Logo
FULL SITE MENU

Why is my Catalina 251 sooooooooo slow

8

84catalina

New member
I have an 84 Catalina 251 that

I have an 84 Catalina 251 that I'm trying to sell. The 305 was replaced long ago with a Chevy 350. I've had this motor at 4500 rpms and it seems not to plane at all and tops at about 13.8 mph. It has a stock reman'd prop on it. The bottom was recently painted with no growth. The trim tabs are fully down.... I'm plowing tons of water. Someone please help !! Everyone I take for a ride questions the "slowness" of the boat.
 
"RE:"stock reman'd pro

"RE:"stock reman'd prop"
I'd start by looking at the prop. Most likely the wrong pitch.

Was it always this slow...i.e., was it this slow when you first put the 350 in "long ago"

Also... when you are at 4800 rpms, how far is the throttle open??? 50, 75 or 100%???

If 100%, the first thing is to check the easiest thing to fix...i.e. at full throttle (at the helm) is it full throttle at the carb? ( with engine off, remove flame arrestor, open choke all the way and look in the carb throat.)"
 
"The motor was replaced before

"The motor was replaced before I owned it.

I did check the throttle at full. It's pegged and is adjusted correctly.

When running at 4800, the throttle is wide open


The pitch is what everyone says to run.... ie stock when new. Seems that the boat just dont have the umph to get up on plane. The engine is working hard at that point. What it feels like is that I'm towing an open parachute behind me.

Maybe transmission slippage? That would be the only thing besides the prop that would cause it. Anyway to test?"
 
What is the transmission reduc

What is the transmission reduction ratio?
Propeller dia and pitch are dependent on the tranny's reduction ratio. Is the transmission original?

I'm still not clear on if this boat ever ran right for you with the 350 in it ?
 
"Mike, are you sure that is th

"Mike, are you sure that is the correct Dia and pitch for that boat engine combination?
Both numbers sound small to me. How many blades is the prop? Does it show a Cup stamp on the hub?

I think you might have two issues. First with that size prop I think that a 350ci engine should be turning in the 5,000 to 5,500 RPM range. I think the engine should be making 250 to 300HP? Does it run smooth or sound like it’s misfiring?

I don’t have first hand knowledge of this boat so I could be totally wrong.

Dont get mad. Now for the stupid question. Your not dragging somthing under the boat?

Let us know?

Just my opinions
Bluecometk"
 
"Verify that the hull is still

"Verify that the hull is still clean!
Your RPM would dictate that the engine is capable of WOT RPM..... a WOT RPM of 4,500 is in the ball park..... but that doesn't get you out of the woods yet!

The propeller is likely the culpret, although a bent prop shaft may cause similar results.

Q's:

**Is this an I/O or an I/B?

**Have you had it on step before? (sounds like you've owned it for a while)

**Have you had it on step before with this prop?

**Do you have a history of this particular size/pitch propeller having worked before?

**Are you able to try the original propeller again?

**Could the prop have been damaged, even ever so slightly?
(You'd be surprised at how little damage can throw a prop off!)

**Have you looked at the transmission oil for any signs of an issue?

**Is your tachometer calibrated accurately? (IOW's, are you actually reaching 4,500 rpm?)

**If you were not reaching that RPM, I'd suggest checking ignition TA (total advance)! Still not a bad idea to do so, IMO! (see OEM specs for this)

."
 
"I had the same problem with o

"I had the same problem with one of the motors in my 281. After messing with different things for 6 months and 3 mechanics look at it, someone suggesting changing the coil. The one on there worked, but it had the same problems as yours. I put a Pertronix flamethrower coil on it and it ran perfect. Ended up putting one on the othre motor to improve the performance on it."
 
"Q's:

**Is thi

"Q's:

**Is this an I/O or an I/B?
I/B

**Have you had it on step before? (sounds like you've owned it for a while)

Never

**Have you had it on step before with this prop?

Never

**Do you have a history of this particular size/pitch propeller having worked before?

Nope

**Are you able to try the original propeller again?

It is the original (came with the boat)

**Could the prop have been damaged, even ever so slightly?
(You'd be surprised at how little damage can throw a prop off!)

Its perfect(as in new)

**Have you looked at the transmission oil for any signs of an issue?

Yes, clean and full

**Is your tachometer calibrated accurately? (IOW's, are you actually reaching 4,500 rpm?)

Maybe not but at the end of the throttle (on the carb)

**If you were not reaching that RPM, I'd suggest checking ignition TA (total advance)! Still not a bad idea to do so, IMO! (see OEM specs for this)

I'll give this a try..}}"
 
">>>>>&#62

">>>>>>>>>>>I had the same problem with one of the motors in my 281. After messing with different things for 6 months and 3 mechanics look at it, someone suggesting changing the coil. The one on there worked, but it had the same problems as yours. I put a Pertronix flamethrower coil on it and it ran perfect. Ended up putting one on the othre motor to improve the performance on it.<<<<<<<<<<<<<<

This I will give a try. I hope i remember by the time spring comes around :-("
 
I have a 74 CC express crusier 25' I have a BB Chevy in it. with a Paragon P21L Transmission 1-1 ratio. My prop is a 13x12 cupped. At wide open throttle which for my engine is 4000 rpm I can run at 30 mph (on my GPS) I am on a river with a strong current so my WOT speed can change based on the current direction. I would check the ratio on your transmission. Have you checked to make sure the key in the prop is not sheared?
Also look at the coupling on the transmission to prop shaft make sure that's not slipping either. If you change the prop you will change the WOT rpms. I would also check to make sure you transmission is not slipping. I would try different positions on the trim tabs. I can change the speed by more or less trim.
 
Last edited:
Back
Top