Yamaha 50 power loss / no rpm past 4400

[jp13]

Hello,

I've read a lot of posts about Yamaha motors, but didn't found how to solve my problem.

I own a 50 HP Yamaha 3 cylinders, year 1989, on a 4,5 meters fiberglass open style boat.

The problem is that the boat wont go past 24 to 26 knots, and the motor can't just go past 4400 Rpm. It runs fine between idle and that speed, but there isn't just enough power.

I'have mounted a 11" pitch prop instead of the original 13", and only gained 200 rpm (4400 instead of 4200).

Otherwise, the motor is a bit difficult to start, and I have to insist several times in order to fire it up. The idle is between 700 and 800 rpm, but after a while idling, the motor just stalls.

I verified in my Selloc manual for timing issues, and all i found is unclear. The motor have a CDI unit equiped with an arrow pointing the advance. In the manual, they say that adjusting the throtle will adjust the timing. I think the timing is right now, because the arrow pointing on the marks on the CDI unit is pointing the full retard mark at idle, and the full advance when at WOT(it was not like that when i bought the boat, and the arrow was pointing far away from the full advance mark when at WOT). The problem is that with full retard, the engine won't start, and i had to adjust the full retard stopper in order to move slightly the arrow to the second mark on the CDI Unit.

On the water, when you push to WOT, from idle, the boat really jump out of the water for 2 ~ 3 seconds or so, then is a bit longer to take off and go to plane. She acts like if there was maximum power for few seconds, and then, loses 15 Horses or so. I don't think it is fuel related, because there is no surging, but it is like if the motor was limited by something (maybe I am wrong with fuel issues). I did clean the carbs anyway without any improvement

Thank you for your reading, excuse me for my poor English, and thank you for your help.

JP from France

 

[jp13]

Re: Yamaha 50 power loss / no rpm past 4400

Hello there,

I come back with an update for my unsolved problem on my 50 horses Yam.

A friend lend me a timing light, and I m now able to verify if the timing is right.

I started with the first cylinder (top one), and checked for idle , 1000 rpm and full advance values (in my manual 4 to 6 ATDC at idle, 0 to 2 at 1000 rpm and 26 to 28 BTDC at full advance) and they are right. So the timing is good.

But, i noticed that at higher rpm (say more than 2000) when the advance is upper than 15 ?, the light seems to miss a lot of fires on cyl 1 and 2 (I mean the flash is not regular, and disappears for few seconds or milliseconds).

I first thought it wa an issue with the old timing light I borrowed, but when I checked cyl 3 (the lowest), it seems to run fine, and at high rpm, the light is flashing really fast, pefectly iluminating the mark on the flywheel... So what ?

Is it possible that de CDI unit is fried and don't trigger the coils when the rpm and the advance increases ? Or could it be related withe two of the 3 pulsar coils ? (i don't think so because I have sparks at idle and rpms to 2000 or so)

I checked the ignition coils (swapped N?2 with N? 3) and there was no change.

I could change a CDI unit, but they are really expensive, and I would like to be sure before spending a lot of money.

Any help would be greatly appreciated, if a Yamaha guru is online...

Many thanks in advance,

JP

 

[BaileysBoat]

Re: Yamaha 50 power loss / no rpm past 4400

Sounds like you are on the right track. I don't have my manual here, but what does the ignition us as a crank reference? Is there an air gap adjustment at the sensor, or dirt or rust or grease could interfere with the magnetic pickup ??

 

[parrfive]

Re: Yamaha 50 power loss / no rpm past 4400

Yamaha?s don?t have many ignition problems. Its sounds more like a fuel issue to me. I would with the fuel pump. If the carbs haven?t cleaned in a while that?s always a good idea. Most all the older Yamaha runabilty problems that I see stem from the fuel system.

 

[zzzzz]

Re: Yamaha 50 power loss / no rpm past 4400

once you get the motor running correctly you'll have to address the prop issue...you should be running in the 54-5600 rpm range

 

[jp13]

Re: Yamaha 50 power loss / no rpm past 4400

Hello,

Thanks for your replies, I appreciate your help.

I cleaned the carbs (but did not find anything unusual), I tried pumping the primer while running, without any effect on the motor's rpm.

for Baileysboat: On this motor, there are 3 trigger coils under the flywheel, and each one is connected to the CDI unit. What makes me doubting of these coils "non properly functionning" is that under 1800~2000 rpm, or bellow 15? BTDC, there seem to be correct sparks on all cylinders. It is only when you go up these values that the motor drop some sparks on cyl 1 and 2.

In my manual, they say that the plate with the 3 trigger coils is not adjustable, so I didn't searched this way. But you are right, I will try to look better how it is designed to see if ther could be an adjustment. I mean if the coil is too far from the magnet, perhaps at higher rpm, there isn't enough current to trigger the CDI unit.

For zzzzzzz: In fact it was because of my motor running at 4400 rpm (max), trimed up an on plane that I changed the prop size, and It only improve the max rpm of 200 rpms... So as you said, I will deal with a possible prop issue when the motor will run fine !

Again thank you for the Help, and if anyone has other ideas, I will appreciate.

JP

 

[Yamajoe]

Re: Yamaha 50 power loss / no rpm past 4400

Check your WOT (advance) timing, it should be 25' +-1. so 26 is ok but if you are higher to 28 then this will cause the loss of power at WOT that you are describing.

I worked on a 50 last xmas and i found the CDI timing pointer set up for static timing procedure to be useless, the only way to get this right was with a timing light.

Check the resistance values of the CDI and trigger coils; specs should be in your manual. test trigger coil inputs to the CDI then test output of the CDI using a peak reading meter or a DVM with a DVA adapter.

Do not discount carbs as a problem yet.

 

[jp13]

Re: Yamaha 50 power loss / no rpm past 4400

Check your WOT (advance) timing, it should be 25' +-1. so 26 is ok but if you are higher to 28 then this will cause the loss of power at WOT that you are describing.

I worked on a 50 last xmas and i found the CDI timing pointer set up for static timing procedure to be useless, the only way to get this right was with a timing light.

Check the resistance values of the CDI and trigger coils; specs should be in your manual. test trigger coil inputs to the CDI then test output of the CDI using a peak reading meter or a DVM with a DVA adapter.

Do not discount carbs as a problem yet.

Thank you for your reply !

I will check again the timing values to be sure they are in the specs and not too high at wot.

For the output of the trigger coils and CDI test, will an analog multimeter work ? I own a digital one, but without DVA adapter... so it is useless for these measures.

What do you think of the flashes of the timing light disappearing for cyl 1 and 2 when the timing advances above 15 ? (rpm above 2000 ) ?

I'll keep in mind to check again the carbs, but I'd like to be sure there is no timing issue before.

Cheers,
JP

 

[Yamajoe]

Re: Yamaha 50 power loss / no rpm past 4400

The timing light may not be good enough to read above 2000 or this could be your problem, a need a dva adaptor so as you can verify those readings at the rpm the problem is occurring; and the analogue is fine.

 

[jp13]

Re: Yamaha 50 power loss / no rpm past 4400

Hello,

Again thanks for your help, I will check with an analogue multimeter as soon as i can. I'll keep you udated then.

 

[timberman]

Re: Yamaha 50 power loss / no rpm past 4400

Bump.

@jp13
I was wondering, did you ever solved your problem? Im having almost exact the same problem with my 60hp yam. and really like to know if you fixed your engine.. tnx!