Don't know what it is so I'm asking...

[Book'em Danno]

I bought a 1999 SeaRay 340 SD equipped with Twin 7.4L Mercruisers Horizons Inboards 760 hrs. I had it surveyed prior to my purchase and other than a few minor fixer uppers, the boat is in good conditions. I am new to boating, so unlike cars and motorcycles, I tend to stress a bit when I am faced with unfamiliar mechanical situations. So here it is; when I am increasing the throttle the RPMs and speed are both gradually increasing. As I get to 2500 RPMs, the boat seams to jolt as if it lost power, sort of a stall if dealing with a car with combustion issues, the gauge for the trim tabs goes crazy going to the further starboard side of the gauge and then returning to the port side. Then suddenly, the boat picks up RPMs to where they were and speed continues to increase as if nothing happened . This has happened to me more than I care to count but I will estimate since owning the boat mid July about 7 times and I've gone out every weekend. It is very weird. It takes about a second or two for this whole sequence to occur. Throttle increased to speed up to plane, boat speed and RPMs increase gradually to 2500 RPMs, the suddenly RPMs drop boat jolts and bow comes down as if decelerating abruptly, trim gauge goes crazy and then as if it never happened, RPM's pick up, speed continue to increase and boat runs like a charm. I maybe new but this can't be right. Oh and I have not activated trim tabs while increasing the throttle as I have not come to plane yet. This is the best way I can explain it.

 

[JimG]

Certainly not normal... Do you slowly increase throttle to get on plane or are you slamming to WOT (I slam to WOT and then back off when plan is achieved)?

I would be curious what the reaction is if you tried to maintain 2500 RPM's :huh:

 

[CliffA]

do both engines stumble at 2,500 rpm's or is it just one engine?.....

cliff

 

[Jimmy Buoy]

You say, "the gauge for the trim tabs"? Most 99 340 Dancers don't have any sort of gauges for the trim tabs… You can get trim tab position indicator gauges, but they are separate LED displays, not a single gauge as you describe. Is the gauge the "Engine Synch" perhaps? This gauge allows the operator to match the RPM's of both engines by sight. If one engine loses power/rpm the gauge would definitely act as described.

I'm assuming that the engines are Multi-Port Fuel Injection (MPI), but could you provide a bit more detail on this? Are they the High Output engines with 380HP?

What type of exhaust setup does your boat have? If you follow the exhaust tubes off of the engine, do they attach to a black can type muffler that is fixed to the engine room floor?

 

[CliffA]

You say, "the gauge for the trim tabs"? Most 99 340 Dancers don't have any sort of gauges for the trim tabs… You can get trim tab position indicator gauges, but they are separate LED displays, not a single gauge as you describe. Is the gauge the "Engine Synch" perhaps? This gauge allows the operator to match the RPM's of both engines by sight. If one engine loses power/rpm the gauge would definitely act as described. QUOTE]

+1....my thoughts exactly...I think he has one engine that stumbles at 2,500 rpm's which is causing the sync gauge to swing wildly side to side....

cliff

 

[rcknecht]

Assuming it is the sync, and by what you said, I can think of three possibilities... 1. Fuel problem: Bad fuel, fuel pump, filter, or other fuel related cause. 2. Electrical (ground, spark, etc.) 3. Water ingestion. Check your oil, if it is milky that is not good...

 

[Book'em Danno]

Certainly not normal... Do you slowly increase throttle to get on plane or are you slamming to WOT (I slam to WOT and then back off when plan is achieved)?

I would be curious what the reaction is if you tried to maintain 2500 RPM's :huh:[/QUOTE

I slowly increase throttle as I figured that be the way to do it.

 

[Book'em Danno]

do both engines stumble at 2,500 rpm's or is it just one engine?.....

cliff

I'd like to say both, but not 100% sure on that I'd have to get back with you on that.

 

[Book'em Danno]

Assuming it is the sync, and by what you said, I can think of three possibilities... 1. Fuel problem: Bad fuel, fuel pump, filter, or other fuel related cause. 2. Electrical (ground, spark, etc.) 3. Water ingestion. Check your oil, if it is milky that is not good...

I'll be able to check on this Friday, so I will respond then. Thank you all for the input thus far. I'm hoping it is nothing serious. I just filled the fuel tank so the fuel is fresh. Filter and the oil I'd have to check

 

[Book'em Danno]

You say, "the gauge for the trim tabs"? Most 99 340 Dancers don't have any sort of gauges for the trim tabs… You can get trim tab position indicator gauges, but they are separate LED displays, not a single gauge as you describe. Is the gauge the "Engine Synch" perhaps? This gauge allows the operator to match the RPM's of both engines by sight. If one engine loses power/rpm the gauge would definitely act as described.

I'm assuming that the engines are Multi-Port Fuel Injection (MPI), but could you provide a bit more detail on this? Are they the High Output engines with 380HP?

What type of exhaust setup does your boat have? If you follow the exhaust tubes off of the engine, do they attach to a black can type muffler that is fixed to the engine room floor?

I checked on on the engine specs and the are Mercruisers MPI high output 380hp. I know I fill both tanks this week so the fuel is fresh. Oil does not have water mixing with it as it does not have the milky look. So I guess my next option is to replace the fuel filters as previously suggested. Based on the way the dial on the gauge shots to starboard side, may lead me to the conclusion that the problem is with the port engine being the one that looses power at 2500 rpms. It is weird because power loss or engine stall takes about a quick second and then the engines continue normal operation as if it had never happened. No strange sounds during or after stall. I will check fuel filter and replace them. I appreciate everyone's input.

 

[CliffA]

IBased on the way the dial on the gauge shots to starboard side, may lead me to the conclusion that the problem is with the port engine being the one that looses power at 2500 rpms.

I am pretty new to twin engines but I think if the sync gauge swings to the starboard side that indicates you have a problem with the starboard engine, not the port engine...

cliff

 

[Do Over]

I am pretty new to twin engines but I think if the sync gauge swings to the starboard side that indicates you have a problem with the starboard engine, not the port engine...

cliff

we were saying the same thing....misread post

 

[JimG]

don't think so....if the needle swings to the starboard side it would indicate all your thrust is coming from the port motor...the needle is denoting how much power each individual motor is making....if it's light on power from either side it will turn to that side.


I think :grin:

I believe that's what Cliff is saying... if it leans starboard, give starboard more power to sync with the port. That's the way mine works.

 

[Do Over]

I believe that's what Cliff is saying... if it leans starboard, give starboard more power to sync with the port. That's the way mine works.

my bad

 

[RollerCoastr]

I wouldn't put the fuel filter very high on the list of suspects, since the engine runs fine at higher RPM's.

I have an issue with my port engine momentarily losing electrical power at higher speeds. I recently came across info that points to the ignition sensor. I wonder if that's what's going on here...?

 

[Sublimetime]

Check fuel pressure regulator- its a small diagram looking device located in the fuel pump/cooler on the bottom of motor. It controls fuel pressure change and it usually kicks in at about 2500-2700 rpm.

 

[dpmulvey]

Check fuel pressure regulator- its a small diagram looking device located in the fuel pump/cooler on the bottom of motor. It controls fuel pressure change and it usually kicks in at about 2500-2700 rpm.

A cool fuel issue? Say it isn't so!

 

[Jimmy Buoy]

I checked on on the engine specs and the are Mercruisers MPI high output 380hp.

No to be alarmist, but I believe those engines on that model had issues with exhaust water reversing and running back into the exhaust valve area after shutting down. This was due to the exhaust muffler "log" type not being adequate. The fix was to replace the OEM mufflers with "water lift" mufflers. I know there were engines that had issues with rusted exhaust valves to ones that needed to be replaced due to water intrusion grenade'n the engines upon startup. This is why I've asked about your muffler type. Water intrusion can have some damaging effects on your engines that could show once load is applied.

Most would have been changed to the "water lift" design by now, but it would be wise to double check. Hopefully your issue is something simple.

 

[Book'em Danno]

Water intrusion can have some damaging effects on your engines that could show once load is applied.

JB water intrusion into engine could be identified by the milky oil rcknek mentioned correct? If so I may be ok as the oil looks normal.

 

[Book'em Danno]

JB also just learned that in 2013 the boat exhaust manifolds, risers and elbows were replaced. I'd hope that this is a good thing right?