250 xb lost 200-300rpm

[mcstr21]

I have lost 200-300 rpm since last Fall I noticed it once in Oct. of last year but it ran fine in Nov. , Dec. I used to get 6300 rpm with 25 trophy now i only get 5900-6000 rpm it also seems like it is weaker on holeshot. I changed plugs and fuel filter/water sep. no change. I put on a like new 24 pitch tempest I have and it wouldnt turn more than 6100rpm. I can feel it surging with this prop especially if I lift off WOT just barely acts like it wants to go on but then it hits a wall and flattens out. Boat is a 21 ft tr triton, lost 5+mph. Just looking for help before spending countless dollars and time trying to figure this out. Also changed battery to 1000ca to try to fix no change.

[Gamblinman]

Make sure you get that motor to a qualified Mercury mechanic and get it checked out thoroughly before you lean it out and melt it down!! A few dollars now will save you thousands in the long run.

Just a wild guess, but I bet the injectors need to be properly cleaned. However, there are a multitude of fuel related items that could be causing your symptoms.

[Oldgeezer]

Two things. A consistent drop of RPM at WOT could be a CDM issue. The motor will not make power beyond the WOT upper limit of 6150. By dropping down to a lower pitch prop, you possibly are on the limiter. One more thought. Make sure that the plugs that you are using are QL77CC. I am sure that others might add a few other possibilities, but my thoughts are based on looking at the Mercury motor manual for that motor. Hope that this might help.

[redline]

+1. Also...the problem could be inconsistent and still be a CDM.

[EuropeanAM]

Coby:

I know this one might sound a bit "stupid"... but I'll throw it out there "just in case".

Many bass boat owners (especially ones who store their rigs "indoors") tend to "never remove the bildge plug from their boat".

If you've not removed yours lately... jack the nose up and pull the plug. See what comes out.... I've had this bite a couple of guys before- they turned on their bildge pump, heard it run, and saw nothing come out, and figured "bildge is dry".
It doesn't take a lot to clog a bildge pump up.... and it's really hard to find that "illusive 200 RPM's" under the hood when it's actually being hauled around in the bottom of the hull.

Worth a check... if you've not already been there!

[G-man]

my XB did the same thing back in Dec ,,, wouldn't run over 5800,,, then a few weeks later wouldnt run over 5400.... after checking a ton of different things it ended up being the injectors - they needed to be cleaned. My guy cleaned them, now I'm running over 6200 again!

[Oldgeezer]

If you have not been using Quickleen, you might want to based on what Tony Brucato has seen over the years. Here is some interesting information based on a thread over at S+F.
"We have flow tested and cleaned a lot of injectors and seen some pretty bad ones.
When we pre-flow a well-used set that looks perfect after 12 years of use, I have to quiz the customer about their maintenance habits.
Twice now this has happened, and both times the customer claimed to have used Quickleen from day one, as well as a fuel stabilizer over the winter.

I wouldn't expect that you could completely restore a dirty set with an additive, and it certainly couldn't do anything for worn injector mechanisms.
It would be good insurance though."
After having read that previously and other information in this BBC section, I am sold and now use it without fail. JMHO though.

[esdbass]

Quickclean & Merc Stabilizer in each and every drop of gas you put in the tank

[mcstr21]

No water in hull, I wish it were that. I am lean according to the plugs. They are white not brown 4 out of 6. When I switched plugs out I used NGK Br8HS. But it was doing this before anything was changed. Are there filters in the cannister that may be restricting fuel flow?

[Oldgeezer]

Given that 4 of 6 are white, then there would seem/could to be a fuel issue-could be injector issues as mentioned. Change the plugs at minimum(no matter what) and have a professional take a look at the problem(Hopefully there is a Mercury certified mechanic in your area that you are comfortable with). Be aware though, that to truly consider the lean/rich condition of a motor(based on looking at the plugs) that you need to run the motor at WOT and then shutdown to get a "true" reading. Not the safest and not a method that I would recommend. We all may have many "good" suggestions but we are behind the keyboard and can not solve the problem directly. IM your email and I will send you .pdf copies of the Mercury manual for your motor if interested(Good reading and educational-LOL). I have the same motor as yourself and a continuing lean condition is a recipe for disaster and $$$$$$$$$. JMHO though. Good luck in all cases!

[EuropeanAM]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mcstr21 &raquo;</TD></TR><TR><TD CLASS="quote">No water in hull, I wish it were that. I am lean according to the plugs. They are white not brown 4 out of 6. When I switched plugs out I used NGK Br8HS. But it was doing this before anything was changed. Are there filters in the cannister that may be restricting fuel flow? </TD></TR></TABLE>

You DEFINITELY should be using the QL77CC plugs. It does sound like a lean condition from your limited "read" of the plugs. Filters, restrictions, improper fuel pressure, improper pressure regulator operation, or clogged injectors are all possibilities.

A couple of filter notes:

You have a water separating filter, a filter underneath the high pressure pump in the VST (on most models), a final filter in the top of the VST (under the pressure regulator), may have inlet filters on the injectors (some do, some don't), AND, if the outlet fitting on the high pressure fuel pump (at the top/front of the VST) has a 3/4" head (a 3/4" wrench will fit on it), there should ALSO be a filter screen inside it.

Verify all of the above- then verify voltage supply and ground supply for EACH injector (this isn't the simplest of tasks). If all check out properly- I'd definitely recommend getting the entire induction system off, and send it to Brucato. Their prices are VERY reasonable... in many cases, you can send it to them, have them clean and test/flow each injector, install new o-rings and seals, and send it back to you- all for LESS THAN THE O-RING KIT WOULD COST YOU!

One thing I will say, is that the EFI setups are more proned to injector restrictions, simply by virtue of their fuel pressures. When compared to the Opti's... the EFI's are running at FAR lower pressures (stock configurations, anyway).

[mcstr21]

im sent

[mcstr21]

You DEFINITELY should be using the QL77CC plugs. It does sound like a lean condition from your limited "read" of the plugs. Filters, restrictions, improper fuel pressure, improper pressure regulator operation, or clogged injectors are all possibilities.

i will buy set of ql77cc, and start checking filters to start with. No change and I will get local mercury man to start in on it.

[Oldgeezer]

.035 on those plugs. Might already know, but is recommended.

[rdb1028]

i think y'all have finally convinced me to change my NGKs and put in the chanpions------does it relaay make that much difference-------------- last dealer servcie they put in NGK&gt; but I bet i can change that.

[Gamblinman]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rdb1028 &raquo;</TD></TR><TR><TD CLASS="quote">i think y'all have finally convinced me to change my NGKs and put in the chanpions------does it relaay make that much difference-------------- last dealer servcie they put in NGK&gt; but I bet i can change that. </TD></TR></TABLE>

It seems to make a big difference in some, and others no difference. I'm running NGK Iridiums, and have been for three years, with no ill effects whatsoever. however, unless you're willing to gamble, I would stick with the Champions.

[kllr bee]

Only use QL77CC in a 3 liter per Mercury racing. I have always put a bottle of fuel injection cleaner in about every 5th tank of gas and never had a fuel issue. A good question is are you using 93 octane fuel all the time? Are you using Mercury Premium plus oil only? Have you checked your throttle to make sure the linkage is opening the butterflies all the way at full throttle? Have you checked your alternator output to make sure it is keeping the voltage up? Also check the plugins on the computers and cdm's they can get patially unplugged when the cowl is put on.Just a few questions that have not been asked but need checked into.
Richard

FYI a 250XB is not on the limiter at 6150 and will make more power above that number.
Good luck

[EuropeanAM]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kllr bee &raquo;</TD></TR><TR><TD CLASS="quote">Only use QL77CC in a 3 liter per Mercury racing....
FYI a 250XB is not on the limiter at 6150 and will make more power above that number.
Good luck</TD></TR></TABLE>

+1

Have seen some motors run just fine with the NGK's. On the other hand- have seen a WIDE ARRAY of problems from using the INCORRECT spark plugs as well- poor performance, skipping, ignition system breakdown at higher RPM's, and even one 3L EFI (running an un-named brand of plugs we'll just call "car-o-lite" that would trip the MPR and shut down the ECM). Have seen multiple cases where each of these were corrected SIMPLY WITH THE CORRECT QL77CC SPARK PLUGS.

Another item that we've not talked about- have you confirmed the accuracy of your tachometer?

[Largemouthlou]

All good tips and advise above... I will add that if a few of the plugs ya pulled out are white don't run till everything here has been done and checked by a GOOD merc tech!!!!!!!!!! Cheaper then the alternitive..

Post a close up pic if ya can of the plug..

[mcstr21]

great info guys and i will try to post pic of plugs, havent put pic on board before but there is no better time than now. Gonna replace plugs, check filters, take out all old oil replace with mec. premium., quickleen in gas(I do run premium), recheck plugs, then if no change I will pass it on to certified merc. mech. I really feel it is probably gonna be injectors. I will also ckeck all wire harness connections didnt think of that. Tach is correct based on past speed in correspondence with rpm. Lost 300-400 rpm and 4mph.