1990 v4 140 wot rpm?

[hermazoid]

Recently purchased:
I have a 1990 Evinrude V4 140HP, Model E140CXESR.
Mounted on a 1974 Dusky 20FT CC.
Boat is used for fishing, I knew it would be no speedster.
Paper work I have (invoice) from previous owner shows the motor was installed by Dusky Marine of FL in 1991, with new Dusky drive (extended transom bracket), controls, etc. so I assume it was professionally installed.

I have a 15 x 17 alum prop, that may or may not have been original.

The boat will make ~4600 max RPM wide open throttle, giving a GPS speed of 23 KTS (25.5 MPH or so).
It seems slow to come up on plane.
I'm told the engine should make more RPM wide open

The motor runs smooth, a little hard to start cold, easy starts warm, and idles correctly. I have no other complaints about the motor.
I'd bet the boat weighs more than factory new, since it had a new deck put on it at one point before the new motor. Tests were done with full 50 gal tank and myself about 285lbs onboard .

I'd love some info/advice please:

What is the Mfg's recommended WOT RPM for this motor.
I'm told going to a 15 pitch prop might raise the RPM by 300-400 or so, and improve peformance
Any thoughts, advice?

 

[wilde1j]

Re: 1990 v4 140 wot rpm?

That engine should be propped for 5800 RPM @ WOT. 4600 is WAY too low.

Before messing with different props, you should make sure engine height and trim are right. At WOT, the AV plate should NOT have water on top of it. If it does, raise the motor until it doesn't. Then experiment with trim for max hull speed and let us know the WOT RPM.

It sounds like you will likely need to drop 4 to 6" in pitch, but you won't know until the other steps are taken. If motor is too low, raising it will increase hull speed, RPM and fuel economy.

 

[countvlad]

Re: 1990 v4 140 wot rpm?

because u just purchased this boat i would at least rebuild the carbs, change the lower unit oil,water pump and new wires and spark plugs....

19 pitch prop sounds a little big for the boat... but before you start changing things you have to make sure everything is in top shape.... check for any air, fuel leaks... then go from there...

wilde1j is correct you should be around 5800 WOT on the motor...

 

[hermazoid]

Re: 1990 v4 140 wot rpm?

OK, well I was able to secure a 15 pitch prop. the engine still tops out at ~4600 RPM, but now I'm getting top speed of 21 KTS (calm water). I ran the boat last weekend in bumpy ocean conditions for 75 miles, burned about 40 gallons. The boat seemed to run real well.
BUT, looking in the manual, there are a whole slew of reasons for the low WOT:

FUEL TANK & FILTER
poor quality/old fuel (nope I've burned about 60gal of good stuff)
fuel tank hose or vent restricted
restricted fuel pickup
restricted fuel supply system
faulty anti-siphon valve
clogged fuel filter
fuel system air leak

VRO SYSTEM
fuel or oil inlet fittings plugged
air leaks on fuel supply side
restricted fuel supply system
pulse hose restricted or leaking
plugged pulse limiter fitting
damaged VRO unit

LINKAGE ADJUSTMENTS
WOT stop screw misadusted

CARBURETOR
Restricted fuel distribution manifold
float valve stuck closed
float valve stock open
float setting incorrect
float valve installed incorrectly
carburetor base gasket leaking
plugged high speed orifice
plugged high speed nozzle vent
incorrect orifice size
pulgged float chamber vent
restricted/misrouted fuel supply lines

INTAKE MANIFOLD & LEAF PLATE ASSY
leaf plate gasket leaking
leaf plates bent, chipped or broken
leaf plate assembly screws loose

Man, this is overwhelming!

Where do I start?

Are any of these items, things I can dismiss since the engine seems to run well?

What is the best way to check for air/fuel leaks?

The fuel line runs form the tank to a canister fuel water separator filter inside the console, then to the transom where it runs thru a 2nd canister F/W separator filter then to an inline filter under the engine cover just before the VRO pump. The filters are all recent. Is this overkill on filters? Could too many filters be restricting fuel flow?

Any help/advice would be appreciated.

My immediate plan is to replace some of the older pieces of hose, check and retighten hose clamps, etc.

 

[Dennisanoka]

Re: 1990 v4 140 wot rpm?

Review what Wilde1j wrote above. If the motor is mounted too low in the water you will give up 200-400 rpm!

 

[hermazoid]

Re: 1990 v4 140 wot rpm?

Review what Wilde1j wrote above. If the motor is mounted too low in the water you will give up 200-400 rpm!

Yes, but the boat is a Dusky, and it was re-powered, including a new Dusky Drive (a bracket engine mount) installed by the factory with the motor in 1990, that puts the prop about 2-1/2 feet behind the transom, and the vent plate about 3" above the bottom of the transom. I'm told this is normal since the water flows upward after exiting the transom. I believe the factory installed the motor correctly.

Changing props should still change the RPMs even if it is mounted slightly off, right?

 

[wilde1j]

Re: 1990 v4 140 wot rpm?

Where the AV plate is relative to the bottom is not terribly important. The AV plate, if the motor is at the correct height, should be runni9ng dry @ WOT. My current boat has T 175's on a bracket, and the dealer who handled the repower several years ago, mounted them way too low. I ended up moving the motors up three holes to get it right. Riggers do this so there is zero chance of customer complaints of cavitation and blowout.

Don't assume the rigger did it right. Very few new boats are.

RPM should have come up 300 to 400 with 2" less pitch, so there's a pretty good chance something else is going on as well.

 

[hermazoid]

Re: 1990 v4 140 wot rpm?

Where the AV plate is relative to the bottom is not terribly important. The AV plate, if the motor is at the correct height, should be runni9ng dry @ WOT. My current boat has T 175's on a bracket, and the dealer who handled the repower several years ago, mounted them way too low. I ended up moving the motors up three holes to get it right. Riggers do this so there is zero chance of customer complaints of cavitation and blowout.

Don't assume the rigger did it right. Very few new boats are.

RPM should have come up 300 to 400 with 2" less pitch, so there's a pretty good chance something else is going on as well.

It looks normal running at WOT (well ~4600 RPM), I can see the plate right at the top of the water.

 

[Fl_Richard]

Re: 1990 v4 140 wot rpm?

Good! But it's still turning too slowly. I would start troubleshooting the engine. You could have bad spark on one or more likely a fouled carb. Running with a fowled carb will kill the engine. If the cylinder cant get gas it cant get oil. Be careful, 40 miles out is a bad place to loose your only engine.

 

[hermazoid]

Re: 1990 v4 140 wot rpm?

Good! But it's still turning too slowly. I would start troubleshooting the engine. You could have bad spark on one or more likely a fouled carb. Running with a fowled carb will kill the engine. If the cylinder cant get gas it cant get oil. Be careful, 40 miles out is a bad place to loose your only engine.

OK. But can an engine with a fouled carburetor or bad spark on even one cylinder run fine across all RPM's , idle perfectly, accelerate normally, no hesitations, no surges, no excessive smoke, no nothing except low WOT?

BTW - I was never more than about 10 miles from land, in good weather, with 2 radios, one a handheld, 2 GPS's, lots of boats in the area & people who knew where I was going and when returning, and I have BoatUS Gold towing.

 

[Dennisanoka]

Re: 1990 v4 140 wot rpm?

If you are convinced the engine is running as it should and the hull is clean then what's left is engine ht. and prop pitch. But theoretically even with hull in need of a cleaning you can still increase the RPM by reducing prop pitch and or raising the engine ht.

As what was said earlier about dealerships and how they set things up- when I bought my boat used, the previous owner assured me it was installed at the dealership but nonetheless RPM's were too low. I raised the engine 2 holes the RPM's came up as expected but it cavitated in sharp turns and pulling skiers so I then dropped it down one hole and reduced prop pitch by 2". I now have my 5500 RPM's @WOT. I started out at 4800 rpm's.

 

[Fl_Richard]

Re: 1990 v4 140 wot rpm?

Yup. A plugged high speed jet idles fine. Two strokes make so much power having a hole out can seem to run fine. Just a little slower. Especially on a new to you boat. You were never in it when it was running right.


Now it could be prop related. You said the 15" pitch prop had no effect on RPM only speed correct? To me this indicates the engine is running as hard as it can and it can only make 4600 RPM. Running depth isnt holding it back; pitch shouldn't be at only 15.. the only thing left is power-head or your boat is REALLY heavy.


BTW- I have twin 95 -150's

FUEL TANK & FILTER ----->All easily tested

poor quality/old fuel (nope I've burned about 60gal of good stuff)
fuel tank hose or vent restricted
restricted fuel pickup
restricted fuel supply system
faulty anti-siphon valve
clogged fuel filter
fuel system air leak




VRO SYSTEM
----->Start with the cheap stuff first -- Look for cracked hoses loose fittings the easy stuff. Does the bulb collapse? This indicates fuel restrictions and tank problems

fuel or oil inlet fittings plugged
air leaks on fuel supply side
restricted fuel supply system
pulse hose restricted or leaking
plugged pulse limiter fitting
damaged VRO unit

LINKAGE ADJUSTMENTS - ---->probably not the problem but easy to check
.
WOT stop screw misadusted

----> These should have been rebuilt recently. They feed fuel and OIL into the engines<----
CARBURETOR
Restricted fuel distribution manifold
float valve stuck closed
float valve stock open
float setting incorrect
float valve installed incorrectly
carburetor base gasket leaking
plugged high speed orifice
plugged high speed nozzle vent
incorrect orifice size
pulgged float chamber vent
restricted/misrouted fuel supply lines

INTAKE MANIFOLD & LEAF PLATE ASSY
---->>>Look for spitting out of carbs this would indicate reed -Leaf valve problems

leaf plate gasket leaking
leaf plates bent, chipped or broken
leaf plate assembly screws loose
As for the check list.