WOT not reached after rebuild

[Chris51280]

I rebuild a 19ft Century Boat over the winter and it won't reach WOT. I only get 3000rpm and after a while 3400 rpm trimmed and a max of 25mph.

The engine is a 4.3L with a 2bbl carb rated at 175hp.
Outdrive ratio is 1.84
Currently run a turning point 4 blade 14x19.
The boat weighs #2700 empty.

Engine is running good and was rebuild over the winter as well. New style exhaust shutters added

What prop should I use? The boat came with a ss 23p prop which I believe is way to big for it.

 

[alldodge]

Engine is running good and was rebuild over the winter as well

What rpm did you get before the rebuild?

 

[Chris51280]

Thats hard to say since I didn't want to push too hard. The transom and stringers were compromised and I didn't want to push my luck. Also the kids and the wife didn't appreciate me putting down the hammer. Had to get them used to boating and not scare em away

 

[alldodge]

Did it do better or worst then what its doing now?

 

[Scott Danforth]

start with a compression test

look at the flappers

check the fuel system, you may need to rebuild the carb.

 

[Chris51280]

start with a compression test

look at the flappers

check the fuel system, you may need to rebuild the carb.

The carb was rebuild last winter and again gone through after I had some problems. Would not start anymore and had it at a marina. I had some debris in it and a stuck float. Then it flooded and the mechanic told me I had a crack in it and needed another carb, I cleaned it and adjusted the float and idle screw to spec. Now it is fixed and running good without the outdrive engaged. See post in the engine section.

The flappers are the new style batwings and are opening freely.

I can do a compression test but the engine was also rebuild over the winter with the valves lapped and new piston rings.

 

[Scott Danforth]

The carb was rebuild last winter and again gone through after I had some problems. Would not start anymore and had it at a marina. I had some debris in it and a stuck float. Then it flooded and the mechanic told me I had a crack in it and needed another carb, I cleaned it and adjusted the float and idle screw to spec. Now it is fixed and running good without the outdrive engaged. See post in the engine section.

The flappers are the new style batwings and are opening freely.

I can do a compression test but the engine was also rebuild over the winter with the valves lapped and new piston rings.

so what is the compression. if the valves are not adjusted properly and hanging up, you would be low on compression.

your target numbers with a fresh rebuild are 150 psi in each bore, +/- about 5psi

the crud in your carb came from your fuel tank.

did you clean the tank out during the rebuild?

 

[Bondo]

Thats hard to say since I didn't want to push too hard. The transom and stringers were compromised and I didn't want to push my luck. Also the kids and the wife didn't appreciate me putting down the hammer. Had to get them used to boating and not scare em away

Ayuh,....... With that said, ^^^ It could be over-propped from since you bought it,....

Ya might need a lower pitch,.....

 

[Chris51280]

so what is the compression. if the valves are not adjusted properly and hanging up, you would be low on compression.

your target numbers with a fresh rebuild are 150 psi in each bore, +/- about 5psi

the crud in your carb came from your fuel tank.

did you clean the tank out during the rebuild?

The tank was empty when installed. I did have a new inline fuel filter added. I did run it on a gas can with just the carb filter protecting in the beginning.

I will check for compression tomorrow since I will be busy today.

 

[Chris51280]

Ayuh,....... With that said, ^^^ It could be over-propped from since you bought it,....

Ya might need a lower pitch,.....

That's my thinking. Just by looking around with other posts about props and such, I came to the conclusion that every boat is different and therefore need a different approach on what is best. Since the 14x19 is at 3000-3400, will a 14x17 4 blade work?
I have to add that I have anti-fouling paint on the bottom that is rather rough (multiple layers). I'm sure that that doesn't help my case. I will remove it anyways since I won't have it in the water that long.

 

[jimmbo]

Verify that the Tach is accurate. If you are getting 3000 - 3400 with a 19, a 17 isn’t going to get you near the proper 4400 - 4800. Also verify if the throttle linkage is adjusted properly and allows the carb to open fully. Is the Timing set properly, and is advancing to the correct spec as the engine speeds up? Are all the plug wires going to the correct cylinders?
You mentioned that the engine was rebuilt, what parts were replaced, was the rebuilder familiar with Marine Engines, or a guy who thinks it’s just a car engine, jammed in a boat?

 

[Chris51280]

Verify that the Tach is accurate. If you are getting 3000 - 3400 with a 19, a 17 isn’t going to get you near the proper 4400 - 4800. Also verify if the throttle linkage is adjusted properly and allows the carb to open fully. Is the Timing set properly, and is advancing to the correct spec as the engine speeds up? Are all the plug wires going to the correct cylinders?
You mentioned that the engine was rebuilt, what parts were replaced, was the rebuilder familiar with Marine Engines, or a guy who thinks it’s just a car engine, jammed in a boat?

Tach works and was checked before the boat hot rebuild. The linkage does open the throttle completely. I checked that when I hooked it back up. Timing was set again by the marina. They said it was off from my rebuild.

I rebuild the engine. I basically just swapped the block and the pistons over to the marine engine.

New rings, bearings, oil pump, gaskets, timing chain, seals.

The engine is capable of revving higher without the outdrive engaged in the water so I know it must be the prop size. a 4 blade 14x19 may be too much for the 175hp 2bbl engine. It is sluggish going on plane at 3000 max. I think the 4 blade 14x17 will be my best guess since the rpm will go up as soon you are on plane. so a higher rev to get you going should work. A smaller diameter @13.75 would probably be ok as well since the 4 blade just barely clears the little fin

 

[jimmbo]

Without the outdrive engaged, the engine would attain very high speeds, even with 1/2 the cylinders not firing. Check the Tach again, back to the rebuild, what parts were reused and what was replaced?

I haven't started on what could be wrong with the boat

 

[Chris51280]

Parts reused from the old Mercruiser: (Cracked and welded Block)
Heads, Intake, Carb, Fuel pump, Lifters, Crankshaft, Damper, Flywheel, Distributor and wires, Starter, Water pump, Alternator, Cover, Oil Pan,

Parts replaced:
Camshaft since the old one had one cam lobe damaged, Oil pump, Seals, Rings, Gaskets, Chain, Exhaust Manifolds, New exhaust flapper style, Carb rebuild, Spark plugs(recommended ones), Thermostat 140deg,

Donor Engine:
Block, Con Rods and Pistons

Engine fires right up with one prime. Temp is at 160F in the water, Oil pressure idling @40psi even when warm.

 

[jimmbo]

OK you did put a new cam in. Was the new cam a Marine Cam?

 

[Chris51280]

yes

 

[jimmbo]

Hmm. Timing is advancing as the engine speed increases?

About the boat. You said the stringers were in bad shape. Rotted? What condition was the Transom? Any water logged Foam? Is the hull bottom straight with no Hook?

 

[Chris51280]

I don't know about the timing advancing.
I believe I have a small hook bottom.
The stringers transom and foam were waterlogged. some areas were bad and some were ok.
The cam was bought on ebay and I compared the two camshafts. Plus it had the cam lobe for the mechanical fuel rod.

 

[Chris51280]

it is not a light boat and with gear and people in it we are easily in the #3400 range.

 

[Scott Danforth]

it is not a light boat and with gear and people in it we are easily in the #3400 range.

at 3400# i would want a small V8