Twin 150 Yamaha sync question.

jasoncooperpcola · #1 04-20-2008, 07:55 PM

On my 250 Sportsman both engines seem to keep up with each other until about 3000 rpm. After that the starboard engine has to be advanced more to keep up. With the shift handle all the way down it only turns 4500 rpm. The port engine still has lots of throttle left. The only way i can think of getting them in sync with each other is to extend the starboard engines throttle cable at the end more. It looks like all i have to do is take it loose from the motor and turn it to lengthen it. Is that the only way or is there another way. At 4500 rpm the boat was running 45 mph. Also the max rpm range (according to the book) is 5000-5500 rpm. What kind of speed san i expect with both engines turning 55000 rpm?

THEFERMANATOR · #2 04-20-2008, 08:48 PM

I would check first to see why the one is only getting 4500 all the way down. Make sure your getting full throttle, and that the linkage is moving freely. Then I would check the props. Also try swapping tachs to see if one is reading differently.

tsubaki · #3 04-21-2008, 04:42 AM

Just curious, how's the fuel draw setup?

jasoncooperpcola · #4 04-21-2008, 12:34 PM

the tank has two separate outlets. Each motor draws from its own outlet.

Blue_Runner · #5 04-21-2008, 02:20 PM

Good info ferm...its all detective work. Much like the software systems that I spend part of my day fixing. (Other part I spend here)

jasoncooperpcola · #6 04-21-2008, 11:12 PM

I checked some stuff today. I took both covers off and turned the engines so i could see the side of the engine from the helm. I pushed both throttles as far as they would go and both engine levers went to the same position. Then i set the throttles to the position where they are both running 4500 rpm and there is a major difference. Could it possibly be a different ratio lower unit? The counter rotation lower unit is one off ebay. And its the one that still has lots of throttle left. I didn't have time to check the props cause i have to take them off to read the numbers. We are also planning on taking the Doel-fins off to see if anything changes. Oh yeah i just remembered it lists to the starboard side when we get above 2500 rpm. We had to tilt the port engine up to correct it. Any ideas on why that is? Thats another reason for taking the Doel-fins off. The only real weight on the starboard side is all the engine cables, hydraulic steering etc.

THEFERMANATOR · #7 04-21-2008, 11:25 PM

I'm not a YAMAHA guy, but it sounds like you may want to check the ratios. Put them in gear and rotate the flywheel 10 turns and see how many times the prop rotates. Then divide it out to find your ratio. I know on JOHNNY-RUDES there was an available optional ration on alot of the bigger engines. A list to one side could definately be a difference in gear ratio or props.