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Post by dukester1351 on Jul 9, 2011 21:58:51 GMT -5
so i just installed a malossi 70cc bbk on my 200 kymco cobra racer. also put in a malossi variator upgrade (stiffer spring, new rollers, etc.) got everything back together and turned it over, no problem. got it to idle for a bit, rode it down the street and back (under 6K, as the bbk said to do for break in). all of a sudden, it didn't want to idle anymore, and chocked out. When i went to start it again, it felt like it was having too hard of a time turning over. i thought weak battery, but even after charging the battery it's still only slowly turning over, like there's a bunch of resistance somewhere. It will not run, and i'm scared to try the kick start for fear of doing anymore damage if damage is what is already done.
any ideas?
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Post by 2strokd on Jul 9, 2011 22:07:41 GMT -5
If there is resistance i would pull it back apart and check everything out carefully. Pull the cvt cover first and make sure nothing is bound in the CVT.?
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theo547
Scoot Enthusiast
Posts: 497
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Post by theo547 on Jul 10, 2011 18:18:44 GMT -5
Check the vacuum on the petcock ... On most that's the upper hose.
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Post by dukester1351 on Jul 11, 2011 17:55:16 GMT -5
alright, here's the update: pulled everything apart, cleaned it up. no marks on the cylinder or signs of major damage to the kit.  then pulled apart the cvt while i was at it and made sure there wasn't any unwanted binding on the belt. everything good there. Then, for poops and giggles i pulled the cover off the fan on the other side of the crank case and found the nut holding the flywheel under the fan had found it's way off!  anyway, i put everything back together, and it now turns over without hesitation. but it won't start! Checked for spark, had spark. bought a new plug in case it was a weak spark, gapped it to the recommended .6 to .7mm, and still won't start. went to work and the guys suggested to check for compression. bought a gauge, and pulled 105psi. my next question to those who have the knowledge.. what psi am i supposed to be pulling, and if that's the right psi, where did i go wrong, and what should be my next move? PS: here's what i'm on my way out to check right now: bad gas? (it was only 3 weeks old, and the engine ran fine on it before, i think) i might have incorrectly set the flywheel under the cooling fan when the nut came off. I'll repost if i find out anything... btw thanx for the help guys, i really appreciate it! |
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Post by dukester1351 on Jul 11, 2011 19:00:33 GMT -5
:thumb: the good news is i figured it out. The key on on the flywheel that times the spark was sheared out :stumped: don't know how, but i'm gonna make a new key @ work tomorrow and update then. I'm pretty sure that was the issue, cause i tried locking the flywheel after lining it up with just the zip nut and it ran for a good 5 seconds before choking out. guessing the spark went off timing again.
;D
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Post by 90GTVert on Jul 12, 2011 6:55:18 GMT -5
Nice find. Hope that's all it was.
105psi sounds a little low, but it should be able to start OK with that much compression. The manual says 198psi, which is what I used to tell people before I built a bunch of these things. That's way too high most of the time. Only time compression that high is gonna work is either on race fuel or with very aggressive porting. I'm not really sure what the ideal compression is for the 49cc, but I'd think 120 or so would be great for a stocker that probably has the squish set wide. Other members here routinely report similar or just slightly higher compression than you have. At any rate 105 is high enough that I don't believe it's causing starting problems. You probably already know this, but make sure you hold the throttle wide open. I also find that kick starting will usually show higher readings.
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Post by 2strokd on Jul 12, 2011 10:39:59 GMT -5
Glad your getting it sorted out.
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Post by dukester1351 on Jul 12, 2011 18:07:55 GMT -5
Thanks! Just took it out for a run, got it up to 48mph w/o tuning it much, just tried to get away from the white smoke (shows how much i know about tuning) but then had a weird experience... kinda felt like the engine wanted to tighten up and seize, taking me from 48mpg to 0 in about 4 seconds. Pulled off, started back up, took off again. Got it back up to 8K and then it did it again. This time I started it mid "slowing down/choking out" period. The next time it did that, (40 seconds later) it wouldn't start for about 3 minutes.
Let it chill out, and took it easy getting home, not going over 6K, and it didn't seize again. Suggestions?
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Post by 90GTVert on Jul 12, 2011 19:21:59 GMT -5
Try a larger main jet. That sounds like soft seizing.
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then pulled apart the cvt while i was at it and made sure there wasn't any unwanted binding on the belt. everything good there. Then, for poops and giggles i pulled the cover off the fan on the other side of the crank case and found the nut holding the flywheel under the fan had found it's way off! 
