89 Regal, 3.0 liter mercruiser, low rpm at wot

[slag]

At WOT in our boat, the tach only reads a hair under 3000 rpm with this 19 degree 3 blade prop, and dead on at 3k with the 17 degree 3 blade prop, both aluminum. If I wasn't firing on all cylinders, would 3k rpm be about the norm? I can never start it up and have it idle without first disengaging the drive, starting it with a bit more throttle, and then dropping it back to neutral.

I know, I know, after I pull the plugs I'll probably know more, but still, was just curious if my tach could be that far off, or would a missing cylinder show the 3k WOT. I'd think on a 4 cylinder I'd really notice a miss, but at WOT, it sounds and feels good..

I did put a can of Seafoam in the tank and filled it up because it had been sitting for a few years previously, but I dont' feel its a fuel issue at this point.

 

[slag]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

i took the carb off and the bowl was filthy. I had good spark on all plugs which is why I did this. I'm going to clean the carb out and try try again tomorrow to see if it runs better.

 

[Eric 3.7LX Alpha 1]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

4-year old gas is definately not a good thing.
If that does not fix it here is a great checklist for you to go over:

http://forums.iboats.com/showthread.php?t=295070

 

[slag]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

Still having this problem:

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
Gone through 1.5 tanks so far, no change
2. Propeller pitch or diameter, damaged blades
2 different pitches, a 17 and a 19, both 3 blade, no change
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
Nope, checked the pickup tube and anti siphon valve and it was clear and worked when blown through.
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
Oil level is correct
5. Marine growth on hull and outdrive
Nope, its clean
6. Wrong gear ratio in outdrive
Possibly, but i think its the original outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
Cleaned with carb cleaner until it drips clean. Looks clean
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
Possibly.. Haven't checked.
9. Poor cylinder compression Compression Test
All checked out fine except rear cylinder which was about 130 PSI. Still ok though.
10. Carburetor defective, or wrong type.
I rebuilt it and its clean and looks good. its a mercarb.
11. Fuel pump pressure and vacuum
Haven't checked pressure yet
12. Boat overloaded, improperly loaded, or improperly trimmed.
Nope
13. Engine Overheating
Nope
14. Engine timing and ignition system operation
Nope. timing is 6 degrees BTDC, Dwell is spot on around 29-30
15. Remote control cables and linkage for proper travel to open throttle plates fully.
Plates fully open when visually checked

I'm at a loss......

 

[Bondo]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

6. Wrong gear ratio in outdrive
Possibly, but i think its the original outdrive
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
Possibly.. Haven't checked.
11. Fuel pump pressure and vacuum
Haven't checked pressure yet

I'm at a loss......

Naw,.... I'd say yer not quite Done yet...

I'm guessin' #6.....

 

[slag]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

I need to get the serial number off the outdrive and see what its set at.

I revved it up without a load on the muffs for about 5 seconds and the valves started floating around 3800 rpm. I don't think this engine can do 4500 rpm.

 

[daydreamer1252]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

Would suggest you confirm boat tach with another tach...a shop tach, maybe
the one on the dwell meter??....It may be that simple...wouldn't expect valve float that early......are you sure it was valve float? Just askin'

 

[slag]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

Would suggest you confirm boat tach with another tach...a shop tach, maybe
the one on the dwell meter??....It may be that simple...wouldn't expect valve float that early......are you sure it was valve float? Just askin'

I ordered a portable tach today but i might use my neighbors on the dwell meter tomorrow, weather permitting.

I hope its just off, but who knows...

 

[Heller1]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

my tach was reading 4,000 at wot. Hooked it to a timing light/tach, it read 4650 at wot. tachs can be way off

 

[HT32BSX115]

Re: 89 Regal, 3.0 liter mercruiser, low rpm at wot

I ordered a portable tach today but i might use my neighbors on the dwell meter tomorrow, weather permitting.

I hope its just off, but who knows...

Yeah, until you KNOW what the RPM is, you're spinning yer wheels (or prop as it were!)