My US41 does not want to run. It will start if you prime it with a little fuel down the carburetor but only runs long enough to burn off the prime (a few seconds). After opening up both needles, it will run but is not very responsive to needle adjustments. I think I have a fuel draw problem. I cleaned out the screen in the carb but this didn't help. The pump is sucking fuel. We hooked it up to my gallon gas can thinking the tank might have been clogged but it didn't help. Any suggestions?

The good thing about gas engines is their simplicity. It only takes 3 things to make them run, but if even one is missing, no go.

1. FUEL: Check your entire fuel plumbing system. Kinks and clogs can be difficult to notice, so inspect very carefully. The first place I always check is the clunk. I had a piece of plastic (where did that come from?) stuck in my clunk, blocking the fuel from drawing into the fuel line. Cleaned the clunk and installed a filter inside the tank, problem solved. Now, I always use a filter inside the tank, and one in the fuel line just before the carb. Next, reset the carb needles to the original factory specs so you'll be sure to be getting adequate fuel to the carb. Check the carb's diaphragm, too. A rip or hole in it will keep it from pumping fuel, so inspect it closely as well. When inspection is complete, go to step 2.

2. SPARK: Take the plug out of the cylinder head and closely inspect it. Is it covered with gunk? Is the gap ok and clean, or does it need cleaning and/or adjustment? Did you short it out and turn the motor over to see if it produces a spark? Since your engine runs for a few seconds, this is probably not your problem. It never hurts to check, though.

3. AIR: I had an old Walbro carb on a Quadra 35 that had a loose butterfly valve. The shaft would turn, but the small disc on it would not move. I had lost a set-screw out of it, due to vibration I suppose, and it never opened up to let any air in, effectively choking the engine to death. Check to make your carb is working correctly.


Finally, make sure you're using a good starting procedure. Here's what I do...

I stick my finger in the throat of the carb, and with the kill switch in the KILL position, rock the prop back and forth against compression until my finger is wet. Flip the kill switch to the RUN position, 2 clicks of throttle, and flip the prop. Should start nearly every time. If you don't get a burp, start over. REMEMBER THE KILL SWITCH!!! Don't want you to take off a finger or worse.

Hope this helps, it has worked for me for years.

If it's been sitting for a while, it probably needs a new fuel pump diaphragm. It's easy to tell--just pull the plate off of the carb, and if the diaphragm rubber isn't totally soft, then replace it. They are usually pretty cheap at the saw shops.

Cliff
http://www.rcfaq.com

You have plenty of good tips. You have a gas flow problem. Check your complete fuel circuit. I had the same problem. My carb's screen was dirty and the fuel inlet meter was plugged. Due to sitting around for a while.
Do a complete carb disassembly and clean, you'll find your problem. The carb kits are plentiful, mower shops, B&B Specialties, etc.

Dan

carl, you have alot of good tips here.
at the very least i would start with a fresh rebuild of the carb so you know where it stands. when you do the carb make sure to replace the meetering needle to . some times they stick. make sure it's not gummed up. i've used glow fuel to clean the tar like varnish out of old carbs. it really works! however it won't touch the hard stuff . remember, a clean carb is a happy carb, ron

Sounds a lot like the problem I just had with a Homelite 25 I converted. I put the carb on the wrong way so the little hole in the carb base to the pump was on the wrong side. No crankcase pressure to the pump. No start. The carb looks like it has two holes in it, but one is just a blind hole. Worth a look before tearing down the carb.

Steve

Is this a new engine or have you run it in the past with no problems and are now trying to use it after a layup? If it is a new engine, I had a similar problem with one of mine, in that the manifold had a small hole in it and was leaking diaphram pressure that should have been going to the carb. Pull the little plastic manifold and check to see if you have the holes lined up. If you do, check the grove that sometimes allows you to turn the carb around 180 degrees. That little grove was perferated on my manifold. A replacement and the engine ran fine.
Check it out.

does anyone know how i can put a cool little picture next to my user name like fighterpilot does?

Carlgrover -

If this is a new or never run engine it may need a bit of help from a big starter. I could not get mine to run with the spring starter until a buddy of mine used his big persuader to crank it over. After a few runs it was fine. Also, be sure to set the needles per the instructions, it should run fine there. Any minor adjustments should be just that - minor, like 1/16 of a turn at a time.

Good luck, Phil