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Posts: 1
Reply with quote  #1 
The motor will start and idle fine but as soon as you give it the gas it spits and sputters and dies[confused]. I have cleaned the carb changed the carb mixed matched carbs and it still does the same thing. I even thought it might be old alcohol so I got some new but it wasn't that either. Any ideas?  

Posts: 198
Reply with quote  #2 
Hill, I have lots of ideas and I think we just need to check various 'boxes' to isolate what isn't the cause.

Carburetor - Your float height is not anything way off?  Even changing jets are you sure that your main jet/emulsion tube isn't gummed up? IF you put the choke on can you get the engine RPM up without it dying? If you can it's likely your main fuel circuit.  Can you try either carburetor on another engine to isolate it to the carburetor?  With methonal, if left in the carburetor (ANY carburetor) it becomes very caustic.  If you haven't maintained your carbs or put them away without fogging them you might have your main metering passage partially clogged with Zinc or aluminum oxide.  

Air leaks.  Do you have any air leaks around the intake?  Maybe at idle the manifold pressure is enough but the minute you crack the throttle the leak causes a large drop in pressure causing it to cut out?

Carburetor overflow - I have seen people run this to their catch can, the same as the crankcase vent without enough venting to allow the system to maintain atmospheric pressure.  Simple put, the breather pressure ends up going back into the carburetor causing the engine to run extremely rich.

Oddities - Could your switch or ground have a short in it?  Maybe it's rubbing with the added vibration.  You could simply disconnect this in a controlled environment and pull your spark plug wire to turn the engine off.  If that isn't it hook it back up so you have this system functioning.

Spark plug wire.  Is there any rubbing OR has a tach wire cut into the high tension lead?  The energy of the coil takes the path of lead resistance and a damaged wire could cause an short.  Plug wire, make sure the connector is snapped into the top of the spark plug.

There are so many other little things is could be but if I were a betting man (which I don't have the money to be) I would  isolate the carburetor by putting it on another engine.  If you can prove that good or bad that really takes a lot of possibility out of it right away.  One the engine you have put the choke on and see if that helps the engine gain RPM without dying.  If that's the case it's likely something in your main circuit.

Write back if you need some more ideas!

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