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Post by motorhead on Nov 7, 2011 11:10:16 GMT -5
I have this 139QB that I just installed a crank and a 70cc BBK on. Problem is it only starts with kick start or jump start from a car. A scooter battery cannot make the starter spin the drive face fast enough. All grounds are connected, the scoot battery is new and charged and reads 13v, and the starter is new, relay is new. Even if i connect the fully charged scooter battery directly to the starter motor and bypass the entire system, cranking is still slow and still hangs up on the compression stroke. The problem here is not electrical. Can the compression be too high? Even when it is kick started sometimes the kick start lever pushes my leg back. Compression too high or is a moving part pinched somewhere? Has this happened to any of you.
BTW, big news coming soon for the QMB metropolitanization thread...
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Post by jmkjr72 on Nov 7, 2011 12:38:36 GMT -5
yes if you are running a higher compresion motor it will be harder to turn over
are you using a factory replacement battery or ove with more cranking amps
for my zuma i found a battery that has 2 times the cold cranking amps and ran a heavier wire for the starter so i could use my e start after going bbk
i could take the battery out of my explorer and it wouldnt even think about turning my firebird engine over fast enough to start yet pull out the 1000 cca big rig battery and the bird comes to life
but also something could be binding or the valves ot opening at the right times that could cause this also
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Post by 90GTVert on Nov 7, 2011 13:00:54 GMT -5
I have seen with my 2Ts that all starters aren't created equal. Some are definitely higher output. If it cranked fine as a 50, a 70-80cc kit alone shouldn't be enough to make it not even want to crank over unless the compression is crazy. If it's that high, it's probably gonna spark knock anyway. A compression test would tell you a lot there. My biggest worry would be piston and valve contact.
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Post by ososlow on Nov 7, 2011 13:42:13 GMT -5
have you tried putting some grease in the bushing on the inside of the cvt cover
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Post by motorhead on Nov 8, 2011 19:44:42 GMT -5
I only installed a 70cc kit in the thing. The compression reads 125psi when i kickstart it. I need to post a video for you guys to better understand what's going on. When i hit the starter button the bendix flies out and starts to spin up but on the compression stroke it stops dead. I've even tried car batteries. I thought the ring gap was too narrow so i opened the gap and still, i have this problem.
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Post by stepthrutuner on Nov 8, 2011 22:18:49 GMT -5
One suspect would be improper meshing (alignment or spacing too close). This can make a big difference in the force required to turn the big gear. After shortening my drive boss in the variator my starter didn't want to turn the motor over as freely as it did before but it didn't take very long for the new meshing pattern to wear in and things were back to normal.
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Post by motorhead on Nov 9, 2011 15:36:23 GMT -5
I figured out the problem and as crazy as this is going to sound... It happened.
The cylinder had too much compression!!! I had a spare head laying around that i know had a bad seat for the exhaust valve and i swapped it and guess what! the valve leak brought the compression down to the point where the bike came on easily.
you learn something new everyday. And all this time we were looking for ways to increase compression but too much of it is a very bad thing. Needless to say, i am keeping this high compression head in a vault!
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Post by Fox on Nov 9, 2011 21:09:38 GMT -5
You can put two base gaskets on the cylinder to raise the entire top end a little to lower the compression with the high compression head if that other head gets too leaky.
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