2000 Mercury 250 Pro XB Bogging issue

[Mike South]

I have a 2000 Mercury 250 Pro XB on a Ranger 522. I bought this as a repo and put a new lower unit on it along with a 26 pitch prop. Initially it started and ran but was Very slow revving up to get on plane and died going down the lake. Since then I pumped all the old gas out clean the VST rebuilt the fuel pump replaced the other fuel pump. Put fresh 93 octane in and tried again. This time it didn’t idle or stay running without giving it gas. I tested the fuel and it had water in it. So I added a water separator, put a new throttle position switch and air temperature sensor on. Installed new fuel lines from tank to engine. put new Chris Carson single stage reeds, cleaned injectors, filled up with ethanol free 90 octane and tested it again. It ran much better with very little hesitation maybe one and a half to two seconds before it took off and planed out up then ran great. I used it for a few weeks and it started doing the same thing again. Sometimes when it doesnt spool up I can pump primer ball and it will go ahead and take off. It doesnt seem to affect the runability after it takes off. The primer ball sometimes isn’t hard like I think it should be. At this point I’m not sure whether I should go back through and re-clean everything assuming I may have picked up some more debris in my old tanks or is there another way I should proceed? I thought about adding a low volume electric fuel pump to Eliminate a supply issue from tank? Also I have a new dual tank switch valve I was going to replace thinking it maybe was sucking air from around the fitting somehow and I still need to replace the fuel lines from switching valve to tanks. Thanks for taking the time to read this and any insight would be greatly appreciated.

2000 Mercury 250 pro XB
serial #0G980846

[Slim95]

I put a low volume Carter electric fuel pump on my XB as I was tired of the same issues. Runs great after it planes out but if I idled to long in gear sometimes it would die or bog down terribly when trying to accelerate. I removed the factory low volume pump made a fitting to block off the hole and installed the Carter and have never had an issue since

[Mike South]

Thanks for the information! I was wondering if this had been done on an XB. I would prefer to fix it in a factory manor but I don’t have many more things left to try. May I ask what type of fuel you run? The highest grade pure gasoline around here is 90 octane. Should I just run the 93 octane with ethanol? Also did you wire the electric pump into ignition switch?

[Gamblerman65]

Could be anti siphon valve at exit of gas tank..

[Mike South]

[QUOTE=Gamblerman65;11431420]Could be anti siphon valve at exit of gas tank..[/

Thanks for the insight! Definitely worth a look. It does bog down on both tanks. That would mean the siphon valves on both tanks are stuck or is there only one siphon valve that runs both tanks?

[Slim95]

I run the highest grade fuel I can find at the pump which on average is 93 with ethanol. Yes I did wire the electric fuel pump to the ignition with a relay. I was tired of rebuilding the mechanical pump and then having to pump the primer bulb. I installed a 100 micron filter before the carter pump and then a return style fuel pressure regulator after the carter pump just incase. Winter goals are to install a roll over kill switch, low pressure activation switch and move the engine mount fuel filter inside the boat. It is louder than I wanted but the XB drowns out the fuel pump noise.

[EuropeanAM]

I do NOT recommend utilizing pressure-fed fuel supply systems for these engines as any leak that develops will become a PRESSURIZED (and volume-fed) leak.

Mike- take a look at the FAQ Section, specifically the "Fuel Lines and Performance Problems" thread.

Very important that NO additional filters be installed as they can cause a supply RESTRICTION.

Also very important that the pulse/diaphragm fuel pump be rebuilt utilizing only the OEM Mercury/Quicksilver kit.

As the referenced post indicates, ALL recommended items should be done at the SAME time, so as to prevent chasing problems around the system over and over.

[Mike South]

Thanks for the reply Slim I really appreciate your insight.

[Mike South]

I do NOT recommend utilizing pressure-fed fuel supply systems for these engines as any leak that develops will become a PRESSURIZED (and volume-fed) leak.

Mike- take a look at the FAQ Section, specifically the "Fuel Lines and Performance Problems" thread.

Very important that NO additional filters be installed as they can cause a supply RESTRICTION.

Also very important that the pulse/diaphragm fuel pump be rebuilt utilizing only the OEM Mercury/Quicksilver kit.

As the referenced post indicates, ALL recommended items should be done at the SAME time, so as to prevent chasing problems around the system over and over.

Thanks I found the thread. When I took my water separator filter off to inspect it was about half full of a brownish substance in the bottom of my jar. The rest was clean gas. I assume this is rusty water as the the top of the water separator which had only been on there three weeks was rusty. I drained both of my tanks completely and had nothing in either of them. I’m going to replace all the lines clean out both tanks and rebuild the pulse pump again

[EuropeanAM]

On draining tanks- make sure that you remove the fuel sending units, orient the boat with jacks so that you can SIPHON from the deepest, darkest corner (that's where the swamp water will reside).

Cannot use the fuel supply line for this purpose as it does not reach that area of the tank.

[Mike South]

———-UPDATE———
I completed all of the to do list: cleaned tanks, replaced fuel lines, new water separator, cleaned VST (there was some particulant in it) and changed fuel pump( the top fitting started leaking), rebuilt pulse diaphragm. filled with 91 pure gasoline with the quick clean and quick . Got it back together and it started on the first crank. Took it to the lake and it smoked heavily and started idling rough. I wasn’t able to take off due to it running rich (which is the opposite of the problem I was having). We just used the trolling motor that day except to load and there was fuel spots I could see behind the boat all day in the water. Started it to load on trailer and it didn’t smoke at all but when I loaded on trailer it leaked a puddle of oily substance on the ground out of the nosecone. Since then I have changed plugs (which helped some) and went back through all I changed to make sure it was done correctly. Fuel pressure was 43lbs, checked vacuum lines, and I’m checking temp now and see if all cylinders are rich. I’m not really sure how else to test this engine as there are no diagnostics that I’m aware of And I’m not sure where to go from here.

[EuropeanAM]

Fuel pressure is a bit high... may have restriction in the final filter at the Pressure Regulator.

Also... check fuel pressure at 15, 30 and 60 seconds after key is turned OFF.

[Mike South]

*UPDATE*
When checking the screen filter in front of the fuel pressure regulator I Found that it was severely clogged. After I cleaned it out it runs a little rich until it warms up but it runs the best It ever has. As of right now I would call it fixed! Thanks to all for the insight and suggestions, and a special thanks to Don at European Marine you nailed it!