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1990 xr 80 ..

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i have a 1990 xr 80 i'm trying to fix for a kid who's family has limited funds.. they got the bike for free & i'm supplying parts & labor.. i build custom harley's so i figure i should be able to handle the chore.. the first issue i found was the timing chain had jumped the sprocket, bent the sprocket & twisted the chain .. i change the chain & installed the new sprocket in time.. i double checked the cam timing, so i feel confident its good.. my concerns were a possible bent valve.. i adjusted the tappets & there was no excessive adjustment needed .. the engine rolled over smoothly & i can see the valves opening & closing at the stem as you turn it over.. so i am assuming they arent bent.. i also cleaned the cab. & modified the half missing air cleaner box so that the splash guard for the rear wheel was functional & added a uni air filter pod.. SO NOW .. heres the issue.. when you try to crank it , it occassionaly blows a puff of flame outa the exhaust & i know its a small engine, but it feels awful easy to kick over.. the points looked good , with no pits or anything like that.. now i know ign. timing is set on the F mark & it appears i have the points set close enough.. BUT ITS A NO GO.. the bike has fire to the plug & its getting fuel .. SO as many of you know far more than me about these lil' motors , does anyone have a suggestion..

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i would do a compression test and see what psi you get, if less than 125 pull the head off, check piston/cylinder condition, and pull the valves out to see if they are bent or not it could be so little that u cant see it but prevents sealing.

it sounds to me like your exhaust valve is bent or is adjusted too tight, just set the clearance very loose and see if that changes compression

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i thought of the tappets being adjusted too tight, but they feel good.. i've always adjusted these honda tappets by feel with no guage.. i will lossen them more & see.. i dont have a comp. guage for these things , but you are right, a top end pull down may be in order.. the valve could account for the "poop" sound it makes when it puffs the flame from the exhaust..which is after about 10 kicks .. any thought on the mild flame throwing after it goes "poop " ..

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the exhaust valve is not sealing so the the a/f mixture is pushed past into the pipe, after 10 kicks it gets loaded up to the point where the spark travels out the cylinder and ignites whats im the pipe

test the valves by pouring some oil thru the spark plug hole if the compression goes up its the rings, if it stays the same its the valves

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i guess the ignition could be retarded, but he said it had no compression, i had a old ct90 that would do the exact same thing after 10 loose kicks itd back fire, i did the oil trick with didnt up compression so i took the head off, lapped both valves... did the same thing, so i adjusted the valve lash intake was fine, but exhaust was like all the way screwed in like a kid hadn't gotten in there and played with it... after that in ran super

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Timing is everything. A collapsed or missing oil felt will give you grief (or make you pull your hair out) setting up the points. Valve adjustment is .002" to .004".

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no backfire thru the carb.. still no compression with the oil trick.. loosened the valve lash up..still no go.. same poop & a flame.. i can hold my thumb over the plug hole.. no pressure.. valves bent, i'd bet the farm.. seems the ign. is a simple set.. gap the points at the proper place....

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any thoughts on setting point gap.. i dont have a spare rotor to rob the lobed part from.. dont know about crank air flow.. what am i looking for ??

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If the points start opening at F and there is no backfire through the carb and the gap is about right. It should be okay for now. But The stator and the advancer are the main culprits with points ignitons on 80/100's. I would just pull the head and check the valves. Just get a new head gasket and base gasket.

Edited by socalxr

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i'm going to pull the top end later today.. may pull the rotor/ fly wheel thing & have a solid look at those points too.. i'm assuming there should be an advance mechanism in there..

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does the cam chain adjuster stuff come off before or after you pull the head.. i'm sorta free wheeling it off prior mechanical abilities.. no manual .. i figure if i can build a 400h.p. 302 ford motor & custom harleys from the ground up, that surely i can handle this..

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take the cam thing on the left side of the head out and loosen the the nut and back out the screw on the back of the cylinder, pull the larger plastic guide out, then you should be good

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thank you all for the advice.. educated advice beats a manual any day.. i appreciate your time..i'll be back with an update ..

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No advice from me, but just wanted to chip in that you are doing a nice thing, making a kid very happy, possibly for years to come.

I have an old 80 that will go the same route soon, get those kids outside on two wheels.

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no real updates as of now.. the motor is apart.. the valves seem to be minimally bent, they bleed straight thru when you spray wd-40 into the ports.. i will also re-ring it & add some cosmetic parts.. thank you yellowhead42 , kids are what its about.. this young fella is stoked up , telling everyone his " uncle dave " { of which i'm really no relation } is fixing him a bike up.. it is a good feeling to help kids like this.. the boys dad , who i work with has thanked me a million times, though i've told him its all good .. i've been working alot the past few weeks , so its slowed me down, & the fact deer season opens this week end.. but i will get back on it soon.. i may just take it to a shop.. i havent decided yet.. if anyone has a supply of spare parts i do need a few things & i'd gladly buy them from you guys.. i need a shift side peg , a throttle sleeve , & grip.. some stickers to dress it up some for him would be nice.. you know aftermarket parts stickers, honda stickers.. whatever..maybe some other things too.. the young man was in a utv accident & the side by side flipped over , injuring all the passengers.. the boy has a broken arm, 4 broken ribs, a punctured lung, a injured vertebra in his neck & a chipped collar bone.. very depressing , but i will press on, his dad says he still want him to have th bike & the boy is still pumped up for it.. he is out of icu now & may go home next week.. life is fragile & often we forget that fact.. i have told the boy about all you guys that helped me with advice here.. he didnt know such places existed.. again thank you all..

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