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View Full Version : Engine bogs out at throtle down



T100
07-25-2010, 09:32 PM
Fuel filter Ok changed fuel pump, has anyone had this problem of bogging out at throttle down, in gear and quitting. What could it be, running great Wed. Any help would be great. Thanks

T100
07-26-2010, 12:43 AM
Any idea's ??? Has this happen to anyone??

NewmbaTX
07-26-2010, 01:09 AM
There has been a lot of posts recently on this very subject, but each is unique in its own way..or they way it is explained. Do a search to see what you come up with.

More info on what you have could help with answers..
What engine? Carb or injected?
Throttle down? you mean when slowing or pushing down as in throttle up?
What else in parts repairs have been done? When summerized too, what was changed?

K_E_N
07-26-2010, 06:19 PM
I have an '04 LSV, fuel injected. I've found that if I go from moderate or fast throttle down to neutral and idle rapidly, my engine dies. It typically restarts with ease. However, I've learned to compensate by decreasing throttle less rapidly. Fuel filter is good, fuel pump is good. I'm suspecting a throttle position sensor, but it just doesn't bother me enough to justify the extra expenditure right now.

T100
07-27-2010, 02:28 AM
I have a 2004 Mobius LSV, 310 hp, carb and when trottling down to gain speed it bogged out and hard to start after. Had no power to the fuel pump when ignition was on, for now have put power to fuel pump by splicing into another power supply and is running great. I have a loose wire some where or throu CanukleHead doing some searching it may be and sounds like the oil preasure sensor is gone. Took it for a test drive and all reading are normal with the way it is now and will find the sensor tommorw, if I can find it and look into it more. Should the pump come on( power to the pump) when you just turn the key before starting??? Thanks CanukleHead for your help as I am at the cabin on my BlackBerry tring to figure this out, the wive is very inpressed! Not!
Thanks for any help

AaronWhitt82
07-27-2010, 03:02 AM
I have a 2004 Mobius LSV, 310 hp, carb and when trottling down to gain speed it bogged out and hard to start after. Had no power to the fuel pump when ignition was on, for now have put power to fuel pump by splicing into another power supply and is running great. I have a loose wire some where or throu CanukleHead doing some searching it may be and sounds like the oil preasure sensor is gone. Took it for a test drive and all reading are normal with the way it is now and will find the sensor tommorw, if I can find it and look into it more. Should the pump come on( power to the pump) when you just turn the key before starting??? Thanks CanukleHead for your help as I am at the cabin on my BlackBerry tring to figure this out, the wive is very inpressed! Not!
Thanks for any help


The fuel pump should only come on when cranking the boat or when the motor is running. It should NOT be running with the key in just the ON position...
It sounds like you have a fuel obstruction somewhere.
As others have said it seems like a lot of people are having this issue and every problem is unique.

I would start at the fuel tank and check the tank vent, anti-siphon valve and the pickup in the bottom of the tank.
Check the fuel line from the tank all the way to the fuel filter and make sure there isn't any soft spots in it or that it isn't collapsed.

You might want to take the fuel filter off and dump the gas in a clear jar and see if you get any separation which will tell you that you have water in your tank.

When you fill your tank up I would be sure to ALWAYS use some seafoam or Stabil marine treatment.

When was the last time the carb was rebuilt? It might need a good cleaning and a rebuild.

I would also check your float levels as well

Also check the accelerator pump arm/spring adjustment to make sure your getting proper fuel shot. I would also check to make sure the circuit is working properly.

As you also said you may want to replace the fuel pump cut off switch (low oil pressure sensor.)
Another way to test that is to hook up a test light to the positive wire on the fuel pump and while running the boat keep and eye on the test light and see what it does.

Make sure your wire connections to the fuel pump are good and tight.

Has it been back firing or popping at all? You may have a bad power valve. (Size is 2.5)

You also might want to disconnect the fuel line at the carb and then remove the fuel fittings which are screwed into the fuel bowls. There should be a screen or a filter inside the fittings and sometimes they can get clogged up.

Another thing with the Holley's is sometimes the fuel bowl bolts can become loose due to them heating up and cooling down. Make sure those bolts are tight and also make sure where the carb bolts to the manifold that those are tight as well, but don't over due it as they can strip out.

That is about all I can think of for now.
Good luck !!!!!!!

jra007
07-28-2010, 05:18 PM
I have a 2004 Mobius LSV, 310 hp, carb and when trottling down to gain speed it bogged out and hard to start after. Had no power to the fuel pump when ignition was on, for now have put power to fuel pump by splicing into another power supply and is running great. I have a loose wire some where or throu CanukleHead doing some searching it may be and sounds like the oil preasure sensor is gone. Took it for a test drive and all reading are normal with the way it is now and will find the sensor tommorw, if I can find it and look into it more. Should the pump come on( power to the pump) when you just turn the key before starting??? Thanks CanukleHead for your help as I am at the cabin on my BlackBerry tring to figure this out, the wive is very inpressed! Not!
Thanks for any help

First id be sure that you do have good oil pressure, if not your fun on the water will be short lived.

If you do have good oil pressure (generally 10psi per 1000 rpm) then a typical "jerry rig" is to just bridge the connection on the oil pressure safety switch. Its on the back of the motor by the distributor, it will normally have 2 wires connections to it (one switched 12v power the other will go the + side of the fuel pump). Your fuel pump will never have power until you have oil pressure the switch just completes the circuit. I dont know what you tapped into to get power to the pump, but if its not switched power then i would un-do it right away. I wouldnt keep the jumper on there forever, get thru the wknd and order the safty switch from the dealer, its a simple do-it-youself job.

T100
07-28-2010, 09:40 PM
Thanks for all the feed back, we were out all day and I watched the oil pressure & temp, all ok. The power to the pump is only there when the key is on. I will be ordering a new switch when I get back from the cabin. Where can I order one from? Online or dealer. Thanks again Guy's!!

jra007
07-29-2010, 04:29 PM
Thanks for all the feed back, we were out all day and I watched the oil pressure & temp, all ok. The power to the pump is only there when the key is on. I will be ordering a new switch when I get back from the cabin. Where can I order one from? Online or dealer. Thanks again Guy's!!

You can find them at most auto parts shops. Though check to see what you have first, some have a 2 pole and others have a 3 pole. Cost is about $20, most likely 2x that at a dealer.

T100
07-31-2010, 01:46 AM
Thanks jra007, I'm still not to sure which one it is by the distributer, I'll dive into it more tomorrow. Ran great today for an hour round trip;] I'll keep you posted.