Please help

[Jcarr]

The motor is a pk 80. Ok so I really need to get this fixed due to this being my only source of transportation. Problem I'm having is motor runs fine at idle and low rpm but as soon as I give it a lot of throttle it just kind of stays at the same speed and seems like it's being limited. I put a new cdi and magneto coil in last week and everything ran great. It doesn't even seem like it wants to go faster. I've tried 3 ngk b6hs plugs. I've moved the clip one notch in either direction. I drilled holes in the baffle and I made sure the air filter was clean but still no change, almost seems to be getting slower top speed. I double checked my electrical connections. Im about 3 1/2 full tanks of gas through the motor now. Do you think it's time to change my oil/gas mixture? I'm stumped someone please help

 

[Deleted member 12676]

without details how are we to help you?
If you say that 27mph is the max then we will laugh and say that is normal.
If you say that 20mph is the max then we'll know you have a problem.
What is your elevation?
Does it "waahhh" when you open the throttle or sputter or run rough?
what size tire do you have?
what size rear sprocket?
Does it run faster with the throttle half way engaged?
Have you checked the float height inside the float bowl?
Have you planed the head and cylinder top to make sure they are flat and therefore getting a moderately good seal (since compression loss causes power loss)? (click my link to read more)
Have you blown through the air filter to see if it feels restrictive to air flow?

 

[Fabian]

The throttle slide needle has no virtually effect from around 1/2 throttle to wide open throttle.

I would be looking at the fuel filter and then looking to see if you have proper fuel flow through the rest of the carburettor and when assembling the carburettor on the intake pipe, make sure to use an o-ring that sits against the lip inside the carburettor bore, where the carburettor will then sit against the face of the intake pipe.

 

[Jcarr]

I'm averaging a max of about 15 mph right now. It was originally maxing at about 30 mph. So huge power loss. Elevation is nt much at all in Pennsylvania. I'd say 500-1000 ft above sea level. It more or less runs rough, not really sure how to describe, the rpms just don't go up after a certain point. 29inch tire with the original sprocket that came with my kit, I believe it's a 44 tooth. It runs great up to 15 mph and just dosent want to go any faster. I pulled the carb apart and cleaned it well everything seems to be in order in there. As far as planing the head no I haven't done that', like I said it was running fine until 2 days ago. Everything is torqued to spec. Air flow is good, I'm really at a loss right now on what to do next.

 

[Fabian]

It took me 2 years to get my bike to run reliably, and it was a painful experience getting it to give me the kind of reliability i demanded.

These engines (although they look simple) are a test of your perseverance and mental toughness, for they just keep throwing problems at you.
Having said that, i have gone through the pain and my bike is now a pillar of reliability, but it has cost me two relationships and a lot of money.

 

[Jcarr]

I'm very familiar with 2stroke motors, I grew up with blasters, banshees, and more dirtbikes than I can count. That being said I don't think I've ever been soo frustrated working on one. I forgot one detail... Seat post motor mount snapped the bolts, could that be the verdict? I just now replaced the studs and have it secure once again. A wee bit late for a test ride though

 

[Jcarr]

I have a no ring on and carb is snug. I have proper fuel flow to the carb, how do I check the carb to see if fuel is flowing properly in it? Again this is why I'm so confused about the problem,

 

[crassius]

a loose motor mount could do that - otherwise a speed drop like yours usually means the cases are not tight enough to seal or your crank seals are blown out

 

[dougsr.874]

What carb do you have??? If its a CNS, then throw it away and put on the standard NT.....they're not fancy but they work...

 

[Jcarr]

I'm pretty sure it's an nt. it's marked speed on the side