PDA

View Full Version : Engine will Only Turn 3300 RPM's and only Run 33 MPH?


tockit
05-24-2012, 11:36 AM
I took my boat out yesterday. First time since last fall.
Everything seemed to run fine, however, after the engine warmed up, I took it up to full throttle and the engine would only turn 3300 RPM's and the boat would only do around 33 MPH on smooth water.

Last year, I was getting about 4400 RPM and 42 MPH.
I initially thought the carbuerator linkage had slipped in the bracket, but I checked it and it was fine, moving the Carb full travel.

Anyone have any idea what might cause this?

The boat has a 3 bladed 13x13 prop, new plugs, spark plug wires, and filter.
The engine ran smooth and normal, no coughing, sputtering, etc, just making full power?

CantRepeat
05-24-2012, 11:44 AM
What year, model, motor, ignition, carb, trans and any other info might help give you suggestions.

Does it run full speed when cold? Did you treat the fuel before you put it in storage?

j.mccreight@hotmail.com
05-24-2012, 11:47 AM
Sounds like another victim of secondary diaphram giving up the ghost...

BrooksfamX2
05-24-2012, 11:50 AM
.......or the cruise control set at 3300 rpm.........dont ask me how I know..........

tockit
05-24-2012, 01:51 PM
The gas was new gas put in just prior to launching and the little bit of old gas it had left in it had stabilizer put in it last fall when I winterized it.

It's a 1988 Mastercraft Tristar with 351 Indmar, Velvet Drive Tranny, Holley Carb (forget the model off the top of my head), whatever the stock Carb was.
It has new plugs and new plug wires, new air filter, with the stock ignition system.

No cruise control.

I didn't try it at full speed when it was cold. What difference would that make?

j.mccreight@hotmail.com
05-24-2012, 10:37 PM
Put a paper clip on the secondary arm right where it meets the diaphragm, go out and run the boat then see if the paper clip has moved, this will help in seeing if the secondaries are opening.

tockit
05-24-2012, 10:55 PM
Put a paper clip on the secondary arm right where it meets the diaphragm, go out and run the boat then see if the paper clip has moved, this will help in seeing if the secondaries are opening.

Ok. I'll try that.

Thanks!

Stx221
05-25-2012, 09:24 AM
Have you tried pushing the throttle further forward yet? I hear that can really help! :D

I don't know much about the carb'd boats, but I wish you the best of luck. Tracking down issues can be a painful thing as I have recently found!

tockit
05-25-2012, 12:41 PM
What's the ignition timing on a 89' 351 Indmar Engine?
I might check that today also if the diaphragm is good.

Thanks!

j.mccreight@hotmail.com
05-25-2012, 02:28 PM
What's the ignition timing on a 89' 351 Indmar Engine?
I might check that today also if the diaphragm is good.

Thanks!

10 BTDC, warmed up in neutral

TRBenj
05-25-2012, 03:24 PM
Initial timing is one thing, but total timing is what is more likely to be affecting a top end issue. If a spring broke in the distributor, or a weight stuck, then initial might be fine, but total may be way off.

Total timing should be in the ballpark of 35 deg, and should be all in by 3k RPM.

tockit
05-26-2012, 12:26 AM
Well, I figure out my problem today. It was a couple of different problems.
The speedo adjustment had gotten moved. I checked the speed with my GPS and it was hitting 42 MPH.
The tach is off for some reason (separate issue).
Anyone every have problems with their tach?
It's only indicating 3200 RPM at WOT (42 MPH).

learjet2230
05-27-2012, 09:59 AM
Well, I figure out my problem today. It was a couple of different problems.
The speedo adjustment had gotten moved. I checked the speed with my GPS and it was hitting 42 MPH.
The tach is off for some reason (separate issue).
Anyone every have problems with their tach?
It's only indicating 3200 RPM at WOT (42 MPH).

Yep...happened to me except mine was showing like 5200 at WOT. Happened right after both of my props were re-done. Ended up taking both props back to get them looked at and nothing was wrong. Ended up "tapping" on the glass of the tach and she dropped to the correct RPM. Prob have a loose wire or something going on inside it....dunno...i live with it. Try it...it doesnt cost ya anything....cheers!