running crap at low rpms, nice at high rpms

DanielMaia

DanielMaia

New Member
Hi there!

Have a very weird problem:

the engine runs like crap at low rpm. After 15mph, the engine starts to scream well, and go to higher speeds with no vibrations at all. Before i realized that have a piston contact on the cylinder head, so i had a head gasket, and it has 2x gaskets now.

Symptoms: No power, vibrates a LOT, very unregular sound. Past the 15mph, the engine wakes up..

At idle its revs really nice

What i tried:
- new spark plug -->the same

Spark plug is gapped at 0.9mm

Can be the CDI?
 
What sprocket are you running on the back wheel?
Also .9 mm millimeters work out to be about .035 inches
That's a little bit to wide..
Try .025 inches or .6mm see how that works for you.
I'm thinking you're geared so that at 15 mph that you haven't started making power yet.
Just a shot...
TiM
 
Standart 44t sprocket

No, because before even at low rpm, i WOT, and she start the rev like crazy, thats the fact!

Now i push WOT, and she starts failing, lots of vibration, revs a little, after 15mph she stars rev very nice, just dont understand...
 
What is the oil ratio? I am assuming this is a 2 stroke? Do you have the choke open or closed? Will it run with the choke all the way closed if so you have an air leak. Just some ideas to kick around. Also I'm not sure the quality of fuel in your country some countries have lower standards than the USA I know Mexico is one I am familiar with. Does it run any better after it warms up?

I like to run like 40:1 the less oil the easier to fire. I use Lucas.
 
Yes, it is a 66cc 2 stroke china girl. Yes, choked on first start, past 30 or 40sec, choke of to run normally.

This just happened after i stripped out a 8mm stud. Replaced the crankcase, new gaskets.

My oil ratio is 5%, never used less, and before this the engine starts on first turn. It has 2600km on it
 
5% is like 20:1 I'd thin that down to half it'll start easier...spray some choke cleaner close to the intake / head gasket and if you hear a difference you have an air leak.
 
But, at high rpms it works nice, the first 2000RPM it vibrates, 4 strokes, no power...past 15mph it runs nice.

Before this happened it revs like a champ, even at low speeds like 10km/h. at 11 or 12km/h, if i pushed WOT, it starts revving like crazy, now its crappy, dont know,

i will test it, thanks!
 
Is there a possibility that when you put the magnet back on(left side front cover) that the woodruff key came out of the slot and the magnet has turned on the shaft just a little bit?
That would throw your ignition timing off .

I know from experience that the woodruff key wants to jump off the crankshaft while you're putting it on and stick to the back side of the magnet rotor.

It won't hurt to pull the cover off and check to see if it's on right.

Just another passing thought...
TiM
 
Yes, thats a possibility, but i checked few times, at piston top position, it was in right place, even so, i will check today ;)

thanks!
 
There's always the chance of a bum carb. I had one yesterday on a build. I totally took the carb apart and couldn't find anything obvious and even added a new main jet with no luck. A replacement carb did the trick and fixed my low end problem. I still don't know what was wrong with the carb, it didn't work on another engine either and its going into the trash as soon as I strip some parts from it.
 
Hey, please, someone shoot me in the head..

I just figured out the ****ty problem..

Dear...facepalm on me.

"suspense mode on", bet your guess
 
I mounted the magneto (the little magneto that spins at the crankshaft) in reverse, the timming is completly different.

The engine only starts with the CDI connected with ground to blue, and blue connected to the ground of magneto. It was 3 hours to find out this crap, omg.
 
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