[labukas]

Hi,

i' have some strange problem with engine runing.
I start the engine with choke lifted up. Engine starts, working normaly. When i'm letting down the choke the rpm rises up to 7k, rise up choke and it calms down, simply idling. Letting down choke and it starts rising rpms

I cleaned carburetor for couple times. Dissasembled till venturi, cleaned every part. Any ideas whats wrong with it? Or maybe it's the engine problem?

Thanks for answers

[mlange]

I think the more experienced ones have to chime in for the correct advice to you, Labukas.

If I remember correctly, the choke is a choke on air, and when it is up, the fuel/air mix is slightly richened.

One question Im wondering is whether you set your idle/air screw correctly and tuned for when the choke is in a down position, because it looks like right now your idle speed is too high.

What is the fuel/oil ratio and main jet settings that you are running?

[labukas]

I think the more experienced ones have to chime in for the correct advice to you, Labukas.

If I remember correctly, the choke is a choke on air, and when it is up, the fuel/air mix is slightly richened.

One question Im wondering is whether you set your idle/air screw correctly and tuned for when the choke is in a down position, because it looks like right now your idle speed is too high.

What is the fuel/oil ratio and main jet settings that you are running?

When choke is lifted up it opens small hole coming from float bowl and line of air, so (as i think) gives mores mixture to engine for a start.
The air screw is half out and the mixture screw is 1.5round screwed out. Carb setting i basic except main jet - it's 172.
Oil/fuel ratio is 1/40.

Could it be a problem with incorrect jetting? I thought main jet does job in mid and high rpms

It seems like when i close the choke the engine receives a doze of mixture but i can't undestand where it goes from
How it works when floats rises up and closes the intake of fuel to the carb? Where goes the presure from fuel pump? Maybe the floats ain't closing fuel properly?

Please share your minds
Thanks

[Mikko Nassi]

Is this happening with the kart on the ground, on a stand, or on the track?

Have you ever had the engine running properly on the track?

[labukas]

Is this happening with the kart on the ground, on a stand, or on the track?

Have you ever had the engine running properly on the track?

Yes, i have 3 or 4 training days since i bought it, everything went fiine, no problems.

One race day the cluch broken. Changed it but some strange noise gone frome engine and started vibrate.
The main crankcase bearing was broken
Rebuild engine:
Changed all bearings, placed new gaskets. Cylinder was ok, piston ok, crankshaft ok.
Placed engine on chassis, started and found this happening. Kart is on stand never been on a track since engine rebuild

Any ideas?

P.S Sorry for my English

[Mikko Nassi]

You mentioned that you even took the venturi (insert) out when cleaning the carb? Has the gasket been put back in correctly? If the progression port hole is blocked or partially blocked it could create the situation you're experiencing - with the throttle closed this is where the carb draws its fuel from. What happens if it is blocked is that your mixture goes very lean causing the rpm to rise, and when you open the choke another passage of fuel is opened up and the engine idles normally.

Is the throttle completely closed (as in the slide)? I don't think it would be that though because the engine would still rev high with the choke. It could be many things . Also check that the floats are installed correctly and aren't stopping the fuel flow.

The easiest way to check if it is the carb is simply to borrow a working carburetor from another Rotax driver and try it. If it's the exact same problem you know to stop thinking about the carb.

Oh yeah it certainly shouldn't be the main jet.

[TB-racing]

are yuo shore that there is no air leak in crank seals or other seals
try to do pressure test to the engine
put a kork in exhaust and inlet mainfold
and then from the induktion hole
pump some vakum or pressure whith pump max 1bar
the pressure shud not drop much in5min