Help...few quesions

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xnicklopezx

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Jul 6, 2011
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Ok...after a lot of troubles i finally got my bike working well, cranking up to 32mph!! i was stoked. I have a skyhawk 48cc gt2b engine, and an NT carb. HOWEVER, it was doing 32 when i didnt realize the muffler was barely hanging on cause the gasket like blew up, SO, i put on the spare gasket and tightened her up, gotta say, MUCH quieter...BUT i lost like 10mph!:-||
now the top speed is like 22mph if im lucky. Is this common? Ive heard buy an expansion chamber...but would that really be worth the 60$? when the muffler is connected would that cause changes that i would have to tweak with in the carb? also when i get to WOT it starts making a wild noise...almost sounds like chain noise but coming from inside the engine almost like there a washer bouncing around in there lol. anyways, help is much appreciated! THANKS!
 
Greg58

Greg58

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May 1, 2011
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A lot of stock pipes are very restrictive, but you need some back pressure. Thats where the expansion chamber helps, if it is " tuned " right it will be a big help. I have not use one on a MB but have in the past did a lot of testing of diff. pipes on motocross motorcycles.
 
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xnicklopezx

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Jul 6, 2011
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hmmm...thats such a bummer...i didnt think it would be a 10mph difference...that sucks. and i guess no exhaust can cause problems right? is there any other things to do other than an expansion chamber? just not trying to drop another 60$ on this dang engine lol
 
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PerryP180

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Jun 24, 2011
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Atlanta, GA
This is only a guess. I can't hear your motor but I'm trying to imagine. I would guess the noise at wot is piston slap or possibly your spark plug is a little too long. I have only worked with the 66/80cc motors. My personal bike makes what I call a "tinkle" sound near wot. It sounds like a washer lightly vibrating. I've searched everywhere and can't locate it. It runs great though. You can try a slightly shorter spark plug. My engines have made different noises that usually go away as break-in progresses. As for the muffler, on my first build I thought the muffler was causing too much back pressure so I gutted it. Bad move. Seems these engines need a certain minimum back pressure. It dropped the speed in half. I've read with no back pressure that the engines will easily over rev. This could be what yours was doing with the muffler hanging. This could have caused some type of damage creating the noise you hear. Just make sure you have plenty of oil and break it in slowly. Not a lot of wot. I've found that the motors start running much better after about 300 miles are put on them.
 
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xnicklopezx

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Jul 6, 2011
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yea...im afraid i messed it up with the back pressure thing....i really hope not...the bike has like 125mi so far, the noise sounds exactly like what u described on your bike...as well mine runs pretty well...just not happy with losing 10mph lol, so is it possible i ruined the engine with the muffler hanging? like does it ever come back to life? lol, how long did you run yours gutted? did the speed drop in half just in general with or w/o the muffler? this bike has been quite the learning experience lol
 
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xnicklopezx

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Jul 6, 2011
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what do you mean port match? like make sure they are the same shape/size? how did you install a second pipe on the end cap? when your bike was real restrictive was it also doing like 22? like i said when the muffler was barely on i was cruising to 32 and accelerating great....but now its just like fighting to make it to 22. btw your bike looks sick :)
 
Greg58

Greg58

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Did you look in the cylinder when you had the pipe off? If not remove the plug or better yet remove the head drop the piston to the bottom of the stroke and look for damage, scratches or gauges.Don't worry about the small line made by the ring end gaps, those are smooth just bad or uneven surfaces.
 
Greg58

Greg58

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May 1, 2011
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I have a full shop at home, I have both mig and stick welders, torch set, hyd. press, metal chop saw, grinders and about any other tool that I thought I might need over the past 30 years!
 
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xnicklopezx

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Jul 6, 2011
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wow thats pretty convenient lol. but no i havent taken off the head at all...im scared haha, but i gotta go somewhere for now...ill check it when i get home, i cant start messing with it now ill end up staying up all night with it >.<, ill also look inside the cylinder? u saying like look up where the exhaust hooks up to? lol, im really new to motors in general, trying to learn more and more. the head needs a little cleaning anyways from when the exhaust was off and it spattered on it....but ill let you know tonight! thanks for quick response. btw what happens if there is damage? lol
 
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xnicklopezx

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Jul 6, 2011
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havent pulled it apart yet...but just a few updates...ive been messing with the needle in the carb...its weird the once i go to 2nd to top and top notch (being lean) the engine doesnt really do anything from 1/2 throttle-full just makes more noise...im guessing that means too much air? and when in middle notch its hard to get it to idle the idle screw has to be like all the way in, is this abnormal? and anything more rich than the middle its extremely hard to get it to idle...i have to give it some throttle...the top speed is staying around 22 on a good day...is it possible thats just what it is? maybe has to break in more? bike has like 130mi on it, still running 24:1...gonna start leaning off that this coming tank, probably go to 32:1, sound good? thanks guys
 
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xnicklopezx

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Jul 6, 2011
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oh btw figured out what the noise was, it was a screw that was off inside the engine, the part where their logo is, in that box where those 2 gears are, noise is all gone now, and engine sounds pretty good...just doesnt go as well as before the muffler :\
 
Greg58

Greg58

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May 1, 2011
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As long as you can get it to idle with the screw it does not matter if its all the way in as long as it works, since the nt does not have an idle air mixture screw like the cns I would set the e-clip where you get the best performance and wait till you decide which oil and ratio you want to run. Some guys run 32/1 , I run 40/1 with lucas semi syn. oil. Some run opti2 at 72/1 or even 100/1. Leaning out the fuel ratio made a big diff. in my bike.
 
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xnicklopezx

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Jul 6, 2011
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United States
cool, well this tank is about spent...im gonna start running lucas at around 40-50/1 as it says on the bottle of it, also might try out opti2 once i try out lucas at 40/1, when you say it made a big difference you mean in speed? sound? reliability? lol thanks for the input man, its much appreciated
 
Greg58

Greg58

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May 1, 2011
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The leaner oil ratio will help overall, idle mid range and wot. I found the oil I liked and tuned my engine to it, get yours broke in good and you may have to make some adjustments. Be sure to do a plug check to see how rich or lean you are. I pulled the head off of mine at 400 miles to check for wear, my results with the lucas at 40/1 were great I did not have any wear.
 
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