HELP! bike runs good then slows down.

[mailloux736]

Hey everyone, so i built my bike maybe 3 months ago and have been having a lot of fun but u have a strange issue. i can get my bike to cruse comfortably around 30 - 35 kph ( so around 18 - 22 ) but every once and a while my bike will hit its "sweet spot" and accelerate really smoothly to close to 40kph but shortly after bogs down to its old ways and goes around 30ish. now according to my parents this is fast enough... but not for me,i want to go faster and maybe be able to cruise at this speed but im not sure what's happening or how to make it run that smooth consistently.

some things ive done to the bike {

new head ghasket (blew the other one when i didnt tighten the head bolts down enough... oops)

new cdi and magneto coil (came dead out of box)
}

so thats about it for things ive changed. i havent really played with the carb yet but maybe thats worth a shot. another thing ive been noticing is when i rev the bike it takes a while for the rps to go down.

ive been running 20:1 for my first 3 tanks (i just learned it should be higher even during break in but my next tank will be 36:1) and the bike seems pretty broken in

 

[Chainlube]

Sounds like an air leak, possibly around the intake to head or carb to intake. Get a spray bottle of water and mist around those two connections with the engine running, if the engine dies, you have a leak.

 

[ImpulseRocket]

Yeah, usually random surging in power is never a good thing. As Chainlube said, try and find any potential air leaks. Generally with 2 strokes if they suddenly start to pick up extra power, it's due to leaning out on the fuel mixture. While this may seem like a good thing, it often results in something bad happening, like a soft seizure, due to the increased heat from running leaner. A less common cause for lean surges like that can be the float in the carburetor getting hung up momentarily which causes the fuel level in the bowl to drop low enough to make it lean out. Then it unsticks and goes back to normal. Just something to keep in mind.

As far as your break-in ratio. 20:1 is just fine. Don't sweat it. There are people that never even run a break in ratio, and just run it at the normal mix the whole time. I don't personally suggest this, but to each their own.

 

[DAMIEN1307]

As far as your break-in ratio. 20:1 is just fine. Don't sweat it. There are people that never even run a break in ratio, and just run it at the normal mix the whole time. I don't personally suggest this, but to each their own.

True enough that...I have always done a break in with Valvoline regular conventional 2 stroke "dino" oil at 20:1 for at least two tank fulls and then go Amsoil Dominator full synthetic 2 stroke racing oil thereafter at 32:1...I have never had to dis-assemble any of my motors for any repairs...One motor is a cheap Seeutec motor that I put 6000 miles on over a five year period before the Huffy beach Cruiser frame snapped on me...The motor was still running strong when I put it up on a shelf if ever needed again.

The Zeda 80 triple 40 that I am presently running has 1300 miles on it over two years now and is running super strong right now as well.

 

[mailloux736]

ok, i will try chainlubes recommendation when i get home. i need to play around with the carb as well and make it leaner but i don’t think that’s a majour part of the problem. i will keep you updated for what happens