2004 Yammie F150 Loss of power issues

[pathfinder101]

Hi All,

Just wondering if anyone can help me... I have a 2004 Yamaha F-150 about 300 hrs on it.. Last 2 outings in the ocean I've notice a slight problem with the motor boggling down and taking a long time to get up to above 4000 rpm (18-20 mph).. At one point, it did not want to go pass 4000 rpm. I had to back off of throttle and push down fast to rev the motor so that it would have enough horsepower to get it up above 4000 rpm.. After doing this several time it did pick up speed slowly.. I thought that I might have too much weight or loosing h.p. due to other reasons... so, I listed the items below...

Parker 2120 (3250 lbs)
3 people (480 lbs)
Main Motor F-150 (488 lbs)
Kicker T-8 (100 lbs)
80 gallons gas (490 lbs)
25 gallon bait tank (210 lbs)
Gear (300 lbs)

Total weight 5318 lbs

I tested in the river with only me on the boat after the 1st outing and had no problems doing around above 5000 rpm going and above 30 mph.. But after the 2nd outing in the ocean with the same result, I thought that It might be a bad plug so I checked all the plugs and it looked find.. It looked kind of grayish on the tip and black on the threads of the spark plugs.. It looked the same for all 4 spark plugs... I did change the motor oil, lower unit oil, changed the spark plugs, water/fuel separator filter, oil filter, fuel filter under the cowling in front of motor.. Also, I changed the VST filters on the top of the VST and inside of the VST... Also did a compression test showing average 160 psi on all 4 cylinders... I also did the fuel pressure test from the fuel rail and at idle it jumped from 38-40-45 psi however, when I put it in gear it stayed right at 45 psi in slower rpm or higher rpm... I'm thinking it might be the fuel injectors so today I went and ordered 4 pcs and waiting for it to get here.. I will test again when my new injectors arrive... If it still gives me this problem after the new injectors, I might switch back to my original alum. prop and test it.. Just wondering if anyone else had this issue or can shed some light as to what might be the problem of power loss....


Thanks,

Jeff

[99yam40]

might want to post what the 2 props are ,
when you changed them out,
and if you ever got OK results with the newer prop

[pathfinder101]

might want to post what the 2 props are ,
when you changed them out,
and if you ever got OK results with the newer prop

Previously, the stainless stl prop had no issues on it... My wot was about 5500- 5700 depending on how I trim.. Of course, that's with only 2 person on board with lighter load... As for the size of the prop I don't remember, I ordered the Yamaha factory recommended size... I will have to check and post both of them...

[pathfinder101]

Hi All,

Recap to the issue with my motor... I took it out fishing in the river last weekend and still having the idling issue.. As for the rpm, it gets up to 3900 - 4000 with no problem.. But, from 4000 and up still takes a long time.. And when it gets going it only goes to 5000 rpm at 30-31 mph...

My injectors finally arrived!!! However, the color of the injectors is green in stead of yellow? I ordered the 63P-13761-00-00 INJECTOR but the ones that came in had a -01 at the end... Anyways, installed it and ran the motor with the earmuffs hooked up.. ***!! what a difference... It idle like it was a new motor.. No problems with the rough idling and a bit of coughing... So,,, I think I might of solved the problem however, I will have to test ride the boat to make sure.. Wish me luck....

[99yam40]

You can send off the old injectors and have them flow tested and cleaned,
They will send an as found and as left test sheet.

Then you will can have spares on hand when you need them

[pathfinder101]

You can send off the old injectors and have them flow tested and cleaned,
They will send an as found and as left test sheet.

Then you will can have spares on hand when you need them

Thanks.. That was my plan.. Once my boat test ride is confirmed than I'm really happy that I found the root-cause of the problem... Now, I need to know what would be the best way to clean the fuel tank.. Seafoam ?

[99yam40]

additives do not do a very good job of cleaning a tank.
Need to have it drained and cleaned by someone that does this type of work for built in tanks if that is what you have.

What is tank made of?

[pathfinder101]

Hi All,

Recapping to the issue with the under power.. I took it out in the river with 4 adults (Around 640 lbs) & 4 kids (Around 250 lbs) total weight of person 890 lbs... I resolved my under powering issue.. Soon as I forward the throttle, it started picking up real quick... It took probably about 5-8 seconds to plane and was doing 18 -20 mph and the rpm had no problem going beyond 4000 rpm... My wot was about 5300 rpm at 33-35 mph depending how I trim the tabs... I think it would do 5800 rpm at 38-39 mph with 2 person on board... I have to test it another day.... Originally, that's what it was doing, of course, depending how I trim on my tabs...