I'm currently working on my uncles 83 Big Red. He had an issue with the carb leaking gas and the engine not being able to run during throttling. I recently purchase a new carburetor for the big red and I'm still having the issue. Here is the run through I can get it to start and to idle but whenever you try to rev the throttle it is not having that it acts like be choked out or something. I've removed the air filter thought maybe it wasn't getting enough air. It will run with a person driving it but it doesn't have close to full power. Now I'm stuck any suggestions? Thanks for reading my post.

 

What is the colour on the plug? Is it just low on power or is it misfiring? whether related or not, I suggest an inline fuel filter, just a small one for a lawnmower will do. I had all kinds of carb related issues with my 84 200M, removed it cleaned it and it would run good for a short period of time then act up again. finally put an inline filter in and havent had a problem since.

 

Check the plug and change it even if it seems ok, it's a cheap thing to check. Check the intake pipe for cracks, you can use carb cleaner and spray it on the carb and intake while the engine is running, see if the idle speed changes. Brand new carb, or new to you? Does the carb have a new kit in it? Check the main jet and needle setting in the carb.

If it's idling fine then it's probably the main jet or needle setting, check to see if the needle is on the center notch (a good starting poing) it may have been set for a higher altitude than where you're at. Do a normal tune up on the engine, check compression, valve clearances etc. This could be (but unlikely) spark related too from a weak coil and such, but more likely it's a simple fix. Good luck.