Could this be an air leak?


Just got back into the hobby after almost a decade-long hiatus, a bit rusty and starting to have engine problems. I’m about ~3 hours on a new 5ivet (stock zenoha 32). Haven’t really tuned it yet, still at about 1.5 low and 2 high. Car has been running pretty rich so far, figuring I’d consider it broken-in by the next tank; however, it started running leaner out of nowhere. I performed the following:
1. Checked needles settings, still at that richer setup.
2. Tried richening even further, almost an extra turn out on both low and high. That didn’t seem to get the car to bog down, produce more smoke, etc.
3. Used WD 40 and sprayed the gap between a) the carburator and cylinder b) the cylinder and crank case c) the cover on the side of the cylinder. None of them produced bubbles.
4. Removed the engine and inspected the head, the gasket is still there, no scores/scratches on cylinder walls/piston.

Didn’t really let it run lean. It ran leaner than what my settings should’ve yielded, but sounded like how it should’ve sounded had I tuned it properly I guess. Spark plug was brown.

But could I really rule out an air leak from the inspection steps I’ve taken? Could it be something else completely?

Since the head/piston looked fine I figured I’d just grab some new gaskets for head/crank and head/carburator, a new 990 carb, and put this thing together and give it another try. Is that reasonable?


The carb doctor👨‍⚕️
First off if it's new there is warranty, call horizon and let them know your issues. We 40 wont tell you much of anything as far as an air leak. You need to use some carb cleaner on it, if it got a leak it will rev up. Air leaks will typically also show as an inability to tune the carb, ie (almost) always want to run lean, and not give a stable idle. If it's sitting for for years on end, it needs a kit. The diaphragms only stay flexible for so long.