Engine won't run for more than a few seconds

[Woddny]

A group of us are trying to repair a go kart, we've got as far as getting it to start but it cuts out after a few seconds. I've put a video on youtube showing exactly how it's cutting out:

http://www.youtube.com/watch?v=fc_FBcKyBC4

Its a two-stroke 125cc Rotax Max engine. Any suggestions on the problem would be appreciated. Thanks

 

[Russ2251]

Fuel starvation. Worst thing for any 2 cycle.

 

[kendelrk]

check the fuel lines, make sure there not hard, and try cleaning the carb out, thats the leaing solution to problems

 

[anderkart]

Also make sure your fuel lines have a snug wire tie at each connection so they wont leak and draw in air instead of fuel from the tank. Its common for the pickup line inside the tank to swell to a larger size or collapse under a vacuum, so double check that too.

If your fuel lines all check out, the problem might just be a dirty strainer, plugged up passage or detective/leaking diaphragm in your carb. (these types of carbs usually have a built in fuel pump feature)

Is that a Yamaha KT100 engine with a Tillotson carb?

Check the numbers on your carb and you'll probably find the correct replacement Diaphragm kit here: http://www.cometkartsales.com/store/carbs/tillex.htm

 

[Woddny]

Thanks for you're comments =)

we checked the fuel lines for any blockages, but not for hardness so that may be one to check next time we take a look at it.

we cleaned out the carb and checked for any blockages inside it too.

However, there were a few bubbles in the fuel line. does this matter? (However, these bubbles do move with the flow of fuel, possibly showing that fuel does flow into the carb. But once the engine is stopped or flow of fuel stops these bubbles seem to return to a central position in the fuel line.)

I will check the strainer too. The carb is a Dellorto carb on a rotax max 125cc engine.

 

[kendelrk]

if there bubbles there might be a sign of a vaccum in the lines, 2 stroke engines are just a big pain in the ***

 

[kendelrk]

try this : get a can of starting fluid, when its about to die, spray it on the carburetor, if it comes back to life and dies a few seconds later, you know that its something with the carb

 

[Woddny]

Thanks will give that a go =)

 

[kendelrk]

do you have to give it gas to start it? because if you have to give it gas it might be your head gasket, because if you blow a head gasket, it needs more gas to create the normal compression and once you let off it starts to loose compression and once it does it starts to die down, had the same problem on my techumseh before i got my clone

 

[anderkart]

Dellorto carb on a Rotax max 125cc uses a pulse fuel pump so that could be defective. There should be a pulse line going from the pump to the engines side cover, try replacing this line (in case its collapsing/flexing) and use wire ties as hose clamps at each end.

Both my race karts use pulse fuel pumps and always have a few bubbles visible in the fuel lines, this is normal and mine work just fine. If you see bubbles moving with the flow of fuel all the way to the carb It sounds like your carb is getting fuel.

The premix in your tank is fresh, not a couple years old right?

Instead of starting fluid as a test, I'd use some fresh premix in a squirt bottle to see if you can keep it running longer.

Have you already tried a new spark plug?

There's lots of possibilities, take a look through this search link for more clues: http://www.google.com/search?source...l=&oq=&pbx=1&bav=on.1,or.&fp=d4a7e52ef0af3d83

 

[Woddny]

Yeah, it's the premix is few weeks old but not years. haha. will take a look at the pump though thanks =)

its not a new spark plug but we have checked that it is giving a spark and seems to be working fine as far as we can tell

 

[kendelrk]

is the head gasket intact?

 

[Woddny]

yeah think so. we've checked that the cylinder is giving the correct compression rate and that was spot on what it was ment to be

 

[kendelrk]

well then its gotta be something to do with the carb,

 

[Doc Sprocket]

try this : get a can of starting fluid, when its about to die, spray it on the carburetor, if it comes back to life and dies a few seconds later, you know that its something with the carb

Be very, very gentle with the ether. There is no oil in it, so for as long as the engine is surviving on ether, it is not being lubricated. Think of it as running a normal 4-stroke with no oil in the crankcase. Very bad.

EDIT- In fact, I'd advise you to forget the ether thing entirely. There are better and safer ways to troubleshoot.

 

[Russ2251]

The fact that there is no oil in starting ether should not be an issue as so very little is needed to get things going.
Very dangerous to use ether in a 2 cycle engine to begin with.

 

[Doc Sprocket]

I was more concerned about the "keep it going" mentality I have observed in the past. I have seen people repeately blasting ether into an engine to keep it running for anywhere from a few seconds to a minute or so. I was just trying to make sure the OP does not do this. Would you agree?

 

[kendelrk]

my dad always had the idea that, if you spray it once, and it starts, and then starts to die, spray one more burst, and if it runs longer, than its a carb problem, but i do agree not to keep blasting either into the carb, that would be like a 2 stroke grenade

 

[Russ2251]

Would you agree?

I just can't imagine anyone doing so...therefore it never occurred to me.
I've never had the need to use the stuff unless it is an emergency or for use as a diagnostic tool.
Ether does not cure anything.
It has been known to blow the seals on 2 cycle engines and the heads off of VW's.
The original intention was for cold starting diesel powered equipment.