Posted October 1, 200816 yr Greetings, and thank you in advance for your input. I am in Malawi (Africa) staying at a friend's house. Going through his garage I found a dusty 2-stroke Yamaha which I have discovered to be a 1976 YB100 (at least mostly). I am considering trying to get it running. Is it worth it? Are there any common failing points that I should check out before getting too involved with this project? Getting spares will probably prove quite difficult in Malawi, so I expect I will be doing some improvising. I have done a little degunking and visual inspection of the outside, nothing looks too far gone. It turns over nicely. Compression test gives about 90 P.S.I. I have no spark. I also have no battery (but from my reading on this forum, that shouldn't be absolutely necessary). There are some frayed wires (repaired in some cases with bits of plastic bags). Does any one have a wiring diagram they could send me? Or a description of the bare necessities for wiring to get spark? In fact, any documentation, specs, or diagrams would be immensely appreciated. Cheers. wkelsey[a]gmail.com
October 2, 200816 yr Moderator Hi and welcome to the forum, Its a simple bike so shouldnt be too difficult, But youre going to need a manual at least Here This one will post worldwide. The problem might be if you need to buy things, You will know more about that than us though, If you do decide to have a go, people on this forum will help if they can with advice. Good luck if you go for it.
November 16, 200915 yr Hi my name is Tony I have owned my '79 YB 100 for over 10 years. Its the first bike I learnt to ride and been my only bike since. I too am trying to get mine running again after sitting outside for 5 years, it was seized but not any more, I got it to run this morning but it revved off it's nut. I have changed things like the idle screw and throttle tension to try and lower the revs but now its not running at all, and I have reset things I changed back to around where they were. I have no settings for any thing and if someone could email them to me it would be appreciated! Email: [email protected]
November 16, 200915 yr Hi my name is Tony I have owned my '79 YB 100 for over 10 years. Its the first bike I learnt to ride and been my only bike since. I too am trying to get mine running again after sitting outside for 5 years, it was seized but not any more, I got it to run this morning but it revved off it's nut. I have changed things like the idle screw and throttle tension to try and lower the revs but now its not running at all, and I have reset things I changed back to around where they were. I have no settings for any thing and if someone could email them to me it would be appreciated! Email: [email protected] If it's revving to red line without any throttle input, then you have an air leak somewhere. Could be crank seals, head gasket, base gasket or a leak in the carb.
November 21, 200915 yr If it's revving to red line without any throttle input, then you have an air leak somewhere. Could be crank seals, head gasket, base gasket or a leak in the carb. Thanks for replying so quick. I didn't even think of that though I have ordered a new head gasket already, just waiting for it to turn up. If that doesn't work i'll try the others. Thanks again for your advise much appreciated.
November 21, 200915 yr Thanks for replying so quick. I didn't even think of that though I have ordered a new head gasket already, just waiting for it to turn up. If that doesn't work i'll try the others. Thanks again for your advise much appreciated. If that doesn't solve your problem, I'd suspect the crank seals...especially if the bike hasn't been run for a long time. What tends to happen is that they harden up with age and don't seal as well. When someone takes a bike out with hardened crank seals and attempts to start it, they can tear, creating the problem you describe. There are two seals, one on the magneto side, and one on the clutch side. You'll know if the clutch side one is bad if you see a ton of white smoke, otherwise assume it's the magneto side (or better yet not assume and replace both of them ). Just so you know, a good way to check for leaks is to get the motor running and spray WD-40 wherever there is a gasket. You'll see bubbles if there is a leak.
November 29, 200915 yr How ya going? Done a compression test and came out with 105 PSI, have got spark, sprayed engine with WD-40 and turned it over quite a few times and no leaks that I can see. No smoke comes from anywhere at all. In high school I had to pull apart and fix a 2 stroke lawn mower, I replaced rings and afew other things and it went first go and it ran for a little while then stopped and wouldn't go again. After pulling it apart again I found I had somehow bent the crankshaft. Could something like this happen to the bike because it should run as far as I know and it did but it doesn't now. Tony
November 29, 200915 yr How ya going? Done a compression test and came out with 105 PSI, have got spark, sprayed engine with WD-40 and turned it over quite a few times and no leaks that I can see. No smoke comes from anywhere at all. In high school I had to pull apart and fix a 2 stroke lawn mower, I replaced rings and afew other things and it went first go and it ran for a little while then stopped and wouldn't go again. After pulling it apart again I found I had somehow bent the crankshaft. Could something like this happen to the bike because it should run as far as I know and it did but it doesn't now. Tony Either the crank was bent before, or something was not put together right. If you split the cases and weren't careful, that would explain the bent crank. Do you have pictures? A bent crank is a difficult fix...and the bike won't run at all like that.
November 29, 200915 yr Either the crank was bent before, or something was not put together right. If you split the cases and weren't careful, that would explain the bent crank. Do you have pictures? A bent crank is a difficult fix...and the bike won't run at all like that. Unless it was bent before which im pretty sure it wasnt and I didnt actually pull the case apart, just the cover off the side. and no pics to show sorry.
November 29, 200915 yr Unless it was bent before which im pretty sure it wasnt and I didnt actually pull the case apart, just the cover off the side. and no pics to show sorry. I'm stumped! Not usual for a crank to just bend like that. Maybe someone has some insight?
November 29, 200915 yr Moderator After pulling it apart again I found I had somehow bent the crankshaft. Could something like this happen to the bike because it should run as far as I know and it did but it doesn't now. Tony Why do you say this...what have you seem? Instructions for posting pics are in the FAQ's section.
December 10, 200915 yr Hi guys, forget the bent crank, that was just what happened to the last 2 stroke engine I pulled apart. I have managed to get it running, It was the round seals inside the crank case had popped out, had to get bike mechanic to work it out but its all good now and im cheering! Thanks for all your advise and help, hope I dont need to much more in the future! Sincerely, Tony
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