Odd Stalling Problem

[Ebuddy]

My Roketa MC-30-150 (B GY6 variant) starts and idles awesome. When on the kick stand, I can rev it up to 7,000 RPM up and down sustained and quickly release and it goes back to idle without a hitch.

When I ride it, it runs and accelerates great. After, say, 1 minute or two at higher sustained speeds (35mph +), when I slow down (like for a stoplight), it slows down and then dies. Following this, it's VERY difficult to re-start it, almost as if it's flooded. Once it does restart, it seems fussy for a short time and then the problem repeats.

When I get it back to my garage and start it up, it starts and idles fine and I can play with the throttle with no issue.

It's almost like it's flooding...but not quite. I don't know what to make of it. I presume the carb is fine since it otherwise runs and idles with no problems but it SEEMS like a fuel delivery problem. Valves were adjusted just a couple hundred miles ago and the issue's gotten progressively worse.

At first I thought that somehow the belt/clutch/variator was somehow getting caught but I replaced the belt and installed new rollers (yea, sliders would have been better, but it only needed to get me until the spring). Everything seemed to look and operate normally.

Any other ideas? I'm going to store it for the winter soon, but want to be ready in the spring.

Thanks! =)

[blueboy5000]

Sounds like valves. Adjust your valves to .004" intake and .005" exhaust.

[qwertydude]

Those symptoms are of a bad fuel pump. Chinese fuel pumps are notorious for this. Best to replace it with a real Mikuni fuel pump.

http://www.amazon.com/Mikuni-Genuine...kuni+fuel+pump

Scooters with the tank in the floorboard need a vacuum operated fuel pump to pump fuel up into the carb. The Chinese ones simply can't pump with the reduced vacuum of high rpm running. The Mikuni's can.

Best thing to do is a desmog since these scooters benefit greatly from that. Then get a new fuel pump and run it on it's own dedicated vacuum line to the intake manifold that's as short as possible and has no T's. It shouldn't if you desmog the scooter.

Those two things thing usually solve the mysterious high speed bogging issues people experience.

[skuttadawg]

Check the valves and adjust if needed http://www.scooterforumonline.com/in...ic,1720.0.html

[Ebuddy]

Thanks guys! I think I will get a new fuel pump. The one on there is the original, but the scoot has about 4k miles so even if it doesn't fix the issue, it's cheap insurance. The only thing is the the scoot doesn't "bog" at speed, it seems to run fine, it's when I decelerate to a stop that it kills and doesn't want to start.

I did do the valves (.003 and .004) just a few hundred miles ago but I will recheck them also.

[Ebuddy]

Well...thanks again! I switched out the petcock and that cured about 95% of the problem. I took it out and it still stalled out twice, but was easy to restart after. Since I've probably been fighting the old, failing petcock I figure I might re-look at the fuel/air mix and idle speed. Nonetheless, she's running well enough to get me to my storage destination! =)

One follow up question: The scoot has the B-variant, long case and 13" wheels. The boss (my wife) might let me get a new motor over the winter. If so, would I be OK with a "standard" GY6 150cc long case?

[blueboy5000]

The "b" variant is theoretically the fastest gy6 150cc engine. Are you certain it has a "b" variant, as the "b" engine is used EXCLUSIVELY with 16" wheels?

If you have good compression and are not leaking/burning oil, then I see no reason to buy a new longcase. 4K is really not bad as far as mileage goes, I know of a bike with a 157 that is at over 15k and runs like a champion.

[Ebuddy]

Yep... Engine S/N starts with "BN157QMJ". It does have a small oil leak that isn't TOO bad. It's probably small enough that it can go between oil changes and still not be super low. Besides that, there is a stripped screw hole for one of the screws for the oil pan. I am debating at the moment, a local, trusted scooter shop in town can sell me a very slightly used motor pretty cheap so I was kicking around the idea.

[qwertydude]

So it does sound like a fueling problem. I can almost guarantee you a full desmog plus the new fuel pump will fix the stalling problem.

[blueboy5000]

That's not a "B" variant, the two variants are "P" and "B" and they read like this " 1B57" or "1P57". The "b" engine is also called an "extra-longcase" as it is significantly longer than a "longcase" to fit 16" wheels. The 'P' variant has larger valves and a taller head, resulting in nominal low-end power gains over a regular 157.

[skuttadawg]

If the tank is higher than the carb no need to get a fuel pump . Most have the tank under the seat or behind it , but a few have the tank in floorboard . Those with the tank in the floorboard a vacuum Mikuni fuel pump would help a lot .

When the valves are too tight they do not open up enough to allow fuel and air to start and keep it running . Way too tight = no start . Tight it starts but stalls once the engine gets warm . My Echarm they got too loose and it would want to stall just before coming to a stop but start right up . After a valve adjustment it was new again and has been for over 17k miles

[Frank Castle]

Originally Posted by qwertydude

So it does sound like a fueling problem. I can almost guarantee you a full desmog plus the new fuel pump will fix the stalling problem.

what does 'desmog' mean?

[Ebuddy]

Hey guys! I'm back. I brought (rode) the scoot home from it's storage place. Started right up and ran like a champ. Same issue however, after it's warmed up it gets fussy and dies on deceleration and is sometimes difficult to restart. It does have the smogger "stuff" still in it and I've reviewed a number of online pages but I'm still not entirely certain what I should/should not remove. I'm attaching pictures of the inside (if it works). I understand how the fuel is fed via vacuum to the carb but there are some extraneous tubes that I'm not sure of. This weekend I might try to re-gap the valved to .004 and .005 for intake and exhaust respectively. Finally, should the various tubes for fuel, air, etc. (other than the obvious ones that are MUCH larger) all be the same size? It seems (using the same size all around) sometimes they go on snugly, others are loose any yet others need to be wrestled on the various fittings. Any other advice would be much appreciated! =)

[Frank Castle]

is that a soda can in your motor?

[Cubby1331]

Originally Posted by Frank Castle

is that a soda can in your motor?

I think its for those long rides when you get thirsty