sam Posted February 1, 2007 Report Share Posted February 1, 2007 I'm working on a 1974 YZ 80, I have no history on this little bike, seems like the same motor as a TY 80. The head is warped, I sent it off and had it machined, have not yet reassembled. My question is, Should I diconnect the oil injection and run it premixed? I just do not understand why this head warped other than not a proper amount of oil in fuel mixture? sam Quote Link to comment Share on other sites More sharing options...
kevin j Posted February 1, 2007 Report Share Posted February 1, 2007 yz about the same at tymotor (or maybe vice versa, not sure which one came first) except for cyl porting, transm gear ratios. cyl head finning is different also for pipe clearance on the Ty, but bascially the same mechanicals. Personally, I'd take off the autolube and run premix. at least you know for sure what is going on then. I did that with all the TY my kids had. don't just disconnect it, as the pump still runs and pumps the idle amount. If the tank runs dry eventually the pumps seize up. You have to remove the side case to get the autolube and gear off. the gear is bigger than the case hole as I recall. make a small plate of alum and bolt on in its place. Or, pull the gear, use the pump housing as a plug. I made cables from carb to Domino throttle, using a universal throttle outer housing, and a lighter than normal core cable. got that from a bicycle shop, 10 speed shifter cable material. Use a solder dip cap to put ends on. search for prior posts on this discusssion. bottom line, i'd run autolube until the next time you have it apart, then pull it off. why warped? overheating, from plugging up fins with mud, maybe lean mix or timing way off? just guesses. plugged exhaust overheats badly also. great little bikes. kcj Quote Link to comment Share on other sites More sharing options...
sam Posted February 1, 2007 Author Report Share Posted February 1, 2007 Thanks Kevin! I hope this is a 74 YZ 80, The bike is grey with a red swoosh on the tank. I bought a new carb from bike bandits, but its for a TY, looks the same though! How many turns out on the air/fuel screw for the proper setting and also any Idea on how much compression this little cylinder shoud have? Once again, thank you so much for the info Kevin? sam Quote Link to comment Share on other sites More sharing options...
lineaway Posted February 2, 2007 Report Share Posted February 2, 2007 You can actually buy the pieces to fit the domino throttle. Add a cable type adjuster from a clutch or brake perch. (screw it into the throttle housing). Add a gas gas throttle cable. Maybe any brand trials? Also the top tube adjustment from a pro carb, which happens to screw into the top of a yamaha carb. It`s about 4 inches too long but sure beats making cables! Quote Link to comment Share on other sites More sharing options...
paulthistle Posted February 2, 2007 Report Share Posted February 2, 2007 Ideal compression on a two stroke is 155 psi. If it is over 120 it should run ok. You said the head was warped. Was it blowing out between the head and cylinder? It would have to be pretty bad to need machining. Usually a piece of 220 and a flat surface will put it straight in a jiffy. If you have the head off, go ahead and remove the cylinder and inspect the piston and rings. I would want to find the reason for overheating. The head is only a symptom of whatever the problem is. Like ignition timing off. to lean. Exhaust plugged. Crank seals leaking. Will the flywheel move up and down? Paul Quote Link to comment Share on other sites More sharing options...
sam Posted February 2, 2007 Author Report Share Posted February 2, 2007 Thanks Paul/lineway for the tips! I can not remember how to do a compression test? 1 kick shows 25lbs-2 kicks shows 50lbs-5-10 kicks and she tops out at about 80lbs. Is this correct? I replaced the cylinder head today, she will not start. Checked plug and it looked like there was crank case oil on it? If the compression is bad, does this mean the rings are cooked or engine seals are also a scenario? Before I had the head repaired, she would start and Idel just fine, but give it gas and it would bog out, no power! So I sprayed brake cleaning fluid around looking for air leaks and located this huge leak around the head, could actually stall out the bike. Lineway, I almost picked up some emory cloth thinking I could level it on my slate counter tops! This little bugger is a puzzle? sam Quote Link to comment Share on other sites More sharing options...
sam Posted February 2, 2007 Author Report Share Posted February 2, 2007 (edited) How to test compression on a motorcycle= http://www.dansmc.com/compression_test.htm Yes, Paul I think I need a rebuild! Thanks again for the tips everybody! Edited February 2, 2007 by Sam Quote Link to comment Share on other sites More sharing options...
sam Posted February 2, 2007 Author Report Share Posted February 2, 2007 Found this information helpful! http://www.dansmc.com/pistons.htm Quote Link to comment Share on other sites More sharing options...
kevin j Posted February 2, 2007 Report Share Posted February 2, 2007 thought of something else: TY at least when main bearings get worn, the timing goes off and won't start. I had to run very tight point gaps (Im thinking .008 inch vs 012 to 016) to make the igntion work as it wobbled around in the bearing clearance. obvisoulty that is a temp fix until proper rebuild, but itm ight be a cause of not revving up properly. sounds like it is just tired out though and needs a rebuild. I used Wiseco pistons and rings, but for some t\reason they didn't have a 10?mm piston pin. had to get from Yam. bearings from the local suplly house, but Yam prices were about the same. carb adjustment is just routine tuning once its running, nothing mystical there. I think TY carb was smaller, but can't recall. I had a GT carb and it didn't work directly on, maybe it was the top or cable mount or something. k Quote Link to comment Share on other sites More sharing options...
sam Posted February 3, 2007 Author Report Share Posted February 3, 2007 I will check the Flywheel for movement, but hoping its just all top end! I'm probably going to buy everything from Bikebandits, Are there any other parts people out there equal to Bike Bandits? This bike is I'm sure a 74 YZ 80, grey tank red swoosh, the tank looks the same on the parts breakdown sheet, all the pictures are black and white though. Wish me luck! sam Quote Link to comment Share on other sites More sharing options...
sam Posted February 13, 2007 Author Report Share Posted February 13, 2007 Kevin, Is this gear pulling of the auto pump for the oil injection easy, you say place a piece of metal to plug the hole, sounds over my head, but I'm going to tear into it today, imagine I'll need a new case cover gasket? looked at the schematics on BikeBanditos, many parts to that little oil pump! Quote Link to comment Share on other sites More sharing options...
kevin j Posted February 14, 2007 Report Share Posted February 14, 2007 I'll have to look for notes at home, its been years. My youngest is now almost 18 years old, been a while since I had to spend all the TY80 miantenancne time, but I don't regret any of it. No, taking off the side is the slow part. I think the pump gear was held on by a pin or key or something easy. Once remove, the pilot hole is exposed to the oil cavity of the primary drive. That hole is what you cover up. Making the cover plate is easy just a chunk of alum or steel with two holes drilled in it. Took some carving to clear some gussets or webs, but I did it with a hacksaw and file. Did two of them. Then just some 6mm screws, silicone seal on the plate and silicone the hole where pump cable came in. Also solder or seal off the inlet to the intake manifold where the little barb fitting is. you are US, Dennis Kirk has gasket sets also. Vesrah brand. No crank seals included, but head and base, all the paper and copper exhaust ones. I have never dealt with BikeBandit, seen their web though. DK is just an hour or two north of me so I can get parts in UPS in about 18 hours from ordering. I can dig around at home. top of house was off for room addition and my life is in storage or piles or covered up. I'll see what I can find. You'll do fine, they are pretty simple to work on. kcj Quote Link to comment Share on other sites More sharing options...
sam Posted February 14, 2007 Author Report Share Posted February 14, 2007 Thank You for the Reply, Sounds easy enough, I'll give it a shot and thanks for letting me know about D-Kirks having gaskets. Bike bandits has been real good, downside is the location is on the west coast. I'm spoiled with companys like RYP, order today, get it tomorrow! sam Quote Link to comment Share on other sites More sharing options...
sam Posted February 19, 2007 Author Report Share Posted February 19, 2007 Very easy to take apart the oil injection pump, thanks again for the help! sam Quote Link to comment Share on other sites More sharing options...
sam Posted March 8, 2007 Author Report Share Posted March 8, 2007 (edited) YZ 80! Cylinder bored, new piston rings and yet after 7 kicks the compression only reads 100lbs. The bike actually starts after a couple kicks, Idles well, but no power. The reeds looked clean to me, after 45 min of riding the plug looks half black but dry not wet at all! Also, I checked for air leaks and did not find any around the outside of motor. So, what now? engine seals? If a exhaust is plugged up can it effect the compression? Mean while I have done the whole top end on my Montesa and she runs great!!! sam Edited March 8, 2007 by Sam Quote Link to comment Share on other sites More sharing options...
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