KTM Forums banner

141 - 160 of 164 Posts

·
Registered
Joined
·
566 Posts
Regarding using a car battery to start your bike:
  • If your system is 12v and the car battery is 12v it is a match.
  • Your starter and ignition system will draw the current they need. They will NOT draw more current. If you have a crappy battery then the starter will suck the current leaving very little for the spark. Also when the plug is in the cylinder head and compression hits it, if there is not enough current the compression will kill the spark. (A little like blowing out a candle). By push starting no current will go to the starter and so this option should provide a better spark. But by using a car battery there will be more than enough amps to use for starter AND spark.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #142
Man I wish my bike had an electric starter. What a luxury that’d be. I’m going to snag a cylinder compression gauge today to eliminate one possibility. I’ll charge the battery too and if it still won’t spark after that I’ll haul it out here for a bump start. I’m swamped with work for the next few days so I won’t be able to touch it for a bit but at least I’ve got a plan.
 

·
Registered
Joined
·
566 Posts
Realise you do not have a starter. I was talking in general terms.

Regarding starting problems. Here what I have learnt about KTM 125sx:
  • If head gasket is even slightly damaged or out of position you will not get the bike to start.
  • We have had a nice spark with plug on the cylinder, but once in cylinder did not have spark. Have had two different problems causing this: 1. Faulty plug. 2. Lead from coil earthing when plug in cylinder head but not when plug on outside. New lead sorted that (there was a small cut in the lead)
  • A crappy stator made a 300Km trip to a race meeting becom a return trip where bike did run only one lap in practice!
  • Faulty CDI. Luckily we had two 125sx bikes (a 2012 and a 2016) so we tested the other CDI and that sorted the issue. Note that their curve is different so only use another 2 stroke KTM CDI to test.
  • If the powervalve is not returning to it's "home" position the bike becomes very tricky to start as the powervalve is open or partly open.
  • Normally worn/damaged reeds will still allow you to start the engine but the bike will run like crap.
  • An air leak after carbi will normally get bike to run poorly but you should be able to start engine even if she will be harder to start as you get more air than there should be when starting.
  • Forgetting to remove the rag we put in to carbi when washing the bike gave us 30 minutes of "bike will not start" issues even after trying push starting...
You might already have answered this question, (my memory is good, just a fraction short...) have you confirmed the CDI is the right one?
 

·
Registered
Joined
·
92 Posts
Discussion Starter #144
I searched the numbers on the CDI and I couldn’t seem to find any way to identify which bike it should be for. All the results were unrelated. I did however find a website called horse power ignition that sells their own ignition parts which look good and reviews say they’re reliable. Also they’re comparatively cheap. I can get a CDI and new coil for 210 before shipping and tax if need be. Wish I new someone with a 125sx to check the CDI
 

·
Registered
Joined
·
566 Posts
As your bike is a 2004 model your CDI would be a Kokusan one with wires coming out of it. That one was replaced in 2006 by KTM with the later flat model one that is still used. Sadly the one you have is not available from KTM anymore, but there are a few after market ones that are available. Best option for you would be to plug yours in to a working 125 sx/xc bike from 2005 or older to see if yours work. But I have no idea where you could find one to test your CDI in sorry.
 

·
Premium Member
Joined
·
1,751 Posts
It would seem the current problem was created by something after bike was reassembled. Possible incorrect wiring of ignition or other mechanical defect. I'm not sure a module is at issue here. It would seem that the bike ran prior to engine work and refuses to run afterwards the trouble could be elsewhere. I have seen stators die in storage, but its unusual for a module to die of natural causes in storage. Not impossible for module to instantly fry if wired incorrectly. I would imagine incorrect wiring could be the culprit for a module failure. The problem with replacement is a new unit installed with the original failure condition/incorrect wiring can possibly smoke new module before it runs again. Perhaps a better method is to find a working used ignition or purchase a new aftermarket stator/ module from a reputable source and be certain the ignition will be plug and play. I would verify engine compression and spark timing and fuel quality and all wiring to ignition is checked and rechecked before purchasing ignition system. Perhaps a quality bike shop or freelance bike service technician can help you troubleshoot your problem. There's no shame in asking for help if you find a good shop to help you. Keep at it now. Good luck to you. Check back for help as needed.
 

·
Registered
Joined
·
566 Posts
Valid points there @augiedoggie . I did not suggest that the CDI was at fault, only to eliminate it from the suspects. As there is spark when plug is out of cylinder I suggest the following steps:
  • Replace plug. If still a no go:
  • Spray "Start ya bastard" in to carbi and in to plug hole in head. If still not even one revolution of igniting of the fuel, then:
  • Replace head gasket. If still no joy then:
As the bike was running and then blew before you started this big rebuild, there might be something you are overlooking that a second pair of eyes on an experienced head could identify. It is frustrating when trying to diagnose a problem from information on a web page and not being able to be there. This is the reason I will often recommend checking parts individually to make sure they work. Augie has recommended making sure the electrics are OK and wired correctly. As you do have spark I have not focused on the wiring. But no harm in making sure all is wired up as it should be!
 

·
Registered
Joined
·
92 Posts
Discussion Starter #148
I see what you mean. Bike ran before so it’s gotta be something that’s not hooked up right or less likely went bad in the year it wast used.
I’ve followed all of the ignition wires and mapped exactly where each wire connects to the components. I’m comparing to the repair manuals wiring diagram. The only difficulty is that the diagram has different colors than my wires.
I did a compression test with the throttle wide open. Gauge got up to 120 and kept spiking to 140 or so on each kick but wouldn’t stay that high. Those numbers are good right?
I do have some questions about the wiring. On the KTM diagram, the coil only has one wire connecting to it externally whereas I have two, maybe three. There’s the white/blue wire from the CDI with a connector that fits into a prong on the coil. I’m confident that is in the right spot because there’s nowhere else with a matching plug. There’s a black/white wire from the same set of wires in the CDI that has a ring connector which makes me think it’s a ground.Also that same wire does not have enough reach to be connected anywhere other than the coil mounting points. And lastly there’s a black wire coming from the coil that has a bracket which fits perfectly to the mounting part of the coil. This wire does not have rubber insulation but what looks like cloth instead. Very stiff wire. I’m thinking that is a ground from the coil. I have attached pics of my diagram, the KTM diagram, a close up of the diagram of the coil and a picture of the wires and coil.
Sorry for my awful handwriting.
So I think compression is good and I was getting a decent looking spark but it wasn’t under nearly as much pressure as in the cylinder and maybe wasn’t at the right time. How do I check the spark timing? I’d prefer a way without removing the head but beggars can’t be choosers right?
taking the battery to get charged now.
 

Attachments

·
Registered
Joined
·
92 Posts
Discussion Starter #149
Did not mean to frustrate you. There are many avenues to explore in search of the issue and yours being the first I heard seemed to be the first forgotten as well. That’s my bad. After the wiring is sorted I will try the start ya bastard and a new plug, gapped to spec. If still no luck I’ll order another head gasket for replacement.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #150
The starting fluid worked but only for a second like you said. Would that mean it’s fuel related or does that reinforce the possible head gasket issue?
 

·
Premium Member
Joined
·
1,751 Posts
The starting fluid worked but only for a second like you said. Would that mean it’s fuel related or does that reinforce the possible head gasket issue?
thats great news... your carburetor needle may have stuck to its seat while the bike was in storage. probably best to remove carburetor for a good check and cleaning and spray carburetor cleaner into fuel inlet with float needle removed to clean any residue from old premix gumming up the works. if carburetor is off best to give it a good spray and dry with compressed air if possible. if carburetor is gummy and skummy make sure to clean it well and be certain pilot jet (tiny jet) is clear. verify it is open and clear or it will be a bitch to start. best to remove jets with a good sharp edge screwdriver that fits screw slot tightly and dont allow screwdriver to slip. be sure to push on carburetor firmly when removing jets. best to put carburetor in a pile of shop rags or towels to protect it while you muscle the jets out. jets are soft brass threaded pieces!! if they refuse to unscrew or break the slots out, best to clean them in place and leave them in. a fine strand of copper electric wire can help check or clear debris from jets. a torch tip cleaning tool works well also, if you have one available. or your friendly motorcycle retail store sells a carburetor cleaning tool with the wire jet cleaning tips. this is all good news my friend. your bike will be running soon. good luck and patience my friend.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #152
I actually got a brand new Lectron carb but maybe there's an issue with it. I'll call them first thing monday for their advice and troubleshooting. there's a screw on the carb that can make it richer or leaner. maybe make it richer if its not getting enough fuel?
 

·
Premium Member
Joined
·
1,751 Posts
It should spit or sputter if there's fuel available. I would troubleshoot fuel system from fuel quality to available fuel at carburetor inlet. Lots of potential problems upstream of carburetor can cause these troubles as well. Don't forget to check for water or contaminants in fuel. Take a fuel sample in clear vial and inspect it. Check carburetor bowl for debris and make sure fuel is available. If you are stumped with lectron, maybe put stock carb on for testing. Good job;)
 

·
Registered
Joined
·
566 Posts
You have a Lectron... now I envy you! We have decided to sell our 2016 125sx and buy a 2018 - 2020 150sx and I really want a Lectron on it!. But they are not cheap... Contat Lectron for advise with carbi. They deal with individual users and will help you make sure all is OK and set up for your bike! And glad you got a stroke or two from that spray! Even w/o being there or hearing the bike I conclude that your ignition setup and timing is OK. As @augiedoggie said, it sounds like there is an issue with fuel or supply of fuel. Focus on the carbi and fuel. Empty tank and fill with fresh fuel (at 40:1). If you still have the Kehin and it is nice and clean and jets are clean also, then test that one. They are good carbies and have won many championships!

Re your CDI, sorry I have never worked with the older type so I would just be guessing. But as you have spark and the spray did give you a result I think you can leave the CDI for the moment.

A good 125sx should have over 130psi. But it also depends on your mesuring equipment and squish setting. The spray will ignite much easier than fuel and under lower compression so I do not yet disregard the theory that the head gasket is not well. But why not get a few? They are cheap. I always have at least one spare in my workshop and I tend to buy them 5 at the time (we change piston at max 40 hours and ring at max 20 hours).

You are making steps in the right direction! Keep on keeping on!!
 

·
Registered
Joined
·
92 Posts
Discussion Starter #155
Fuel is new ethanol free 87 mixed 32:1. I emailed Lectron and they said everything looks right so I guess I’ll order some head gaskets and throw the old carb in to see if that works
 

·
Premium Member
Joined
·
1,751 Posts
you may want to try old carburetor first. it seems unlikely motor would fire on ether with compression leakage. it seems more likely you were not getting fuel into cylinder through lectron it was defective or plugged/restricted. you can confirm fuel system/carburetor function by substitution of a known working carburetor. cant hurt to have an extra set of cylinder head o rings also. try to run the higher octane fuel if possible. for the few pennies of cost difference, it gives you better detonation protection. good luck my friend
 

·
Registered
Joined
·
92 Posts
Discussion Starter #157
I remember the old barb taking a lot of kicks to start but it did start so I’ll give that a try on Friday. Wish I could get higher octsne but 87 is the only ethanol free gas within a reasonable distance
 

·
Premium Member
Joined
·
1,751 Posts
87 octane will run fine. 2 strokes like higher octane because the oil in fuel naturally lowers it. 2 strokes like leaded fuel also. I add 1 gallon of leaded race fuel or leaded aviation fuel to my 5 gallon premix fuel can. Leaded AV gas is 1/3 the price of race gas and will not hurt anything at the ratio used, but the lead will raise the octane of the 5 gallon batch....and it smells great :)
 

·
Registered
Joined
·
92 Posts
Discussion Starter #159
SHES ALIVE!!! Just had to play with the air screw a bit to get it going but oooohhhhh yes she sounds beautiful and the smell of two smoke is in the air. Thank you all sooooo much for your help. Honestly could not have done it without your sage advice. And big thanks for the maintenance schedule so I can keep her running well for a long time to come. Can’t tell you all how elated I am. I’ll be breaking the motor in over the next two days and hopefully hitting some trails come Monday
 
141 - 160 of 164 Posts
About this Discussion
163 Replies
6 Participants
Axzon
KTM Forums
KTM Forums is the forum community for dirt bike motorcycle enthusiasts covering the KTM Duke, Sport minicycles, Off-road bikes, KTM 1190 RC8 and all KTM Motorcycles.
Full Forum Listing
Top