1976 T-179 original prop size

[JohnsonT-179]

Hello all! My wife and I have a ‘76 T-179 with the 2.5L mercruiser. The guy we bought the boat from had “found” a prop and stuck it on there. Am I correct in saying the engine RPM at WOT should be around 4200 for this engine? From 3000 RPM to 38-3900RPM I’m picking up 1MPH.... The engine has more throttle left, but I feel like theirs a lot of slippage. The prop is chewed up and I know it’s not the correct size. He had to trim the cavitation tab to make it fit.... the boat maxes out at around 30 MPH, but I feel like it should have a lot left in her.

Can someone steer me in the right direction as far as pitch and size? Would like to run a 4 blade to help get heavier skier (myself) out of the water.

Thanks!

[Hyperacme]

Welcome to the forum Mr. Johnson !

Can't offer any input on size.
But some info from Glastron PIG's  & Merc spec's.

[Plugcheck]

I had a cvx-16ss with 140 merc.  Seems my best overall performance was with a 14.75 21p prop.  Some dealers will let you try various props if you buy one.

[75starflight]

From my experience...I own a 1975 V-179, Same boat just changed the v to a t in 76. With the 120 or 2.5 the best option I found for speed was a 21p laser II prop. But you will run into a lot of steering torque with that prop and i had to do some upgrades and add power steering when i repowered to a 140 or 3.0.

For a best all around prop with the 2.5 I found a 19p stainless prop was the best of both worlds speed and pulling. When I had the 120 still in the boat i think my max speed was around 34 to 36 with the 19p and i reached 38 with the 21p Laser II

[Jason]

Brandon,

Did you have a trim tab on the boat when using the Laser II? I run a 23p laser II on the CV16SS with a 140. No power steering. I had to cut a notch in the trim tab to clear the prop but I have little to no torque on the steering wheel when trimmed properly. I believe you can also buy an offset trim tab that will clear the prop.

[75starflight]

Brandon,

Did you have a trim tab on the boat when using the Laser II? I run a 23p laser II on the CV16SS with a 140. No power steering. I had to cut a notch in the trim tab to clear the prop but I have little to no torque on the steering wheel when trimmed properly. I believe you can also buy an offset trim tab that will clear the prop.

Yes. I had the Mercruiser Extended tab. I had it adjusted so the torque steer was minimal. I believe it might be something in the hull design that creates the torque steer one direction. It has been 3 years since i have driven the boat, but i believe it happened when i turned left. the power steering removed it and made my 179 very nimble.

[JohnsonT-179]

Thanks all! That original sales bulletin actually lists the prop for the 120ME! That’s a great start! I would like to look at a 4 blade just for the oomph to get skiers out of the water a little better. Thanks for everyone’s input!

[75starflight]

Thanks all! That original sales bulletin actually lists the prop for the 120ME! That’s a great start! I would like to look at a 4 blade just for the oomph to get skiers out of the water a little better. Thanks for everyone’s input!

Four blade might be good, I have the best luck with a 19p stainless when pulling someone with my 179. It launches right out of the water  and has very little slip in the corners.

[JohnsonT-179]

well, got my new 14.5x21 prop put on before the 4th of July, and sadly it was flat out terrible... the engine struggled to get about 3,200 RPM and seems to have valve clatter around 3,000 RPM. also thinking tank is full of crud as well. after hitting some good chop on the water the boat had symptoms of running out of fuel, boat would start to cough, fall on its face and i could get out of the throttle, idle and then it recover and go again... I'm going to get fuel out of tank, and attempt to pull tank out and assess. the tank seems to be well "glued" to the flooring.

the spring advance in the distributor seems very tight. im wondering if this is causing some of my RPM issues, ive updated to a pertronix ignition system and a pertronix blaster coil as well. much better starts but engine just seems very sluggish now.

any advice would be greatly appreciated!

[Plugcheck]

Lack of timing advance will cause issues, but so will bad fuel, poor pump, or carb issues can all contribute to the symptoms you described.  A timing light with electronic advance will show if the distributor is providing the correct advanc.   Having a clean fuel supply is critical.  Checking and cleaning the tank, as well as checking filters and pump is worth doing.  Since the engine cut out when bouncing around could indicate carb issues, such as a bad float or poor inlet control.  When was the carb gone through last?  Your engine should be able to turn the 21 fairly well.

[75starflight]

You will have to lift the tank with a pry bar to get it loose. I had to do this to remove mine. Also, you may find soft wood in the floor in front of the fuel tank(very bad spot for rot) when prying. Be careful. The clamps are very difficult to get to on the hoses and the hoses will be very difficult to remove from the tank(very tight space under the walk through to the bow).

[JohnsonT-179]

I rebuilt the carburetor this winter and put back on this spring. All new components and thoroughly went through cleaning carb body.  After the ride I noticed a bunch of black crud in the clear view filter.... the pump also quit pumping fuel when it supposedly ran out of gas. We let it sit, knocked on the tank and hit switch and boom, fuel flow again.... I’m really leaning toward fuel delivery and timing now. The valve clatter happened once before, but octane booster made it go away. That motor seems to like high octane fuel, but my ethanol free pump only has 90 at the local station.

[Plugcheck]

Valve clatter and knock(pre-ignition) are not related.  The latter condition is rather serious and can lead to engine damage if not corrected.  Given the information so far, I'd guess your advance mechanism is malfunctioning.  Too much advance can produce a knock.  Possibly the advance is frozen, allowing too much at low rpms, and not enough on the higher rpms, thereby limiting performance.  It should advance smoothly and be all in around 2300-2500 rpm.  Total advance should be around the low 30's.

[JohnsonT-179]

PLugcheck,

thanks for the information. it'll literally only makes a rattling tapping noise at 3,000 RPM. none before, or none after. its a weird noise and i don't much care for it. I've noticed a fair amount of pressure/vapor coming from the vent tube off the top of the crank. i'm going to do a compression test on the motor and see what its looking like. ill pull valve cover and lifted cover and check for correct valve lash as well. i'm going to run the motor off a 6 gallon tank to see about eliminating the fuel supply scenario. ill also check timing with a light to see how she sits.

thank you everyone for all the information you've given me. may have a winter project of a motor overhaul in the off season!