89 Merc. 45hp - WOT Loose RPMs

[brstock]

First the following link contains historical details related to what I 've done on this motor:

http://forums.iboats.com/showthread.php?t=415480&highlight=air+fuel+filter

I now have it running on the water but when I go to WOT it planes out then startes to loose RPMs. If I pump the ball again and get fuel into the filter it will again start to plane out then loose RPMs again. My guess is that I have an air leak between the tank and pump. Everything is new from tank to carbs and I've rebuilt the fuel pump. Carbs have been rebuilt and everything is new except the floats which seemed fine.

I'm going to get a new bulb, new fitting at the motor and use a new tank that I have but wanted to get input while that stuff comes in. Does this sound like an air leak? I'm still in the process of adjusting everything and it currently only gets to about 4000 rpms at WOT. I run out of throttle travel so I have a feeling that needs to be adjusted. Right now the carbs are sitting at 1.5 out. I can't seem to get the knack of adjusting them but will give it another try once I have this fuel delivery issue resolved. Where they sit doesn't seem to have any hesitation on a hole shot.

I'm making progress and learning on the way. The person I got this from was having problems with air in the lines from the oil injector. I don't have that on there now and I'm thinking they monkey'd around with the settings before they figured out there was an air leak.

 

[zorak]

Re: 89 Merc. 45hp - WOT Loose RPMs

It sounds like the fuel pump or one or both carbs need the float level checked.I know you have already done work on them both but... don't box yourself into thinking that there couldn't be an issue with either of the above.You could have done something incorrectly or there could be something else such as a piece of trash that became dislodged when you did all of the fuel system repairs.I would put my money on one carb being starved for fuel (trash in the needle valve or incorrect adjustment).One other thing, did you use hose clamps or panduit straps.The factory used straps but the base of them is curved and regular straps can also cause a leak

 

[brstock]

Re: 89 Merc. 45hp - WOT Loose RPMs

I used hose clamps on everything, not ruling out anything.

The reason I think it is an air leak is the fact that the fuel filter empties and fills with air. I've been though the carbs 3 times and cleaned them each time even though there wasn't anything in them that I could see. I don't know if I got the right fitting at the motor end of the fuel line, it is a quick connect and when I took it off on the water the plastic disk holding in the ball bearing pulled off (luckily the bearing fell into the boat not the water.) When pumping the bulb if I push in the connection the filter fills up with fuel easier than if I don't push it in which is why I think that is leaking air there.

Just trying to figure it out through the process of elimination. If I can get it running consistently at 1.5 turns out I'm going to find a mech. here in Cincinnati and have them adjust the carbs. I've tried to adjust them but as I turn in the screws I don't notice an increase in the RPMs. There is a slight increase but this is my first attempt at adjusting them and although people say you should see and increase in RPMs I'm still learning and figuring out how much of an increase I should see (50 rpms, 100 rpms, etc.)

I'll get it eventually and appreciate everyone's help.

 

[zorak]

Re: 89 Merc. 45hp - WOT Loose RPMs

The tank and motor fittings are different.Took me several tries to find the proper fitting.The main difference is the part that looks like a headphone plug is longer on the tank fitting vs the motor fitting which means that it probably isn't fully seating because the clip never engages the fitting.Its just sitting on there by friction alone.That could be your problem as i could easily see that causing a fuel starvation issue.

 

[brstock]

Re: 89 Merc. 45hp - WOT Loose RPMs

Ok, replaced the tank and line/ball and fittings and that resolved my issue loosing RPMs. I'm pretty sure it was the fitting at the motor not sealing correctly. I'll test the other parts one by one until I find the issue. I'm only getting about 4400 RPMs at WOT which gets to me to between 25 and 28 mph based on the speedo and the fish finder speedometer. I forgot to take my GPS but will next time. I'm not sure of the pitch of the prop, it isn't stamped on the outside so I'm going to have to take it off to look on the back. This is with two adults in the boat. I'm going to search for posts related to that. Thanks for everyone's help.