Hi All. I have a 4.3L Mercruiser with a 4B Weber carb. I noticed the last 2 times that I've used the boat that the engine will bog down to a stall. It seems like bad gas. However, I start the engine and let it run at idle and after a couple of attempts to plane off, it starts running fine. On both of these last two trips I ran the engine quite a bit, several hours and it ran great so I'm thinking it might not be a fuel problem since the stalling would continue. I haven't been using the boat much this entire season. The last time I used it was 3 weeks ago and the last time I refueled was in July. maybe the accelerator pump is hanging up?
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Mercuiser Engine Bogs down then runs fine
- Thread starter seachunk2
- Start date
Was it still cold on the stumbling? It sounds like it could be a choke issue since it ran fine following for several hours. I would check that the choke heater is getting power with a meter and inspect any linkage to make sure something isn't rubbing against it. If it's bad gas, you're taking care of that by using it up.
What Stephen is saying, is it sounds like you're trying to run while the carb is set too lean (too much air) for one reason or another. We also have to know how fast and how far you're advancing the throttle and how that may be affecting the lag.
The choke is temperature activated and a good place to start.
The other side of the coin is you're running too rich (too much fuel). Both of these conditions can also be caused by a sticking float valve. we'll get into that after a bit.
First, it's how you advance the throttle and where and when the bogging happens.
The choke is temperature activated and a good place to start.
The other side of the coin is you're running too rich (too much fuel). Both of these conditions can also be caused by a sticking float valve. we'll get into that after a bit.
First, it's how you advance the throttle and where and when the bogging happens.
Thanks for the replies. This past Sunday I launched the boat and cruised down the canal in a no-wake zone for 10 minutes and then I was in the open bay. I throttled up to get the boat on plane and initially it all seemed fine and then the engine started to bog down. I was losing power. I backed off the throttle and went to neutral at idle speed. I tried to power up but there was obvious hesitation for the engine to respond. However, after 3 or four attempts to get the engine revving normal, the engine finally powered up and the boat was on plane and cruising nicely. I traveled about 20 minutes at 3800 rpm to my destination and dropped anchor for a few hours. I then started the boat and it ran fine for the entire trip back to the launching ramp.
This is the second consecutive time this happened. About 3 weeks ago the same thing happened although I had launched from a different location. About 10 minutes into a no-wake 5mph cruise the engine began bogging down. This time it occurred before I went to plane off. Brought the throttle to neutral idle speed, goosed the rpms a few times and then it ran excellent the rest of the day. On this trip I ran the motor for at least 2 or 3 hours at various speeds in between several drifts while fishing throughout the day. Ran flawless. Why I'm getting this bogging down puzzles me. It feels like I'm not getting fuel but that's just a guess based on what I'm feeling. On both trips, I started the engine from a cold start at the launching ramp and warmed the motor up for 5 minutes. The engine started up without problems. Hope this explanation gives you some more insight as to what is happening. Thanks!
This is the second consecutive time this happened. About 3 weeks ago the same thing happened although I had launched from a different location. About 10 minutes into a no-wake 5mph cruise the engine began bogging down. This time it occurred before I went to plane off. Brought the throttle to neutral idle speed, goosed the rpms a few times and then it ran excellent the rest of the day. On this trip I ran the motor for at least 2 or 3 hours at various speeds in between several drifts while fishing throughout the day. Ran flawless. Why I'm getting this bogging down puzzles me. It feels like I'm not getting fuel but that's just a guess based on what I'm feeling. On both trips, I started the engine from a cold start at the launching ramp and warmed the motor up for 5 minutes. The engine started up without problems. Hope this explanation gives you some more insight as to what is happening. Thanks!
- Joined
- Jun 23, 2002
- RO Number
- 9099
- Messages
- 1,089
I've never cleaned out the gas tank but had the pick-up tube pulled several years ago when I replaced the fuel line just to clean up the pick-up. Maybe it's due for another clean- can't hurt so I'll do that when I winterize. The last several seasons I haven't been using the boat that much. I've used Stabil as needed and the current fuel was primarily from a fill back in early August combined with whatever was in the tank. Of the 50 gallons total, it was 60% newer fuel 40% existing. Makes sense that the infrequent use and possibly partially stale fuel could be a factor. It only surprises me that the problem in momentary and once it clears up (both times in less than 1 minute), the engine performs flawlessly. If aging fuel was the problem, wouldn't the engine performance suffer throughout the entire day?
It is an electric fuel pump and I haven't opened the distributor cap (btw, it's a 4.3L Mercruiser LX 1995 wAlpha drive). I'll also inspect the cap and check the choke operation before getting started with winterizing.
Of all the possibilities, could what I'm describing point towards a choke hang-up problem more than anything else? Thanks to all for the replies.
It is an electric fuel pump and I haven't opened the distributor cap (btw, it's a 4.3L Mercruiser LX 1995 wAlpha drive). I'll also inspect the cap and check the choke operation before getting started with winterizing.
Of all the possibilities, could what I'm describing point towards a choke hang-up problem more than anything else? Thanks to all for the replies.
Also, since it's only happened twice I can't say I'm 100% certain but if I'm recalling correctly the problem may arise during a throttling up stage- accelerator pump issue possibly? If I get he chance I'm hoping to get out for a few more days of fishing before I have to wrap up for the season. I'll pay more attention to confirm the occurrence if it repeats itself.
My Merc 350 2BBL seemed to always bog down or have a rough idle. I put up with it for two years before I finally bit the bullet, drained the tank, and used fresh fuel. I had tried all of the tricks - mix with fresh gas, use this or that additive, nothing worked. Use up what you can by EOY and then siphon off the rest. It'll work fine in your car at 5 gal per tank full and you easily discount the fuel as being the issue next year. By the way, I did the siphon thing for three years. This year I didn't siphon it out in the spring and it still ran fine. I assume my problem was really stale fuel, water, and just too many additives.
quote:
Originally posted by randalnh
Check anti-siphon valve for sticking too.
+1 on the anti-siphon valve. The same thing was happening to me. I could run fine one day and then the next time out it would happen. Replaced the anti-siphon valve and it's never happened again.