decibles Posted May 5, 2007 Report Share Posted May 5, 2007 If the pistons are the right ones and installed correctly the onlny thing I can think of is that you aren't getting any air in the cylinder, if you were to cap the carbs completely your compression would be really low, maybe a rag in the reed boots to keep dirt out or maybe your son left his plastic easter eggs in the open carbs cuz he hid them there and forgot. oh wait that was my sone I got confused for a moment. Quote Link to comment Share on other sites More sharing options...
blowit Posted May 7, 2007 Report Share Posted May 7, 2007 If the pistons are the right ones and installed correctly the onlny thing I can think of is that you aren't getting any air in the cylinder, if you were to cap the carbs completely your compression would be really low, maybe a rag in the reed boots to keep dirt out or maybe your son left his plastic easter eggs in the open carbs cuz he hid them there and forgot. oh wait that was my sone I got confused for a moment. Keep me posted on this one. I am curious as to what you find. Brandon 1 Quote Link to comment Share on other sites More sharing options...
Olds Eddie Posted May 7, 2007 Author Report Share Posted May 7, 2007 Keep me posted on this one. I am curious as to what you find. Brandon I plan to lap the head on a piece of thick glass and reinstall with factory head gasket. I'll let you know what happens. How much could I mill it and still run pump gas? Quote Link to comment Share on other sites More sharing options...
wrecker03 Posted May 7, 2007 Report Share Posted May 7, 2007 I plan to lap the head on a piece of thick glass and reinstall with factory head gasket. I'll let you know what happens. How much could I mill it and still run pump gas? Wow your determined to mill that head, just kidding. Before you do set the head on the plate glass and go around it with some feeler gauges, or just put a straight edge across it. You'll find out real quick. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted May 7, 2007 Report Share Posted May 7, 2007 I too think you should fix your other problems before you mill the head. Why make matters worse by adding compression (read....STRESS) to a motor that's not even right to begin with. The need for higher octane depends on two things, taking into consideration the bike is jetted properly: Compression and timing... No one can tell you for sure what to do... Some guys run 170PSI plus on pump gas, some run 150 and need higher octane.... Quote Link to comment Share on other sites More sharing options...
Olds Eddie Posted May 10, 2007 Author Report Share Posted May 10, 2007 (edited) Well I lapped the head and it did appear warped. I sterilized the mating surfaces and installed an OEM head gasket. After torqing the head in three stages I decided to do a compression check. Both cylinders showed 57psi. The pistons are installed correctly and I checked my compression guage for accuracy. I am out of ideas other than removing the cylinders and checking for stuck rings. Would stuck rings cause this much of a compression loss on a 2 smoke? Edited May 10, 2007 by Olds Eddie Quote Link to comment Share on other sites More sharing options...
blowit Posted May 10, 2007 Report Share Posted May 10, 2007 Well I lapped the head and it did appear warped. I sterilized the mating surfaces and installed an OEM head gasket. After torqing the head in three stages I decided to do a compression check. Both cylinders showed 57psi. The pistons are installed correctly and I checked my compression guage for accuracy. I am out of ideas other than removing the cylinders and checking for stuck rings. Would stuck rings cause this much of a compression loss on a 2 smoke? Yeah, but I thought this engine was new? Stuck rings would do it but if it is new, they should NOT be sticking at all. Did you by chance " port" these cylinders? Please check your squish clearance with a piece of solder and lets start there. I know this problem is going to be something simple. Brandon Quote Link to comment Share on other sites More sharing options...
Olds Eddie Posted May 10, 2007 Author Report Share Posted May 10, 2007 Yeah, but I thought this engine was new? Stuck rings would do it but if it is new, they should NOT be sticking at all. Did you by chance " port" these cylinders? Please check your squish clearance with a piece of solder and lets start there. I know this problem is going to be something simple.Brandon As far as I know it has stock porting. I think it has aftermarket reeds. I plan to do solder trick next. What should this clearance be? Quote Link to comment Share on other sites More sharing options...
dajogejr Posted May 10, 2007 Report Share Posted May 10, 2007 Everyone has their own preference when it comes to squish. However, .035 to .050 should be ok. Quote Link to comment Share on other sites More sharing options...
J-Madd Posted May 12, 2007 Report Share Posted May 12, 2007 Did you ever check to see for sure if you've got 795 series pistons? I guess when you check the squish you'll find that out, though. The 795's probably won't even touch the solder. As mentioned, if these are the correct pistons, I'm completely stumped as well. Quote Link to comment Share on other sites More sharing options...
blowit Posted May 12, 2007 Report Share Posted May 12, 2007 Did you ever check to see for sure if you've got 795 series pistons? I guess when you check the squish you'll find that out, though. The 795's probably won't even touch the solder. As mentioned, if these are the correct pistons, I'm completely stumped as well. Yeah, thats kinda why I called out the squish check. I am thinking we have wrongs pistons here. There is just too few of things that can cause this and that head was not one of them. Like no rings on the pistons or squish is "exactly" 2mm long. Just a guess though, I am hoping for a final post to let us know. Brandon 1 Quote Link to comment Share on other sites More sharing options...
flyhighprerunner Posted May 13, 2007 Report Share Posted May 13, 2007 hdy if it makes you feel any better i just installed a new set of pistons in my bike and after thinking about it because my compression is also 75 pds. i never had it honed and this is my 3rd or 4th top end since i had it bored last so i think it might be time after this motor because its taking a couple more kicks to get her started...so by chance did you hone the cylinder or have it bored, if not maybe shes just getting tired maybe needing a good ole fashon'ed tune up..... Quote Link to comment Share on other sites More sharing options...
Olds Eddie Posted May 14, 2007 Author Report Share Posted May 14, 2007 Yeah, thats kinda why I called out the squish check. I am thinking we have wrongs pistons here. There is just too few of things that can cause this and that head was not one of them. Like no rings on the pistons or squish is "exactly" 2mm long. Just a guess though, I am hoping for a final post to let us know. Brandon Well I found my old solder which is thick enough for this test and guess what. My squish is exactly 2mm! I guess that means wrong pistons. Quote Link to comment Share on other sites More sharing options...
Olds Eddie Posted May 15, 2007 Author Report Share Posted May 15, 2007 I pulled her back apart and they are marked 513's. The pistons come within about a 32nd of an inch of reaching the top of the bores. Could Wiseco have marked them wrong? Quote Link to comment Share on other sites More sharing options...
J-Madd Posted May 16, 2007 Report Share Posted May 16, 2007 I pulled her back apart and they are marked 513's. The pistons come within about a 32nd of an inch of reaching the top of the bores. Could Wiseco have marked them wrong? I'm not sure of the 513, but you can google the entire number on top of the piston and find out what it is. I think the number ends in 795 for the 795 series pistons. Quote Link to comment Share on other sites More sharing options...
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