mercruser 888 wont rev past 2000 when in gear in the water

[mauro.]

Hi guys I am back again, with still the same issue. My 888 wont go above 2000 rpm under load here is a list of things new on engine and its shape:
new comp cam
new comp lifters
new comp pushrods
rebuilt carb
new pertronix electronic ignition distributor
new coil
new wires
new spark plugs
good compression 145-160 psi on all cylinders
new fuel new oil and filters
correct firing order
and new hustler four blade 19 pitch prop
I am at the end of my wisdom I have been chasing that problem for the whole summer now and just cant seem to figure it out completely. a thought i have had is that maybe the sterndrive is drawing power bearing seized or something? Also when running it on dry ground with muffs there is a loud howling noise coming from sterndrive when going above 2000 rpm(it does that no problem it will go to 3-4k but that doesn't mean much I guess is this normal? Any way any help would be greatly appreciated thanks a lot
Mauro

 

[alldodge]

Assuming same drive
What prop was on the drive prior to rebuild?

 

[kenny nunez]

Have you ever removed the suction tube from the tank? There is a fine mesh filter in it that clogs up over time.
Get a 6 gallon outboard tank and take take the boat out. If it does better the engine will empty the tank pretty quick.

 

[racerone]

Start motor in the water.-----Pull one plug wire at a time.-- Note difference in RPM / sound.---Sounds like plug wires are not hooked correctly.

 

[kenny nunez]

888 firing order 13726548. If it only idles smooth with 15426378 then you now have a 170 hp engine.

 

[mauro.]

Assuming same drive
What prop was on the drive prior to rebuild?

three blade 21 pitch re pitched to 17 pitch mercruiser prop

 

[mauro.]

Have you ever removed the suction tube from the tank? There is a fine mesh filter in it that clogs up over time.
Get a 6 gallon outboard tank and take take the boat out. If it does better the engine will empty the tank pretty quick.

I tried pouring in some fuel in the carb while it was at 2000 but made no difference it actualy even slightly staled

 

[mauro.]

888 firing order 13726548. If it only idles smooth with 15426378 then you now have a 170 hp engine.

The new comp cam has the older 15426378 firing order instead of the 351 firing order. It is suposed to put out around 200 hp with that cam

 

[racerone]

I think something is wrong with firing order / wrong distributor cap / plug wires going to wrong cylinder.

 

[mauro.]

Start motor in the water.-----Pull one plug wire at a time.-- Note difference in RPM / sound.---Sounds like plug wires are not hooked correctly.

so it will still run smooth if hoked up incorrectly? it does not back fire it purrs like a kitten just wont rev up no power

 

[mauro.]

what do you mean by that? is it possible to have a wrong cap? I rechecked the wires and they are going round the dist the correct way and correct firing order leading to the correct plugs. except if cylinder are numbered incorrectly is that possible on those fords? thank you for those replies
Mauro

 

[alldodge]

three blade 21 pitch re pitched to 17 pitch mercruiser prop

So it was actually a 17P?
If it was a 3B-17P, using a 4B-19P is the same as a 3B-21P

The new comp cam has the older 15426378 firing order instead of the 351 firing order. It is suposed to put out around 200 hp with that cam

This brings up another question for clarification. Your original motor did have same firing order as the new cam? Both were and still are 15426378 correct

 

[mauro.]

So it was actually a 17P?
If it was a 3B-17P, using a 4B-19P is the same as a 3B-21P


This brings up another question for clarification. Your original motor did have same firing order as the new cam? Both were and still are 15426378 correct

no the original cam had the 351 firing order of 13726548. as for the prop do you think it is to big? I thought changing pitch by one inch only changes the rpm by 300 is that correct?

 

[alldodge]

Going from 3B-17P to 3B-19P will change rpm 200-300. Changing to 4B prop that is like 17P to 21P

Going to need someone better then me to wonder what changing the compression and exhaust stroke for 6 of the 8 cylinders will or will not do to power

 

[mauro.]

so far every body that i have asked cant explain why i have no power they all got to the end of their wisdom same counts for me

 

[alldodge]

Going to need someone better then me to wonder what changing the compression and exhaust stroke for 6 of the 8 cylinders will or will not do to power

Hey @Scott Danforth can you advise if it makes a difference

 

[Scott Danforth]

the two SBF firing orders are basically like an SBC/BBC 4/7 cylinder swap. it evens exhaust pulses, bearing loading and fuel distribution and smooths idle a bit. its good for about 5-10hp not enough to stress about unless trying to eek out every last bit of performance however that is the way Ford ground the cams for the 351 and 302 HO motors.

302 15426378
302 HO and 351 13726548

lets look at things that can limit power:

first thing I see.... Pertronix...... what is the curve you have? what is your base timing? what is the all-in timing at what RPM? Have you verified the timing curve of the distributor. My guess is the points dizzy had a better curve.

Second thing I see. Rebuilt carb. rebuilt by whom? Not reving under load is a classic indication of lack of fuel. could be fuel flow (restriction to the carb), could be fuel distribution (plugged and gummed carb). reading fuel pressure at the carb while under load will help troubleshoot the inlet side.

Next, since the intake and carb were off, was the throttle cable throw verified? does mashing the throttle lever on the controls actually pull the throttle plates open fully?

Now onto the cam. how was this flat-tappet beauty broken in? because todays oils are not conducive to flat tappet longevity. Comp cams recently had a bad batch of cores, and the flat tappet lifters are iffy. measure the actual cam lift and compare to the cam card. The cam was broken in at 2000 RPM for 20 minutes with a high zinc oil, correct?

How was the cam degreed? Just slapped in, hoping the key and timing chain are in the right locaiton, or was a degree wheel

Did you measure the pushrod length and verify proper length?

spark plug gap? what did you set the plugs to?

howling on the muffs. this is not something you normally hear out of an MC/MR/Alpha. so something is wrong there

pouring fuel in the running engine is never a good thing. the fuel isnt atomized, it could hydrolock, or worse, backfire setting your eyebrows on fire.

 

[mauro.]

wow thank you a lot I will answer those questions from the top on down wards.

The timing curve is the one with the silver springs it goes to 24 degrees advance at around 15 hundred. I loosened the dist hold down bolt while engine was running maxed out didn't make a difference was set correctly.

The guy who rebuilt it is a reputable race engine builder so i don't suspect anything foul there I had it apart and looked nice and clean fuel pressure though would be a thing to check I guess. If you figure pouring a mist of fuel down the carb cant determine that.

Throttle opens as far as it will go

yes cam was broken in with a zddp DRIVEN break in oil varying the rpm from time to time between 2000 and 2500 for 35 min. Then drained oil and refilled with marine oil and LUCAS zddp additive

cam was aligned with timing marks lined up correctly as they say to do in the service manual

pushrod length was measured for proper length

spark plugs are the NGK ar6fs the correct one bran new

Thank a lot

mauro

 

[mauro.]

oh and another thing for one turn ofthe engine the prop will turn about 1 and an 1/8 of a turn can you tell if this is the correct gear ratio maybe some body messed up there? any way appreciate your help
Thanks a lot
Mauro

 

[alldodge]

No way the ratio should be that high. That means the prop is turning faster then the motor, and it should be the other way around