Idle is a mess, but runs like a jet

DanielMaia

DanielMaia

New Member
Hi guys,

have a lttle problem on a 66cc engine, all stock, with 250 miles on it.

The idle, with engine cold, is near the perfection. Very stable and smooth. As the engine gets hotter, the idle starts to increase, and i notice the engine a little "overheated". The engine runs like a jet, lot of acceleration, runs really very good, with no hesitation, lots of scream.

Things i did:

- change the carburetor (a new one)
- new cylinder base gasket
- new head cylinder gasket
- new intake gasket
- new spark plug
- new intake manifold

None of these worked on this engine, and i really dont know what should i do..
 
Start looking for an air leak in the induction system. The most likely place will be where the carburetor attaches to the intake manifold. The next will be the intake manifold gasket at the cylinder. What you are describing is the classic symptom of air entering where it's not supposed to.
Good luck. Let us know what you find.
Tom
 
It also could be leaking from a crank seal or the gasket where the crank case halves meet.

Here's one of the most definitive and not too hard to do ways to check everywhere possible for an air leak:
Leak Down Test For 2-Stroke Engines.avi - YouTube

Here's another one:
Pressure Testing a Minarelli Horizontal 2-Stroke Scooter Engine - YouTube

If there is a leak you WILL find it by pressure testing. No guessing, no cursing, no what if's.
Well, you might curse if it is the center gasket at fault.......
 
DanielMaia said:
but i instaled a new intake manifold and a new gasket, with no success..

maybe a new crank seal!
Click to expand...

Remove the left side cover to expose the magneto. It should be dry in there. Any oil residue can be an indication of a crankshaft seal gone bad.
The right side seal is behind the small primary gear. That side can be messy do to gear lube and clutch pad wear but it shouldn't be oily.

Typically I've found the magneto side to be the most common in terms of seal failure. It's usually due to the seal not being pressed deep enough into the case and the magnet (rotor) rubs and damages it. If you find oil in that side get back to us; there are steps to take to replace the seals that we can pass on to you.
I understand that you replaced the intake gasket but did you also seal the carburetor to the intake?
Tom
 
Yes, tha would be no problem cause i installed lots of new seals on many engines, but in this engine i dont see any oil residue, left side or right side. Even so, i will install 2x new double lip 15x27x7 on the 2x sides, and see what happens!
 
Hi there guys!

Just instaled the 2x oil seals from the crankshaft, and its quite better, but i have 2x problems here:

Engine is all stock, i made a run, checked the spark plug and its white! Never seen a "white" spark plug, the electrode is dry, and white. The engine is quite struggle, but that's because the new oil seals...

but even so, i didnt understood why im getting the "white spark plug". The engine gets a little hotter, but doesnt run bad at high rpm.
 
A white spark plug is an indication of a very lean fuel/ air ratio.
A lean burn is a hot burn and will cause serious damage in short time.
The engine is not struggling because of the new seals, but rather because the fuel/ air ratio is wrong.
This lean condition could be caused by 2 reasons: carburetor is not tuned correctly or an air leak still exists.
Do not try to tune the carburetor to correct an air leak. Correct an air leak then tune the carburetor.
Have you tried the pressurized air and soapy water method to find an air leak?
It is the industry standard and nearly foolproof.
I recommend 5 PSI pressure maximum or you risk blowing the seals out on these cheap Chinese engines.
 
I will take some photos to you guys see,

I installed a new intake gasket, new intake flange, changed carburetor, installed 2x o-rings on carburetor..and so on.

I noticed that i have to clockwise the idle screw of the carburetor to the max, if not, the engine dies
 
Randomly throwing parts onto an engine may fix it if you are lucky.
Why not try diagnosing the problem methodically and just replace the part(s) that are the root cause of the problem?
 
The same problem happens if the fuel petcock is only partially open or the petcock filter is partially clogged. When the engine is cold it has been sitting and allowed fuel to build up in the carb and fuel line. You start running it and the fuel is getting replaced too slowly. It you have an inline filter it could be clogged. I remove the petcock filter as they are a pain to clean. If the tank was not cleaned before installation you'll find a lot of debris in it. This would also cause the white spark plug. It's a low cost check either way.
 
But i already did it..the problem was the idle when the engine was hotter, the idle starts to increase, and its not steady

changed the carburetor, a new intake, a new intake gasket, fullfilles all that little holes of the intake, where the carburetor attaches with a rsv high temp sealant, with no success

But now, the problem is the white spark plug, but i will do a little more runs, with 6% of oil mixture
 
Guys, the engine its perfect now.

The needle was setted all way up, and that was the reason of the main problems. Now at second position (stock) runs sweet

Now the idle its perfect on 1700RPM, and revs very good.

thanks!
 
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