85 HP Force fuel pump question! Rebuilt engine.

[3DCNCIN]

Hi all,
Long time reader, first time poster.
I love all the info everyone donates. Much thanks.

I have an 85 hp force that is a 1986 on a 16 ft bayliner. I have just rebuilt it boring it .040 over. Most everything looked good on the first run out. After Running a good while I goosed it and it seemed very sluggish. after looking into it, the top 2 cylinders run leaner than the bottom judging from the piston and the plugs appearence. The carbs look clean. The odd thing is when I put the new fuel pump kit in, the new diaphram looked thicker than the old one. The old one looked like rubber and was about .016" thick. The new one looked more like a gasket mat'l and was .040" thick. I got a second one and it was the same. My question is, has anybody else ordered this part and noticed the same thing? The 3rd cylinder is the strongest and I notice an immediate response when adjusting the idle screw. The top 2 idle screws take longer to make an impact on engine performance. So thats why I feel that the fuel pump is not putting out the required amount of fuel to pump to the top carbs. I plan on hooking a pressure gauge to it to look at fuel pressure, but I'm unsure of how much I should even have. Any thoughts are greatly appreciated. If there are any other thoughts, please let me know.
Thanks, in advance,
Brian

 

[Frank Acampora]

Re: 85 HP Force fuel pump question! Rebuilt engine.

If I remember correctly, it should put out about 2 psi at idle and up to 6 at full throttle--but don't quote me. I never did like the system for feeding multiple carbs, and someday when I get A Round Tuit I am going to fabricate a manifold with individual feed to each carb and a nice little electric pump.

I have never seen a thick diaphragm and that one just doesn't sound right. However, the pump uses crankcase vacuum and pressure pulses and if the diaphragm is as flexibile as the original, the thickness should not matter. Check to see that all three button valves in the pump are opening and closing correctly ( you do have the old style pump, not the new style square mercury pump, don't you?) Be sure the 3 inch long hose is not kinked or leaking, cutting off pulses to one stage of the pump. Check that the hole from the pump body through the bypass cover is not clogged with carbon or aluminum particles (you did melt a piston and that's why you rebuilt, isn't it?)
If you have the new style square pump be sure the gasket behind the pump is on correctly and not closing off the hole sealed with the O ring. Also, be sure the O ring is in place. Be sure the internal rubber flap valves are not leaking.

 

[MWBROWN]

Re: 85 HP Force fuel pump question! Rebuilt engine.

On my 1984, 85 HP, I put a new pump diaphram in a couple months ago.
The new one was thicker, which I atributed it to the old one being cracked and dried out. (it was quite old). Any how, the slugish holeshot went away after changing the diaphram.
Point is, I think, that the diaphram is not the problem. Do what Frank suggests.

Mike

 

[3DCNCIN]

Re: 85 HP Force fuel pump question! Rebuilt engine.

Hi guys, thanks for the replys. The reason I rebuilt it was there was some odd scoring on the Top piston and the rings were frozen on 2 of the cylinders. So I tryed the sea foam trick without much luck and then lost spark on the top cylinder. So I went to replace the Top piston and re hone it and found that the top was .030 over and the other 2 were standard. So this with no spark just talked me into rebuilding it. The lack of spark was due to the stator. Thanks for the psi ratings. I'll make a rig up to check this at different points up the carbs. Yes, it is the old style fuel pump. I only had it since last year, but it seemed to run better last year than after the rebuild. I apperciate the help you guys are lending.

 

[3DCNCIN]

Re: 85 HP Force fuel pump question! Rebuilt engine.

Just wanted to post an update and also had another question. I took this boat out again after finding what I thought was the problem. When idling in the yard, the motor definitely had some issues. Only top carb adjustment would make any changes. I then rechecked the primer bulb, it would squeeze down fairly slowly. So I plugged the fuel line at the carbs, and I could still squeeze it down fairly slowly. I then plugged the line before the fuel pump, at which point it was firm. I proceeded to recheck the freshly rebuilt fuel pump, Out of curiosity I guess. The "diapraghm" was split on both stages of the pump. That diaphragm was gasket mat'l. I was trusting the manufacturer knew what they were doing. Luckily I had another used pump around just to try out. It made a huge difference just idlilng. It was idling at 800 rpm, with the pump change it idled at 1400 rpm without any other changes. I guess the bottom 2 cylinders were completely flooding out from the tears in the pump. So then I decided to go try it on the lake again after it has sat for 2 years from disgust.

I had a few problems at first, nothing major, just shaking the rust off of my launching skills I guess. I babied the motor at first being it's still freshly rebuilt and all. After a while I wanted to see what rpm it would turn wide open to see if the motor sounded healthy. It would turn 4800 rpm and had some decent spunk out of the hole. So i thought I was the greatest outboard guru around for all of a minute or two. I then let my buddy take it for a drive being he never drove a boat before. He hammered it, got it on plane and the backed down to about 4000 rpm or so just keeping it on plane. It was running like a top when he looked at me and said "I'm losin it". I said push the throttle back down, here he allready tried this. It wound down to about 2500 rpm at full throttle. It was slowly winding down. we pulled to the side with it running terribly at which point it stalled. I first changed plugs, and it would still barely start. The plugs looked good when pulled though. All plugs had some black on them around the electrode, but all looked the same. When I could get it too start it would idle for 5 to 10 seconds and pop and shut off. I tried pumping the primer bulb and all that. Nothing helped. I was just happy to get it on the trailer, it was the sunday after the 4th of july and it was pretty busy. All the linkages look right. I didn't check spark at the time, I know I currently have sparks on all 3 cylinders but this is after it cooled down. Just looking for any ideas anyone might have. The impeller is still good. the fuel pump looks good still also. The carbs are clean as I checked them yet again. The compression is 125 on all cyls. I think it's a spark issue when hot, my buddy is telling me it's lack of fuel. He's a gearhead himself. Has anybody else run into anything similar to this? Any help would be greatly appreciated.