SBC, down on power

[mneal]

1st off, I am unsure of the rules of the forum, whomever moderates this feel free to delete post it outside the boundaries/rules. Anyhow I know there are couple very knowledgeable marine techs here so i thought I would post here as well. On to my question, I have a 99 Vovlo Penta 5.0 GL with about 700 hrs on it and it has been down on power lately. I do a ton of wake boarding and typically have a lot of weight (ballast) in boat so the power decreases super noticeable. (struggles to get on plane). The tune up is relatively fresh (~50 hrs) and I checked easy stuff first. (throttle linkage for PP etc. to ensure it is going WOT, all checks OK). It runs smooth, good idle etc so I doubt it is valves or something internal etc. I have not done compression test lately but plan to do that for warm and fuzzy. I checked timing advance and my factory manual says it should start at 3degree at 600 RPM and go to 26 BTC at like 3400 RPM and above. I checked it today while boat was in water and it stopped advancing at 22 degrees. The mechanical counter weights seem to operate smoothly by hand and and rotate as far as they are supposed to. What would limit the total advance and think that is it? I also noticed that although the motor has 4 barrel intake , it has adapter plate and holly 2 barrel so I might upgrade to a holly or edelbrock carb 4 barrel. I would hate to give it low end torque though (wake boarding). I suppose a properly adjust carb with secondaries would not though...true? Any thoughts on the timing or reason for power decrease?

[R&T Babich]

Maybe you have a little water in your fuel system. My friends 2004 Malibu Wakesetter did not come with a fuel/water seperating filter - just a regular in-line canister type. Last week he took it out and was losing power at higher speeds. It has an Indmar 350 fuel injected GM engine. When he opened up a fuel rail a little water came out with the gas. He then drained the tank (of course has had just filled it up) by pumping it thru a new fuel/water seperator he got at Walmart for $25. No more problems after that. He had never filled it with gas at a marina, but had not always kept the tank full over the winter. It seems after 3 years the water condensing in the tank just became a problem. Our 2000 21V 350 Mercruiser Mag MPI has a fuel/water seperating filter mounted on the engine by Mercury. So did our 1975 302 Ford Mecruiser.
Anyone have and Indmar? Did it come with a filter/water seperator from Indmar or did Tige put it in?

[mneal]

It has factory seperating filter, I can replace that and drain old one too look for water. Easy enough to try.

[mneal]

Changed filter tonight. I drained the old one into clear glass and it was fine, no water. I double checked and the advance stops about 20 degrees. (is 3 BTDC at idle, right where the manual says it should be for 87 octane. I might try to advance it slightly and sea trail it to see if it pings, but since it all electronic I doubt it moved.

[FIC]

I dont reccomend changing the timeing its electronic and really dought thats the problem, has the engine ever overheated ? the reason im asking is if it ever got marginally hot there are to flaps in the exhaust which melt and will restrict the flow. The reason its not wise to advance the timing is these engines are under load constantly and run lean if you run more advance you risk burning a piston. Also make sure that your prop is good , the rubber inner sleave could be going bad and slipping.

[mneal]

It did get hot once about 2.5 yrs ago (real hot, hit a plastic bag and thought I killed the motor). Anyhow it and melted the internal flapper on one side (starboard got hotter that SBC water flow I guess). VP does not sell the flappers anymore as they deemed them unneeded so there is none. As i type this I think about it more and I am 98% sure I removed the other side too while I was at it but it was like 3 yrs ago so not 100%. Maybe I should pull the drive and see if it is stuck in transom or Y pipe.

As far as timing, that is what I was thinking with the timing to, no points all electronic so it should not move..ever. (well i guess lack in timing chain would move it...slightly.
I checked compression tonight and changed plugs, compression was about the same as it was ~250 hrs ago. One odd thing is back plugs were wetter as I did compression test. I thought they were getting wet, I thought from the cranking with no ignition doing compression test , but the front side on the last side were pretty dry when I got over there. (started the compression test and did it in 1-3-5-7-8-6-4-2 order)

Anyhow the compression test results:
#1 172psi
#2 160psi
#3 169psi
#4 170psi
#5 175 psi
#6 165psi
#7 172psi
#8 170psi

Numbers look god too me, so I guess it is not major internal problem.

[FIC]

You never said about your prop, also you could have a bad power valve in the carb.

[spharis]

Could also be trash in the metering block.

[mneal]

I have two props I typically run, a 17 pitch to keep it in the sweet spot for wake boarding and a 19 for cruising. Power is down with both so I am sure not the prop. I cleaned and metering block and checked power valve too.

[R&T Babich]

Is your engine completely enclosed? We had a '75 Cobalt 302 Ford that had a split in the exhaust bellows that was putting steam in the engine compartment under load with a subsequent loss of high end power. I opened the engine cover when it lost power and the speed picked right up. It was hard to tell there was steam because it wasn't enough to get everything wet.

The 302 had a Carter 2v and I replaced it with an Edelbrock 4v manifold and a Holley 450 cfm 4v. It pulled better across the board, but I think trying to get all the exhaust out thru the prop on the Mercruiser outdrive was limiting the power.

[FIC]

You might want to due a fuel pressure and volume check it might be border line, are you able to reach top speed and rpm.

[mneal]

No, it is down both in top end RPM and speed. The VP has a electric fuel pump so I really did think much about the decreased volume/pressure but I guess it is worth checking. It does not really act like fuel starving situation, never feels "lean" just reduced power. I honestly thought the PP was mis-adjusted and I was not getting WOT because otherwise runs perfect. (I have checked that and sadly not the case.

You might want to due a fuel pressure and volume check it might be border line, are you able to reach top speed and rpm.

[mneal]

I took drive off this afternoon, I really hoped to see a stuck flapper like FIC suggested, but sadly it looks clean in thru the bellows to the "Y" pipe.

I was due to take drive off and grease everything and check alignment anyhow so all is not lost.

[FIC]

What is your top rpm mine use to go to 4700 to 4800.

[mneal]

Used to go about 4800 RPM with the 19, with the 17 I never hammered it WOT top end because I knew it was always under proped. I dunno what it is now but I would guess 4100 maybe.