With a cold start, engine 4 strokes, no power

DanielMaia

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Jun 24, 2009
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Maybe is very common, but i see other 2 stroke engines: even in cold starts it rev's very good, no hesitations, no 4 stroking, nothing, as good as a warmed engine.

The thing is: a friend of mine has a 60cc, and i installed a SBP expansion chamber, ada racing air filter, i didn't touch in main jet, only put the c-clip at the top (leaner) - 1st position. Even in break-in period that engine screams like an animal. Even in cold starts (in cold starts i dont usually revs high), it revs good, no 4 stroking, a very good engine!

Now the engine have 150km or so, but it have that problem. It starts very well, but when i take a ride, (my first 1-2km), it 4 strokes a lot, it has no power...nothing. after 2, 3km, the nice 2 stroke sound comes back..

I think its not normal, because my kreidler florett 50cc and my chainsaw partner 7000 plus it revs very good, and with no 4 stroking on cold starts..
 

Norman

LORD VADER Moderator
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Jan 16, 2008
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Back when I was racing motocross motorcycles my Honda would not run good until it warmed up. Once warmed up it would rev good and strong if you tried to rev it cold you could damage it by scuffing the cylinder or the piston. The engine needs to reach operating temp so all moving surfaces are expanded to their proper sizes. Some 2-strokes are very picky about this more so than 4 strokes.
What the piston is made of and how it is made will also effect how they run cold or warm.
Newer pistons( some not all) that are aluminum are machined with a taper fatter at the bottom than the top and most are barrel shaped fatter on the front and back narrower on the sides. Also the make up of the aluminum will affect the expansion of the piston. Some pistons made with a high silicon content do not expand much so they can run tighter(less clearances) in the cylinder.
So just because type x engine revs good cold while another won't can be due to how and what it is made of. These china engines are bottom of the barrel crumby workmanship(not all but some) some will work great and some will not unless you do a lot of work to them. Some you might be better off tossing them and buying a new engine if it has ate a piston or broke a ring.
I learned very quickly to take the engine apart and inspect it before I tried to use it a lot of the engines I bought had nasty trash in them,one had a cigarette butt in it. Almost all had metal shaving inside of them along with dirt.
 
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DanielMaia

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Jun 24, 2009
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Thank you Norman, very informative post ;)

Other thing, when i take a big ride..if i close the air (choke ON) the engine stops, that means something relevant?

Because in my other 66cc engine that not happens..
 

Norman

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The bike that dies with the choke turned on is probably running ok. When you choke the engine that means more fuel less air so it goes over rich and kills it.
The other if you've checked and are sure that the choke plate is in fact closing then it could mean either it has an air leak somewhere allowing it not to reach the over rich condition or it could be running a little more lean with the choke off. You might want to do a spark plug check on them to get the fuel air mix set to the chocolate brown color on the center electrode insulator. You do not want it white(lean) or oily(rich).
I know some engines can drive you crazy messing with you when tuning them.
Its best to do one thing at a time check the results then if it's not working think about it and see if you over looked something or went the wrong way.
 

DanielMaia

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Very nice,

My other motor has 66cc, and it has 2400km, and its really perfect. The idle is at 1600, 1700RPM ( i installed a TTO tach), it revs like a charm, and pulls me up hill at 46km/h.

I will check the spark plug, and take a photo ;)