Yamaha 50TLRD revs and bogs revs and bogs...

[99yam40]

did you check with a timing light to see if timing or spark was a problem before replacing the CDI?
could be a bad connection into or out of the CDI was the problem, hard to tell unless testing things completely as manual calls out

 

[Jim Hawkins]

did you check with a timing light to see if timing or spark was a problem before replacing the CDI?
could be a bad connection into or out of the CDI was the problem, hard to tell unless testing things completely as manual calls out

No, I didn't. When I removed the adjustment arm from the CDI, the brass threaded piece moved and made crunching sounds. It appeared to have gotten very hot.

 

[99yam40]

Ok,
I changed the CDI on my C40 to get the idle timing correct after working on the used motor I bought to fix it also

 

[Jim Hawkins]

So, just got back from a test run with the new CDI. All the old connections were clean but I shmutzed the new ones up with dialectric grease for good measure. I adjusted the linkage 2 turns which put the timing arrow on the marks. Checked with a timing light and it was bouncing between 6 and 8 degrees ATDC. Starting it up it immediately sounded nice although the idle is a little low and I will adjust it when I get my new Tachometer on Thurs.

Out on the water it was obvious right from the start things were better and the only problem was cavitation. Before putting the boat in for the first time after I bought it, I noticed the motor was way low, so I moved it up about 2.5 inches. Well, that might have been fine for a regular V-hull but I have found with pontoons and catamarans that that setting is not as straight forward. So back down it will go (a little) but first I want to test a new prop.

This is, as I said, a pontoon boat and so the 11X15 prop that was on it was pitched way too high for a 50HP on a 20' boat. I opted for a 12X10 (which is in the recommended range) and I expect I will be satisfied.

So, all's well that ends well. She ran real nice up on plane even with the cavitating and I feel real bad about all those filthy names I called her before.

 

[Sea Rider]

As for any cavitation, prop aeration issues those Yams likes to be motor/transom matched at a certain height in which the hardened water flow skims right under the upper small plate when on plane, top setting in which the motor achieves its max prop thrust. Try it, nothing to lose, much to gain.​

For that scenario to happen will need to test said motor at different transom heights on flat calm water cond, with deck load well distributed and motor trimed to 90 deg till visually is confirmed being there.

Out of curiosity will be great to test both 15 and 10 pitched props with a tach and report what wot rpm each one dialed and if the latter prop is revving at least middle to max wot rpm range factory stated for that nice 50 HP Yam motor...​

Happy Boating

 

[Faztbullet]

Make sure you use the big rounded ear prop not the K style. The Merc 48-73132A4 with hub kit would work good. I use Propco props on all my customers toons and cavation is not a problem.

 

[harmanoff]

I had a 1986 50hp Yamaha, loved it but sadly it died, we used a whale tail on it to help with porpoising and cavitation.