help, no rpms

[mh11]

Hello it's me again 1978 galaxie 22 xl merc 260

Got it on the water today, runs worse than before last year.

Used to turn 3900-4000 rpm

Today 3000 rpm, and it backfires worse at WOT.

Replaced fuel filter at carb, and the water seperating unit as well.

Help!!!! Should I blow out the anti siphon valve on each tank?

 

[Don S]

Re: help, no rpms

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.

 

[Bondo]

Re: help, no rpms

Today 3000 rpm, and it backfires worse at WOT.

Replaced fuel filter at carb, and the water seperating unit as well.

Ayuh,... Probably Trash in the Carb,.... Rebuild, or replace it...

 

[mh11]

Re: help, no rpms

1. Fuel condition. Type and Octane possibly old fuel
Brand new fuel
2. Propeller pitch or diameter, damaged blades
prop 3 runs on it 17p
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
Oil is correct level
5. Marine growth on hull and outdrive
Hull and outdrive are clean
6. Wrong gear ratio in outdrive
Gear ratio is correct
7. Restricted carburetor air intake (clogged flame arrestor)
This is where I think I may have a problem, the engine compartment is closed off except for the vents that go to blower, should I cut hole in top of engine cover and put scoop on?
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
Should I pull risers off and check this
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
Seems as if this might be problem, should I buy new rebuilt one?
11. Fuel pump pressure and vacuum
Can local boat shop check this for me?
12. Boat overloaded, improperly loaded, or improperly trimmed.
Trim is correct, boat not overloaded
13. Engine Overheating
Boat runs 135 to 140F steady, not overheating at all
14. Engine timing and ignition system operation
Local shop set timing and evrything for me. Should be good.
15. Remote control cables and linkage for proper travel to open throttle plates fully
Checked these, looks like they open all the way.

Let me know what you think please Don, thanks!

 

[gdombroski]

Re: help, no rpms

3. Restricted fuel pickup tube or anti siphon valve Fuel System Test

You didn't have an answer to this one. Blowing it out will probably not do any good. Just replace it about $15.