Mech

"Of course not all spark systems are wasted spark, but I am guessing this one is. If the atv only has a pickup coil on the crank then how would it know what stroke it was on? ".. Don't guess, be sure. If you want to know how the electronics involved work read up about "voltage doubler", and digital logic "flip-flop". The stator sends out pulses of alternating power, they get "stacked" to charge a capacitor to a higher voltage, then the trigger coil triggers a discharge of the charged up capacitor. On a two stroke they fire every revolution, and on some four strokes that's fine too and they do run a wasted spark. Some engines though, because of a combination of valve overlap and ignition advance, don't like that, so they count the low voltage pulses as they charge the capacitor, and don't let the trigger coil do it's thing till more than one full revolution has happened after the last firing, then it triggers at the next trigger signal. Your backfiring with the engine start spray is likely because of what Cookie was saying..

You make a good point there about opening the throttle wide open to lift the slide Cookie. If it's right down the ether isn't going to get in there. And I agree, starting fluid isn't a good test really. It's full of oil or kero or something and can foul the plug. A teaspoon of fuel down the sparkplug hole is better. Stale fuel can also foul sparkplugs. Have you got fresh fuel CJ ?

i just had a look at the wiring circuits of a couple of yfm250/350 manuals I have, older models though, and they both have a power feed into the cdi when the starter's being operated. On a car they feed starter signal into the ecu because the timing pickups and airflow sensors aren't accurate at cranking revs, so the starter signal sets the timing fixed at a suitable point for starting. On that thing, it could be either providing power to charge the capacitor, or to alter the timing.. If it has a feed from the starting circuit. Probably worth checking that signal's getting in there if it has it.

I wonder if there's something in the bottom of the plug hole preventing the mix getting to the plug... mud maybe, cobweb of soot.... Never seen it but... It's strange that fuel down the plug hole didn't even get it to kick. No air or no ignition of the mix.

"re: plugs in series... isn't that basically what a spark tester does, though?" A spark plug tester puts compression on the plug while you check it's sparking. A cdi tester just simulates the electrical system of the vehicle. A coil tester simulates the vehicle too, either a cdi vehicle or a traditional coil vehicle. The later two do say to use an air gap of about six mill to test the spark, but most vehicle manufacturers warn against cranking things over with the spark plug leads off lest the high voltage causes a short or damages the electronics in the cdi or ignitor. I'm about out of ideas for you. Compression, fuel and properly timed spark. So no backfiring, no smell of burnt fuel, dry plug.. all I can think of is that it's not drawing fuel in.. Blocked exhaust.. You'd think it would be in the muffler, but perhaps the header's double walled and it's collapsed the inner or something highly unusual.

Not all spark systems are wasted spark. Some only fire every second rotation. Some cdi systems that run off the crank, that is get their low voltage off the stator, need more than one rotation before they will fire. They have to see several low voltage pulses before the trigger coil will fire them. The cam might need turning 180 degrees so the valves are closed on that second rotation of the crank. MarkinAr sounds like he's familiar with these yamahas.. I'm not, but I'd check what he's suggesting.

Hmmm.. You sound thorough and competent, I'm assuming that you are checking things carefully. For the spark to be 360 degrees out I agree that it would have to have the cam retimed, and even then it may or not cause a 360 degree off situation. Some cdi systems that run off the crank, that is get their low voltage off the stator, need more than one rotation before they will fire. They have to see several low voltage pulses before the trigger coil will fire them. If the cam timing hasn't been changed though that will not have happened. If it was firing 360 degrees off it should fire out the inlet too. The dry plug either means it's getting no fuel, or it is but it's getting burnt off but not firing up because of bad timing. You could pour about a teaspoonful of fuel down the plug hole and try starting it. I don't trust starting fluid. it can flood plugs. The timing could be off if the voltages coming out of the stator were getting shorted together. I've seen that. Check the wiring pug going into the engine isn't full of mud or wet. Remove the plug cap in case it's shorting. Your putting the two plugs in series was a good test for strong spark, and it will have tested the coil's not shorting, but it won't have tested the plug cap. I should point out though that they probably wouldn't recommend that as a test in case it causes a short in the coil. Check the sparkplug cap, put fuel into the cylinder. If it fires then you need to figure out why it's not getting fuel. Carby, airleak, blocked exhaust.

Lol... and just remembered we are talking suzuki.. Don't worry.. I've done a lot of them too.. and honda, yamaha, kawasaki, ajs, bsa, norton, triumph, harley, matchless, bmw, duke.. puch, vespa, james, philips.. probably some others.

No problem my friend.. just thought I'd add those after thoughts. If it changes better though when you wind it out and do snappy changes it really keeps sounding like a clutch problem. Hard to find neutral also sounds like a clutch dragging problem. When clutches get worn one of the first signs, before they start slipping, is for them to drag. Practice your gear changes without using the clutch and just throttling off to change up and giving it a rev to change down. If you get the revs and speed right for the gear you are in they should change nicely. That would prove it's the clutch. I don't know what gears that guy you mentioned was talking about, but gears are too hard to file. If he did it with the engine tipped over it must have been in behind the clutch cover, the actual gearbox though is right in the center of the two main cases. Hopefully you wouldn't need to do that because it's a total engine strip. I think you should try and get a manual and check whether there is a clutch adjustment on the cases, probably a screw and locknut. If the cable is the only adjustment, and it is adjusted right, then I think you are going to need to pull the side case off and check/overhaul the clutch. That's a relatively simple and cheap job. All you should need is a set of friction plates and a gasket. If you are lucky, it will even be do-able with the engine in place. Unfortunately we don't have those models here in NZ, but if you need a hand I've done dozens of clutches on hondas and should be able to help a bit with a picture or description. I'll keep an eye out pending your getting around to it. Cheers. Oh and the issue I was just talking about is deep inside the gearbox.. Forget that.. haha. I really think(given what you've just said about riding it some more) that it's a clutch problem.

Yeah that's the gasket on there. That should be all it has, it should poke up a little above the surface when you fit it. Try the loctite and you will love it. It can be wiped off the outsize with a rag with or without petrol on it, it doesn't smear everywhere and get on your hands, it never dries in the tube. Just the fact you can use a tiny bit from the tube, and then have the tube sitting on the shelf for years till you need it next is a huge benefit. You save money, and you always have some there any time you need a little smear. Silicon needs the surfaces really clean and dry or the silicon doesn't stick, and if you use silicon on some things, like rubber gaskets, or hoses, it can cause them ti slip/squeeze out of place. The loctite can be used on slightly oily surfaces and it sticks, and it holds hoses and rubber gaskets in place if you need to use it on them. And silicon, as we all know, goes hard in the tube no matter how well we seal it up. Grrr

Any luck with this Chris ? I remembered the other week.. I have seen damaged quad gearboxes from doing donuts.. not rolling though. It was about five years ago and I didn't work on the bike because it had blown the box twice, and my sons told me the owners sons were always doing donuts on it, and the bike was only a year old and had been fixed once already by the dealer. If I'd taken the job on I would have assumed the warranty.. haha. I also remembered another couple of honda two wheelers that I had fixed. They have/had a gear that was pressed onto a shaft and they could slip on the shaft. The gear could only be taken off and reused twice honda reckoned. One bike made a squawking noise deep inside when it was under a big load. It was near forty years ago now, but from memory it was second gear. I only found it by putting the shaft in the vice and using a 24 inch pipe wrench on the gear. It made the noise and slipped. I wonder if your bike still uses a pressed on gear.. You could ask a dealer if they know and if it has been seen before.

And.. Do you know that when you get the new thermostat it will have a small hole with or without a jiggle valve in it, and that the hole has to be fitted to the top... That's important.

The thermostat likely has a rubber gasket fitted onto it. A new one should come with the thermostat. I'd never use silicon anywhere on a bike, the excess squeezes out inside the engine and can block or jamb things up. I'd highly recommend a syringe of loctite master gasket. You shouldn't need it for the thermostat but it's the best to use if you need a gasket sealer. A thin smear is also good on the inside of water hoses. It squeezes out of the syringe in a thin line/smear, which is all you need, it doesn't harden till it's clamped up between surfaces which is really handy if it's a complex assembly or you get held up, it never ever hardens in the tube, any excess dissolves into oil, petrol, (and even water eventually), without blocking filters or doing any harm, the fresh unhardened or old hardened seal cleans off easily, it seals water, oil, petrol, air joints. I dispense with most gaskets and just use loctite. It's far superior, and more convenient, than paper gaskets. I've been using it without gasket for near fifty years and never had any problems with it.. Silicon is terrible stuff !! I'd suggest you never put that anywhere near your bike.

oh true. I hadn't thought of that. Yeah if you can drain the coolant without getting crap into it you could put it back in. Coolant is cheap anyway compared to having to do a head gasket. I go to some trouble to keep the water jackets full if I can. You could probably get most of it out clean by draining it at some hose, then risk getting contaminant in the last bit when you drain it from the thermostat housing or water pump drain.

You could fill the motor with water now the radiator's in. The water will drain out when you go to do the thermostat, which is still in there ? Else slip the thermostat cover back on with it's old gasket/o ring, perhaps with a bit of grease on, and it will hold water. The drying out is bad.. Motors do blow headgaskets after drying out. Not straight away, but they do blow !

You could also check the fuel has a little pressure. Put your finger over the pulled off fuel hose while it's idling, it should squirt with a tiny bit of pressure. The vacuum sucks a diaphragm against a spring, and the spring sets the pressure. If the spring's weak it might have flow, but not enough to shove it past the float needle at the right rate. It's only about three or four pounds of pressure it's meant to have.. I think..haha It should squirt a little distance though, a foot or so.. If you pull the hose off the tank and try the tap you'll see if the filters are blocked.

If you've got a timing light, check it's firing on the mark.. I doubt it will be 180 out, but I've seen them sparking out of time because the wires going into the engine/stator/pickup were saturated and shorting together.. They generally did run though, with a lot of backfiring and missing. They soon dried out also.

The track isn't something you are likely to see.. Take the rubber boots off, if not the whole plug cap, and look and listen for sparks. If you have a timing light, put a screwdriver through it's pickup, and poke around down the plug porcelain looking for a flash of the light. Check around the coil and plug lead the same way..

If it starts to go ok for a second or so at wide throttle, then falters, it sounds like a fuel supply problem. If it falters as soon as you open the throttle wide, and recovers quickly when you back off, it sounds like jets, air or fuel jets. You can test the pump and in tank filters by testing it as I suggested. Here's another test though that might show us something.. Take the fuel pipe off the carb and lay it in a bottle on it's side. Pull the vacuum pipe off the manifold and suck on it two or three hard sucks, then let the vacuum off suddenly. It should shoot out a good full flow squirt of fuel. Then connect the vacuum hose to the manifold and start the engine and let it idle, it should flow petrol still at a good flow, near full diameter but not so fast as the first test. Then blip the throttle wide open while watching the flow of fuel. If it drops right off, it's because of low vacuum, which will be dropping right off when the engine's under load and the throttle's open. So check you've got good fuel flow, and vacuum, and then vacuum under load. You could load the engine to test for weak vacuum by putting it in gear, brakes on, sitting on it of course, and then open the throttle till it's labouring on the centrifugal clutch. The hole in that pipe poking out of the manifold needs to be a good size. Check it's the same size as the old manifold's one. It should be more than about three mills. On later models there are different vacuum ports for different purposes and if you use the small port(about 1.5mill), the pump struggles, use the big port(about four mills), and it's all good. The vacuum hose going to the fuel pump needs to be thick walled, fuel hose is best. If you use a thin walled vacuum hose, that's hose sold as vacuum hose, it gives/collapses too much with the pulsing vacuum. The pump has to get a good pulsating vacuum to it. A partially collapsing hose gives a steady non-pulsating vacuum.

The dunking in water might have caused a crack or track down the sparkplug cap.. It might look like it's sparking good when the plugs out, but be shorting when there's compression on the plug. If it's possible take the cap off the end of the lead. Even taking the waterproofing rubber boot off might make a difference or allow you to hear the spark jumping down the porcelain. It could have done the same thing to the ignition coil. Once there's compression on the plug the spark has a harder time jumping, and can short somewhere else.

Well, I'd want the headgasket wet, and the waterpump, and all the hose connections staying wet if I could.. Drying out antifreeze is corrosive. Gaskets dry out and then the new antifreeze has a low surface tension and it creeps into the gasket and causes corrosion of the head and cyl surface.. It's best to keep things wet once they have been in contact with antifreeze. That's why I suggested the hose joints, they trap a bit of antifreeze even though you flushed the system. Even the aluminium castings will try to corrode. The manual I see also stipulates ethylene-glycol, which doesn't penetrate gaskets as readily as some of the later chemicals. If your head gasket is "paper", rather than a steel gasket, then I'd definitely use ethylene-glycol. I'd us it anyway.

Good work man.. Spotting the radiator was a good job. That oil.. The mobil 424 I looked up is no common oil, it's anti-everything.. https://tinyurl.com/yk6n63w4 The Lucas oil doesn't claim some of the features the mobil has. I'd use the mobil. The new agricultural oils are bloody tricky. I've seen problems from using very similar oils, designed for the similar applications, but not good for the particular make and model of tractor. And I'd fill it up with water while I waited if I could. The aluminum under hose clamps might start to corrode and it will keep on going once it starts.. Best not to let them sit empty..

Yup it is a good site.. Just watch out for the bun fights.. haha. Hope you've got the lad on the job too.. Assuming here he's a young fellah.. Good project's bikes.. and riding together.

Checked fuel's getting into the carb ? Loosen the drain bung and see if fuel comes out, after it's empty crank it over and check that more comes out. Tests the flow and pump. Take the spark plug lead's fittings off(if you can) in case they are shorting.. Use a tiny split pin jambed up the wire to the plug. Loosen the exhaust at the head perhaps. Blocked exhaust stops the suck too. It's got a new plug huh ? And fresh fuel ?

Oh yeah.. It might be worth checking the fuel pump delivery is right before pulling the carby off.. It's simpler to do. And bad fuel supply could give your problem. Pull the fuel delivery hose off the carby and lay it into a bottle on it's side. Start the bike and let it idle and the fuel should be squirting out full diameter of the pipe... Er, squirting out of the pipe full diameter of the pipe. A trickle is a bad pump and may or may not get it up big hills, or when the tank gets low. And that "boot" you are mentioning, between the carb and head, that's called a manifold... If you're mentioning it in the future.