358 with a 300-400 rpm difference between engines

VIPER7 · 08-17-2004, 01:57 AM

The Starboard engine lags the Port engine by 300-400 rpm's. I have ran bravo 1's and lab finished bravo 1's with the same results. Engine has been checked by a dealer for computer code faults and compression check. The engines are new HP 525's with 30 hours on them. Can anyone tell me what type of engine rpm differences they are getting and what differences are acceptable. I thought Mercury was to match twin motors.

45sonic · 08-17-2004, 10:04 AM

power steering

Sydwayz · 08-19-2004, 10:23 AM

It should have PS pumps on both motors; one just set to recirculate. This is easy to check, just make sure you have same accessories on both motors.

Are you sure your throttles cables are set properly? Take off your air cleaners, with the engines off, and move your throttles together, and then compare the throttle body butterflies' postions, especially at 'full throttle'. You may have to adjust your cables for one that is not openning all the way.

Downtown42 · 08-19-2004, 10:42 AM

Have you synchronized them by ear? You should be able to open your exhaust when on plane, and listen to the HUMMMMMM between both engines. When they hummm together, now what does the tach's read?

If still 3-400 rpms low on gauge, then you may have a sending/gauge problem.

VIPER7 · 08-21-2004, 01:04 AM

I have checked the throttle butterflys and they are together. Ialso have checked the engines by sound and the starboard engine is down on rpm's compared to the port. the only way that I have been able to sink themis to move the starboard engine throttle ahead of the port at crusing speed and to trim the starboard much more than the port at wot. Any other info to solve this would be appreciated.

45sonic · 08-23-2004, 09:03 AM

prop pitch. Have your props checked to make sure they are what they say they are.
You might want to have your gears checked to make sure they are the same

Thunder32 · 08-23-2004, 06:25 PM

Bill-
I believe you've got the answer. I had a pair of 26's that were 200 rpm's off, took them off and put on 28's and problem solved.

Sydwayz · 08-23-2004, 07:05 PM

I nebber thought of that Adam.

Try switching your props, and running the boat in Reverse (which will now be forward) to see if the problem switches side to side. Be careful though, it will affect handling and docking is a bear with reversed props.

GO4BROKE · 08-23-2004, 08:16 PM

Quote:

Originally Posted by VIPER7

I have checked the throttle butterflys and they are together. Ialso have checked the engines by sound and the starboard engine is down on rpm's compared to the port. the only way that I have been able to sink themis to move the starboard engine throttle ahead of the port at crusing speed and to trim the starboard much more than the port at wot. Any other info to solve this would be appreciated.

If you have the engines synched by ear properly and still see a difference, I would be checking the tachs. When the resonance goes away, the rpm's are very close.

VIPER7 · 08-23-2004, 11:42 PM

I have changed the props to Hydromotive P5-X's and the RPM's are within 150. The engines do not have 2 power stering pumps. Only the Starboard engine has a pump and the Port has an idler. The stern drives are ITS. Could this be why there is only one pump. The 31SS that I previously had had a pump on each engine. I would also recommend to anyone that has a 358 to try the Hydromotive 5 blade props. The handling of the boat improves like the difference in day and night and the efficency of the prop goes to 92-93% as compaired to 85% with the Bravo 1 4 blades.