250 XB HELP NEEDED

[jamiefrench]

First of all I will give you a little history about the problem. The problem started about 2 years ago. I lost speed and RPM. I use to run approximately 80 and now I have a hard time getting to 60. It has bee in and out of the shop 5-6 times. And $5000 later I still have the same problem. No here is what it does. Sometimes I can get it up on plain and sometimes I can't. If I have someone go to the front of the boat it will get up o plain, but it does not have the power and speed it did. I was running a 27 pitch Yamaha prop when it was running good. Now I have a 25 pitch Tempest. The same thing happens. Put on a 19 pitch prop it shot me right up on plain and right to the rev limiter. I am rumming premium gas and the correct spark plugs. Yesterday I decided to put motor in a tank and check for spark. I had spark on all 6 cylinders, but I did notice when it was idealling it was back firing a little. I also noticed that there was no exhaust coming out by the prop, but when it backfired you could feel a little burst of exhaust coming out. The exhaust was coming out thru the ports above the lower unit. Is this normal????? I do not know. T

[CRIMSONGAMBLER]

Drop the lower unit and make sure the exhaust is clear and reach up inside and make sure the tuner has not come loose and turned.

[jamiefrench]

Where should the exhaust come out at idle???? One more thing I also noticed when it would backfire/sneeze I could also hear air coming out by the injectors I think. Thinking about making the 18 hour trip down to Don at European.


Modified by jamiefrench at 10:08 AM 4/24/2010

[kllr bee]

First thing to check is the throttle linkage. If you have a hotfoot get someone to mash the pedal all the way and make sure the butterflies are opening all the way. If no hot foot more control lever to full throttle and check. This is very important because the throttle position sensor reads fuel and time imput by how far the butterflies are open. I had this problem on my boat. It slowed to 80 from 98 . Second on the sneezing at idle. That is caused by the throttle sensor being set too lean, it needs to be set but you need a test harness to set it. Cost about 80 bucks and Don can get it for you. Also with the harness you can check the TPS for a dead spot which could be the culprit. Check the throttle and post results then we'll go from there.
Richard

[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">First thing to check is the throttle linkage. If you have a hotfoot get someone to mash the pedal all the way and make sure the butterflies are opening all the way. If no hot foot more control lever to full throttle and check. This is very important because the throttle position sensor reads fuel and time imput by how far the butterflies are open. I had this problem on my boat. It slowed to 80 from 98 . Second on the sneezing at idle. That is caused by the throttle sensor being set too lean, it needs to be set but you need a test harness to set it. Cost about 80 bucks and Don can get it for you. Also with the harness you can check the TPS for a dead spot which could be the culprit. Check the throttle and post results then we'll go from there.
Richard</td></tr></table>

+1

You also might need to check VERY carefully for an "intermittent fire condition". This can be caused by an intermittent CDM or coil, OR- it can be caused by a stator which has an overheating winding. In the later case, resistance checks of the stator (and VISUAL INSPECTION of the stator bobbins for signs of discoloration) may be benefitial.

[jamiefrench]

jamiefrench (6:32 PM 4/29/2010): Don I took your advice and found a dealer in Fon da lac, WI that had a dino and that would take the boat out on the lake. They had a rep from Mercury Racing come over and they checked it all out, they put it on the dino and that said everything was great. They are going to take it to the lake when the wind dies down. Is it ok if they can't figure it out for them to give you a call?? THANKS Jamie

[EuropeanAM]

Jamie.... they can certainly try.

However, if there's a Merc Racing Representitive there.... they've got access to a very wide array of information.