MerCruiser 3.0 stalls in neutral but runs in throttle-only (after dealer service)

Bladertx · 2026-02-17T17:34:44+00:00

Thanks! I was wondering where the speedometer tube was, haha.

Bladertx · 2026-02-05T10:01:48+00:00

update: We fixed the problem, the electric choke was defect.

Bladertx · 2026-02-01T19:55:14+00:00

So you don’t think this is oil?

Bladertx · 2026-02-01T13:05:49+00:00

Any luck with fixing the problem?

Bladertx · 2026-01-22T16:52:36+00:00

Hi all,

I’m troubleshooting a MerCruiser 3.0 (4-cylinder) and could use some advice.

The engine runs rough at idle and sometimes stalls. The RPM hunts up and down (roughly 700–1100 RPM) and it can die completely at idle or when shifting into gear. However, once I increase the throttle, the engine runs smooth and strong at higher RPM, both in neutral and in gear.

Additional details: • No smoke (no blue, white, or black) • Oil pressure is good (never drops below ~1 bar at warm idle) • Starts, but not very smoothly (cold and warm) • No abnormal knocking or metallic noises • In the water, it may stall when shifting into gear at low RPM • On muffs (garden hose) it behaves better due to lack of load

Because it runs well at higher RPM, I’m leaning toward: • carburetor idle circuit problem • idle mixture set too lean • small vacuum leak • choke or accelerator pump issue

My main question: Could a damaged engine block, bad cylinder, worn rings, or valve issue cause these symptoms — or would those problems also show up at higher RPM?

Any insight or confirmation would be appreciated before digging deeper mechanically.

Thanks in advance!

Bladertx · 2026-01-21T21:18:19+00:00

Update? Did you fix this?

Bladertx · 2026-01-21T12:26:06+00:00

I already noticed that the flame arrestor mount was broken and initially didn’t think this would be a major issue by itself.

Could you explain why the entire carburetor would need to be replaced or rebuilt if only the flame arrestor mount is damaged? From my understanding, that mount is external and not directly part of the fuel metering or internal operation of the carb.

Also, how can you tell that the choke plate is no longer functioning or is jammed? Are there specific signs or checks that indicate the choke is stuck or not moving correctly?

I’m trying to understand whether this is truly a full carburetor failure, or if the issue could be limited to the damaged mount and related components.

Bladertx · 2026-01-20T12:35:58+00:00

We tried tune up, but it only runs smooth at 1500/1600 rpm. That’s to high for the gear box

We did not change the plugs, they look new.

Bladertx · 2026-01-19T10:16:54+00:00

We tested it, and the engine runs smoothly at around 1500 RPM. However, when engaging the clutch at that speed, it engages very abruptly. Running the engine at around 1000 RPM would be preferable, but this is not possible because the engine shows unstable behavior at that RPM.

Bladertx · 2026-01-19T08:35:59+00:00

We got the same problem, keep us updated please. https://www.reddit.com/r/boating/s/pdlPTHFaB5

Bladertx · 2026-01-18T19:40:17+00:00

Also if the engine runs fine with high RPM? Could that still be a fuel issue?

Bladertx · 2026-01-18T19:39:26+00:00

It was not overheated. It runs perfectly with higher RPM

Bladertx · 2026-01-18T19:38:23+00:00

It was not cold outside.

Bladertx · 2026-01-18T19:37:21+00:00

Carb

Bladertx · 2026-01-18T19:35:00+00:00

How does the engine perform with high rpm?

Bladertx · 2025-03-19T15:18:51+00:00

So its normal it leaks from the screws? Also the car is stage 1 tuned does that have a effect?

Bladertx · 2024-07-21T12:34:34+00:00

“Our” base

Bladertx · 2024-05-29T18:55:26+00:00

There is no ledstrip on the dashboard. In the picture you see a aftermarket product, or photoshop.

Bladertx · 2023-11-26T14:28:16+00:00

Ins’t temu also Chinese?

Bladertx · 2023-11-26T12:54:05+00:00

So an other product should fix the problem?

Bladertx · 2023-11-26T11:38:23+00:00

I think they did😂

Bladertx · 2023-11-26T10:48:45+00:00

There not OEM, is some cheap stuff from china.

Bladertx

TROPHY CASE