2004 F90tlrb Fuel Problems?

[501nmc]

I have a hesitation problem with this motor. I talked with a few different shops about a hesitation when applying WOT, they suggested a carb cleaning. When I apply WOT, the motor will hesitate about 2800 to 3400 RPMS and the throttle has to be brought back to about half, the boat will get up on plane and then I can apply WOT and the motor will achieve it. I also have trouble putting the boat on trailer, with the motor tilted up, it will stall about half throttle and die. If I trim the motor down so the top of the motor is level with the water, it will run normal. Are both of these problems associated with the floats in the carbs? I have had the carbs off and cleaned twice, the main fuel line taken off and checked for the flaking of a deteriorating hose ( nothing found). Bulb is good and carbs are synced using a manometer. Can anyone give me some advice to correct this problem.

 

[99yam40]

Re: 2004 F90tlrb Fuel Problems?

not sure how far you are tilting motor and trying to run high RPMs but the fuel levels in carbs could be a problem if you are up very far.They are not designed to run that way.
It does sound like a fuel problem with the hesitaion. When was the last time the carbs were gone through? Did you go through them twice trying to solve this problem with no luck?
Check the fuel sytem with a pressure/ vacuum guage it will tell you if there is a problem with delivery. There is a good thread on this under frequently asked Questions

 

[501nmc]

Re: 2004 F90tlrb Fuel Problems?

Thanks for answering! I have cleaned them twice (ultrasonically) I took the jets out and cleaned the passageways and checked the gaskets, orings, etc. I don't tilt it up very far. My trim has a two stage piston (I think), you can hear when the motor sounds different, this is where I usually stop and try to go fwd. When trimmed all the way down, is when it hesitates with acceleration or up when loading. These problems occurred at the same time so I figure they are related. The unit has heilin carbs. The manual says to set the floats at .41-.61 inches, I will pull them off and see if they are set within spec. I did notice a wear ring on the needles that are attached to the floats, may need replaced as manual says, I don't know. I know with hydraulic systems, there can be no groves on the needle for it to operate properly, but with low pressure and rubber material, maybe I can bend the tabs to compensate for some of the wear. Just for reference, are the High speed jets supposed to be submerged in fuel for them to work, or does there have to be clearance for the venturi action to work? Not much on carbs, but learning. Thank you for your fast reply.

 

[99yam40]

Re: 2004 F90tlrb Fuel Problems?

Sounds like you have the problem trimmed up and/or down. I thought you said it ran ok some times with no hesitation. If you are sure the carbs off idle passages are clean, try enriching the idle mixture just a little and see if that helps.
The carbs on my c40 have the jets stuck down in the bottom middle of the bowls so they are submerged in liquid fuel all the time and I think all jets need to be. I do not know much about your carbs, never even looked at one on a 90.
The Yamaha carb kit I bought came with new floats, needles, and seats. But did not come with the o-ring that goes on the seats, so check to make sure you get everything you need if you buy one.

 

[501nmc]

Re: 2004 F90tlrb Fuel Problems?

I adjusted the throttle position sensor today to what the manual said to (.7 +/- .02 vdc. This took care of the trailer loading problem. The hesitation problem is still there, but not as predominant as before. My carbs are adjusted 1-3/4 turns out, will try to adjust them tomorrow (God Willing). The hesitation problem is better but different. I apply WOT now, the boat will accelerate without having to return the throttle. I hope this is the problem that you mentioned above. If I am sitting on the trailer and rap the carbs several times in a row ( by hand) they will backfire or sputter through the carb, is this a lean/rich problem? Just want some knowledge. Thanks for your help.

 

[99yam40]

Re: 2004 F90tlrb Fuel Problems?

When you "rap the carbs several times in a row ( by hand) they will backfire or sputter through the carb" are you moving the carb butterfies but not the TPS? I am not familier with your set up on that motor.The TPS is what gives the CDI unit the info so it can change timing according throttle opening and will not act right without it.
Did you readjusted all linkage and carbs acording to manual after you cleaned them

 

[501nmc]

Re: 2004 F90tlrb Fuel Problems?

Yes, I am just moving the butterflies. I adjusted the linkage as per the manual. My setup has 4 carbs that are attached together by a rail or snap on connection that attaches to all 4 carbs. The linkage only attaches to the bottom carb which is the slave or master carb. The TPS attaches to the linkage that goes to the bottom carb from the throttle cable. I can email you a picture from the manual if you like or a digital picture so you can see it. I took it out today and the idle was off. I noticed yesterday that the throttle cable had some slack in it and I adjusted it out. I will check it again to see if the throttle is returning to the stop on the linkage. If it doesn't come back, it throws the tps off. It has always idled great never any problems.

 

[501nmc]

Re: 2004 F90tlrb Fuel Problems?

Solved my problem about 2 months go, just an update. I replaced 2 jets(pilot) and two of the float valves. I adjusted the floats to what the solec manual specs are and the problem has gone away. I believe that the float adjustments were all that was wrong the whole time. Motor runs like a top, better than it did when I first bought it. Thank you for your help.