atocp Posted August 27, 2009 Share Posted August 27, 2009 Hi all, Wondering if anyone had any ideas as to what might be going wrong here. I cleaned out and set the carburetor of my yb100 and put it back in. Then tried to get it going. Battery fine, petrol in, oil ok. It wouldn't go when i tried to kick start it tho. I was trying for a good five minutes and nothing. Then I replaced the spark plug, and it started on the second kick! Here's the problem, the first spark plug was new, and not spoiled in any way. It went in shiny, and came out just as clean. When it was running, it was idling high, so I reduced the stop screw down till it was running relatively low, then I did it a wee bit too far and it cut out. Then it would not start from then on. Even after I put the stop screw back up to try and get it started, and nothing. It will no longer start now. It has fuel, it's battery and oil are fine, and it's just the same as it was before I started the whole thing, but nothing. I replaced the second spark plug in case it was spoiling them, but it came out clean as well. And the new one wont start it either. Does anyone know what I can do or check to see if I can get it going more reliably? When it runs, it sounds quite smooth, for a 2-stroke. But once it runs once, and stops, it wont run again anytime soon. And i'll be kick starting the hell out of it, and nothing, not even a splutter. I doesn't appear to be spoiling the plugs, so I don't think that's a problem. Thank you for any help or advice you can give me on this one, because its driving me crazy!! cheers, Atocp Link to comment Share on other sites More sharing options...
atocp Posted August 27, 2009 Author Share Posted August 27, 2009 Ok, so i think I've found the problem. Turns out the head gasket wasn't sealing properly because one of the cylinder rods wasn't tight enough. Looks like I've ripped out the threads on the engine block where the rod screws in. I'll add some Super Steel epoxy weld to it and hope that the rod can stay in tight, and report back as to the success of it. I'm hoping this works. cheers, atocp Link to comment Share on other sites More sharing options...
fosdyke Posted August 27, 2009 Share Posted August 27, 2009 Ok, so i think I've found the problem. Turns out the head gasket wasn't sealing properly because one of the cylinder rods wasn't tight enough. Looks like I've ripped out the threads on the engine block where the rod screws in. I'll add some Super Steel epoxy weld to it and hope that the rod can stay in tight, and report back as to the success of it. I'm hoping this works. cheers, atocp Hi Let us know how you get on - but with this bike the state of the battery is irrelevant as it is a magneto start system and the battery is only for the secondary electrical system. You need 3 things for the engine to go: 1. Fuel, 2. Spark, 3. Compression seems you may have 1 & 2 (but check the plug smells of petrol) but do you have 3? See if you can borrow a compression tester - this bike is relatively easy as the spark plug is a larger size so you can use a car tester! You want at least 100psi when you kick it over - and remember to open the throttle fully and kick it two or three times before taking the reading. Good Luck Link to comment Share on other sites More sharing options...
JimR Posted August 27, 2009 Share Posted August 27, 2009 Hi Let us know how you get on - but with this bike the state of the battery is irrelevant as it is a magneto start system and the battery is only for the secondary electrical system. You need 3 things for the engine to go: 1. Fuel, 2. Spark, 3. Compression seems you may have 1 & 2 (but check the plug smells of petrol) but do you have 3? See if you can borrow a compression tester - this bike is relatively easy as the spark plug is a larger size so you can use a car tester! You want at least 100psi when you kick it over - and remember to open the throttle fully and kick it two or three times before taking the reading. Good Luck Hi dont forget compression testing a 2 stroke is not relieable. given this bike has a striped cylinder stud the may indicate a lack of compression but they tended to start and 'pop' thro the head gasket with the cylinder head not torqued to spec. Back in the day the YB suffered other ways with running/starting problems, The major one was incorrect ignition timing .. if this was too far out you got no spark and if you were lucky to get a spark the plug glazed/fouled within no time, hence clean plug & no spark.. I would not lend anyone a compression tester to do a 2 stroke as all that oil mixed with the fuel will get into the tester & ruin it & I used the finger on the plug hole method (if your finger got hot/blown off compression is sound). Regards Jim Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 27, 2009 Moderator Share Posted August 27, 2009 The only true fix for the stripped thread is a proper thread insert, I doubt if the bodge method will be good enough. Thread insert Here Would also recommend that drilling be done on a pillar drill so that you get a dead straight perpendicular hole, this will save any tears if you dont get dead straight and cant get the head back on... Link to comment Share on other sites More sharing options...
little dave Posted August 27, 2009 Share Posted August 27, 2009 have to agree with oldgit on this one, helicoils are the way to go. any epoxy that i know of will eventually degrade when put into contact with wayward bits of fuel. (and if anybody knows of one that wont, i have a leaky gas tank that could use some) Link to comment Share on other sites More sharing options...
fosdyke Posted August 27, 2009 Share Posted August 27, 2009 Hi dont forget compression testing a 2 stroke is not relieable. given this bike has a striped cylinder stud the may indicate a lack of compression but they tended to start and 'pop' thro the head gasket with the cylinder head not torqued to spec. Back in the day the YB suffered other ways with running/starting problems, The major one was incorrect ignition timing .. if this was too far out you got no spark and if you were lucky to get a spark the plug glazed/fouled within no time, hence clean plug & no spark.. I would not lend anyone a compression tester to do a 2 stroke as all that oil mixed with the fuel will get into the tester & ruin it & I used the finger on the plug hole method (if your finger got hot/blown off compression is sound). Regards Jim Agree with Jim on the first bit - obviously with a questionable cylinder head, the compression test is not necessarily going to be accurate. As to the thumb on the plug hole - my YB pulls 150psi on a compression test but can barely blow my thumb off - and runs fine. So if your thumb isn't blown off it doesn't necessarily mean compression is low - the only way of satisfactorily confirming low compression is with a tester. (Jim I've had my tester over 20 years and used it on countless bikes and cars - and it still works perfectly.) Two strokes are pretty finicky over ignition timing although the adjustments are fairly small but they will at least run (maybe not long and maybe not good) if the timing is enough to give you a spark - I was assuming that you had tested for a spark by removing the plug and whilst holding it to earth (not with your fingers!) checking fo a fat blue spark on every kick. Keep us up to date on progress. Link to comment Share on other sites More sharing options...
JimR Posted August 29, 2009 Share Posted August 29, 2009 Agree with Jim on the first bit - obviously with a questionable cylinder head, the compression test is not necessarily going to be accurate. As to the thumb on the plug hole - my YB pulls 150psi on a compression test but can barely blow my thumb off - and runs fine. So if your thumb isn't blown off it doesn't necessarily mean compression is low - the only way of satisfactorily confirming low compression is with a tester. (Jim I've had my tester over 20 years and used it on countless bikes and cars - and it still works perfectly.) Two strokes are pretty finicky over ignition timing although the adjustments are fairly small but they will at least run (maybe not long and maybe not good) if the timing is enough to give you a spark - I was assuming that you had tested for a spark by removing the plug and whilst holding it to earth (not with your fingers!) checking fo a fat blue spark on every kick. Keep us up to date on progress. the ignition timing was going to be the second post where I think the problem lies !!! but back in 82 or so I trashed 2 compression testers from non starting two strokes ... the one was quite funny ... as the test was done the oil came up the guage and attacked the paper readout (like a lorry tacho) there after it failed to work ... the old man after I trashed £200's worth of plant was not happy the next one I trashed was supplied via Yamaha which in turn had the oil destroyed the guage ... but I guess there is a diifference between hobby & commercial use my observations were on the latter & not the former. I would guess tho 150 psi would warm the thumb nicely Regards Jim Link to comment Share on other sites More sharing options...
atocp Posted September 2, 2009 Author Share Posted September 2, 2009 Hey guys, I've 'glued' the rod into the engine block where the threads had been stripped. I would just like to take this opurtunity to praise the wonders of Plastic Padding's Super Epoxy Steel Weld. My goodness I'm going to use that for everything. It really is amazing how strong that stuff is!!! Anyways, enough of that. The same problem is happening. The suggestion of the timing being out is the next thing for me to try and fix. Although not having a TDC gauge might cause it to be slightly less accurate. I'm going to try two methods: 1. The, stick a screwdriver in it and when it's pushed its furthest out, that's TDC approach has been suggested by my mechanic brother. 2. The other, my own personal favourite, "Clamp, nut and bolt gauge" uses a long bolt being slowly unscrewed outwards until TDC is found, then screwing it in the smallest fraction so i can hear when the cylinder bore 'hits' it. This is just an update, so i'll let you guys know how well both of these work. Unless anyone has another simple way to do it. I've also bought new contact points so hopefully that'll help. Cheers for the support, I'll hopefully have it reliable soon!!! atocp Link to comment Share on other sites More sharing options...
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