New 250B no fuel to the combustion chamber By flyawaydoug (Read 1,411 times)

[flyawaydoug]

This is my first motorized 2 wheeler of any kind. It's 4 months old with 698 miles on it. I bought it new. I'm an older dude and a pretty fair mechanic, but this has me stumped.

It's the Linhai/Yamaha 257
I took 3 weekends to do the PDI before riding it the first time.
At about 500 miles it started to do the infamous stop light stall. So I changed all of the fluids (2nd time). Pulled the plastic and adjusted the valves.
Ran like a top after that until 2 weeks ago.
The starter wouldn't engage. Relay would click but no starter. Long story made short, I added a ground wire from the gound connection to the frame by the battery back to one of the starter mounting bolts. Starter engages without fail now. A side note, when I get into situations like this, I use a 70 amp booster with the battery to keep from sucking the life out of it.
Last week it became very difficult to start. It also had to warm up several minutes to keep from stalling. I originally blamed the cooler weather (below 50 F). Now it won't start at all.
Good battery.
It has spark (yellow arc, not blue but I am blaming that on the battery driving the spark).
17 to 18 inches of vacuum on the intake stroke.
Fuel pumps to the carb.
Carb bowl fills showing good float and needle action.
Valve lash triple checked.
I turn the engine over, and it won't fire.
The spark plug is dry.
I pulled the intake and the valve is not sticking.
I thoroughly cleaned the carb and inspected the diaphrams. Reset the mix screw to 2 1/2 turns. Checked the enricher and it is retracted when cold (unpowered). It takes about 3 minutes to extend when powered.
Still won't start. Still has a dry plug.
Ether did nothing even when sprayed into the chamber throught the spark plug port!
Any ideas of what I've missed or what I'm doing wrong? Help!

[Alleyoop]

Well to start it is the PILOT JET and Enricher that feeds it fuel. The Main Jet and Diaphgram do not play a role for starting and idleing and even up to about 20mph.
Now when you checked for spark did you check it holding the Spark plug to the ENGINE for ground? Holding to the frame and getting SPark from there does not mean you are getting Spark when it is on the engine. The Engine must have a good ground for the Spark Plug to Fire.
If all that is good then Next thing would be to check your compression. If you have a gauge use that if not Take the Spark Plug out and stick your finger in the hold and HOLD THE THROTTLE wide open and crank it. If it has descent compression it will blow your finger off the Spark Plug hole.

Now the gas may be reaching the Carb and filling up the Bowl but if the PILOT JET and or the ENRICHER pasages are CLOGGED it will not suck in fuel from the bowl.

Take your carb off and Get A Spray Can Of Carb Cleaner they come with a LONG THIN straw.
Take the Pilot Jet out and Make sure that is Clean and Spray goes through it. THEN with the Pilot Jet still out SPRAY into the Pilot Jet Hole.


Then take your ENRICHER off a lot of time the AIR PASSAGE of the enricher gets Clogged from crap on the Air Filter Side:

Alleyoop

[ce]

CDI
Coil and plug wire
Kill switch
Rectifier
Alarm

[flyawaydoug]

Thanks all. I have the carb off and will follow your instructions above. My carb looks a bit different but I should be able to translate. I will recheck spark again grounding to the engine. I have an inline tester and the light flashed when I used it so I think the ground to the block is OK. Can't hurt to double check. My compression gage won't fit between the frame and the engine so I will repeat the finger test. Thanks again.

[bhinch]

check your compression with the throttle closed...not open.....never heard of holding the throttle open to check compression....your defeating the purpose...

[Alleyoop]

Sorry, to check compression you need to have the throttle wide open to open the BUTTERFLY to suck in AIR. If you don't your readings will be very low.
Alleyoop

[sunlproblems]

do the valves again they closed back up mine did

[flyawaydoug]

>:(No luck.
Compression good.
Spark good (grounded to engine)
Valves good.
Vacuum good.
I thoroughly cleaned the carb. I have a concern about the passage between the enricher and the pilot exit port. I could not get a consistent flow of cleaner every time I shot it. One time would fountain back out the opening for the choke. The next time it would blow back and not appear to blow out through the choke. I drew a box around the area on the picture.
The spark plug still comes out dry no matter how much I crank. I can't help but think that the carb is the only thing it can be. If the spark timing was off, I show see fuel fouling the plug. I think
I want to be reasonably sure before I cough up the $ for a new carb.
Man am I frustrated.

Attachments:

[flyawaydoug]

I meant to say choke outlet not pilot.

[Alleyoop]

Flyawaydoug,
Try spraying from the OUTLET SIDE BY THE BUTTERFLY look at the Picture above to see where the OUTLET for the ENRICHER is.

Sure looks like something is really clogged.
Alleyoop

[flyawaydoug]

;D Got it running. I discovered 2 problems. I may have had others that cleared in the process.
1. Even though I saw a spark, it wasn't hot enough to ignite ether. I replaced the CDI and the coil assembly. When I sprayed ether, it will stumble and try. Which it would do before this.
2. I adjusted the float to allow the snorkels for the jets to be submerged in the fuel. After that it started right up and ran.

It's very possible in all my cleaning that I cleared an obstruction without clearly seeing it. Owning a Chinese scooter is quite a learning curve.

[go4it]

You said that while having the problem a spray of ether would cause it to try to start? To me this indicates you had spark all along but yes it could have been weak. Especially if it still reacts this way now that it is starting. Personally, I think your problem was always in the carb and/or enricher. You ether finally cleaned the carb problem, got the float adjustment just right or at least for now corrected a yet to be identified problem with the enricher.

Knowing the problems I had with my 54B and now my CF Moto V5 my vote is on the enricher first then on the float. Of course dirt can always be a problem but lets face it you have a filter and it sounds like you cleaned the carb several times. Assuming you did it correctly that wasn't the problem.

It would be interesting to know what would happen if you put the old CDI back on. If it still runs then install the old coil. It's great to have it running again but personally I'd want to know for sure what the problem.

Bob

[Alleyoop]

FANTASTIC Flyawaydoug!! Good job, Persistence pays off.
Alleyoop