scorpa0259 Posted September 29, 2017 Report Share Posted September 29, 2017 (edited) Hi everyone, So, I bought a 2004 2T SY250. Soon figured out it needed a new piston and cylinder, then delved deeper and found out the crank was shot too. It was a bitch to start from the day I bought it, and it's exactly the same after I've rebuilt it. So, it's had the following: Crank rebuilt New piston, rings, bearing etc Cylinder re-plated New crank seals New main bearings New gaskets including Reed gasket Air filter has been cleaned and lightly oiled. Spark plug has been replaced with new. New kill switch has been fit Carb has been stripped to it's full and: All jets have been cleaned out (Jets are standard size) All passageways have been cleaned out and air-lined Float height is set to 22mm (standard height) Air screw works between 1 and 2 turns out, less than 1 and it wants to cut out, and 2 to 3 turns out there's no real change in idle speed Needle was on clip 2, now put this to clip 3 (standard) Float needle moves freely and is not stuck Choke operation is fine, and once engine is running the revs stay up if choke is applied, so all good New fuel has been put in (5ltr fuel to 80ml oil) the tank along with an in-line fuel filter Confirmed fuel tap works as it should I've tested spark and with the lights off, you can see it sparking well. I've double checked the timing marks are lined up properly for the stator. I've even tried another known working stator. I can kick this bike all day long and one in several kicks will get it going eventually, once it's running it seems to ride fine. One thing I have noticed, is that the electrical wiring seems to be really rough, there was exposed wires where the insulation has come away, and I've covered this back up with electrical tape, and some wiring is exposed where the connection blocks are. Like I say though, it runs fine once started started, so I'm assuming the electrics are the problem, but it's the only thing I can think that's causing it. Any help massively appreciated, i'm started to loose patience with it now! Thanks Edited September 29, 2017 by scorpa0259 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted September 29, 2017 Report Share Posted September 29, 2017 Here are some possible things you didn't mention Air screw maybe set too lean Spark plug cap failed inside Spark plug wire failed inside Colour of spark Reeds sitting against seats What you are doing with the throttle as you kick it Is it any easier starting hot or cold The SY250s I've been involved with won't start unless they get spun over fast enough but run fine once running. Quote Link to comment Share on other sites More sharing options...
scorpa0259 Posted September 29, 2017 Author Report Share Posted September 29, 2017 6 minutes ago, feetupfun said: Here are some possible things you didn't mention Air screw maybe set too lean Spark plug cap failed inside Spark plug wire failed inside Colour of spark Reeds sitting against seats What you are doing with the throttle as you kick it Is it any easier starting hot or cold The SY250s I've been involved with won't start unless they get spun over fast enough but run fine once running. Hi Air screw has been adjusted and tested between 1 and 2 turns out, neither really make a difference in how it starts Spark plug cap and wire, surely this is ok as it sparks fine and runs ok once started? Colour of spark is yellow and crackles away nicely Cleaned the Reeds out and checked the flaps were all sitting against the seats I'm not touching the throttle at all, although sometimes it only seems to start with several kicks, choke, and throttle (which is wrong I know, but it's the only way sometimes) Once the engines warm, it starts easier, but still not as easy as it should Thanks Quote Link to comment Share on other sites More sharing options...
b40rt Posted September 29, 2017 Report Share Posted September 29, 2017 Sounds like choke circuit problem. 2 Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 29, 2017 Report Share Posted September 29, 2017 You could bypass the carb issue by laying the bike on its side, (Fuel on) pick it back up after about 15 seconds and you should see some fuel spilled. This should prime the cylinder with fuel. It should start within 3 kicks. If it is electrical, you just gave it a dose of too much fuel. 1 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted September 30, 2017 Report Share Posted September 30, 2017 Yellow or orange or red means weak spark. A good spark is blue. It can have a weak spark and still run OK but start poorly because the spark voltage drops off with reducing RPM and kickstart RPM is lower RPM than running RPM. Problems with the HT lead or cap will reduce the spark voltage. The spark when you look at it with the plug out of the cylinder will always be a better spark than what happens inside the combustion chamber because the pressure in there is higher (a higher voltage across the plug electrodes is required for a spark when gas pressure is higher) Another way to test for a weak spark is to reduce the plug gap and see if it makes an improvement to starting. Try about 0.5mm gap. This makes it easier for the spark to jump the gap but is only fixing the symptoms not the problem. What I've written here about the spark is just for diagnosis. The fact that it starts better when up to temperature makes me think that your starting issue is more likely a fuel/air ratio issue. If it revs up a fair bit with the choke on when starting cold, that can mean that the starting circuit is not letting in enough fuel. The "leaning the bike over" test is good for diagnosing this. You can also see what happens when the bike is up to temperature and idling then you put the choke on without touching the throttle. If the motor stops or runs very rich then your choke is working OK but if it revs up or runs normally with the choke on and throttle closed when at running temp, there is too little fuel going through the starting circuit for cold starting. 1 Quote Link to comment Share on other sites More sharing options...
hoodie2 Posted September 30, 2017 Report Share Posted September 30, 2017 I found the Scorpa often wouldn't start on closed throttle. If it didn't go after 2 kicks it would fire up on the third with the throttle fully open. I think I maybe read that in one of Birks SSDT prep guides. Quote Link to comment Share on other sites More sharing options...
the yukon sizzler Posted September 30, 2017 Report Share Posted September 30, 2017 On 29/09/2017 at 2:36 PM, scorpa0259 said: One thing I have noticed, is that the electrical wiring seems to be really rough, there was exposed wires where the insulation has come away, and I've covered this back up with electrical tape, and some wiring is exposed where the connection blocks are. Like I say though, it runs fine once started started, so I'm assuming the electrics are the problem, but it's the only thing I can think that's causing it. That's a big clue, and maybe why the previous owner got rid.....by no means a common problem but I have known a few sy's that have had a broken wire in the harness giving a "completely dead" or "sometimes it will, sometimes it won't" situation, maybe the previous owner had a go at finding it if the harness has been hacked about ? You seem to have thoroughly covered all other bases. These venerable Yam motors are normally bulletproof, hence their popularity,so look at the scorpa part of the bike rather than the Yamaha motor. Keep us posted. Quote Link to comment Share on other sites More sharing options...
scorpa0259 Posted October 1, 2017 Author Report Share Posted October 1, 2017 (edited) Thanks for the replies guys. I find that it only ever really starts with WOT and giving it plenty of kicks, without throttle it never starts. I put a new plug in yesterday and went out for a 2 hour ride, at the end of the day I failed a steep hill climb and the bike tipped on it's side. I managed to get it going again but after 30 secs of riding it cut out (like it ran out of fuel) and wouldn't start again. I brought it home, today I took the new plug out and it looks good, light brown in colour but with some fuel on the plug, not sure if it was wet yesterday which is why it wouldn't start, but I checked the spark on this plug in the dark and it seems to be firing a white spark. I put an older plug in from when it was running really rich and this was sparking nice and blue. Currently, the pilot screw is at 1 turns out, and this seems best for throttle response once the engines up to temp, but I find that as soon as it's running, it takes a good few minutes of me having to leave the throttle on for it to stay running (with choke on), could this have anything to do with me needing to give it WOT on startup? Edited October 1, 2017 by scorpa0259 Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted October 2, 2017 Report Share Posted October 2, 2017 something wrong in carb Quote Link to comment Share on other sites More sharing options...
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