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Old 03-21-2010, 01:39 PM   #1
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xr50 88cc big bore kit questions

alright...

so for those who dont want to read thru the whole thing, heres my questions...
1) getting a sharp noise when kick-starting... no noise when turning over by hand, no noise when running... any ideas?
2) what is proper break-in procedure for big bore kit?

so after about an 8 hour ordeal, we got the big bore kit installed... put oil back in it, turned it over by hand a bunch of times to make sure everything was ok... seemed to be ok, a little tougher at one point, but not stopping or anything... so we decided to try to start it...

kicked it slowly a few times to get gas runnin thru, then it sounded for a minute like it was gonna catch, but made a "bang" and stopped... this kinda worried us, werent sure what that was about... but decided whatever, try again... made the same noise, but started and surprisingly enough =P, seemed to run real smooth... idle was kinda high, but we havent done any adjustments to the carbs yet...

as far as i know, we did everything by the book, only thing i wonder about is the camshaft... instructions said to insert the new one with the cam lobes facing down, which i took to mean not lifting the arms... theres only two ways the timing sprocket could screw onto the camshaft, so we went to the closest one once we had the parts together... seems to me like it wouldnt run if this wasnt correct?

anybody know what this noise might be? it almost sounds like a backfire, but sounds a little metallic too... so far, we have gotten this noise everytime we kicked it over... no noises when cranking over by hand, and no noises like that when running... so not sure what thats about...

other question is, what is the proper break-in procedure for the big bore kit? one of my buddys was convinced that you have to let it idle or ride around slowly (keeping the revs down) until it reaches operating temp, then shut off, let it cool down, and repeat this a few times...
my other friend was convinced that you should ride it like you normally would (aka, beat the crap out of it =P) until operating temp, let it cool down, and repeat a few times...

im leaning towards taking it easy for maybe half a tank... other way sounds like a good way to blow up stuff...

any input/comments/suggestions greatly appreciated!!
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Old 03-22-2010, 09:30 PM   #2
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Re: xr50 88cc big bore kit questions

so for those who care, i figured out what the problem was...

i brought it in to work today, had one of our mechanics look at it... figured out that the gasket between the head and the jug was leaking/faulty/not installed correctly/didnt torque headbolts to spec... or some combination of the above... apparently it was blowing out the side... he revved it up a bit, which i didnt do for fear of ruining something, and it was definately poppin and blowing smoke out the side between the head and jug...

so now i have a whole new set of gaskets coming (because of course you cant buy just that one =P) , and gonna hafta take the head off when they come in, reinstall a new gasket, and hopefully that will fix it... i believe that is the only problem, the mechanic said other than the gasket leak he thought it sounded like it ran fine, timing was ok...

i do have two more questions however...

sorry in advance for the crappy quality of the pics, they were taken with my phone at night...
first question is, what the hell is this black box?
Click the image to open in full size.
originally had a tube coming from stock air intake, but no hookup on the new air filter, so i just left it open... bike runs without it, so im hoping its not too crucial, but im wondering if i should at least rig up something to keep crap from getting into it...



second question... for those who have installed the big bore kit... it may be kinda hard to see in this pic, but my carb overflow nozzle runs almost directly into the top of the jug, with no room for the overflow tube... how can i get around this? can i bend the nozzle outwards, or will i snap it off? i dont think i want gas spilling onto the jug/head after running hard for an hour or two... =S
Click the image to open in full size.
comments / suggestions appreciated!! =)
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Old 03-22-2010, 09:57 PM   #3
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Re: xr50 88cc big bore kit questions

There is no problem with the fuel dripping on the head mine has done it the whole time i have had it and never any problems. By black box I think you mean the rev limiter box and you deff need a upgraded one my 88cc kit allows me to go like 55mph with it.
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Old 03-23-2010, 05:33 AM   #4
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Re: xr50 88cc big bore kit questions

On the oem parts break down it says the black box is a storage tank..... not sure what it stores? But i know you don't need it!
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Old 03-23-2010, 01:51 PM   #5
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Re: xr50 88cc big bore kit questions

you might check the head torque, if it is too loose the engine will pop out the head gasket pretty lowd. It won't do damage and usually only does it in low rpm under load. hit it to 8ft/lbs with a torque wrench on the top 4 nuts on the rocker cover.
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Old 03-23-2010, 04:55 PM   #6
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Re: xr50 88cc big bore kit questions

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On the oem parts break down it says the black box is a storage tank..... not sure what it stores? But i know you don't need it!
from other forums, it sounds like it is crankcase breather... still not technically sure what it does, but i think i might just throw a tiny piece of cloth over it to keep crap from getting in there, and call it good...
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Old 03-23-2010, 05:00 PM   #7
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Re: xr50 88cc big bore kit questions

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you might check the head torque, if it is too loose the engine will pop out the head gasket pretty lowd. It won't do damage and usually only does it in low rpm under load. hit it to 8ft/lbs with a torque wrench on the top 4 nuts on the rocker cover.
yeah thats what the problem was, i'm waiting on a new gasket kit now...

i've read online anywhere from 8 to 10 ft/lbs. on the cylinder head cover nuts, so i think im gonna go with 10, and see what happens...
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Old 03-23-2010, 07:42 PM   #8
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Re: xr50 88cc big bore kit questions

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yeah thats what the problem was, i'm waiting on a new gasket kit now...

i've read online anywhere from 8 to 10 ft/lbs. on the cylinder head cover nuts, so i think im gonna go with 10, and see what happens...
you might be able to get away with the gaskets in it, tighten it down and givit a shot!
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Old 03-23-2010, 08:15 PM   #9
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Re: xr50 88cc big bore kit questions

I had the same problem, I tightened them all at 8lbs then 10ibs and it was golden. The problem I have is if I crack the throttle wide open at idle the bike stalls. This normaly isnt a problem when doing tricks but every now and then it sucks. I'm wondering if its the carb? Im not sure if its right BUT its definatly from China. It looks the same as the picture above. What do you guys use for jets?
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Old 03-23-2010, 08:26 PM   #10
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Re: xr50 88cc big bore kit questions

I had the same thing happen. I tightend them to 8lbs then to 10lbs and it was golden. The gasket was fine, if its bad you'll know what it sounds like now!
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Old 03-23-2010, 11:23 PM   #11
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Re: xr50 88cc big bore kit questions

well thanks to some super fast shippingClick the image to open in full size., i got the new gaskets today, i was all set to go with a torque wrench borrowed from my work...

tore the head off, put the new gasket on, started putting everything back together, and thats where things started going wrong... Click the image to open in full size.

either i dont know how to use a torque wrench, or 10ft/lbs. is too much for the head bolts... the 3 acorn nuts torqued to specs fine... but it was the weirdest thing i ever seen, it stripped the inside threads right out of the last plain nut and left them sitting on the headbolt... course i had to ruin the threads on the headbolt while getting the stupid nut back off... Click the image to open in full size.

then i also managed to snap one of the timing sprocket bolts off inside the camshaft... 6.5 ft/lbs. on that bad boy didnt seem to faze it the first time we put it together, must have weakened or something...

managed to pull the remainder of the bolt out with an extraction drillbit, so thankfully i shouldnt need a new camshaft at least... only good news of the day... Click the image to open in full size. i did get a metal shaving or two in the bearings from drilling the bolt out, but blew air through the bearings real hard while spinning them, and that seemed to get rid of it...

so now i need a new headbolt and nut, and a timing sprocket bolt... Click the image to open in full size. and hafta figure out what to do for torque ratings... idk...

i just wish i could get this stupid thing running good enough to ride it... would relieve some stress... i was about ready to kick the thing into the wall when those bolts and nuts snapped...Click the image to open in full size.
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Old 03-24-2010, 08:32 AM   #12
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Re: xr50 88cc big bore kit questions

Thats wierd... The bolts will give and spring back because they are so long. You cant just put the wrench on them and turn.... Kinda pull it gently back and forth and you can feel it click. Try tightening a bolt in a vice or somthing first... 10lbs isnt very much at all.

As for the camshaft I dont know... 6.5lbs shouldnt break plastic bolts.
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Old 03-24-2010, 07:23 PM   #13
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Re: xr50 88cc big bore kit questions

I would get a hold of who ever you got the kit from and tell them you have a defect. Those bolts shouldn't snap with that little amount of pressure on them.

Or ask your mechanic to help you next time with torquing the bolts down.
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Old 03-24-2010, 10:12 PM   #14
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Re: xr50 88cc big bore kit questions

ALRIGHT!! ENOUGH SCREWIN AROUND!!

of course nobody has the parts i need in stock, they're all gonna be a couple days out...

so instead...

borrowed a mechanics "thread restoring kit" , needle torque wrench as opposed to a clicker...
ran to the hardware store, got me a new nut and two screws for the timing sprocket... he didnt have hex heads in that size, only philips head... also grabbed a tube of red locktight...

went home, used the die on the headbolt, managed to clean it up halfway decent, threads were still a little mushed but not horrible...

threw everything back together, couldnt really torque the timing sprocket screws, so just tightened them as best as i could by hand and called her good...

torqued the headbolts down with the needle torque wrench, with locktight on the headbolt with the hex nut... didnt torque them to 10 ft/lbs., called it more around 8-9 this time...

turned the flywheel a bunch of times by hand to make sure nothing was stickin... first kick started it right up... Click the image to open in full size. rode it around the yard for about 10 minutes with low revs.... then shut her off, retorqued the headbolts and checked the oil...

then said to hell with breaking it in, i need to do some wheelies... Click the image to open in full size.

cracked the throttle a bit, holy hell that thing runs like a raped ape!!! Click the image to open in full size.

was doin sitdowns in 3rd gear no problem, when before i had to stand on the back pegs and physically yank the front end off the ground... lol crazy fun...

seemed to run fine, no backfires or anything, only thing i noticed after a little while is that if i rev a bit under load, i hear a faint metallic knocking... Click the image to open in full size.

any ideas what this might be? valves not adjusted correctly? timing chain off?
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Old 03-24-2010, 10:14 PM   #15
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Re: xr50 88cc big bore kit questions

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I would get a hold of who ever you got the kit from and tell them you have a defect. Those bolts shouldn't snap with that little amount of pressure on them.

Or ask your mechanic to help you next time with torquing the bolts down.
the headbolts are still stock... so i dont know what happened there...

i ended up using a needle torque wrench instead of a clicker, that way i could tell when i was getting close... seemed to work a lot better...
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Old 03-24-2010, 10:54 PM   #16
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Re: xr50 88cc big bore kit questions

you got her goin then?
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Old 03-25-2010, 09:35 AM   #17
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Re: xr50 88cc big bore kit questions

I have a knock or tick also, I set the valve lash and its still there. I just run it!!

Do you know what size jets your running in the carb?
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Old 03-25-2010, 10:08 PM   #18
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Re: xr50 88cc big bore kit questions

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you got her goin then?
yuppers!
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Old 03-25-2010, 10:18 PM   #19
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Re: xr50 88cc big bore kit questions

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I have a knock or tick also, I set the valve lash and its still there. I just run it!!

Do you know what size jets your running in the carb?
yano i honestly dont know, i got the trailbikes 88cc big bore kit, came with the 20mm carb, not sure about jet sizes...

havent even messed with the carb, threw it straight on, seems to be running fine so far...


glad to know im not the only one, im just worried about messing the engine up if i dont figure out and take care of it...

think it might be from not breaking in the engine properly?
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Old 03-25-2010, 11:32 PM   #20
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Re: xr50 88cc big bore kit questions

When I got the bike it already had the kit on it so I dont know how it was broke in.

I figure these things are pretty strong runners so it should be good for awhile. But I am open for suggestions to get rid of it.
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Old 03-25-2010, 11:32 PM
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