1990 Yamaha 130 Bogging under load

[Crisp]

Boat is new-to-me, little known history, engine very very clean under the cowling.
Compression test is 120 on #1, and 125 on 2,3 & 4
Carbs removed and cleaned, again, fuel filter on engine cleaned, again...
Main tank and water separators bypassed due bad fuel from sitting for 1+ years, 12g plastic moeller with new gas, new lines and bulb being used...

Oil tank on engine always full, New plugs, and look very slightly wet/oily after 10-15 minutes idle. Good spark on all cylinders.

On Land, engine idles nicely, moves well thru RPM's in Neutral, and acts normally under load in a tank.

At sea, bogs after a 20 minute 5kt cruise to harbor entrance from the dock.
In Neutral, again fine thru RPM range, and always zero problems in reverse. Only bogs in forward under load above 2000k rpm. Seems like it is going into a limp home mode or something. Not noticing any alarms on the digital guages, but maybe some/all sensors not working...

3 different mechs. stumped... say it sounds great, acts normal, but I still have problems at sea.

Too little fuel? Too much Fuel? Electrical?

 

[Crisp]

Re: 1990 Yamaha 130 Bogging under load

Hi Group,

Quick follow up, forgot to mention that the motor uses gas. It seems to really burn gas for the idle/troll/cruise speed I've been able to acheive. I know from past experience that these older carbed 2 strokes sucked down the fuel, and this motor is doing just that, maybe even too much for the slow speeds. Point is, I'm thinking the motor is not having trouble getting fuel out of the tank, which leads me to believe the fuel pump and carbs are doing their job. I sincerely appreciate any insight you guys might be able to give me, this motor is a bit of an enigma to me...

 

[birdseye418]

Re: 1990 Yamaha 130 Bogging under load

might want to try the fuel pump. I had a semmiler issue w/my 90 yamaha
$40 new fuel pump.

 

[Crisp]

Re: 1990 Yamaha 130 Bogging under load

Thanks for the reply! Will replace the fuel pump and see what happens. Something else I found yesterday was that a little vaccuum hose from the airbox to the intake was not connected (on the airbox side). At idle there was a pretty good amount of suction at the hose. I reconnected the loose end to the airbox. I'm wondering if this might have had something to do with my problem?

 

[99yam40]

Re: 1990 Yamaha 130 Bogging under load

Test the alarm system to make sure it is working properly.
Make sure compression and spark on all cylinders is good.
Check timing at problem RPM to make sure it is advancing properly. The timing light could also show if you are loosing spark on the different plug wires by moving it to the different wires

If all that is good then it is back to looking at the fuel again