, 2015 23:43:25 GMT -6 dozer187 said:

once i back it off a bit it stays just below 8k rpm and stays steady at speed.

That test I told you to do is an OLD TRICK OF THE TRADE. Very easy and very accurate means of finding what the motor needs when it acts up.

If when you back off 1/8-1/4 and the motor speeds up it is telling you it needs more fuel it is running LEAN.
If on the other hand the motor settles down and runs at speed then that tells you it is getting to much fuel it is RICH.

And by the way this works at any throttle position all you have to do is pay attention to what the motor does when you back off a little on the throttle.

So in your case to much fuel is being sucked in.

Things to check would be your AIR FILTER make sure is it not dirty and or clogged or restricted.
You may want to try a more free flow filter. Also what size carb is on there it may be to big and if so then the jets have to be down sized. Or try a #85-#88 main jet.

What size is your pilot JET? Does it start up nice and easy 1 or 2 hits on the start button? How many turns out is the Fuel Ratio Mixture screw?
Alleyoop

[dozer187]

its a stock size carb just not sealed. pilot is a 35 from what i recall it starts up fine and idles real nice and is real smooth, its just up at around 8k that it spazzes, its more of a bucking than stuttering like its cutting off ignition

[Alleyoop]

Well you proved it is running to rich on the top end so its up to you to decide what you want to do to correct the problem. I gave you some things to check out and or do.

[dozer187]

i think the jet that cae in the carb was an 88 i think ill give that a shot, appreciate all the input.

[Alleyoop]

Great, I was going to suggest a #85-#88 main. Let us know if it solved the bucking at high rpms.
Good luck Bro
Alleyoop

[dozer187]

threw both the 85 and 88 mains i had in, neither helped the problem, gona have to try a uni filter instead of the stock airbox i guess

[Alleyoop]

BUMMER!! What was it doing with the smaller JETS? How about sounds that the motor is making DOES it make any types of sounds when this happens?
Reason I ask is You went from an 85-95 and you say no change and that is very hard to swallow that nothing at all changed.
The amount of FUEL from 85-95 is HUGE and something had to change either that or your not describing the problem correctly and we are going in the wrong direction.

Can you get a VIDEO SOUND going when you run it up at WOT so we can hear the motor and what it is doing.
READ THIS THREAD ABOUT SOUNDS A MOTOR CAN MAKE:
scooterdoc.proboards.com/thread/8628/motor-sounds-tells


But Before you go and get a UNI FILTER First try taking the FOAM FILTER off and run it at WOT without the Filter that will suck in a lot more air.
Alleyoop

[dozer187]

my further testing will wait till tomorrow, getting to late here now to be runnin wot lol, with the 85 it was running to lean it kept accelling when i backed off the top end, 88 was a bit better, 90 has run the best so far, i think overall its not getting enough flow thru the stock airbox even with the restrictions pulled out of it

[Alleyoop]

Ah see, you did not say that before. But now you know how it works , the 85 it gained speed when backing off(LEAN) so from there you can go up.
Now you know when you get the free flow filter you will again have to tune the jets. Hopefully one will be very close and the FUEL RATIO mixture will dial it in. But your on your way now that you know how to test for lean or rich condition.
Alleyoop

[dozer187]

ok so im back after a very busy few weeks, ive ordered a unifilter for my bike, now what will have to be done to install it properly? will i need vacuum caps for the lines that come off the stock filter setup?