10 Pts to Answer 5.7 4100 WOT

[jeremyhuston]

I have a 98' Maxum 20 ft. with Mercruiser 5.7 When I purchased the boat it had bad gas. I since have pumped out the old bad gas, replaced with new high octane shell gas. I have replaced the water seperator/filter. New cap, plugs, rotor, wires. I set timing to 10 degrees advanced base time, set the mixture 1.5 turns out at base time setting. I went from 3800 RPM @ WOT to 4100. Verified with my timing light and it seems correct. I am at a LOSE!.. my prop is a 3 blade aluminum prop which is 14.5 x 19. This thing should scream. I also set idle RPM to 650.. WHAT AM I MISSING?

 

[jeremyhuston]

Re: 10 Pts to Answer 5.7 4100 WOT

BTT.... Come on guys.. someone has ideas. The thing seems like it runs ok.. Just can not figure out why this thing doesn't idle near 4800?? Speedometer shows 42 . Not GPS verified.. just seems like it should have more power. Ive also checked oil level

 

[cooter2506]

Re: 10 Pts to Answer 5.7 4100 WOT

Try ALL of these do not skip any. Your answer is in this list. Good luck to you.



List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[jeremyhuston]

Re: 10 Pts to Answer 5.7 4100 WOT

Notes below

Try ALL of these do not skip any. Your answer is in this list. Good luck to you.



List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel (done, new premium)
2. Propeller pitch or diameter, damaged blades (As noted 14.5 x 19.. Should be under propped)
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test (will check, but doesn't seem logical)
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse (checked)
5. Marine growth on hull and outdrive (clean)
6. Wrong gear ratio in outdrive (stock 1.47)
7. Restricted carburetor air intake (clogged flame arrestor) (cleaned)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive (help here? doesnt overheat.. what else to check)
9. Poor cylinder compression Compression Test (150 across the board)
10. Carburetor defective, or wrong type. (?? Factory.. It runs? what else)
11. Fuel pump pressure and vacuum (Again, runs?)
12. Boat overloaded, improperly loaded, or improperly trimmed. (nope. Me and wife)
13. Engine Overheating (stays at 180)
14. Engine timing and ignition system operation (checked as noted above, 10 advanced base timing, new tuneup)
15. Remote control cables and linkage for proper travel to open throttle plates fully. (verified, hits stop on carb)

 

[Fordiesel69]

Re: 10 Pts to Answer 5.7 4100 WOT

How about a vacuume leak on the intake manifold or the carb? The flappers may not cause overheating, its hard to say unless you look.

Also how do you know the timing is reaching full advance when at WOT? You can have perfect base timing and have NO advance, or little advance.

 

[jearl]

Re: 10 Pts to Answer 5.7 4100 WOT

dont know if this boat carbureted or fuel injected but if it has a carb would suggest rebuilding as you mentionedbad gas and could be nasty crud inside.

 

[Lyle29464]

Re: 10 Pts to Answer 5.7 4100 WOT

Could the boat have some water logged foam in it. Does it feel heavy? will it pop over a wave or plow through it?

2 nd thought is did you check your timing at 3000 rpm? If so what is it?

 

[picklenjim]

Re: 10 Pts to Answer 5.7 4100 WOT

Also how do you know the timing is reaching full advance when at WOT? You can have perfect base timing and have NO advance, or little advance.

This is where I would be looking.

 

[QC]

Re: 10 Pts to Answer 5.7 4100 WOT

12. Boat overloaded, improperly loaded, or improperly trimmed.

What about soaked foam? It's a 20 footer so may not have any floatation, but still worth considering.

 

[zx9rstv]

Re: 10 Pts to Answer 5.7 4100 WOT

pitch of the prop may be too big. larger the pitch the lower the rpms.

 

[jeremyhuston]

Re: 10 Pts to Answer 5.7 4100 WOT

First off. Thanks for suggestions.

I am sdfinately thinking I should rebuild carbon.

Next question. Is the thunderbolt ignition electronic advanced? What would keep this fromk on car advancing? Can I throw the muffs on and rev. To 3k rpmx in driveway to check advancement?

Also. No wet foam. This boat is super light.. actually wish it was a little heavier.. anyway.

Going to see if I can get a carb. Rebuild kit.

If anyone else can think of something let me know. Ill also spray something to check for intake leaks. I can check manifold vacuum as well.

 

[Lyle29464]

Re: 10 Pts to Answer 5.7 4100 WOT

First off. Thanks for suggestions.

I am sdfinately thinking I should rebuild carbon.

Can I throw the muffs on and rev. To 3k rpmx in driveway to check advancement?

"YES" see if this is your engine. http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF

 

[QC]

Re: 10 Pts to Answer 5.7 4100 WOT

Also verify the tach accuracy and can you get a GPS to double check speed?. Are you positive about the gear ratio?

Edit: Checked with a slip calculator and the Tach seems right to me at this point.

 

[krisnowicki]

Re: 10 Pts to Answer 5.7 4100 WOT

if the boat has tb V ignition, did you set the timing in base mode when you set the timing?

 

[Don S]

Re: 10 Pts to Answer 5.7 4100 WOT

10. Carburetor defective, or wrong type. (?? Factory.. It runs? what else)

Hi speed jets plugged up? Old dead fuel replaced in tank, what about all the junk in the carb? Rebuild?

11. Fuel pump pressure and vacuum (Again, runs?)

If it's low, it may not supply enough fuel to the carb at high rpm.

12. Boat overloaded, improperly loaded, or improperly trimmed. (nope. Me and wife)

Do you trim it up when running? If you have the drive all the way down, it will plow through the water, try trimming it up to raise both the rpm and speed.

14. Engine timing and ignition system operation (checked as noted above, 10 advanced base timing, new tuneup)

Did yo check the total advance to see if it's in spec and working?

 

[jeremyhuston]

Re: 10 Pts to Answer 5.7 4100 WOT

Ok. Im going to rebuild the carbon tonight. My marina said the carbon kit has an accelerator pump that may or may not work. What's up with that? Boat has a mercarb 2 barrel. Anyone. Have correct rebuild kit number? Ill also check timing advance. What could fail that would not allow timing advance?

 

[jeremyhuston]

Re: 10 Pts to Answer 5.7 4100 WOT

Ok. I rebuilt the carb tonight. Didn't have a chance to run it yet. I also read one old thread about that thunder v not advancing and it pointed to the module. I trued to see if the timing advanced and im uncertain. Will report how it runs tomorrow.

 

[NHGuy]

Re: 10 Pts to Answer 5.7 4100 WOT

Also use up that high test, change the fuel / water separator and switch to regular fuel. The regular stores more energy. On your motor there is a knock sensor so you really can't detonate the fuel due to low octane.

 

[180shabah]

Re: 10 Pts to Answer 5.7 4100 WOT

carb rebuild - include complete soak and blow out of all passages or just replacement of parts?

+1 for skipping the "high test" it doesn't do anything for you except cost more.....

 

[John_S]

Re: 10 Pts to Answer 5.7 4100 WOT

FYI: The '98 boat, may have a '97 5.7L 2brl (210hp), which does not have vortec heads, or a knock sensor. If vortec (250hp) it would have a knock sensor. While the T5 does have some adaptive features and might be able to take a small advantage of higher octane, 87-89 is all that is needed.

Advance is controlled by the ICM, and they can go bad that they do not adavance fully. Do not assume that seeing it move off the base timing that it is fully advancing. You need a timing light with adj delay to get reading at 3K rpms. If timing is retarded, and you have a knock sensor, the sensor and knock module need to be tested.

What elevation are you running at?