Old 80cc bike no acceleration or pull.

[Deleted member 29767]

Hiya, I'm pretty new to motorized bikes. I just recently bought one used for a great deal, and was having fun with it for a while. When I first got it going, it didn't have much acceleration but it kept speed and was very fun. Occasionally at higher speeds it would have some spurts of acceleration. However I took it out a second time, and it can't even keep speed. I warmed it up and everything.

Some notes:

• The fuel filter was backwards when I got it. I've corrected that.
• Fuel leaks out of the air intake when the bike is off, as long as the tank valve is open.
• The bike has been broken in a long time ago.
• When I mixed the gas, I put in exactly one gallon of gas into a gas tank along with 6.4 fl oz of oil, should be 20:1 ratio. It is kinda cheap oil, dollar general brand.
• The carb is angled diagonally.

Any ideas? A different brand of oil? The person who had it before me seemed to ride it fine with that oil.

I can perform additional diagnostics as needed.

 

[Mcdonns]

One thing’s for sure.., your float isn’t closing the needle. There should never be fuel creepin’ out th’ carb, valve off or not. It could be an over-tipped carb/bowl, not allowing the float to lift, but most of these can actually handle a good fifteen-degree or so (plus, or minus), still seat and close the needle. You may needa adjust the float tab, or even rebuild with a new needle/seat, but a $20 carb swap may be a quick fix, over the frustration of a rebuild and adjust. Your oil could have something to do with that (the “surging”, as well as the leak), if it sits for periods or has been. There are much bigger brains out there, maybe they have better solutions, but StaBil may clean some of that up over a few runs.

Unless you’re gonna race th’ thing or tryda run it fer 10k miles, oil quality and ratio are pretty simple, in the 2-stroke world. It’s an overgrown weed-eater, generally. Mix can absolutely impact performance, but it’s a fairly forgiving range — just don’t mix so heavy you start lookin’ like a mosquito sprayer, or so lean you start spittin’ ‘luminum at th’ dirt. Your 20:1 is maybe a little oil-heavy, for something well broken-in, but by no means harmful — you pro’ly jus’ git a few more drips out th’ exhaust than ye’d wish.

Maybe a pic of th’ angle of th’ bowl, while it’s on level ground?

 

[Deleted member 29767]

Spoiler: Carb placement

As requested.

Based off the picture, do you think I have room for a performance carb? Which carb would you recommend?

What ratio should I be using?

 

[Mcdonns]

You’d be amazed, how common that problem is, but how simple it also is to fix. You’re not alone! The pic below shows an available black intake offset, but you can get ‘em in chrome, and from a few different suppliers. Mine (also shown) is a pretty tight fit too, being a small-core large-tube Mongoose Excursion ($148 WallyWorld special). You definitely have a LOT of engine tilt, attempting to get the carb and air-cleaner inside the core. Use the offset, reposition the engine more to level, and you’ll pro’ly solve most of your float and “surge” problems right away, without a carb change or rebuild.

The oil question (again, there may be folks out there, with better thoughts and a good deal of experience to back it up), I’d think you could run closer to 30:1, especially if you’re noticing a heavy drip or blue-smoke exhaust at your current 20:1.

 

[Mcdonns]

Also, I don’t know how much any “performance” carb would really get you, unless you’re gonna try to start racing. The one I have, I chose for the better gate valve, spring/auto-release choke, nothing more.

 

[Spare_Parts]

If that's how the fuel filter is installed now it is backwards lol.

 

[Mcdonns]

Spare_Parts is right -/ the magnet should be on the pre-filter (inlet) side, for the big stuff.

 

[Deleted member 29767]

Whoops! I'll be sure to reverse it. I was told to point the arrow towards the carb, but I guess I misread.

I read the perf carbs have a lot more to them than just performance, like the auto release choke and whatnot, but they're also supposedly better built as well.

So I can move the motor so it's at a different angle? How?

 

[Mcdonns]

Take a wider-view pic, from either side. Let’s see what the core real-estate offers. You’ll have some work to do on the mounts, but there’s a lot of meat on ‘em. Start with a pic.

 

[JerboaJohn]

just a side note, after break in, you can go to 32:1 (4oz to 1 gal). that'll help power.
another way to adjust angle is shim the front /rear mount with innertube or anything stiffer and turn the motor this or that way a bit then adjust the chain again.