LT80 problems starting

[Andyjack]

Hi everyone new to this forum, i just got a LT80 for kids to learn on but can’t get it started. There is a spark but not very good so changed coil but got one with separate cdi so wouldn’t work cleaned car but still no joy. Fuel is getting in as plug is always wet. Im baffled. Like i say there is a spark i was thinking timing might of slipped so going to try that. any help please really appreciate it.

[Mech]

Is the fuel fresh ? Have you tried a new spark-plug ? If it's got a pull-start, does it feel like it's got compression ? If it doesn't have a pull start, take the plug out and stick your finger in the spark-plug hole hard and give the start button a push. If your finger gets blown out it's got enough compression. If you can hold your finger in there it might need some work.. perhaps a valve adjustment.

If it's got fresh fuel, a new plug, and compression, turn the fuel tap off and try to get it to start. It might take a while if it's flooded but eventually with a bit of playing with the throttle it should start trying to go, and with a bit more messing with the throttle it might fire up. If it does fire up, run it with just a little throttle till it starts to sound like it's about to run out of fuel, then turn the tap on and keep it running with the throttle. If it dies again after the fuel got turned on, then it's flooding and the carb probably needs more work. If it stays running, drive it a bit and then turn it off and see if it will restart.

[Gwbarm]

Couldnt reaally tell from the photo, is it 2 stroke or 4 stroke.

[Andyjack]

Its a 2 stroke. Ive had a compression tester on it and its showing 100 i have changed head gaskets has i noticed a bit of leaking from head but still no joy. I did change plug. It also has a pull start but its not turning it over it only turns over by button. Il try that with fuel because it is wet each time i check it so could be flooding but it is a new carb. Lad who i bought it from lives near me i seen him out on it  last year then he put it away over last winter got it back out a few months ago and wouldn’t start. Its not even firing at all. I took exhaust off when i fid head gasket and they was fuel in exhaust, quite a bit. But if it was flooded wouldn’t it at least try to fire ?

[Mech]

Stale fuel can cause those symptoms. Make sure it's got fresh fuel. And, stale fuel can bugger spark-plugs in one single firing without even starting. They burn something onto the porcelain that looks oily and that shorts the spark down the porcelain when there is compression. A plug like that will spark out of the engine, but doesn't spark under compression.. If you have a gas ring you can burn them clean, but they are always susceptible to fouling again after that. Once the engine is running, and has been got hot, you can refit them and they are often ok untill someone floods the engine using the choke and then they start playing up.. They can be really really deceptive.. and it's caused by trying to start engines with stale fuel.

I'd drain the carb and tank, put fresh fuel in, turn the fuel tap off, leave the spark-plug out and crank it over till there's no more fuel spitting out the plug hole, then I'd turn the tap on for a bit to fill the carb, then turn the tap off and fit a new plug and start trying to start it.

If the fuel tap is off, and working(not leaking), then it will eventually dry out and sooner or later it should fire.

Edited December 4, 2023 by Mech

[Andyjack]

Thank you il have a go today 

[Andyjack]

Well changed fuel and plug turned it over with fuel off for 10-15 mins then turned fuel on for five mins but still nothing. Flattened battery i was trying for that long. This is really testing me, ive just ordered a pocket meter as my multimeter wont go down to 1k it says on manual test coil on a multimeter that goes to 1k and should read between 12-15 so il try that meter. It will be here tomorrow. I’ve tried plug, suppressor cap, fuel, cleaned carb even stripped all wire ring to make sure nothing split or earthing. I will order another plug as the new plug was tried with other fuel.

[Andyjack]

Well ive just took the side casing off due to the pull start not working and noticed that the Drive Face Sheave is knackered and the nut that is holding it is threaded too so this is why the pull start isn’t working but this wouldn’t stop it from starting would it ?. i have electric start too which does work.

[Gwbarm]

Are you using premix or an oil tank for 2 stroke , if using separate oil taank sometimes they will put out too much oil and not combust properly, and sometimes the oil will leak past the pump seal and fill the crankcase.

[Andyjack]

Im premix 32-1

[Gwbarm]

Thats good, the only reason i mentioned all that is because of one i was working on , it was chinese and the oil pump was hooked to the crank, no way to disable it except spend a half day tearing it down to remove the pump, it ran off a gear attached to the crank, couldnt run it dry or the pump would burn up and have to remove it anyway. I tried using premix in the oil tank but it was too thin and leaked past the seal, so ended up taking it out anyway. Hope you dont have any of these problems.

[Mech]

Ah Gw...  this is a LT..  It's made properly..  haha.

The oil mix or an oil leak is a good thought though. 32:1 should be fine.

That drive unit won't make it not go..  A worn out crank seal could make it not go, but then it wouldn't be getting such a wet plug all the time.

It's also possible the choke might not be going right off, but turning the fuel tap off will over come that too..  Turn the fuel off, dry the internals out, then try a new plug and see if it will at least start to fire..

 

[Andyjack]

Thanks, ive never had this before, normally if i have a spark fuel getting through then i at least get an engine to try to start but with this there is nothing. I have a new multimeter coming today to test the coil make sure the spark is good enough. I also noticed there is no cdi by the look of the manual its built in with the coil thats a new one for me to. So il check coil while waiting on the new plug and try again. Thank you for the help I appreciate it 😀

Edited December 5, 2023 by Andyjack

[Andyjack]

 When i got the LT i noticed there was some spillage from head so i changed gaskets because the lad who i got it off had just put new head piston ect on to it. But ive just took plug out and noticed a spot of oil on it, they is 100 compression tho, but what if oil is getting through to the head would this stop it starting or just smoke ?

[Andyjack]

Just took flywheel off to check timing and it was out by maybe a mm so can’t see that been a problem but all connections on coils were rusty as hell so i cleaned them off and did a test on coils. In manual it says to put red probe to b+r wire and bkack probe to coil plate and should read 170 which it did but it says nothing about the other coil wich isnt reading as anything is this right or should they both read ? Sorry for all questions but i need this quad going for kids Christmas ( hopefully )

[Gwbarm]

If you are getting a double dose of 2 stroke oil from premix and the oil tank it would be harder to start and smoke and fowl the plug.

[Mech]

So at the moment you are using the original cdi/coil that came on it right ? And it's a two wire model ?

Have you tested how far the spark can jump ? And is it a blue spark ? If the spark won't jump double the plug gap then it's too weak, and if it's yellow it's not right either.

The seal between the crank and gearbox could be leaking and letting oil get in. I'd still expect the engine to at least fire occasionally, at least on the first try with a cleaned plug.

And if the key on the flywheel had broken I'd still expect it to kick and back fire occasionally.

You could try a squirt of ether to see if it will fire on that.

[Andyjack]

Just pre mix.. yes original coil, cdi coil with 2 wires . I can test plug out of engine and there is a spark but i have 2 testers one lights up as it should showing its sparking the other you can adjust the gap and see the spark but I can’t get a spark with that one but i can on my other bike but was thinking it might be with it been a different coil

[Mech]

When you look at the spark at the spark-plug, is it blue ?

And do you know what year this is ?

Edited December 6, 2023 by Mech

[Gwbarm]

Just looking over all your posts, it does seem like you might still have weak spark.

[Mech]

Just read post #15.. only the one wire from the stator is for the cdi, and that was right at 170 ohms. You could also give the engine a spin and check that some small AC voltage is produced between that wire and the earth, then connect that back up to the wiring loom and go to the cdi unit and disconnect it and check that you get the same AC voltage between the two wires there. That will check the wiring and the kill switch.

Then you can check the resistance between the spark plug lead and the earth wire on the cdi/coil unit and it should read 12 to 17.7 Kohms.

That's all they say you can check on the cdi, but I'd also check the engine had a good earth, and I'd disconnect the kill switch and see if the spark improved.

The only other check on the cdi is to plug it into a test unit that puts an AC voltage through the cdi and see that it makes a spark. The testers are fairly common and a local bike shop should have one, or, they use the same sort of tester in chainsaw and small motor shops. At a pinch you could use a power supply to put about 120 volts AC through it at a low amperage.. You'd need a resistor in the 120 volt line to limit the current..  Unless you know enough about how to do that you shouldn't try it though, so I'm not explaining any further.

The good news is that the new cdi and coil you bought will operate off that stator. The stator is the same for the old two wire cdi and the new six wire cdi. It looks like you only need to modify the bike wiring a little so that the cdi gets a signal from the start button, and an extra earth... and, I suspect it will even work without the modification. I'd try just connecting up the new cdi to the stator as the old one is, with two wires, and two other ones to the new coil, and try it.

[Andyjack]

The spark is blue, very small but blue. The new coil i got, the one that needs a separate cdi hasn’t a cdi with it but i also have a small 150cc m2r pit bike im sure i could take cdi off that to try. Thanks.

[Mech]

Blue's good. If the cap comes off the plug lead take it off and try the spark..

[Gwbarm]

Blue sounds like good spark, but doesnt explain why your spark checker worked with the other bike and not with this one, maybe try a new plug cap sometimes they develop unwanted added ressistance.

[Mech]

Yup..

[Andyjack]

Just an update. Well I’ve tried everything that everyone suggested but still no joy. Might have to call it a day and send it to shop. So far ive replaced plug, fuel, stator, head gasket, gone through all wires. baffled

[Gwbarm]

Yeah you have covered the bases , so it still won’t fire at the plug or just won’t start.

[Mech]

Well I can suggest some more things if you want.. 

The first thing would be take the carb off and strip it and clean it and check it's float height. Even though it's new it might still have a problem. If you try spraying some engine start in and it fires a bit it would suggest the fuel mix is not right.

They can get blocked exhausts, and the reed valves can get dust and stuff jammed under them right near where the reed attaches and bends so they don't close properly. Both those things are fairly easy to check.

They can get leaking crank seals. The one into the gearbox is hard to do but if it leaks you get gearbox oil in the mix and so it's kinda obvious, but the flywheel side lets air in which is more common and that one is generally easy to change.

Another thing that happens and gives symptoms like this is the barrel distorts right where the bypass ports are. Once the barrels off you put a ring in the bore and push it down bit by bit holding the barrel up to the light looking for light between barrel and ring. They look good till you get to the bypass ports sometimes and then you start to see light .. That ring leak there plays havoc with the starting, and running to a degree. It really effects starting though.

And you have actually pulled the flywheel off and checked the key isn't half sheared haven't you ?

 

[Andyjack]

Yes ive checked the key. But il check eveything else like you say, thanks fir your help and time I appreciate it.

[Andyjack]

Does anyone know what i can use to replace the batterie while doing work on bike. At moment im charging batterie every few hours as it keeps going flat because of trying to start quad.