My personal 80cc 2 stroke nightmare :"")

ilovesalami

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11:36 AM
Joined
May 4, 2024
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Location
Hillsboro Oregon
Hello.. I am not sure if people will actually read this but I am at my whit's end and am begging for help.

Just to clarify, I am 17 and this was my first time physically working with an engine, though I have been interested in cars, engines, mechanics, etc for a long time so I do at least have some idea of what I'm doing.

Also, apologies if this is long but I want to cover all the bases just in case it helps with giving any of you a clue to what could be wrong.

The reason I am so lost here is because this is as basic as engines can really get, and EVERYTHING seems to be working but the engine refuses to start... I have had this kit for roughly 1 and a half years and it ran fine for a while until it died on me. It would not start, no matter what I did, and eventually I decided to take apart the cylinder and discovered that the rings had imploded and destroyed the cylinder along with its housing. I would come to learn that engines need oil.... (such a stupid mistake...) I learned my lesson and ordered exact replacements. After I installed them the bike just wont start.. this was about a year ago...
In that time I have I have disassembled and reassembled this engine countless times. I have bought new carbs, cleaned old carbs, bought new spark plugs, new cdi's, all of it. But it just. Wont. Start.

Here is what I know.

1. I know the spark plug and magneto are good. I have run the magneto manually with a drill and held the spark plug against the wall of the cylinder. I can physically see a spark, and the spark does not seem to be weak.
2. The fuel is not old. I had heard that gasoline could "go bad" after a month or two so I decided to get new gasoline hoping that it would at least help.
(87 Octane unleaded gasoline)
Important to note that I am currently not mixing my oil and fuel and am running it as rich as possible to try to get it to start/idle. I did apply 2 stroke oil along the walls of the cylinder when I installed it, and if I can get this thing to start I will obviously be mixing the correct ratio for actual use.

3. Starter fluid is having literally no effect at all.

4. Gasoline IS making its way through the carb, and every time I attempt to start it there will be unburnt fuel dripping out of the exhaust.

5. The seals are all fine and the suction/ pressure feels no different than it did when it was running previously.

6. When I attempt to run with it and start it, there will be literally zero combustion at all unless I click the kill switch on and off as fast as I can while holding the throttle open. When I do there will be the occasional single complete cycle or maybe 2 or 3 in a row with a little jolt forward but nothing past that point. It will not idle or even come close it is completely dead.

7. The choke is not having a noticeable effect, though there is occasional backfire out the exhaust after I use it.

The final important detail is that I am attempting to start this thing without riding the bike/ pedaling. I don't have a high budget so I bought a used bike frame and built the bike with used parts and never got around to figuring out where to get a crank chain and pedals because the engine used to start if I just ran fast, gave it full throttle, and dumped the clutch.


So.. this is what I have been thinking..

1. Could my cdi be bad? Could the spark be fired at just slightly the wrong time? I had bought this cdi new from Bikeberry so I assumed it was working but maybe not!

2. Could the speed I am attempting to start at be to slow? Do I need to attempt to start at higher speeds? ( Is full speed running 8 to 9ish mph?)



To be completely honest I'm about to just throw this thing away. My passion for this motor that hates me has been squeezed dry after a year of refusing to start and posting here is my last resort. I truly would appreciate ANY help. Thank You.
 
1) Never even try to run without the proper oil mix, no matter what (break-in 20:1 ish)

2) Yes since your cyl/housing is 'new' your back to the break-in period. If you've been running just pure gas this whole time you've likely destroyed it. Doesnt matter if you put oil on the parts during assembly.

I remember my first engine during break-in may take at least 50/75feet of pedalling to start. Ya got no pedals/chain/etc thats a problem. Every single one of these engines are different. After 700 miles or so now on my engine it fires up pretty quickly but the first 100 or so it took awhile to fire up.

3) You dont say anything about spark plugs. Get a good NGK and throw the stock chinese one into a river.

4) IF YOUVE BEEN RUNNING (TRYING TO RUN IT) WITHOUT OIL its already toast.

5) Head nuts - make sure they are torqued to 12 ftlb
 
The crank bearing is liable to be toast. But if it spins freely it may run a little longer. I wouldn't put much trust in it unless I did a full rebuild top to bottom(like split the crank, full)

You have spark, properly torque the head and you ought to have compression. Only variable left is fuel. It sounds like you have way too much.
 
Unfortunately, running without oil has probably toasted your crank seals. Even though you went through the rest of the top end, with bad crank seals it will be very difficult to start. It's kinda like trying to pump water with a hole in the side of the pump.

Here's a replacement for it, if you can scrape together the money. Offer him 50 for it, probably be 75 shipped.
 
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1) Never even try to run without the proper oil mix, no matter what (break-in 20:1 ish)

2) Yes since your cyl/housing is 'new' your back to the break-in period. If you've been running just pure gas this whole time you've likely destroyed it. Doesnt matter if you put oil on the parts during assembly.

I remember my first engine during break-in may take at least 50/75feet of pedalling to start. Ya got no pedals/chain/etc thats a problem. Every single one of these engines are different. After 700 miles or so now on my engine it fires up pretty quickly but the first 100 or so it took awhile to fire up.

3) You dont say anything about spark plugs. Get a good NGK and throw the stock chinese one into a river.

4) IF YOUVE BEEN RUNNING (TRYING TO RUN IT) WITHOUT OIL its already toast.

5) Head nuts - make sure they are torqued to 12 ftlb
I see. I have been taking the engine apart every other time I have tried to start making sure the cylinder was not being damaged, and it still looks brand new.. I think it should be ok right? I will absolutely be mixing the correct ratio from here on out. I will walk down to the bike shop later today and get a start on finishing the bike I did manage to find a bike chain in my parts bin :). Thank you so much for your help it means a LOT!!!
 
Unfortunately, running without oil has probably toasted your crank seals. Even though you went through the rest of the top end, with bad crank seals it will be very difficult to start. It's kinda like trying to pump water with a hole in the side of the pump.

Here's a replacement for it, if you can scrape together the money. Offer him 50 for it, probably be 75 shipped.
Thank you so so much. I will take it apart and give it a look when I get home!!
 
Links to eBay may include affiliate code. If you click on an eBay link and make a purchase, this forum may earn a small commission.
The crank bearing is liable to be toast. But if it spins freely it may run a little longer. I wouldn't put much trust in it unless I did a full rebuild top to bottom(like split the crank, full)

You have spark, properly torque the head and you ought to have compression. Only variable left is fuel. It sounds like you have way too much.
I will be mixing the correct ratio from here on out. Thank you so much for helping me!
 
I'm sure you have heard this many times by now but the most important thing with these motors is the correct fuel /oil mix. You are not the first to make this error. Don't be discouraged, Carry on, stiff upper lip and all that.
 
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