Please help

[sawman84]

Hey guys and girls I need help.

Recently I had bought a chinese 80cc motor off Amazon, fought with it for a bit, but got it going.

It was good for a couple weeks then all of a sudden when I would throttle up it would slow down then nothing.

Couldn't get it started, I think it had a low rumble only when i peddle with clutch off.

I had already been debating buying 100cc so I figured might as well now lol. motor came in, I swapped the motor, the carb, from a nt, to hp, and left the rest the same.

So I jump on the bike coast down a hill on my street it fires up no issue with low rumble but seems to be the same issue I was having before the swap so I thought magneto so replaced the coil everything except magnet and still won't go please help im ready to throw in the white towel.

 

[Nickt919]

A lot to unpack in this post above....
If I understand correctly, you are currently running a new 100cc engine with an HP carb.

If this is correct my suggestion is put the stock NT carb on and go from there.

I have never tried one of those HP carbs, but I did help someone with an HP on a stock engine. We never did get it to work right. Ended up putting the NT carb on and the engine woke up and ran like it was supposed to.

Not many experienced builders run the HP. They seem to have an unfavorable opinion of the HP for the reason stated above.
The vendors list those carbs as a performance upgrade and the price is about 2 times the cost of an NT or Bofeng carb. It leads you to believe your engine should be better and faster.
In the end, it creates builder headaches instead.

 

[Chainlube]

Go take a look at your original engine and put a wrench on the head nuts and see if they are loose in any way.

Most new builders don't realize that the aluminum head will compress with each heat cycle and needs tightening after each ride until it gets broke in.

Don't ride it too hard at first, let come up to temp slowly. Pedal more and help it along, good for the cardio too. Before too long it will be all engine doing the work.

Take the float bowl off your carb and inspect the float, they can get/or come with a crack and sink.

 

[GW's Motorized]

I personally love my BoFeng carb and they are easy to tune.

If you ordered a 100cc engine and put a carb on it for an 80cc your jetting could be off. You should swap back to the original carb. This could also be caused by not letting your bike properly warm up

 

[Nickt919]

A good sticky check list of bullet point line items in 2 stroke engines would help a lot of people starting out in the beginning. Even for builders who have been at it for a while.... it's easy to get consumed with trouble shooting and not go about it in a logical fashion when things go wrong.
A way to go check...check, check.... eliminating points of possible failure.

From correct fuel/oil mix.... to magnet/magneto inspection, all air leak points/proper sealing, carb float, spark plug, ect.
All the things that must be right for the engine to perform well.
The engines we use are basic and quite simple but..., if you do not know where to start or what to look for it can be frustrating and overwhelming to set up and trouble shoot.

The best advice many gave me was "Only one change at a time." If you make multiple changes each time you try something, you'll be all over the place and never know how each of any change affects your work.