2550 Can(39)t get on plane-gctid407066

[Guest]

Took our new to us 2550 Ciera Sunbridge out for the first time last weekend. Started up great,filled up with gas left the marina warmed every thing up went to take off and would only reach 3000-3200 rpm 10-12 knts and won't get on plane. Engine has god compression temp is good 160-180 under load. Timing is at 12 btdc at idle, 32 at 3500rpm mercruiser ignition. Just got boat and am unsure of prop pitch will try to remove prop this weekend. Boat is now 50 miles away so its not easy to work on. I've had the engine out over the winter to replace the flywheel cover due to failed pds bearings. The admiral has the cabin seriously loaded for all conditions. I told her we don't need an epirb they can follow the debris trail to us, haha! Anyway the PO only used the boat in the bay as a party barge and it may have the original 15x19 prop that bayliner states as standard. I feel the boat is seriously over propped for the weight. It will take off like it going somewhere but when it should be getting on plane it stalls at 3000-3200 rpm. I found a 15x15 prop to try on ebay but was wondering what others are running? Engine is a reman 350 that came with the boat 150-160 compression took the plugs out while it was out and checked the cylinders and pistons with bore scope all looked good. I know it is a short fat heavy boat and don't expect a racer. I have new engine in the works 90's one piece seal truck block stroker crank vortec heads reverse dome pistons 9.0:1 comp which should help. Any advise would be appreciated. The nada spec on weight are 5100lbs. 105 gals fuel (700 lbs) 20 ish gls. water (160lbs.) 2 people 450lbs. plus gear so 6500 lbs+ ? Maybe 13 pitch untill the new motor is ready. Also what about the trim pin it is in the middle setting 2 would trimming under farther help? Again any advise would be welcome. The next mod will be duo prop but that isn't in the budget yet. On that note what year duo props would be a easy swap it currently has a 1985 280sp drive?

[Guest]

are your four barrels opening>?

[Guest]

Is the choke stuck closed or partly closed?

Too much weigtht in the back / transom area?

Excessive growth on the hull below the waterline?

Excessive growth on the leg, prop?

Wood / stick / branch stuck somewhere under the hull? Ie: between the leg and hull?

[Guest]

bradner wrote:
are your four barrels opening>?

Going out tomorrow I'll have to check those.

[2850Bounty]

MT Jeff wrote:

• 1 wrote:
• Timing is at 12 btdc at idle, 32 at 3500rpm mercruiser ignition.
• On that note what year duo props would be a easy swap it currently has a 1985 280sp drive?

The center set pin location seems to work best for these.

Is this propeller in good tune?

Is the bottom of the hull clean?

Ditto checking the carburetor's secondary throttle plate function.

• 1 wrote:
• I know that you are seeing 32* @ 3.5k rpm. Is there a chance that your advance becomes Full In any earlier than this?
  
  If it's coming Full IN too early, you may be detonating and not know it.
• Many of the AQ series 1.95:1 ratio Duo Prop lowers can be made to work..... but don't forget that re-shimming must be done.
  
  Also, if you go with a properly built 377/383 Stroker Engine, you may be able to use the 1.78:1 ratio.

[Guest]

makonnen wrote:
Is the choke stuck closed or partly closed?

Too much weigtht in the back / transom area?

Excessive growth on the hull below the waterline?

Excessive growth on the leg, prop?

Wood / stick / branch stuck somewhere under the hull? Ie: between the leg and hull?

Only extra weight in rear was a 48qt. cooler and the magma grill 2 adults, bottom in clean but not slick, has anti-fouling paint no debris you can see it herehttps://"http://s1159.photobucket.co...view=slideshow

[2850Bounty]

Many of the early 280 drives used the exhaust bellows flapper.

You may want to pull the bellows from the Intermediate housing connection, and look inside.

See if the flapper is OK, and make darn sure the bellows is installed in the correct direction for the flapper.

The bellows must also be indexed correctly, since both the flapper and Intermediate housing port are somewhat oval shaped. Wrong indexing, and the flapper will not fully open.

NOTE: if the flapper is shot, rather than replacing the bellows, remove the flapper from the bellows completely.

Then retro-fit a 290 exhaust flapper onto the lower unit exhaust outlet.

Less exhaust restriction this way.

.

[Guest]

My exhaust comes out the rear of the lower with flaps there it doesn't have the snout on it would it still have the flap? And is the in the intermediate where the bellows from the trans shield attaches? As for the rate of advance in the ignition I would have to check that. I have a snap-on advance timing light. It has a Mercruiser electronic ignition with the advance built into the module no mechanical advance in dist. I would have to get the numbers off the ign. box too compare I have a list some where with the different advances for various Merc modules.The hull is pretty clean I just took of the trailer the day I tested Its not slick as it needs new paint but no growth. When I bought it the PO said it smelled like burnt rubber I food the water inlet clogged with barnacles and one exhaust hose had a blister inside. The exhaust bellows was split also so it may warrant further investigation inside the exhaust. It does feel restricted so ill check the secondaries and if nothing there look into the exhaust. Im also going to see if I can get the prop off and determine the pitch, I've seen others on here with similar boats had to run 13-15 pitch props when loaded and the engine got older. I have one piece seal roller block with a fuel pump pad and set of vortec heads in shed I plane on working on this winter. That should help. But for now I have to work with what I have.

[Guest]

Went down to the boat today pulled the prop but couldn't find any numbers. Checked the secondaries on the carb all good. Changed the trim pin to the 1st hole (farthest in). Went out and did 19knts (21mph) at 3600rpm going out against the tide and wind and 21knts (24mph) at 3800rpm. I wish I could have found some numbers on the prop though. I purchased a 15x15 no EBAY to try if its not better at least I'll a spare. This was a big improvement over the 10-12 knts at 3000-3200rpm from last week though.

[Davidlyne]

Was that at WOT?

[2850Bounty]

MtJeff, is it safe to assume that your current WOT RPM is 3000-3200 rpm????

Something is holding your engine back from reaching WOT RPM. Propping down will give you a temporary fix for what is essentially being caused by a greater problem.

BTW, your center set pin location will be best.

I'll suggest again that you pull the exhaust bellows from the Intermediate housing and peek inside.

In either scenario below, the bellows flapper is not necessary. If one is there, I'd remove it!

If you have the exhaust outlet flapper, one of several things occurred;

1.... you have a rare 280 lower unit w/ flapper.........

2.... someone was lucky enough to have found a good 280 flapper and installed it......

3.... you have a 280 that has been retro fitted with a 290 flapper.....

4... you have a 290 lower unit.....

Any chance that you could plot out your ignition advance and post the numbers here?

Best to mark off your balancer with either a degree decal or hand mark it.

If decal, then it must be correct for the balancer diameter (probably 6-3/4" or 7").

If by hand, make a same size circle on paper and divide this into a 30* wedge.

Using a divider, set the points for the TDC-mark-to-30*-mark at the circumference, and transfer this dimension over to your balancer from TDC towards Port side, and scratch a new 30* mark onto the balancer.

High-lite this new mark with a white paint pen or _____!

Between the new 30* mark and the timing chain cover Zero notch (plus the 2, 3, 4 degrees each way) you will be able to time this engine for TA (total advance).

(make additional markings if you want to)

Strobe your timing marks with a timing light while in standard mode (iow..., stay out of the digitally advancing mode).

See what the progressive advance is at: 1k, 1.5k, 2k, 2.5k 3k and 3.2k rpm..... and then take it further and see if it continues advancing any.

Post these numbers here.

Everything can be dang near perfect, but if the progressive advance is not as per specs, you will not get the correct performance from your engine.

If nothing else comes of this, you'll at least have eliminated this as a potential cause.

Attached files [img]/media/kunena/attachments/vb/711292=30513-Degrees transfered to Harmonic Balancer.jpg[/img] [img]/media/kunena/attachments/vb/711292=30512-SBC TDC markings on Balancer.jpg[/img]

[Guest]

Davidlyne wrote:
Was that at WOT?

Yes at WOT

[Download_Complete]

MT Jeff wrote:
Yes at WOT

Something is very wrong. This engine should wind to 4500 RPM at wide open.

Standard prop on that boat was somewhere around a 15x15p.

CHeck the timing, and give it a full tuneup. Put a stock prop onto it, and test again. You should see mid 30s wide open, and 4500 RPM.

If you still aren't seeing that, time to do a compression test and to check the ratio in the drive.

[Guest]

Download_Complete wrote:
Something is very wrong. This engine should wind to 4500 RPM at wide open.

Standard prop on that boat was somewhere around a 15x15p.

CHeck the timing, and give it a full tuneup. Put a stock prop onto it, and test again. You should see mid 30s wide open, and 4500 RPM.

If you still aren't seeing that, time to do a compression test and to check the ratio in the drive.

I guess what I need to know is what are the operating parameters for this boat. I've only had it out a couple of times. It is a 2550 (wide body) 260hp Volvo 280sp drive. What prop, speed are others running? I don't know the current pitch prop it came with the boat, I pulled the prop and couldn't find any numbers. I purchased a 15x15 but it is a short hub so I need a spacer before I try it. Is this all I need to change from a long hub to a short hub? I'm a mechanic with 30+ years exp. so if I had a base line it would be big help. I have another block and some vortec heads in the shed so I could build another motor pretty cheap but I was wanting to build a 383 out of it. My manual says a 15x 19 prop which seemed like a lot of pitch for this size boat. I guess I'll try the 15x15 when the spacer gets here and see what she does. I replaced the plugs checked the cap and rotor changed the fuel filters set the timing at 32' at 3500rpm idle is is good, adjusted the idle mixture. The hull is clean, not slick but no debris it is hauled and rack stored and washed. Been in my driveway for a year so I know the bottom is clean. What is kind of puzzling is the dramatic change in speed by just changing the trim pin one hole to the furthest under setting.

[Mileskb]

MT Jeff wrote:
Only extra weight in rear was a 48qt. cooler and the magma grill 2 adults, bottom in clean but not slick, has anti-fouling paint no debris you can see it herehttps://"http://s1159.photobucket.co...view=slideshow

Your boat is much bigger than mine, but I'm just gonna throw this out there anyway.. My 21' Santiago is real finicky about getting on step (on plane) with anyone in the very rear seats (the seats on either side of the engine).

It's extreme. The boat bogs down, I can't reach 3000 rpm etc etc... all they need to do is take a step forward, like in line with my rear facing seats, and the extra weight has no affect at all. Also once on plane there is no affect of anyone sitting back there. But for some reason, if people are sitting in those seats, it won't get up and go. My boat runs great. In fact I actually have to hold it back as while the "rated" WOT is 3800-4200 I try to keep it at around 3000-3200 and it seems like I'm constantly pulling the throttle back especially if water gets real flat. At 3000 rpm I'm going about 20 mph.

In any case, I just wanted to mention the loading issue. It may not apply to you, but frankly I didn't think it would apply to my boat either.

Also, how are you trying to get on step ? I see a lot of people start with the prop up a little, then lower it as they speed up. For me, I do the opposite and it's the fastest for me to get up.

I start with the prop all the way down. As I already know the cruising position I move it there in two stages. At about 10 mph I trim up a little, then as I reach cruising speed I move it a little more into the cruising position and can back off the throttle a little so it settles in at about 3000 rpm. My bow is never really up this way. The whole boat just rises up and it all happens pretty quick.

I don't know where I read this method, but I really like seeing where I'm going at all times with all the crab pots and kayaks and such that are around here early in the season.

Anyway.. just food for thoughts