300xs. Problems

[Rayzor]

Do realize that the motor becomes much louder at idle after performing this mod. These cowls are thouroughly insulated for sound deadening, and when you remove a section of the insulation and vent the cowl, the noise from the air pump becomes much louder at an idle from 800 - 2,000 rpm. at a low idle, 600 - 800, the noise isn't bad. I've removed all of the insulation from my cowl for weight reduction, and I noticed it was retaining water at the lower edges. With the vent in the top and all the insulation removed, I will admit that the engine noise is somewhat annoying when at a fast idle, but I'll put up with it to not have the problems associated with the problems caused by the factory air inlet setup........

[Revolution141]

Got home yesterday and turned my cowl over to check the insulation. It had a perfect black oily ring directly above the intake and was starting to cut through! Ripped out all insulation except piece over air compressor. Took down to the river (perfect conditions) and ran only to still have the problem. Took the cowl off and ran without and checked for water near tps. It is spotless dry. What I do have is a hairline crack in starboard head just between 1 and 3 in the outer water gallery. You can't even see it except for the water pushing through in a perfect line about 5cm long. I'm certain this crack is only on outside in water gallery and at wot it is just a tiny trickle of water escaping. Will probably just Devcon for now. Unfortunately im still no closer to finding a cause for the miss/loss of rpm??

[Adam McKeon]

I would still hook the computer up to it and do a throttle sweep to see if the output of the TPS is correct... the TPS is VERY key to the motor performing properly. The butterfly to the throttle body can be wide open but the motor wont do much without that TPS being in 100% perfect working condition. Good luck..

[hp1050]

Get it to a dealer or someone with diagnostic software look at your coils under load use cylinder cut out, also have a close look at the coil harness check all connections apart from that remove the fuel injectors and have them flow tested but ensure that they do it as a full cycle test not just at maximum.

[Revolution141]

Finaly got some pics up of the boat.

[Revolution141]

Went down thismorning armed with spare PCM, trigger, TPS and plug leads (swear I replaced these 70 hrs ago). First thing I did was swap plug leads. Ran it for an hr solid at wot and tried everything including trimming in and trim tabs full in. Never missed a beat. So I'm thinking I'll be, it's a dodgy plug lead. Then I swap back to old leads and run the begesus out of it again.... Won't do it now either. At the end of all this I got no idea the cause. Just hope it doesn't start doing this again in 12-18months time!

[jpf091959]

I am going to try something like this
http://secure.mckinneycorp.com/AMAZI...asp?Cc=NACA&Bc=

or

http://stillen.com/product.asp?id=PW...r=&make=&model=




or

[native2]

I am going to try something like this
http://secure.mckinneycorp.com/AMAZI...asp?Cc=NACA&Bc=

or

http://stillen.com/product.asp?id=PW...r=&make=&model=




or

I like these!!!

[Skater 32]

Very nice ! But for those who want a NACA duct that fits the upper countour of upper cowl try these on . Made from ABS plastic . The forst few were pulled from molds and next week will have more info

[Skater 32]

more pics

[jpf091959]

Can you integrate a filter, I live in the desert and dust storms can come up anytime.

[Skater 32]

why not just alter a K+N fiter over intake ? At first I thought this was a Joke !

[Revolution141]

Well my worst fears came true and my cutting out problem has returned again to haunt me.
after I last had the problem which I seemed to have solved by changing plug leads she ran like a clock for 6 months or more. I was running down a channel a month or 2 back (dead calm conditions wot) for about 40 mins when it felt like I hit something in the water. After another 15 sec same again, that's when I realized the motor was actually starting to miss. Got progressively worse until I found if I backed off 5% on the throttle it cleared up and ran fine. Have run it a few more times and it has got to a point where at any rpm or throttle position it feels like its down a cylinder. Tried swapping tps as suggested in previous posts with no difference. Was testing yesterday and found it would just intermittently drop in and out on one cylinder, at one point it was running on all 6 wot when it suddenly felt like it was tightening up, I backed straight off and came to a stop where engine completely died. I feared the worst but tried a restart in neutral. Motor fired, ran rough for a while but eventually cleared up and idled and free revved like normal. Have today pulled plugs and found all are very sooty and show almost no sign of the electrode tip being white like my old plugs. I'm assuming I'm loosing spark at least on one cylinder and seem to now have weak spark on all. No alarms on smart craft. Voltage good, fuel pressure good, water pressure good. Any suggestions?
Will be changing plugs, however this doesn't explain sudden shut down with no alarms.
really want to just unbolt this motor at sea, have had same issues from day one, now motor is 4 years old and mercury don't want to know about warranty even though I believe it's been the same issue intermittently coming and going.

[Revolution141]

Just pulled throttle body and checked reeds. All ok. Looked through spark plug holes (can't see much obviously) nothing obvious there. Put all old spark plugs back in bar one which had lots of corrosion on metal outer, swapped it with one still good from previous change out. Ran on trailer and hooked up timing light to every lead, all fired on test light. Could the trigger be faulty?

[revlimiter]

You held it wide open for 40 minutes,then it starts to act up and you back it off 5%?Im sure it appreciated it.