Why does my boat never go above 3000 RPM even in WOT?

[samocamo123]

Hi, I have an Ebbtide Montego 170 with a 3L OMC Stringer 400 (302STHRCOM) and I noticed in WOT I only reach 3000 RPM, it can't be my prop as its a 13 3/8 x 17 pitch and is what I believe to be the factory prop (its a little dinged up but not enough to make a noticeable difference). It also couldn't be gearing or outdrive as they are stock. I set my timing with a timing light to about 4 degrees BTDC and it didn't help much with RPM. Although I am not entirely sure if my timing was set correctly as I just set it while idling in neutral as I couldn't find any instructions. It idles in neutral at a little above 1000 RPM. It runs a tiny bit rough (still runs fine most of the time) idling in gear, but with any throttle applied it smooths out. The engine reaches 3000 RPM at about 3/4 throttle but seems to increase in power going to WOT but doesn't increase RPM. The engine isn't overheating either as it runs about 150-160 idling and about 170-180 at WOT. What could be causing my low WOT RPM?

 

[kenny nunez]

First how long have you had this boat and did this problem start all at once? Does the throttle open up all the way? What is the compression? With the distributor cap removed how much can you move the rotor shaft, a worn distributor can keep an engine from not going to rated RPM. The RPM should be as slow as the engine will idle when setting base timing, try to let it idle @ 5-600 RPM, try to set the timing 6-8 degrees advance then reset the idle speed around 700 RPM. Also converting the ignition over to a Petronics electronic will help if the distributor is worn slightly .
What kind of shape is the fuel system. Have you checked the filters, in addition to the one on the fuel pump, there is one in the inlet fitting on the carburetor that could be clogged up. There is one also in the suction tube in the tank. Replace the fuel hose from the tank to the fuel pump. These are the kind of things that can cause your problem.

 

[HT32BSX115]

What could be causing my low WOT RPM?

Howdy,

Also, here's a list of stuff to check..... https://forums.iboats.com/forum/eng...es-outdrives/479878-adults-only-no-exceptions

#15 talks about reasons for low WOT RPM. :thumb:

Regards,

Rick

 

[jbetzelb]

For what its worth I had this issue once. Went through everything looking for an issue. I had the best tuned 4.3 OMC around but couldnt get over 3K RPM. I was using the boat tack. Put on a different tack and it turns out WOT was well over 3K RPM.

 

[samocamo123]

For what its worth I had this issue once. Went through everything looking for an issue. I had the best tuned 4.3 OMC around but couldnt get over 3K RPM. I was using the boat tack. Put on a different tack and it turns out WOT was well over 3K RPM.

I kinda think my tach may be bad because it gets to 3K on it at 1/2-3/4 throttle and stops increasing even though the motor sounds like it continues to rev higher.