Please Help!! 88 OMC Cobra low power under load

[Capt_Sully]

1988 Bayliner Cuddy (1952CK) with OMC Cobra 5.0/4V (chevy 305).

I bought the boat in the fall after taking it for a test run. The boat jumped out of the water and quickly hit 55 MPH at around 4200 RPMs.

Since then, I have had the outdrive serviced/engine aligned, new distributor cap/rotor/points, plug wires, and plugs. Also new exhaust manifolds, riser, bellows, fuel filter and oil filter and oil. I also sprayed a crap load of carb cleaner through the carb and even let it sit for an hour with pure Seafoam (cleaner) in there. So...I thought I had cleaned out the carb good.

I put the boat in the water today and set the timing with the engine in forward idle gear. I set it at 9 degrees BTDC (one of my manuals says 8 BTDC and the other says 10 BTDC---I split the difference).

The engine sounds great with drive disengaged--not missing at all. Very responsive and revs up easily over 4500 RPMs (I didnt push it). I took it out past the no-wake and tried to open it up, but it had very little power. It slowly picks up speed and tops out at 33 MPH and 3000 RPMs. It seemed to be starved for fuel? I had some autolite plugs in there...but today I bought some NGK and that didnt help.

To recap...with drive disengaged (neutral), the engine is running SUPER! With drive engaged (under load), it only hits 3K RPMs/30MPH and very sluggish.

PLEASE HELP! I am supposed to take my family to Solomon's Island on Wednesday for 3-days of boating.

Thanks all!!
Sully

 

[Bondo]

Re: Please Help!! 88 OMC Cobra low power under load

I also sprayed a crap load of carb cleaner through the carb and even let it sit for an hour with pure Seafoam (cleaner) in there. So...I thought I had cleaned out the carb good.

Ayuh,.... You Thought Wrong,...

It takes a Carb Kit, a Diptank,+ Compressed Air to Clean a Carb......

It sounds like it Is a fuel delivery Issue,.....

Check the fuel filters for Water,+ Rebuild or Replace the Carb,.....

 

[MikDee]

Re: Please Help!! 88 OMC Cobra low power under load

On a used boat, I always like to check the mandatory antisiphon valve (check valve) at the beginning of the fuel line at the fuel tank, and any in tank filter. These can get clogged up over the years. Don't ask me how I know I'll just say it's not a pleasant day on the water, sucking fuel out of the fuel line, just to get home! Yuck! I had my cousin there helping me who thanked me for the free volatile cocktail! He still teases me to this day, about it

By the way, Welcome to the forum!

 

[Don S]

Re: Please Help!! 88 OMC Cobra low power under load

List of possible causes of low WOT.

Engine Won't Reach Operating RPM. Check

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

 

[Capt_Sully]

Re: Please Help!! 88 OMC Cobra low power under load

Thanks gentlemen. I'm going to see what I can do right now at the river. I will post my results.

Thanks!
Sully

 

[CaptSully]

Re: Please Help!! 88 OMC Cobra low power under load

I disabled the ESA module and it had no effect today....however, with just me in the boat I did hit 4000 RPMs and 35 MPH just now (with and without the ESA). If I am at NO-WAKE and I open the throttle completely, it bogs out big time and slowly picks up speed. SUCKS!

Looking at the list below...and after I rule out the items I already verified....I'm left with:

• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Restricted carburetor air intake (clogged flame arrestor)
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[danond]

Re: Please Help!! 88 OMC Cobra low power under load

Engine off, look down the carb throat while someone pushes the throttle forward. You should see fuel squirting at a downward angle into the throat. If you don't, your accelerator pump isn't working (plugged, busted, hooked up wrong).

That pump keeps the engine from starving for fuel when the throttle plates are opened quickly. The result when it's not working describes what you're experiencing, anyway.

Plus, the comment about rebuilding a carb is dead on. You didn't do much, if anything, to help your carburetor. Take it somewhere and have a pro shop dip it and put a kit in it.

 

[CaptSully]

VICTORY!! 88 OMC Cobra low power under load

VICTORY!! 88 OMC Cobra low power under load

VICTORY....the boat is running at about 97%.

Here's what I found:
1. Number 6 spark plug wire (NEW) defective (grounding out)--compression on 6 cylinder good.
2. Number 8 spark plug wire (NEW) defective (grounding out)--compression on 8 cylinder good.
3. Carb gummed up

Here's what I did:
I replaced all the spark plug wires just to be safe and ran a half a can of seafoam carb cleaner through the carb. It is very responsive and fast now. I hit 4200 RPMs and 50 MPH. It does not LAUNCH out of the water...but it does jump pretty hard without bogging down.

Here's what's left to do:
1. Reset idle/timing. Dont know how to check/set dwell.
2. I have a 14 1/4 x 21 prop on there now. I am sure if I drop that down to a 19 I can get a few hundred more RPMs and get a better whole-shot to pull skiers.

I also got my first compliment on my boat....by an actual boat mechanic at the Marina. He actually stopped working on a boat and walked all the way over to tell me that my boat looked awesome. Wow...that was nice.

Here is my restoration photo album: http://rides.webshots.com/album/561348175yADjFQ?vhost=rides

Thanks everyone....finally time to enjoy my boat!!!!

Sully