1990 xr100 smokes and bogs after new top end

[2-strokes-4-life]

on my xr100 i had the cylinder bored and we replaced the piston with a wiesco.the head was destroyed, the cam had made the groove it sits it big enough for it to wallow all over the place it looked to me from lack of lubrication.the cam lobes where worn pretty bad and looked like they had melted alittle to me from the way the edges looked.the rocker arms where also worn bad enough that they had grooves in them which i dont think should have been there i figured the arms should have been flat but am not sure.ok well back when i was working on the bike even though i thought the cam and rockers should have been replaced my dad said they where ok to use.we also used the old valves and valve springs.after we got it all back together it fired right up but smoked really bad and bogged terribly,basically it would idle maybe take just alittle throttle and thats it.we adjusted the carb several times but it didnt change anything. i suspected the carb wasnt it after all the fiddling with it and no changes, but i really wasnt old enough to help him at that point.well after running it for awhile it never did stop smoking and it fouled plugs constantly.i do remember however,that if i flipped the choke up and down a few times while turning the throttle i could get it to rev eventually and at that point i gunned it down my field and it had plenty of power but it only ran this way long enough for me to get to the end of the field and come back befor it started bogging again. i still have the motor and always wanted to know what was wrong with the thing since we put so much money in it so im thinking about trying to fix it once and for all if for nothing else than to sell it to get some money out of it. i dont have much experience with 4 strokes.anybody have any advice?sorry for writing a book here but any advice would be great :ride:

 

[nickyd]

did you set the valve clearance when you rebuilt the motor?

 

[2-strokes-4-life]

i spoke with my dad this afternoon and he told me that he did check the valve clearences after we got the motor back together.he was thinking that maybe the way the cam lobes and rockers had worn that they may not be working correctly.it seemed to me it was sucking alot of oil from somewhere with all the smoke and constantly fouling plugs.i also remember him saying something about the oil maybe getting by the valve stems or something.i'm trying to figure it out but am kinda lost at this point.anymore advice or suggestions of things to check out would be great

 

[nickyd]

did you change the valve stem seals?

 

[2-strokes-4-life]

sorry for taking so long to reply,he thinks we did replace the valve stem seals.if its not those any advice on what to check out next?

 

[QKENUF4U]

from the sounds of it buy a GOOD used head and start over. sounds like you have MULITPLE PROBLEMS that should have been taken care of but your dad didnt know any better.
get a service manual and start over.
valve stem seals (if not replaced)
valves (bent ?)
valve seats (did ya lap the valves in)
rings (did you bore/hone the cylinder to the right size and make sure you had the right ring end gap ?)
to much oil in crankcase ?
cam/rocker arms should have been replaced from the sounds of it
head if it was actually grooved/wallowed out
etc..
good luck

 

[2-strokes-4-life]

we did replace the head with a brand new one.the cylinder was bored and the new piston was bought befor the shop bored it.QKENUF4U you are right,we should have replaced the cam,valves and rockers when we did it.he did lap the valves,but they probably should be replaced as well along with the springs.i will go ahead and replace the valve stem seals as well.now that im older i will at least have a better concept of whats going on when we start working on it again.i will start by replacing the above mentioned parts along with getting a service manual befor we start tearing it apart.i was thinking maybe it could have been bored wrong.what do i use to measure the bore and where can i get it?also how do you check ring gap?

 

[QKENUF4U]

have a machine shop check if for you. that way you get an accurate measurment of the bore and ring end gap (take the top ring with you for the machinist to use).

 

[Halfast816]

Chances are you installed the scrape ring upside down. There is a sealing ring, retaining ring and a scraper ring. If the scraper ring is installed wrong it will allow oil to pass into the combustion chamber. The rings have a top and bottom, usually markings face up. Make sure the end gaps on the three rings are not lined up.