Mech

Oh ok... I'll look in from time to time.

Had any luck with this ? Ninety is low for one of those. It could be burnt valves or bad rings. The way to tell which it is, is to put a little oil down the spark plug hole, give it a quick spin to distribute the oil then do a compression test. Oil will seal the bad rings up quite a lot, but have bugger all effect if it's the valves. If it's the rings the compression should come up to perhaps 110 or more, if it's valves probably only 95.. It depends how bad the rings or valves are.. You could also look at the exhaust for sign of oil burning which would indicate the rings. I suppose you have changed the fuel ? Stale fuel can make for no start by fouling the plugs even though they don't look fouled, they will even spark when they are out, but not once the compression comes on. And, once stale fuel has fouled the plugs, they seldom come right unfortunatly. You could try holding them over a butane flame and try to burn them clean which sometimes works, but often not. If it's been sitting I'd do that and try to get it going, the compression might come better with a run.. perhaps.. by a little.. but it's not really sounding too hopeful. It's always a good idea though to try and give things a run before you strip them down so you can check the gears and crank for noises etc.. It would be a shame to rebuild the top end and then find the bottom end was shagged.. and since someone has been modifying the inlet, we'd have to suspect it's been thrashed..

The manual I have is for a 250 but I'm sure they are the same.. If the wire colours seem wrong let me know and I'll check my manuals for the colours you have. I'm in New Zealand and we have different models here..

How did you get on Billy ? I've got the wiring diagram for that thing here and there isn't much to it. There's one red wire that goes from the battery to both those fuses. It branches inside the wiring before it gets to them. One fuse is for the auxillary power plug, and the other one feeds the key switch and the voltage regulator. The wire coming out of the aux fuse is red and white, and we can ignore that one, and the other one coming out of the other fuse is all red. That red wire coming out of the fuse branches again inside the wiring loom, and goes to the key and to the voltage regulator which I think is up near the front of the fuel tank and on the right hand side. Unless the regulator is shorting out it won't be causing the problem, and if it is shorting out it should have blown the fuse. To be sure though that it isn't shorted and draining any small amount of power that might be getting through a bad connection somewhere, it would be a good idea to unplug the regulator.. but it is hard to get to. If you can't get at the reg don't worry about it at the moment, we will diagnose it by elimination. In the meantime you should check for power at the back of the key switch, it is easy to get to. you pull a bit of plastic off in front of the dash and it's right there. There should be power to the red wire. Since you have an electrical gauge I guess you understand how a dirty connection can let a little bit of power through when there's no load on, but then show no power when there is a load. That's why it would be good if you can to disconnect the regulator in case there is a bad connection, such as the join inside the wiring where the red wire branches. But don't worry too much at this stage about that. So.. First check what the battery voltage is before you go checking the key, and be sure to check the battery voltage with the key off and also with it turned on. It should be twelve volts with the key off and stay near twelve when the keys on too. If the battery doesn't have near full volts in both cases you have a bad/flat battery. Then, if the voltages are ok, check the key switch red wire at the switch with the key off and it should have full battery voltage. If it does, then turn the key on and check the voltage there again.. It should be near twelve still, perhaps eleven and a half. If the voltage drops below about ten when the key is on, then there is a bad connection between the fuse and that point. Check those things and take note of what the various voltages are at the different places and with the different key positions. You could draw up a little grid chart with key on, and key off columns, and the various test points drawn across under them. If you have any questions or aren't sure what we are doing here holler out and I'll explain further.

http://quads.ddns.net/service-manuals/ More options.. Good name FlyinBrian..

And the compression you have should be enough to get it going.. Engines will start and run down to about 80 lbs.. 60.. probably not or only with a real fast spin or tow. If you don't grind valves it's always a good idea to tip the head upside down and fill the combustion chamber with petrol and it should stay in there.. if petrol leaks out the valves need a grind.. Simple check for next time..

Well you see the thing is, if it fires every time the crank turns, it's going to be sparking at tdc on compression, and also at tdc when the exhaust valve is just closing and the inlet is just starting to open.. right ? And that would/could cause backfiring out the inlet.. So that thing is probably set up in it's electronics to only fire every second turn, and perhaps that's your problem, and what I was trying to ascertain with all that turning back and forwards.. Try and check somehow that the spark really is happening at tdc(or a bit before), on the compression stroke... Snap !

Hi. I'm in New Zealand and we have different models here, or different names anyway... This is a fourstroke huh ? A little quad.. And an auto clutch ? So no push start.. So the motor does turn ? It's not seized... And the battery is charged and got good power ? You could try using jumper leads and feeding power straight to the starter.. That might get the starter to work.. If not... some of those small starters they use on bikes wear out their brushes in the starter pretty regular. Or if it had been dunked the brushes could be stuck in their holders. Not starting could be that it's not sucking the fuel in, which could be an air leak on the inlet, or a blocked exhaust which can stop them sucking.. Here in nz we have something called mason bees which build mud nests in holes like exhausts.. Sometimes the little buggers crawl six inches or more up the exhaust and block it up. You could try poking a wire up there and screwing it around, or take the exhaust off at the front and try starting it. Once you get the starter to work you could try putting a little fuel down the spakplug hole and seeing if it will fire at least once. Also.. how long since it last went? Did it get shut down or stop running while being ridden..

That valve timing looks right. But perhaps it's not timed to match the ignition. Have you tried turning the crank back from firing by half a turn, with the sparkplug out and attached to it's lead, and then turning the crank forwards that half turn as fast as you can with a socket or spanner? Lots of cdi will make a spark with a half turn.. If there is no spark near tdc then turn the crank till both valves are open and it's at topdeadcentre, then turn it a half turn backwards again, then forwards as fast as you can with the socket again and look for spark again.. It might be firing when the pistons at top but with both valves open, the exhaust just closing and the inlet just opening.. It's a long shot because I'm presuming the ignition trigger is on the crank, and mostly those sorts fire every rotation..but some only fire after two turns.. That should be enough compression to get it spinning, and as you say, the compression will come up once it's had a run, but if it isn't spinning even once when it pops then I'd suspect it's firing on the wrong stroke of the piston.. Also the way you describe it, as a pop, that doesn't sound like a proper firing with compression huh.. it should really make a good hard bang..

http://quads.ddns.net/service-manuals/honda/ Page 111 in the manual.

I'm not familiar with polaris at all, and wouldn't know if it's two-stroke or four, but if it is a four-stroke...Check the valve clearances. They might be closing up when it's hot causing the valves not to close properly.

Oh ok.. In that case, being that bad, and only hot.. I am thinking it's an electrical fault perhaps afterall.. an electronic fault in fact. So if you stop the motor for about five minutes, so the engine's still hot/warm, does it still do it. How cold does it have to get before it comes right again. If you have headlights you could try turning them on and seeing if it fixes it.. A faulty battery or bad battery connection could cause the voltage regulator to give you those symptoms.. Which brings us to... The fact the neutral light goes dim when you're starting means there is a flat/crook battery, or a bad connection.. or a seized starter motor. First check the battery water and charge it. Check it's terminals are clean and tight. If you have an electrical gauge check the voltage at rest and again with the motor running.. It should have about 12.6 at rest, and no more than 14.7 running. Then if you had some jumper cables you could try putting positive battery power straight to the starter and see if it cranks. If it doesn't it might be a shorted/seized starter, or a bad earth. You could put another jumper from the battery earth to the starter body and try the button, or the power straight to the starter.. Try one thing at a time till you figure out if it's one of those two cables causing the no start

Oh... went back and I see it runs good cold.. good man.. bad me.

I'm assuming that when the relay clicks... the neutral light doesn't go dim does it ?.. That would be something you should mention if it did.. haha The more details you can give us the better. I see an awful lot of expensive parts getting thrown at bikes in here to no avail, because of bad or no diagnosis.

Ok. So you say when you increase throttle.. so is this when you are already driving along, or just sitting revving it up ? And if you are driving it at the time, how much throttle do you reckon you are or can give it before it backfires ? Does it still backfire if you don't give it more than a quarter throttle say, or does it only do it when you are already over a quarter and getting nearer three-quarters or full.. We need to be quite explicit. If you open the throttle slowly, is it better, or conversely, if you snap it open is it worse ? It sounds like in the carby or fuel supply, but we might be able to pinpoint it a bit better if you can really take notice of all these small details.. It's what mechanics do when they are road testing.. we don't just go for a blat, we try things, and take note.. hot/cold/always, lots of throttle or little, immediately we throttle or only after a few seconds, on the flat or only up a big hill or under a long load.. The starter.. you could try putting something like a screwdriver across the starter relay terminals(the two big ones), if you can find it. If that gets the starter going then it's the relay that's playing up. If bridging the starter relay doesn't make the starter spin, then it's a cable or the starter.

So tell us what circumstances it backfires under.. wide open throttle, opening throttle, inttermittently when it's idling etc, and whether it's out the exhaust or aircleaner. Have you checked or changed the sparkplug and fuel filter ? Both good first steps probably. The starter.. is the battery charged, does the neutral light come on, do you need to hold the clutch in to start it perhaps ? Has it been going recently or has it been parked up ? You need to be more explicit about the problems and the circumstances.

Small 2stroke engines can warp their barrels down where the transfer ports are. It's always a good idea while you have it apart to push a ring down there with the piston and then hold the barrel up to the light and see if you can see light between the ring and the cylinder wall, then push the ring another half inch and check again.. check for warpage right through that area where the transfer ports are. 2strokes can run ok when you only get sixty pounds during a compression test. They are pretty fickle to check the compression on. once they are running the compression is often higher that the sixty.. sixty should still start. Last time it was going did it get turned off or did it stop by itself ? Was it going good right before it stopped ?

If it flashes for a few more times as the engine slows down, then I'm wrong...

That sounds like an electrical problem really rather than a mechanical problem.. I sure wouldn't be pulling it apart.. Have you pulled the sparkplug out after it's tried to start and looked to see whether it's wet or dry ? I'm guessing that the starter circuit's somehow sending power into the bikes electrical system while you are holding the button in, then it's loosing electrical power when you let the start button off.. Do you have a wiring diagram ? Do you have a timing light ? If you connect that up and watch whether it stops flashing as soon as you let your finger off the button, that would confirm my theory.

No trouble. I should add that it's important that the idle speed adjustment is in the right position when you are adjusting the mixture too. When the throttle butterfly is in it's closed position there is the hole where the idle mixture fuel comes out into the venturi, and that hole is between the butterfly and the engine by a tiny amount, about one mill perhaps, but there is another hole that comes out into the carby just about a mill or less on the aircleaner side of the butterfly. Both holes are connected and when the butterfly is closed the air gets drawn down through the hole nearer the aircleaner, and that air mixes with the adjustable idle mixture and dilutes it a little and atomises it thoroughly before it comes out the other hole on the engine side of the butterfly. As the throttle is opened the air stops getting dragged down and mixed and the mixture richens a little.. It works a bit like an accelerator pump does on a car carby. On some carbys both holes end up discharging fuel into the engine. If you try and adjust the idle mixture with the butterfly open too far the idle mixture isn't getting atomised properly and you get flat spots and/or difficult idle mixture adjustment.. So the procedure is to go around in circles adjusting the idle speed, then adjust the mixture till it's running at the highest revs you can get with the mixture screw, then raise or lower the idle speed, then adjust the mixture to the highest revs again, then the idle speed screw again.. Most problems people have are either starting technique (no throttle while you are giving it choke), or adjusting the idle speed too high thinking that will make it start or adjust easier... Good luck with it.

When you say it fires for a second, do you mean it starts for a second or so, or that it makes smoke and a noise but not spin the motor ? If it spins the motor when it fires then the compression and ignition timing will be correct. If it burns the fuel and makes smoke but doesn't spin the motor up then you might have the ignition timing not matching with the cam timing. I'm not familiar with that motor but some motors you can time the cam and have comression but have the ignition firing on the wrong position, by which I mean it might be firing when the pistons at the top but the exhaust valve is just closing and the inlet just opening.. not on the compression stroke. You can probably check that by taking the sparkplug out and turning the crankshaft by hand and checking the spark occurs when the piston's near top on the stroke that has both valves closed. If that's correct then I'd suspect no fuel or a vacuum leak on the inlet. How long was it apart ? Any chance a mason bee could have made a nest in the fuel line or carby inlet ? Any chance you have a split in the rubber inlet manifold? Or a blocked exhaust stopping air being drawn in...

Hi. I'd like to make a few suggestions.. It's important that the idle speed screw is at the right setting or the choke mechanism doesn't work properly. The choke doesn't actually choke off the air supply as a butterfly type does. In the carbys with the plunger, the plunger being lifted when you put the choke on is meant to let extra air and fuel through a separate passage to assist with cold starting. That won't work though if the throttle is open, or the idle is set too high. The choke has to have good vacuum to suck the fuel up high to that plunger, and through that extra passage, and it can't do that if the throttle is too far open lowering the vacuum. So don't give it throttle while you're trying to enrichen it for starting, that stops the choke/enrichener from working, as does having the idle speed wound up too high. With a conventional butterfly choke that doesn't apply and you can give it throttle while the choke is on and it will still deliver extra fuel.. but not with the plunger ones. If the choke/enrichener doesn't seem to be working, try winding the idle speed screw out a little.. count the turns so you can set it back again if it's not the problem. That often gets them firing and then you can slowly open the throttle to get them to start. Secondly, there are two types of idle mixture screw setups. If the idle mixture screw is near the inlet manifold, as most suzukis are, then its cutting off the fuel as you wind it in, making the mixture leaner. In the other setup the idle mixture screw is near the air-cleaner end of the carby and as you screw those in they cut off the air supply to the idle mixture making it richer. This applies whether the screw is underneath or on the side of the carby. If it's near the engine it's cutting the fuel off, making it leaner, and if it's near the air-cleaner it's cutting the air to the idle mixture off making it richer. Hope that helps with the understanding what's going on.

Is your battery good ? Faulty batteries, or regulators, can cause that symptom. Try turning the lights on and see what happens.

Hi. I'm new here and hope this isn't an old thread. That circlip wont be from the piston because it's an external clip, it fits on a shaft, not into a piston. You could perhaps identify it be estimating it's original diameter and then looking in a parts manual online for suitable sized circlips... probably in the gearbox or shift mechanism I should think.