One Stumped Mechanic By bolts (Read 1,400 times)

[bolts]

I am currently working on a sunl 150cc scooter, and the customer said that it was working when he got it, but that over time it has stopped working. I was told that he was driving it to work and back (about a 15 min drive, including a brief stint on the freeway). I originally thought that it was a carb problem,and so I cleaned it out. That didn't fix it, so then I saw that all his vacuum lines connected to the fuel valve switch, and the gas line went right to the carb. I changed everything back to how it is supposed to be, and then found out that the intake manifold was cracked all the way through. Changed that out, and it started up and ran until the stop sign where it would die at idle. (Then the belt shredded, and had to be replaced) So I adjusted both valves (0.08mm) thinking that it would do the trick, because I have had that issue on other scooters and that solved the problem, not on this one. It will idle until it is warm and then die. I can even rev it up during this time, and it will bog for a split second at first, then pickup and go like it is a carb adjustment problem, until it is warm and then it dies and won't start until it is cool again. 

So I have tried EVERYTHING. I replaced the vacuum lines, carb, intake manifold (same as mentioned above), automatic choke, spark plug, ignition coil, CDI, fuel lines and filter, adjusted the valves (as stated before), and still nothing. 

Is there something that I am missing? I am planning on doing a complete top-end rebuild; cylinder, piston and rings, gaskets, and valves. But before I spend $150+ on that, I want to make sure that there isn't something that I am missing. 

Any help would be greatly appreciated! thanks

[Alleyoop]

Can you keep it running if you hold the throttle a little open? If it keeps running with the throttle a little open then I would say the PILOT JET PASSAGE is clogged actually the tiny Pilot Jet fuel outlets by the butterfly.
Turn the fuel ratio screw 1/4 at a time try counter clockwise(richer) and see if the idle goes up if it does repeat until you get the highest idle. If it goes down counter clockwise then repeat but CLOCKWISE(LEANER). You want to get the highest idle out of the fuel ratio mixture.

Also the Idle may be to low it should idle around 1500-1800.

But before tearing it apart test the compression if its lower than 140psi then it needs some work.
Alleyoop

[bolts]

It idles just fine at 1500-1600ish until it is warm. I thought the same thing with the idle adjustment, I even had the idle set screw all the way in at one point, but it still ended up stopping.
With the fuel ratio screw, I have been playing with that as well, but it doesn't seem to be making a difference either way.
i pulled the carb and auto choke off of a scooter with the same engine setup, that I did a crankshaft replacement on, and it was running perfect when I pulled it off. So I know the carb works and is clean

[Alleyoop]

If it idles at 1500 or so started cold that sounds like fuel is only being sucked out by the ENRICHER and when the Enricher extends and shuts off the extra fuel it dies.

If turning the fuel mixture screw in either direction doesn't change the rpms that is a dead giveaway that your PILOT JET and OR ITS PASSAGE are clogged which is what I suspect seeing it will only run at a higher rpms.
Most when they do clean out the carb all they do is clean out the JETS and that is it. But the most important part is the PILOT JETS passage and really the TINY fuel outlets by the butterfly. They are real tiny and any little speck of anything will clog them.
Alleyoop

[bolts]

I will take a look, but it seems crazy that the carb would work just fine on the other scooter, but not on this one. I was able to do all of my adjustments on the last one with no problems, but this one just refuses to run no matter what I do. Let's say that it isn't the carb, that all the jets are clean, all the different ports are cleaned and that I ran it through a parts bath for 15 minutes straight, but it still does the same thing. What would be next to test?

(I will check the carb again, and also the compression) Thanks heaps for the help, giving me good ideas

[Alleyoop]

Then I would rec-check your valves, are you sure you had it at Top Dead Center when you adjusted them to .004 inchs? The only other thing is bring it up to TDC and check where the Timing Case Marker is pointing to on the flywheel, maybe the woodruff key is damaged and it is out of time.
Alleyoop

[tvnacman]

could it be the spark plug , how does it look (color)

John

[bolts]

Ok, I was sure that I did have it at TDC, but I will check again and make sure that it is TDC and see where it all lines up.
Thanks again! I will post after I check all these things

[bolts]

I thought of the plug as well, it was dark, but I used fine grit sand paper to clean it, and even switched it out for one fresh out of the box, but same thing. Great thought.

[Bashan]

.08mm is .003"....kinda tight for a 150. It heats up, the valves don't seat....pffft somebody farts. Then the bike dies. I'd try Alley's gap...and then set the valves! I'm here all week! Rich

[bolts]

Ok, I will try the bigger gap. I have used this gap on 3 other 150's with out problems, but at this point I am willing to try anything. Thanks

[tvnacman]

I use .004 inch for both , sometimes I have to do it 3 times to get it stable .

John

[bolts]

I did it 3 times this last time, sucks to do it again, but at least it doesn't take too long to set them

[Alleyoop]

I really do not think the .003 gap is your problem I think fuel from your pilot jet is not being sucked out and why it dies after the enricher cuts off the extra fuel for starting and will again start and idle after it retracts.
Alleyoop

[Alleyoop]

You can also try this, take the Air Filter tubing off and cover part of the intake with your hand and see if it then stays running after it has warmed up.
Alleyoop