80cc wont start... Seized?

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hoglyfe

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Aug 19, 2013
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My 80cc has done about 200km/120miles and have been running it on 20:1.

Motor slowly died on a short trip this morning, like the spark plug had fouled. Bike would start, but wouldn't run for more than about 20 seconds and had no pull.

Pulled the plug out and cleaned it, made sure carby was getting petrol and tried again... same result!

After a few more attempts, when I tried to start it, it didn't even kick over, like the piston was not moving? It just slows down to a quick stop when I release the clutch with no engine noise...

If I give the bike a jolt backward tho, the piston seems to move...

Issues with the clutch internals?

Please share some ideas with me
Cheers
Raf
 
Last edited:
Pablo

Pablo

Master Bike Builder & Forum Sponsor
Dec 28, 2007
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IMHE (and opinion), when a plug is really fouled sometimes cleaning the plug will not remedy the fouling. Only a new plug will suffice, and also eliminate an area of concern.

Do you have good strong compression? (with zero head leakage?)

Is your exhaust free flowing?

Is your fuel REALLY free flowing from the tank when the engine is RUNNING?
 
crassius

crassius

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Sep 30, 2012
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first, take out the spark plug and roll the bike with the clutch engaged - if the motor turns it isn't seized - if it isn't seized, then put the plug back in and try it again, if it doesn't turn, your clutch needs adjusting

BTW, 20:1 is a LOT of oil after the breakin period of about two tanks
 
KCvale

KCvale

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Feb 28, 2010
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crassius said:
BTW, 20:1 is a LOT of oil after the breakin period of about two tanks
Click to expand...
Ya, way too much oil for 120 miles of running.

If your bike was brought to me with those symptoms I would do the following in this order:

Drain your fuel.

Pull the plug and exhaust and pedal it up the street and back with clutch engaged to blow out whatever buildup you have in the crankcase out.

Blow your pipe out well with a compressor, it may be very clogged.

Gas back up fresh premium gas mixed 32:1 with synthetic 2-stroke oil.

As an option drop in an NGK BPR7HIX Iridium plug in which will make a difference on any of these 2-stroke motors and what goes in all my new builds but if not make sure your plug is clean and gaped right.

Fire it up and be happy ;-}
 
H

hoglyfe

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Aug 19, 2013
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So I pulled the plug and exhaust and gave it a peddle. put a fresh tank of 32:1 fully synthetic in, new spark plug and cleaned out exhaust system as well as unscrewing the drain screw at the bottom of the carby and let the old petrol out.

Bike started first go but didn't want to keep going, couldn't build up revs and it died within 20 seconds. Tried again and same thing but it lasted a shorter period.

Checked spark plug for a spark but I couldn't seem to notice one...

Could it be the stock CDI? I have heard that they are quite **** to say the least...
 
KCvale

KCvale

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Feb 28, 2010
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Tough call now blind, can you post some pics of the bike, your center cavity so we can see carb angle, gas line, wiring, etc?
 
crassius

crassius

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Sep 30, 2012
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if it was smoking a lot, you may have fuel in the bottom of your motor - take out the plug and peddle it a lot to blow it out

you may also want to check that your muffler isn't clogged
 
Kioshk

Kioshk

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Oct 21, 2012
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With the clutch engaged, roll the bike forward SLOWLY. If the wheel rolls/engine chugs, your compression's too low. As for the CDI: I've had one go bad on me, from what I understand; when they go bad, they go ALL bad. The fact that you can turn the engine over precludes a bad CDI. You MIGHT then have a bad connection in the ignition-system. I consider myself to be a pretty competent China Girl mechanic after a year's worth of experience, although just last week, I was semi-stumped with a bogging-issue at high-speed. Turned out that the connection between my CDI and my spark-plug wire was loose. I thought for sure it was foaming in my carb-bowl. Oh well...ride and learn. Do some research on ignition troubleshooting. Also, Crassius may be right; you have low-mileage, but your initial high-oil content may have fouled the mufler. I had that problem last-year and it drove me nuts since it took me so long to figure out. I ended up cutting open the muffler and removing the fouled-baffles: problem solved. You can quickly determine if this is your prob by taking the bie for a quick run WITHOUT the muffler attached, this won't harm the engine on a short trip, although your bike will sound like the Sopwith Camel and your neighbors will curse you. Good luck.
 
H

hoglyfe

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Aug 19, 2013
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compression is great, exhaust is baffle free and has great flow and petrol line is free flowing into carby. however, when I tried to check for a spark by holding attached plug against engine while rolling bike, I couldn't seem tolocate a spark. the bike has also never really blown any smoke either. I think all this is why I think I'm leaning toward the CDI.
 
maniac57

maniac57

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Oct 8, 2011
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Has the coil gotten wet? Even a little water in the cover can cause intermittent or no spark.
I've seen several bikes with water damaged coils that would run for a few seconds then cut out.
Drove me crazy until I learned to check for water signs.
 
H

hoglyfe

New Member
Aug 19, 2013
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Nah the coil is fine, never had the slightest bit of moisture in there.

I just got it started and it ran for maybe 20 seconds but I had to keep the revs up to it. I did this a couple of times until a kind of tight squeaking noise appeared. the queaking got a little worse over say 5 seconds then the motor shut off.

After this I wasn't able to start it again, same thing that happened the other day. the piston didn't seen to be moving and the bike would just come to an abrupt stop.

the squeaking noise is almost like so.ethingwas tightening up on itself and straining the engine, before it shut off..

This is doing my head in!!!!!

Who knows anything about the bottom end of the motor and the drive line etc...??
 
Kioshk

Kioshk

Active Member
Oct 21, 2012
1,152
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Connecticut
Squeaking might indicate blow-by on the head-gasket. Your compression will seem fine at startup, but at the higher pressures of combustion, mix/gasses can escape the head. Check the torque on your head-nuts. If this is the issue, you may need to lap the head.
 
CTripps

CTripps

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Aug 22, 2011
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I'd start by checking the head gasket. Fold/roll a bit of paper towel up and slide it across where the head and jug meet, check for gunk, and repeat. If it stays clean all the way around, that's not it..

Have you checked the rings?
 
H

hoglyfe

New Member
Aug 19, 2013
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Thanks heaps for all your input guys... been a tough one!
Ended up tearing the bottom end apart myself and turns out the big end bearings had blown to shreds!! Have now got two new HCH 6202 2RS C3 bearings and am about to start the reassembly process...
Anybody got any pointers or tips when reassembling, as this is my first time?? cheers
 

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