Small Engines (Lawn Mowers, etc.): Toro Snowthrower Carb Flooding/Leaking, mikuni carb, gasline

Question
Hi Fred,

I have a 2 cycle Toro CCR 3000 GTS (Model 38430) with a Mikuni Carb.  I was having leaking problems with

the carb (gas leaking near the spitcup and down the exterior body of the bowl).  I suspected a faulty

float pin and seal so I replaced them both and cleaned the carb with carb cleaner (also blowed out the

areas that might contain debris).

I put the carb back together and before attaching to the engine, I tested to see that the new pin and seal

were working - they were - after adding a certain amount of gas, the bowl fills and the float engages the

pin to seal and prevent gas from flooding the carb.  

I empty the carb of my "test" gasoline and then re-attach the carb to the motor.  I start pooring gas in

the tank which flows down the gasline into the carb...  I start priming to get some gas to fill the bowl,

and then it starts to flood/leak again!  The gasoline runs right through the carb as if the float is not

engaging and closing off the fuel intake - it runs out of a small crack where the spitcup attaches to the

carb body (according to specifications, there is no gasket required between the spitcup and the carb

body).  The leaking only happens when I attach the carb to the motor!  When it's off the motor - I have no

problems...  

All I can tell is that when I attach the carb to the engine, if cuts off what appears to be venting holes

on the side of the carb that attaches to the motor.  Some questions:

1.  Shouldn't the bowl fill up all by itself without having to prime it? (I noticed I had to prime to get

gas to flow into the empty carb - as if something was keeping the gas from flowing into the carb - lack of

proper venting)?

2. Is this a venting issue?

3. How might attaching it to the motor cause the gas to run through this thing?  

I'm dumbfounded...  Please help...

S

Answer
You should not to have to prime the carb to make it fill with gas. As the carb fills air pressure is vented to the throat of the carb.  The float floats and the needler is pushed into the seat.  

A little spit back is normal but it should not be noticeable unless you are checking for it.  No way should it cause a leak.   The fuel and primer lines are not switched, are they?

The first thing I would do is remove the carb.  Take it apart.  Be sure you get the nozzle out and remove the seat.  Inspect the seat to see if there is flaw, inspect the needle tip to see if there is damage.  Hold the float under water, it should not bubble.  Take a wire from a twist tie and clean every fuel and air passage you can find.  Blow out with carb cleaner or compressed air.  reassemble using a new carb kit if you suspect anything.  Reinstall using new mounting gaskets.  

Clean the fuel cap vent.  Fill with gas.  The gas should fill the bowl without priming it.  Start the engine using normal procedures as stated in operators manual.  Run for a few minutes to reach operating temp.  Turn off the blower and there should be no noticeable leaks from the carb or spitback cup.  There could be an oily residue on or around the spitback cup and carb bowl.  The needle should seat and the fuel flow should stop.  

If after you run the machine you start to inspect it turning or tipping the machine you could cause a leak.  Set the machine on a piece of cardboard and leave it for an hour. There could be one or two drips but the carb should hold pressure.  

Excessive spitback could also be caused by excessive compression.  This can come from a blocked muffler or a new engine.  The more hours you get on the engine the better it will be.  

If none of the above the only thing I could suggest it to replace the carb.  Good luck.