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Post by waterjunk on Aug 9, 2011 16:18:03 GMT -5
The bike: 250cc Jonway yy250-t Grand touring edition  The backstory: It's a shiny black beauty that visually, is in excellent condition. Now once you've figure out which of the 4 keyslots on the dash actually start the bike (they all open different compartments and what not) you will find it starts first rotation and idle's smooth as a china bike goes. At about 1300 miles on the odometer this could be a really nice ride. Then you twist the throttle... The problem: Fast forward through the troubleshooting, through the 27 pieces of hardware holding just the seat bucket, continue right past the many pushes back to the shop to our current situation. Fuel starvation is my issue. This model has the gastank mounted between your feet in the typical 250 hump style. The fuel pump seems to be a typical 250 application pump. www.monsterscooterparts.com/fuel-pump-250cc-scooters.html <---- Link for example If i manually fill the carb and start the scooter with a little rev the pump will fill the line all the way to the carb and as long as you keep a good vacuum up there will be no problems. However at anything less then heavy vacuum load i.e. Idling or even just sitting with the motor off you can watch the fuel in the line slowly drain back down into the fuel pump. The problem with this is the bowl in the carb doesnt seem to be large enough to support re-"priming" the fuel line when you want to take off from a light or even after idling for long periods. You will litterly have to pump the throttle with the bike on to get the gas to work its way back to the carb before your bowl goes dry. My first thought is to replace the whole pump and be done with it. I hesitate only because this pump seems to work so well. Is this a flaw in the design mounting the fuel pump halfway below the tank? Is the fact that there are 2 vacuum ports off the manifold which then both T off 2 other locations (EGR, Carb and what not) leeching too much suction from the pump? I want to avoid ordering a new fuel pump just to watch the gas flow right back down the line again. |
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stitts
Big Dawg
JCL MP250A
Posts: 28
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Post by stitts on Aug 9, 2011 16:44:57 GMT -5
I had the same issue. Mine started right away though after I got it. I bought a low pressure electric fuel pump from JC Whitney cost $53 tax ship and all. Easy install and works great. I havent had a problem since. I recommend getting rid of the vacum pump. I can post pics of it for you later.
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Post by WarrenS on Aug 10, 2011 8:40:13 GMT -5
Sometimes the T connections can be bad. Replace with good Y connectors can help.
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Post by vince on Aug 10, 2011 9:13:47 GMT -5
put an electric pump on her shell be good my pump did the same thing i put a new one on now she runs great
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Post by unclebuggies on Aug 10, 2011 9:58:35 GMT -5
I fixed my starvation problem with a better vacuum fuel pump, just a $20 Mikuni. But if you don't have enough capacity in the carb to re-prime the line from the pump to the carb, you either have a vacuum leak or a bad pump. My scoot can idle 30 seconds or more with no fuel line connected. So check the lines for rigidity and the connections for leaks, then sink $20 into a plug-in solution before you try the electric route - I wasted lots of time and money trying electric first. Wish I hadn't.
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Post by leo on Aug 10, 2011 21:16:00 GMT -5
I fixed my starvation problem with a better vacuum fuel pump, just a $20 Mikuni. But if you don't have enough capacity in the carb to re-prime the line from the pump to the carb, you either have a vacuum leak or a bad pump. My scoot can idle 30 seconds or more with no fuel line connected. So check the lines for rigidity and the connections for leaks, then sink $20 into a plug-in solution before you try the electric route - I wasted lots of time and money trying electric first. Wish I hadn't. i agree with the "no electric" pump. i have heard a lot of good stuff about mikuni and they are available at small engine shops. my tank is above the carb so i don't have any problems like this. direct connection and a manual valve and i'm good to go. |
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Post by waterjunk on Aug 20, 2011 14:54:27 GMT -5
Well thought i would run a quick update for everyone that might be paying attention.
My mikuni pump came in the mail and was eagerly installed by your truly.
This seemed to take care of my fuel problem (not keeping gas in the lines) and made it start everytime first turn.
Fast forward past all my test runs, fixing the fuel issue seemed to uncover another underlying problem originally thought to be a symptom of the pump.
While riding if you hold speeds between 40-55 mph for about 2 minutes the scooter will lose power and you must pull over to restart it.
Once restarted applying any form of throttle will shut the bike down and you must restart it and let it idle. This idle will need to be held without touching the throttle for about a minute before you can gingerly twist the gas and start the scooter moving again.
After this point it will actually start to have further problems with shutting off at maintained speeds. It will start to run poorly after that but its an off and on thing.
1 mile shell ride ok with a little bog then the next mile no power at all just idle the next mile after that will be perfect riding again.
Rather then throw parts at it im hoping for a general direction to start in. I've seen CDI's and sometimes Coils act up in this way but not so intermittently.
The sporadic nature of this puzzles me...
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Post by bhinch on Aug 20, 2011 17:20:20 GMT -5
Sounds like the valves need to be adjusted....remember, the engine is an airpump....intake...compression....power...exhaust....so if your fuel pump is not working correctly, you have low compression....because the valves are not closing completely to have full compression....which gives you vaccum to operate the fuel pump....even with a electric fuel pump you still have a compression prob..... .004 intake .... .006 exhaust....on the 257cc Linhai.....not sure if you have the Honda 244cc... it should be required to adjust the valves on a brand new scooter...the boys across the pond can not adjust them correctly..after adjustment you can set the idle....1700-2000 rpm...no rear wheel turning...give it a try...
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Post by waterjunk on Aug 21, 2011 10:48:05 GMT -5
Let me clarify a little as well, the fuel line is staying primed and full of fuel during these sustained speed shut offs.
If you let the scooter sit for about an hour u can drive it around with no problems for about 20 mins. This is far after the thermo sensor shows the bike at operating temp but NOT overheating.
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Post by waterjunk on Aug 23, 2011 10:59:41 GMT -5
shameless bump.. valves make a little noise but i don't see them causing random shut offs during riding..
I'd go ahead and spec them but i will practically be pulling the motor back from the frame to even pull exhaust valve cover
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Post by ce on Aug 23, 2011 11:16:34 GMT -5
Vac line air leak, maybe on PAIR valve or fuel vapor receovery system.
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Post by waterjunk on Aug 23, 2011 11:33:11 GMT -5
can any of these things be bypassed? I considered blocking off vacuum for all the extra stuff and just running the pump.
I;ve done this with the 150's and bypassed all the extra EGR stuff. There seems to be a little more complicated system on the 250's but i dont want to leave anything unvacummed that might hurt the engine
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Post by waterjunk on Aug 23, 2011 15:14:22 GMT -5
Parts for scooters shows this carb with a "cooling hose" should there be coolant in it? lol
From what i see it just goes from one port on the carb to the other...
I've managed to narrow the problem down to losing all power from motor when you maintain speeds for more then 2 minutes.
You'll have to pull over and let the bike "chill" for about 10 minutes and then you can restart it and slowly give it throttle. This is rinsed and repeated.
The problem does not occur for the first 5 minutes of your ride after a cold start. Coolant is full and it shows normal temp when running.
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jmd
Junior Dawg
Posts: 8
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Post by jmd on Aug 23, 2011 16:56:14 GMT -5
I have just put a new yy250t on the road started fine and then got harder and harder. Now with a grand total of 26 miles it doesn't start at all. Turns over fine but no firing and no smell of gas from exhaust outlet. I obviously have to check all elements of the fuel delivery system but how do I get to it? I want to avoid removing panel sections I can leave in place. Where do I start
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Post by ce on Aug 24, 2011 8:53:01 GMT -5
Just open the battery compartment in the seat bucket and examine all the hoses and wires you can get to in the engine bay.
A loose vac line will disable the fuel pump, and a loose connection in the wiring will stop spark.
It's not uncommon for a new scoot to vibrate stuff loose, so check all fuses and trace wires and hoses to see where they go.
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jmd
Junior Dawg
Posts: 8
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Post by jmd on Aug 26, 2011 16:45:41 GMT -5
It makes sense that its the pump/vacuum problem. However, when I removed the battery cover it convinced me that I would need to remove cowling to really work on the fuel system so I needed to confirm the problem as fuel. I gave the air intake a shot of starter fluid and the thing burst into life. It also appers to have 'fixed' the problem since the scoot starts any time I try it. I suspect the original probem was priming and it is likely to re-occur, So I will carry the starter fluid with me and not try to fix the problem unless it becomes insistent.
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jmd
Junior Dawg
Posts: 8
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Post by jmd on Sept 2, 2011 11:05:08 GMT -5
Following up on the above. The fuel system quit on me again. About half mile from home. A heavy squirt of starter fluid got me rolling until it quit again --- in my driveway. Guess I will now have to fix it.
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Post by dumbass on Sept 2, 2011 11:20:13 GMT -5
Following up on the above. The fuel system quit on me again. About half mile from home. A heavy squirt of starter fluid got me rolling until it quit again --- in my driveway. Guess I will now have to fix it. Just a thought.......the next time it stalls like that remove the gas tank cap and see if it starts again. Maybe your fuel tank is just getting a vac lock and not allowing you to draw gas. You may have made a temp fix by installing a stronger pump. But as you used more gas it takes stronger pumping to do the same amount of work. If you find removing the gas cap helps you can add a tank vent. This is a common problem on CF Moto V5s. Bob |
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jmd
Junior Dawg
Posts: 8
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Post by jmd on Mar 21, 2012 14:42:04 GMT -5
Question for 'Big Dawg'. Which J C Whitney pump did you fit to your scoot. I plan to do the sme thing rather than go chasing vacuum leaks
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Post by chromestarhustler on Mar 21, 2012 15:50:39 GMT -5
take the gas cap off, (just close the flap) and go for a ride, if the scooter will stay running then its a vent problem on the gas tank, they have some one way valves that if installed backwards or get clogged will allow the tank to create a vacuum as the gas is pumped out that air needs to replace, if that doesnt happen it fights the pump until it can not longer over come it. these vents run to pcv, A.I.R., and all that other bs.
you can drill a tiny hole in the gas cap, or unhook the tank vents and just run a small fuel filter on it so the tank can breathe, or run a dirt bike style vented cap, (it has a small tube running out of it)
this is what "dumbass" is talking about.
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jmd
Junior Dawg
Posts: 8
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Post by jmd on Jun 29, 2012 13:44:30 GMT -5
Following up on my decision to fix the fuel supply problem I purchased a Mikuni pump and replaced the exisiting unit in about 10 minutes (plus 2 hours getting to it!). It has solved the problem. I also covered all jointing 'T's and 'Y's with a coating of silicone sealant. Alot easier than replacing possibly leaking units. Joe
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