Mercruiser 3.0LX Boggs down over 2K rpm IN GEAR ONLY

[MikeDobbs]

Hey Everyone,

The saga continues. Headed to the water today excited for my first trouble free outing with the wife : )

Boat started right up, idled beautifully, and ran well in gear while we made our way to open water. Ran well under a little more gas as well- I'd say up to about 1500 or 1700 RPM. As we left the channel I started to give more throttle to put the boat up on plane, and the engine started bogging very badly. No matter how much throttle I gave, it wouldn't get much past 2,000 rpm or so, and it kept almost stalling out. I had to work the throttle quite a bit to keep her running while I turned around and headed for protected waters.

Once back in the calmer waters I tried idling around again, and the engine ran wonderfully. I was able to go in and out of gear. Forward and reverse- no problems at all. As soon as I tried to give more throttle the engine felt unresponsive to additional throttle, and would start to bog down and die out. Anything much above 1500 rpm, and certainly bad by the time it reached 2,000rpm.

I should also mention that the engine runs FINE in neutral. I can rev a high as I like, and the engine is quick and responsive to throttle position. Never a hint of bogging or missing.

What do you think this is? I have just recently adjusted the timing on the boat, and put in a new set of lifters (not sure either of those would affect this). The last time we had her out (couple weeks ago) this was not an issue at all. She ran very well through the entire range of throttle.

I'm leaning towards fuel- possibly as simple as replacing the fuel filter? Does this sound like a carb issue to anyone? Carb recently rebuilt (few weeks back). I'd like to try to address any possible cause, since the only was I can test this is out on the water (meaning I have to trailer boat back again).

Thanks!

 

[MikeDobbs]

Forgot to mention that the boat backfired two or three times while I was furiously working the throttle to keep her running (when trying to make my way back to safer waters).

 

[skippy2235]

Get a fuel pump pressure reading, carb 4-8 psi.
check for blocks dirt debris water in fuel system.

 

[ematz22]

Add dry gas to the tank. Had the same thing happen to me. After a month of replacing everything and having carburetors rebuilt and not fixing it added dry gas and problem went away. Adding a fuel water separator to my boat because I don't have one.

 

[MikeDobbs]

Add dry gas to the tank. Had the same thing happen to me. After a month of replacing everything and having carburetors rebuilt and not fixing it added dry gas and problem went away. Adding a fuel water separator to my boat because I don't have one.

That's a good idea- I do have a fuel water sep in the fuel line, but I suppose it can't hurt

 

[flipbro]

Mike have you changed that filter?

 

[MikeDobbs]

Hey flipbro! I am doing that now. The inline filter in the carb looks good. I realized there's a "secret" filter in the fuel pump- pulled that just now. Crazy gunk in the cup. I'm pretty sure it was the original factory filter in there (still a pumice stone not a paper filter). I'm on hold with WM right now to get a replacement. Also changed the large inline filter I installed, but can't check that one (it looks like a large oil filter).

Going to put it all back together and head to the water to see if that does the trick. If not, I'll pull the carb and bring it to my carb guy. Any other suggestions?

 

[flipbro]

Your on the rite track. The one that looks like a oil filter is a water/fuel separator. Change it don't just dump it and put it back on. As ive heard of guys doing. If you want dump the contents of the filter in a jar or like Bondo does a zip lock bag to examine. Good luck..

 

[MikeDobbs]

Update: Changed out all filters. The one under the fuel pump was mind-bogglingly cruddy; solid cm of gunk in the bottom of the bowl. Went to the water- same problem (perhaps slightly better). So, I started making small adjustments on the distributor, then trying to get up on plane. Eventually I found the spot where it started to pre-ignite, then backed off a drop and the engine ran pretty well! I was able to get her up on plane and moving well at about 3500 rpm, so huge difference from the other day. Still something off about the engine- when moving from about 1200 or 1400 rpm it starts to die out, and I have to "goose" the throttle a touch to pump some gas down into the carb. Once I get it past that hump though it runs great. I'll post this as a new question on the forum, but in case anyone has any ideas feel free to reply here : )

Thank as always for the help

 

[skippy2235]

Fuel psi, ? and maybe the accelerator pump in carb.

 

[Dinows]

I have the same issue, run her up hard at the dock but breakes down under a load. I got a lot of water in the gas last year and filled my tank this year without knowing. I have a water seperator and haver to drain it every day. Anybody have any ideas ??

 

[flipbro]

Did you check your fuel pump pressure yet? As someone had already suggested.

 

[Dinows]

I didnt check my pressure but did install an electric pump to help the old diaphragm pump. I don't think there is a pressure problem . but it now "surges" and seems to be starving for gas at 2500. Either this is still the remnants of the water or fuel is not getting to the engine. don't know where else to look

 

[MikeDobbs]

Did you check your fuel pump pressure yet? As someone had already suggested.

How do I check the fuel pressure with a hard fuel line? Do I need to cut the line?

 

[GA_Boater]

I have the same issue, run her up hard at the dock but breakes down under a load. I got a lot of water in the gas last year and filled my tank this year without knowing. I have a water seperator and haver to drain it every day. Anybody have any ideas ??

Dinows - Start your own thread. You are confusing this thread with your questions on top of MikeDobbs.

 

[flipbro]

Mike im not sure how your fuel water seporator is. But on mine I have an in and two outs one to the carb and one pluged off. I just pull that plug and have a gauge I plumbed for it...Im not sure psi is the problem though since you say its just in the 12 to 1400 rpm range. Whats your Wot rpm?

 

[MikeDobbs]

flipbro- My filter/water sep is before the fuel pump since it's mechanical. There is nothing between the pump and the carb and it's all a hard line from that point.

I've not yet had the boat at WOT, however I can tell you this issue has now been resolved. I changed out all the fuel filters, brought the carb to my guy to do a quick check on it, and replaced the plugs. She ran great on the water yesterday. Idled very low, in and out of gear, and responsive to throttle at all positions : )

Thanks for the help everyone!

 

[flipbro]

Glad to here it.

 

[Eric 3.7LX Alpha 1]

Remove the metal fuel line between the fuel pump and carb. Pick up an inline fuel pressure gauge and tee fitting for 3/8" fuel line.

Pick up a small section of 3/8" metal brake/ fuel line from the auto parts store.. a 12" piece. This will have the factory flare ends and fittings the same as your pre-bent metal line that will be removed. Make a cut in the middile of the new 12" piece so you now have 2-pieces, each with a flare end and a plain end.

Get a section of 3/8" fuel hose long enough to reach the two cut ends, one on the fuel pump and one on the carb inlet. Add the new fuel pressure gauge somewhere in that new hose and take it for a test run. Using hose clamps to tighten the metal to the hose.

Auto Zone and some other parts stores offer free tool rental. They may even rent (for free.. return it when done with it) a kit to test fuel pressure on carb engines.

Rubber fuel hose in marine is suppose to be A1 rated marine fuel hose. It has a longer burn time in a fire, but this set up is only for a test. Once you get it figured out put your metal line back in.

You should take off the electrical fuel pump. There is no reason or desire to have two pumps inline from each other. Some things redundancy is good but this case is bad practice.

What is the timing at now that you adjusted it by feel on the water?