2 Stroke bike doesn't start when cold, feels like air is coming out from head?

Algebruhm8

New Member
May 3, 2021
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Hello everyone this is my first post on this forum and my second day riding my 2 stroke cruiser bike and like a lot of beginners, I have a lot of questions

So yesterday I ran my motorized bike on and off throughout the day and around the 3rd time running it, it felt perfect and smooth. But after that, some problems started to occur. For one after I try to start it when it's cooled off for an hour or two, I feel some sort of air pushing on my leg and it won't start at all. I feel this little "pocket" of air near the head when it tries to start. Also noticed one of the bolts on the head is loose and if I try to tighten it, it just becomes loose again and it's an endless cycle. And another related problem is when pushing in the clutch, it seems to rev high which makes it difficult to idle when coming to a stop sign, an air leak maybe? This is probably a good time to mention that we forgot to screw in one of the exhaust screws all the way in from the engine so a little bit of air does come out of there but even with a loose exhaust, everything was running fine, and the clutch worked like a charm. Just worried since this is my first time building an engine kit, some of these problems will be long lasting which I wouldn't want to use this long term. (I do have all stock parts that came with my kit so is there a chance this air leak from the head can be fixed by putting on the original head?)

Link to the engine kit I bought from Bikeberry
A photo from where I feel the air is pushing on my leg
 

wrench

Active Member
Aug 20, 2019
254
185
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So Cal
Hello everyone this is my first post on this forum and my second day riding my 2 stroke cruiser bike and like a lot of beginners, I have a lot of questions

So yesterday I ran my motorized bike on and off throughout the day and around the 3rd time running it, it felt perfect and smooth. But after that, some problems started to occur. For one after I try to start it when it's cooled off for an hour or two, I feel some sort of air pushing on my leg and it won't start at all. I feel this little "pocket" of air near the head when it tries to start. Also noticed one of the bolts on the head is loose and if I try to tighten it, it just becomes loose again and it's an endless cycle. And another related problem is when pushing in the clutch, it seems to rev high which makes it difficult to idle when coming to a stop sign, an air leak maybe? This is probably a good time to mention that we forgot to screw in one of the exhaust screws all the way in from the engine so a little bit of air does come out of there but even with a loose exhaust, everything was running fine, and the clutch worked like a charm. Just worried since this is my first time building an engine kit, some of these problems will be long lasting which I wouldn't want to use this long term. (I do have all stock parts that came with my kit so is there a chance this air leak from the head can be fixed by putting on the original head?)

Link to the engine kit I bought from Bikeberry
A photo from where I feel the air is pushing on my leg
.
Leaking head and a stud bolt keeps coming loose?
High revs is because ya probably got a case or intake manifold air leak
Leaking head, it sounds like the case threads are striped where the stud screws into the case
If it is your gonna have to use a Helicoil to fix that - $30 for a Helicoil kit

Also change the acorn nuts to regular nuts They can run out of threads, bottoming out causing the stud to strip out the case threads from overtightening.

Put a muffler strap to frame to help keep your muffler from wiggling The wiggling muffler is probably why the exhaust manifold nut comes loose.
 

Algebruhm8

New Member
May 3, 2021
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Thanks and will do for the muffler strap! I fixed up the head by putting the stock one instead and I'll take your advice or regular nuts when I go to the hardware store tomorrow. Another question I know seems obvious but, is it normal for the engine to be.. kind of slow in terms of speed? I am during the break-in period running a 16:1 ratio and it seems I top out at 24MPH just barely hitting 25MPH as I don't want to run the engine at full throttle for a long period of time. I know the engine isn't at its full potential yet but any advice is highly appreciated.
 

wrench

Active Member
Aug 20, 2019
254
185
43
So Cal
If changing the head worked The other one probably needs to be resurfaced.
Or it will work after changing to regular nuts.

There are different opinions about break in
But 16:1 for the first gal then 32:1 after that is fine
But some go 20:1 then 40:1

After ya break it in it should pick up in speed
 

Greg58

Well-Known Member
May 1, 2011
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Newnan,Georgia U.S.A.
Good advice, it is a good investment to get a torque wrench, it's easy to get the head nuts tightened uneven resulting with striped studs or warped head. Torque 8mm studs/nuts to 12-14 foot pounds , don't over tighten. Harbor freight has entry level torque wrenches that work well and won't break the bank.
 

wrench

Active Member
Aug 20, 2019
254
185
43
So Cal
When re torquing head bolts never do it when the engine is hot or warm It will stretch and pull the threads.

Always tighten the head bolts when the engine is cold.
If your in a hurry when the engine is hot. Put a fan in front of the engine and it will cool off in under 10 mins
 

Algebruhm8

New Member
May 3, 2021
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4
3
18
There are different opinions about break in
But 16:1 for the first gal then 32:1 after that is fine
But some go 20:1 then 40:1

After ya break it in it should pick up in speed
Hmm I'll use 32:1 after my gas container finishes from the 16:1. Since I didn't have a measuring cup at the time I think I overdid it with the 8 oz of oil so that can be another reason for the slow performance.