erbrod Posted March 16, 2015 Share Posted March 16, 2015 ive finished rebuilding the top end and engine after exhaust valve dropped and thrashed my piston. all new oem partts inside, except for clutch and tranny. now, she starts and i can ride her but she backfires and when i accelerate she jerks slowes down then jerks forward and speeds up again on any gear but it is worse on third, fourth and fifth she cant even reach her max speed with all that going on. I have tried to adjust the fuel mix screw on carb and still the same. i have the stock air box on and have not changed the exhaust. what could it be? the fuel is new and so is the oil. i have checked the valve clearances and they have been set as suggested by the manufacturer. the sparkplug is also new, because i cannot ride her for long in this condition it is difficult to ascertain if shes lean or rich just by looking at the plug, it looks good. the air filter is damp with the oil that is recommended and the intake manifold rubber boot is in good shape. the petcock is good and the carb is getting fuel. i have super tightened the exhaust bolts and do not suspect there is an exhaust leak, to be frank, i couldnt tell if there is one, how could i? its been breezy here at the beach so it is not possible to see it smoking out of where it connects to the cylinder head. I am a true rookie but ive tackled this and know this bike really well. still i cant get her to perform and i am stuck,stuck,stuck!!! when she pops i cant tell if its the carb or if it is coming from the exhaust, how does one figure that out ? with the bike rumbling and all i cant really point out where the backfiring is. is it electrical? could it be the rectifier? how do you know if it is functional? is there a way to test? the fuse is good and she starts easily. i am back with the carb...WTF??? what if i give another turn to that screw? should i open the main jet or leave it be? i need help, cant afford a pro. i can fix her, i need her, ive spent a pretty penny on her and i can get her to perform again, but i am not proud,i need help. i apologise for the poor grammar. my typing skills are nil. i still cant find a way to post a pic on this forum. thanks boys and girls. for those living here at the beach, the weather is perfect and i wish to join you on the road soon, ride safe Link to comment Share on other sites More sharing options...
KevtheRev Posted March 16, 2015 Share Posted March 16, 2015 You wouldn't be a tooth out on the cam or anything like that would you ? Don't overtighten the exhaust bolts , better to get as new copper ring seal as they are only a few cents . Was the bike running well before , and did you replace the camchain ? I can't tell if you've done many miles after the rebuild but I'd check the top end for oil starvation esp if any rubbery instant gasket goo has been used . Don't panic , it could be a small electrical or fuelling problem and you'll just need to eliminate the suspects one by one in a methodical fashion . Best I can say on the info you gave . Fair dues for giving it a bash . Link to comment Share on other sites More sharing options...
KevtheRev Posted March 16, 2015 Share Posted March 16, 2015 P.s. Your best bet is to get an workshop manual for a few bucks and make sure you've the carb back to standard setting , that'll be one off the list . Link to comment Share on other sites More sharing options...
KevtheRev Posted March 16, 2015 Share Posted March 16, 2015 P.s. Your best bet is to get a workshop manual (Haynes are good ) and get your carb back to standard settings . That'll be one off the list and a good starting point . Link to comment Share on other sites More sharing options...
KevtheRev Posted March 16, 2015 Share Posted March 16, 2015 P.p.s. You don't have sand in the float bowl do you ? Link to comment Share on other sites More sharing options...
DutchFJ1200 Posted March 16, 2015 Share Posted March 16, 2015 P.s. Your best bet is to get a workshop manual (Haynes are good ) and get your carb back to standard settings . That'll be one off the list and a good starting point . If that's the same block as an XT-250, which I believe it it is, I may have a Yamaha workshop manual floating around. I'll have a look. Link to comment Share on other sites More sharing options...
erbrod Posted March 17, 2015 Author Share Posted March 17, 2015 ok, there is no sand in float bowl, curious as to why there would be any though?ive not been able to ride her after the rebuild for long due to that backfiring and jerking action... slowing and speeding up up on all gears. What do you mean small electrical problem? i have today cleaned the carb proper and used high pressure air where the jets sit. as for the manual i have the factory service manual and frankly i believe these manuals were made fro pros not novice grease monkeys like myself, however i was able to rebuild engine with it. there isnt much on the carb and in fact it suggests not to change setting on fuel mix screw since it is set at the factory, too late for me since i have already turned it a couple of turns more. please let me know what you mean by electrical... is it the rectifier? the stator? i cant think of anything else but will order new bigger jet perhaps the bigger piston demands i change jet on carb. thanks for the advice Link to comment Share on other sites More sharing options...
KevtheRev Posted March 17, 2015 Share Posted March 17, 2015 You never mentioned a bigger piston , and I mentioned sand as you said you lived on the beach . I've seen new piston rings break because the bore wasn't honed properly after a re-bore . That'll cause backfiring and sticking too , usually accompanied by rattling and vibration . As for an electrical problem , what's your battery like ? If the reg/rec is fooked the battery won't charge and could affect running if it goes flat ., or a broken or shorting wire to the HT coil or points/CDI unit/ignition . Is your stator plate aligned properly (did you mark it's position before removal ?) . A bigger piston doesn't necessarily mean you need to increase the main jet size . Is the spark plug wet and/or sooty as a sticking choke or rich fuelling can also cause the symptoms you describe . Link to comment Share on other sites More sharing options...
erbrod Posted March 18, 2015 Author Share Posted March 18, 2015 Right i forgot to mention the piston but it was rebored by an engineer who has been doing that for at least 30 years. battery is brand new one of the acid type 12v. as for the stator plate it is in the only position it can be it is held in place by 2 screws. sparkplug is sooty i noticed after a quick test ride today. oh yea i live in Virginia Beach but i dont ride her around the boardwalk and i live in the marshier part of the town but i see your point regards to the sand in carb. today i didnt get the backfiring but i did get that slowing down when i shifted from first to second and on all the gears she was not performing as she ought to. slow then she would jerk and speed up. weird. Link to comment Share on other sites More sharing options...
erbrod Posted March 18, 2015 Author Share Posted March 18, 2015 i dont know what slipping clutch feels/sounds like but tomorrow a friend who rides will have time to take her for a spin and will know if that is the problem with the bike. today still the same as yesterday, Link to comment Share on other sites More sharing options...
Recommended Posts