Surging motor on NEW carb!?

The tank looked very clean, though I didn't remove it and actually clean it. So I suppose its possible. The line and carb are new brand new so the tank is the only place dirt could have come from.
 
Be sure to check the fuel cap also. Often times the rubber seal around the inside edge gets brittle, cracks and fails. These small chunks of rubber stop up the fuel nipple and float around in the bottom of the tank. I have cleaned out a lot of tanks over the years.
 
You have a Quantum 190cc engine with a primer start. It has no idle jet circuit. Great carb design, very simple. Generally, very easy to clean. In the video how did you start that engine with the air box and primer off? Did you use starter fluid? It appears it is running too lean. That is why it is surging. That large O-ring you mentioned goes between the carb and the air intake tube. You can often reuse the old one with out any issues. You might as well replace it and make sure you bolt it up tight. Not car lug nut tight but firm. make sure that grey or black colored air intake tube is not cracked. You need to remove the shroud to inspect it. Also a good time to clean out the grass. The air intake tube is plastic and I have seen small cracks in them cause a lean condition. As mentioned before, you may have the wrong or a defective aftermarket carb. Why don't you clean the original OEM carb? You may need a new gasket kit or new needle and seat but this way you know it is jetted correctly. Those rebuild parts are availble. You can risk buying aftermarket on those. The cheap Asian carbs are great until they are not. You never know if they sent you the correct one. They can be mismarked. You do not know if it was made correctly. Just becasue it looks the same does not mean it is. The jets in carbs are criticlal. Being off a few thousanths of an inch can make or break it working or not. How much time have you already spent on this. You could have cleaned the OEM carb by now and be mowing. One last check when all else fails is, is the governor set correctly. Plenty of good videos on how to confirm that. It is too complicated for here. Great input by Rivets too. Good Luck
 
l008com said:
The tank looked very clean, though I didn't remove it and actually clean it. So I suppose its possible. The line and carb are new brand new so the tank is the only place dirt could have come from.
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There is a screen on the inside of the tank that may be restricting flow. I doubt this is your main problem but it may still need addressing. Pop off the fuel line and see what kind of flow you get. If it is Drip, drip, drip or a tiny trickle you have an issue. Clean the screen with brake or carb cleaner and compressed air.
 
Fortunately, they have finally molded in a decent size (permanent) cleanable screen in the bottom of the tank where it can be seen.

Some of the early models actually had a tiny pencil type filter that was shoved down in the fuel line end, right at the tank where it connects. Those tiny filters were a real pain to get because no one stocks them.
 
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Ok I'm outside working on it right now, here are some updates.

I took the air filter and airbox off and it started up and did NOT die. Now its running and it still surges every few seconds but not bad any more, not like its going to die. But its not running smooth thats for sure.

Ran with no fuel cap on, no change.

If I partially cover the intake with my hand (manual choke), it does NOT improve the running at all. It just kills it or almost kills it.

If i manually push the throttle lever open, it revs right up no hesitation. But if i over-rev it, the governor will pull it back.

This all suggests that the problem is not the carb or the fuel flow, right? Somethings else?

I'm going to let it run for a while longer and then maybe take things apart more and see what I can find.

I'm not sure why it was dying with the air filter on, and running much better with the air filter off, when the filter itself is super clean and spotless. Very strange. Its kinda like someone sprayed clear coat on the filter so it looks good but doesn't let air pass. That said, I held the air box and filter in place while it was running and it didn't kill the engine so maybe it was just a coincidence.
 
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Here's a video of the current state:


It runs, but poorly. I push on the spring to open the throttle (not WOT i don't think) and it runs much better. Then I let go and it runs like poop again.

A broken governor inside the crank case?
Throttle return spring thats too weak?

Its outside running right now. Its not getting any better or getting any worse.
 
The air bleed jet located just below the idle set screw (pressed lightly down into the carb housing) has too small of an orifice hole. Try swapping with the one from your original carburetor.

These aftermarket carburetors are a luck of the draw and not factory built for your particular engine. They fit multiple engines which all have different running dynamics.

Watch some generator repair videos by James Condon. He deals with this problem quite often on aftermarket carburetors.
 
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