Driggs Posted March 15, 2010 Report Share Posted March 15, 2010 So I rebuilt my top end (bought it used and didn’t have much compression) and after running hard, I melted my left piston. Did another rebuild, installed new crank and top end, rebuilt my carbs, went to 300 on my jets, did a leak down, held 6lbs for 6 minutes and this past weekend, after running WOT, melted the same piston again!!! My mods are..T5's, K&N, stock air box, no lid, 300 jets, boysen reeds. Been told that my jugs have had port work done just don't know what kind. What would be causing this issue? Something in my left carb maybe? I don't want to rebuild this thing for the third time just to have the same issue. She ran amazing before the melt down but just got the opportunity to run WOT this past weekend. She would die when I would let off the throttle and I was dumping the clutch to start her back up then she just died for good. Quote Link to comment Share on other sites More sharing options...
VegasJeff Posted March 15, 2010 Report Share Posted March 15, 2010 x2 with zilla,I'm thinking your running it lean due to gas cap vent,plugged petcock or the float is set wrong. Quote Link to comment Share on other sites More sharing options...
01banch Posted March 15, 2010 Report Share Posted March 15, 2010 Did you check your plugs? 300 sounds lean especially if in fact thee is some porting. Quote Link to comment Share on other sites More sharing options...
01strokedshee Posted March 15, 2010 Report Share Posted March 15, 2010 did u replace the crank seals if u fucked the seal up putting it in u will have a air leak witch will make it run lean on that side just a thought man Quote Link to comment Share on other sites More sharing options...
Driggs Posted March 15, 2010 Author Report Share Posted March 15, 2010 I did replace crank seals. I'm going to do another leak down before I tear it apart to make sure that isn’t the cause. I'll post pics of the plugs tonight. Was planning on doing a plug chop this weekend but as soon as I went WOT, it melted. I'm going to replace the petcock and gas cap this time around to be safe. The float height is good. Quote Link to comment Share on other sites More sharing options...
Duneman101 Posted March 15, 2010 Report Share Posted March 15, 2010 It shouldn't be a crank seal or intake boot if you were holding pressure with a leak down test.... take a look at the floats, but if she was running amazing right before the melt down that sounds doubtful too. Quote Link to comment Share on other sites More sharing options...
dave5.0 Posted March 15, 2010 Report Share Posted March 15, 2010 I've ran stock cylinders with the same mods at around 310-320 mains with stock carbs. If you have porting I would think you would be a richer on your jetting. Where are you at? Elevation, temperature, compression, type of gas? Is it detonating? What are you running for a head? Is it getting hot? Did you run the jetting up until it started puking on itself then back down until it cleaned up? Then check your plugs. That's the only way I know to make sure you are rich enough and not smoke it. Do you have a plate in the airbox for the K+N? How is it mounted? Not sucking dirt or something? Quote Link to comment Share on other sites More sharing options...
Driggs Posted March 15, 2010 Author Report Share Posted March 15, 2010 Forgot about the Cool Head w/ 20 cc domes on the list of mods. I'm running pump gas, 93 octain. I do my riding in south GA and central FL and the weathers been 60+ the few times I've rode before this happened. The K&N has the plate for mounting in the stock airbox. I was at 270 when the first melt down happened, then went to 300 this time around. It was running very strong in 1st, 2nd, and 3rd. The only time I got up to the higher gears is when it melted. Sounds like I need to go up even more on the jets next time. Bought a set of carbs last week on here, looks like I'll try them next time just to be safe. I just hope all the metal shavings didnt f up my new crank with less than 3 hrs on it!!! Thanks for all the help. Quote Link to comment Share on other sites More sharing options...
Invader Posted March 16, 2010 Report Share Posted March 16, 2010 drop down to 21cc domes. Your probably getting some detination. I ran 20's with california "premium" gas and did the same thing as you. Dropped to 21cc from 20cc and it been great. Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted March 16, 2010 Report Share Posted March 16, 2010 300 sounds too small to start at, i like to go real big then back down till the plugs look good. plugs are alot cheaper then rebuilds Quote Link to comment Share on other sites More sharing options...
White97Banshee Posted March 16, 2010 Report Share Posted March 16, 2010 Definitely too lean. I run 330's with my stock carbs, T5's, VF2 reeds and k&n pods with no porting. You should be using at least a 330 if not higher. Quote Link to comment Share on other sites More sharing options...
firebanshee Posted March 16, 2010 Report Share Posted March 16, 2010 Forgot about the Cool Head w/ 20 cc domes on the list of mods. I'm running pump gas, 93 octain. I do my riding in south GA and central FL and the weathers been 60+ the few times I've rode before this happened. The K&N has the plate for mounting in the stock airbox. I was at 270 when the first melt down happened, then went to 300 this time around. It was running very strong in 1st, 2nd, and 3rd. The only time I got up to the higher gears is when it melted. Sounds like I need to go up even more on the jets next time. Bought a set of carbs last week on here, looks like I'll try them next time just to be safe. I just hope all the metal shavings didnt f up my new crank with less than 3 hrs on it!!! Thanks for all the help. Sounds like you might still be slightly lean, you are running to small of dome for pump gas if you are around sea level. Between the 2 it doen't take much to melt a piston. Quote Link to comment Share on other sites More sharing options...
bansheesandrider Posted March 16, 2010 Report Share Posted March 16, 2010 With that small of a dome you should at least be running a pump/race mix if not straight race fuel. I would also say it is to lean with 300s, I would put 330s or 340s in it and do a plug chop and go from there. I would not change carbs, I would make sure all the passages are clean on the carbs that are on it when you rejet. Take them completely apart 1 at a time so nothing gets mixed up between them, some parts are different between the left and right carb. Once they are apart, spray cleaner through all the passages and blow them out with air and then put them back together. Quote Link to comment Share on other sites More sharing options...
Driggs Posted March 16, 2010 Author Report Share Posted March 16, 2010 Can't believe my jetting was that far off. Hate learning the hard way but it's only time and money, neither which I have lots of. I'll rebuild and use bigger jets and try again. Thanks for all the help guys. Quote Link to comment Share on other sites More sharing options...
sheefreak Posted March 16, 2010 Report Share Posted March 16, 2010 You are gonna learn another hard lesson if you put that motor back together w/o splitting the case again to completely clean the bottom end of all debri. If you melted down a piston and run it like that again w/a new top end, you may as well of thrown a handfull of sand down in the case why you were at it. You need to clean everything and roll all bearings of the crank to feel for grit or resistance in the bearings. You should be able to clean everything up an be ok but do not put that thing together w/o a clean and inspection. And you are definately lean. As mentioned, it doesn't hurt to start out so rich that you are fouling plugs, you can always go down from there. 340-350 range should give you an idea. And when you go to ride it, don't just pin it right away. Slowly give it some throttle, working up to very short bursts of having it pinned. Take your time unless you have a buncha cash you wanna throw away. Quote Link to comment Share on other sites More sharing options...
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