View Full Version : Boat Won't go over 3,950 RPM's
05-10-2008, 10:48 PM
Hey guys had the boat out today for the first time on the water this year.
Everything ran great like it should have.
I brought my new GPS I just bought to dial in the Airguide speedos.
I had it wide open as far as I could get the throttle to go.
GPS read top speed of around 36.8 MPH; however the RPM gauge was only reading around 3,950.
I couldn't figure out why it wouldn't go over 4,000 because WOT should be between 4,400 - 4,800 I believe.
Anyone have any input as to why it won't go anymore? I'm stupmed because it runs perfect except for this problem.
Also on a good note...... First time I got on my board since I broke my femur last August. Air temp was around 66 and water temp was about 62. Wasn't too bad with a heater shirt and just boardshorts. Felt really good to be back out there and I'm looking forward to Summer.
05-12-2008, 10:13 PM
Well I found my answer.
Just in case anyone else has the same problem then here ya go:
List of possible causes of low WOT.
Engine Won't Reach Operating RPM. Check
* Fuel condition. Type and Octane possibly old fuel
* Propeller pitch or diameter, damaged blades
* Restricted fuel pickup tube or anti siphon valve Fuel System Test
* Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
* Marine growth on hull and outdrive
* Wrong gear ratio in outdrive
* Restricted carburetor air intake (clogged flame arrestor)
* Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
* Poor cylinder compression Compression Test
* Carburetor defective, or wrong type.
* Fuel pump pressure and vacuum
* Boat overloaded, improperly loaded, or improperly trimmed.
* Engine Overheating
* Engine timing and ignition system operation
* Remote control cables and linkage for proper travel to open throttle plates fully.
05-13-2008, 07:23 PM
Which one was yers?
05-13-2008, 09:17 PM
Well I meant I found a list of things to check that could be causing it, but I'm tired of messing with it and taking it into the dealer tomorrow......
We'll see what happens from here.
05-14-2008, 05:26 AM
With all you've done to her already, I'm putting my money on the prop
05-15-2008, 01:25 AM
According to the Dealer they "assume" the secondaries aren't opening on the carb, but I called Holley to confirm that the boat needs to be under a load for them to open and they said correct. Dealer never water tested it and said "well everything runs great and smooth, but we think your secondaries aren't opening" I told them that the secondaries wouldn't open without a load on it and they acted confused. I wish there was a damn Carb specialist around me that knew what the hell they were doing and could figure out the problem.
I'll confirm on Saturday if they are opening or not. Dealer said if they are opening then its a "non" carb related issue.
As far as I know, I'm 99% sure it still has the stock 13X13 prop on it, but I'll double check it.......
05-15-2008, 10:54 AM
This probably isn't it, but one time I was stumped on an older outboard that wouldn't reach WOT RPM so I thought I'd share it with you. After a while the motor would just shut down completely when a full load was put on it so I knew there was a fuel supply issue. I finally found a section of fuel line under the motor cover between the connector and the fuel filter where it took about a 180 degree turn. The line was old enough that it had softened (especially when the motor warmed up). It would function at low RPM, but under a full load the fuel pump was actually sucking the line closed and pinching off the supply. Fixed for about $4, including some new clamps.
The moral is that sometimes it's something really simple like a fuel line. Good luck!
05-15-2008, 10:56 AM
Aaron, I forgot to mention that all this occurred right in your neighborhood on the IL River in Ottawa. Sure did have some fun out there. Don't miss waiting till Memorial Day to fire up though.
05-15-2008, 08:57 PM
I think I got the problem figured out.......
I believe I have too heavy of a spring in the secondary vacuum housing and it isn't allowing the secondaries to open.
I ordered a spring kit and I'm going to start with the lightest spring and then see at what RPM the secondaries open and adjust from there.
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