2 stroke mini bike startup&idle problems

[uhh-khakis]

Hi all,

I recently got a small mini bike with a 2 stroke weedeater engine. It's fairly small, only 43cc. Currently, i'm having issues with idle after a piston replacement. The bike will only start up when I open the throttle and manually pour fuel into the carb. It drives fine, i can gun it with no power issues, but when i slow down to a stop it stutters then dies, and I cannot start it with the rip cord until more gas is poured into the carb. I'll mention that the carb is brand new so it couldn't be that. The gasket they included with the cylinder kit did not properly fit the bolt holes for the block, but after I chiseled out the shape it seemed to seal fine. I can see a small buildup of residue however that looks like partially burnt gas/oil mixture leaking from the seal between the new cylinder head and the block.

I apologize for the paragraph, but I wanted to be as detailed as possible as I am at a complete loss. Any help will be appreciated!!

 

[Street Ryderz]

Hi all,

I recently got a small mini bike with a 2 stroke weedeater engine. It's fairly small, only 43cc. Currently, i'm having issues with idle after a piston replacement. The bike will only start up when I open the throttle and manually pour fuel into the carb. It drives fine, i can gun it with no power issues, but when i slow down to a stop it stutters then dies, and I cannot start it with the rip cord until more gas is poured into the carb. I'll mention that the carb is brand new so it couldn't be that. The gasket they included with the cylinder kit did not properly fit the bolt holes for the block, but after I chiseled out the shape it seemed to seal fine. I can see a small buildup of residue however that looks like partially burnt gas/oil mixture leaking from the seal between the new cylinder head and the block.

I apologize for the paragraph, but I wanted to be as detailed as possible as I am at a complete loss. Any help will be appreciated!!

You're going to want to readdress the gasket issue, there should be no leaks between cylinder and block/case or anywhere for that matter. if your ripping on a new cylinder and piston/rings without a proper brake in it possible there is damage done in there already.

 

[uhh-khakis]

You're going to want to readdress the gasket issue, there should be no leaks between cylinder and block/case or anywhere for that matter. if your ripping on a new cylinder and piston/rings without a proper brake in it possible there is damage done in there already.

I thought about taking a trip to auto zone to pick up some rubber sealant. Because this is a foreign and old bike, I doubt I will find the specific gasket so I figured it could work. I also did not check the spark plug, which seems to be very fouled with residue so I will be getting a new one as well and update tomorrow.

Another thing I didnt mention about the cylinder rebuild is that the bike ran and rode fine last week until it "popped" and died. After this, the bike would only run for a split second. I figured this was a piston ring which led me to buy the whole cylinder kit because the piston was very cruddy and obviously worn. This seemed to remedy the issue, but starting the bike is where I am lost. It idles *sometimes* without issues, but at kinda high rpm and its uneven. that could be due to the spark plug as well

 

[Chainlube]

I thought about taking a trip to auto zone to pick up some rubber sealant. Because this is a foreign and old bike, I doubt I will find the specific gasket so I figured it could work. I also did not check the spark plug, which seems to be very fouled with residue so I will be getting a new one as well and update tomorrow.

Another thing I didnt mention about the cylinder rebuild is that the bike ran and rode fine last week until it "popped" and died. After this, the bike would only run for a split second. I figured this was a piston ring which led me to buy the whole cylinder kit because the piston was very cruddy and obviously worn. This seemed to remedy the issue, but starting the bike is where I am lost. It idles *sometimes* without issues, but at kinda high rpm and its uneven. that could be due to the spark plug as well

Sounds like an air leak.

 

[uhh-khakis]

Sounds like an air leak.

Could this be an issue with the mixture screw on the carburetor? I figured it wouldn't need to be adjusted since the piston and cylinder are identical to the old ones. But now that I think about it, the ripcord does seem to be a bit easier to pull than i remember.

 

[Chainlube]

You can buy gasket material by the roll, get the Fel-Pro 1/16, it will make a lot of intake gaskets. Go on you tube and search making a gasket to learn how to tap one out with your small ball peen hammer.

 

[Chainlube]

I polished the ball on my little hammer just to make gaskets.

 

[Wrench]

Here ya go @uhh-khakis

Gasket Making 101

Howzit Everyone, $SAVE MONEY$ Gaskets made easy. Don't reach for the razor blade. Grab your 8oz alignment tool (ball peen hammer) and tap it out, Lightly tap gasket around the edges. As you tap out the bolt holes (or punch) put bolts in to help keep gasket aligned. The 1/32" rubber fiber sheet...

motoredbikes.com

 

[uhh-khakis]

So, it's been a bit since my original post, and I have gotten the bike running and riding, however I have a few updates;

1) I managed to find a replacement set for the gaskets, and they happened to be exactly what i needed for the cylinder. the head gasket fit like a glove, and now there is no more uneven idling or sputtering when decelerating.

2) The leaking was actually an exhaust leak, caused by the airbox not being properly secured to the cylinder. not exactly sure what they're called, but there's two long bolts with threads on either side, and one of the nuts was missing. i "borrowed" a small bag of nuts at lowes and fixed this. no more buildup as far as i can see.

3) the bike is still a pain in the ASS to start. i've got to pull the mixture screw out almost entirely to start it. Problem is, when i have that much gas going in the carb there is no power. probably maxes out at 8mph. when i screw it almost entirely in, counting my turns, it has a much higher top speed but has absolutely no acceleration and twisting the throttle too much will choke the engine with air causing it to die. i'm assuming there is some kind of happy medium that I'm not achieving with the carburetor.

So the intake screw seems to be the antagonist at this point. my local laws allow for bikes under 50 cc to travel on roadways, so i've been taking it out in the nice days. people blow by me giving me the finger but i can push 25mph on this little 2 stroke. i just smile and give the finger right back

 

[Street Ryderz]

So, it's been a bit since my original post, and I have gotten the bike running and riding, however I have a few updates;

1) I managed to find a replacement set for the gaskets, and they happened to be exactly what i needed for the cylinder. the head gasket fit like a glove, and now there is no more uneven idling or sputtering when decelerating.

2) The leaking was actually an exhaust leak, caused by the airbox not being properly secured to the cylinder. not exactly sure what they're called, but there's two long bolts with threads on either side, and one of the nuts was missing. i "borrowed" a small bag of nuts at lowes and fixed this. no more buildup as far as i can see.

3) the bike is still a pain in the ASS to start. i've got to pull the mixture screw out almost entirely to start it. Problem is, when i have that much gas going in the carb there is no power. probably maxes out at 8mph. when i screw it almost entirely in, counting my turns, it has a much higher top speed but has absolutely no acceleration and twisting the throttle too much will choke the engine with air causing it to die. i'm assuming there is some kind of happy medium that I'm not achieving with the carburetor.

So the intake screw seems to be the antagonist at this point. my local laws allow for bikes under 50 cc to travel on roadways, so i've been taking it out in the nice days. people blow by me giving me the finger but i can push 25mph on this little 2 stroke. i just smile and give the finger right back

It's best to post a pic of the carb, the mixture screw really only effects idle and just off idle and it's a good starting point at about 2 turns out from closed. After that it's the needle height and the jetting to tune it well, sounds like your having fun though and that's the best part!