89 Force 50 Missing In Midrange

[AGrayEngineering]

I know its long but it gives the whole story :

Background: I bought the boat in Feb of 2009, replaced plugs, new gas and it has run fire for 50 hours and though I hate to admit it last weekend I ran the boat out of gas.

Then yesterday with 2 full tanks I take it out for an afternoon of wakeboarding with some friends, I back her into the water, fire up the motor pick them up at the dock and we?re off, after a few runs wakeboarding I hear the motor sputtering in the midrange with an obvious power loss. I swim back to the boat and try it myself. Low range is fine, midrange it misses and sputters and once it gets to high range its fine. So as I work my way back to the dock I try a few things to start to diagnos the problem, pumping primer bulb doesn?t do anything so I don?t think its lack of fuel due to a fuel pump issue. Swapping to gas can 2 helped a little but not enough to cure the problem completely. At the boat ramp I pulled the fuel filter screen ? completely clean, I pull the carb off check the bowl ? completely clean. I reassembled it and tried again, this time it?s defiantly better then before with very little missing but still something isn?t adding up. Good enough to keep going we wakeboard for another hour or so with almost no issues at all, after running the gas can 2 down I switch back to gas can 1 and again some sputtering occurs.

My first instinct is that I picked up some junk when I ran it out of gas and its blocking one of the jets, though if this were the case it should have still been a problem with the second gas can. Next I?d blame the gas itself, but I got both cans filled on the same day so the gas should be the same.

I don?t really know where to go from here, my plan for this afternoon is to take the carb off, and clean out all the passageways, clean the fuel pump and fuel system back to the tank, empty both tanks and get new gas.


Let me know what you think, we had a day on the lake planed for tomorrow so hopefully I can fix it tonight.

Thank You

 

[john from md]

Re: 89 Force 50 Missing In Midrange

You really need to start from scratch when troubleshooting. You are assuming that running out of gas caused the problem. That may or may not be the case. Start checking the basics, timing, spark, fuel flow, fuel vent, etc.

Let us know.

John

 

[AGrayEngineering]

Re: 89 Force 50 Missing In Midrange

Will do, hopefully I can take a look at it tonight, and test it tomorrow.

 

[puddle jumper]

Re: 89 Force 50 Missing In Midrange

As John said you need to start with the basics. It sounds like you may be picking up air in the #1 fuel tank causing your engine to lean out.

 

[AGrayEngineering]

Re: 89 Force 50 Missing In Midrange

Saturday ? Mixed Results
http://forums.iboats.com/images/smilies/confused.gif
I started by removing and completely cleaning the carb, I tested the fuel pump by cranking the motor and it seems to be flowing a satisfactory amount of fuel, certainly enough to keep the bowl full. I cleaned the fuel filter screen and drained the entire fuel system. I visually checked the spark plugs for spark and both produced a good even spark every time. I also visually checked the reed valves and electrical connections. I then filled both tanks with new gas and proper 50:1 oil mix and headed to the lake. Starting with my number 1 tank (the one I though brought on the problem before) the boat fired right up and proceeded to work fine for at least 1.5 hours. In that 1.5 hours we started and stopped a hand full of times as well as run the motor through all rpm ranges with no issues. After running the number 1 tank empty, I switched to the number 2 tank and the motor started to miss again in the midrange. I first tried to pump the primer bulb to make sure the carb was getting fuel, and the bulb was hard as it is when the bowl is full I then pulled the cover to see if there was anything I could see, and the only thing I noticed was that very time the motor would sputter or miss the carb would stop atomizing the fuel and there would be a droplet of fuel entering the throat of the carb. I head back to the dock and as we do the problem seems to get worse. Before it would only sputter and miss in the midrange and by the time we got halfway to the dock I could only keep it at an idle or it would start acting up. When I got it home I pulled the plugs again, they were a little dirty but well within functioning range. I again visually checked the spark and it was also still good. As you guys had mentioned I can?t rule anything out just yet my plan for this week is to get a compression tester and check the compression, as well as trouble shoot the entire electrical system with the instructions in my force shop manual.

I really appreciate everyone?s time and suggestions. As a man who has rebuild motorcycles, automatic transmissions, and built my own buggy. I hate the though of taking her to the marina.

Again Thank You.

 

[john from md]

Re: 89 Force 50 Missing In Midrange

Here is another thing to check if possible. I don't know about 50hp engines but the larger Force engines have a fuel recirculation system. This recirculates unused fuel back to the crankase so that the engine doesn't load up. In this system, one fitting, usually under the lower carb, has a small orfice that can get clogged. I opened mine up to a number 60 drill and it stopped getting clogged. If this system is not working properly, your engine will run rough, usually at the lower speeds and you will have an increased fuel burn. Check it out.

John

You might

 

[AGrayEngineering]

Re: 90 Force 50 Missing In Midrange

Re: 90 Force 50 Missing In Midrange

Not that it makes that much of a diffidence but I was looking back through my notes and found that my motor is a 1990 not an 89. Though it doesn't look like the parts change much between those years.

 

[puddle jumper]

Re: 89 Force 50 Missing In Midrange

Just a thought could your fuel tank vent be not venting on the tank that the engine is acting up on. It just sound odd that one tank work good and the other has problems.

 

[AGrayEngineering]

Re: 89 Force 50 Missing In Midrange

I'm going to check the fuel tank vents on my next test trip. Though I don't think its a tank issue because it has happened with both of my tanks on different days.

 

[AGrayEngineering]

Re: 89 Force 50 Missing In Midrange

Update:

Last night I did some more diagnostic testing. I first looked for the fuel recirculation system which my motor does have, though its not the same as the 2 pictures in my Force manual, go figure. I also checked the compression and got readings of #1 Cyl = 141psi and #2 Cyl = 140psi. Probably best news I?ve had yet. I also used inline spark testers on to check spark and found something interesting, when I crank it over the #1 wire shows a constant light where as the #2 wire flashes. To try to eliminate any differences in my two testers I switched them around and the problem stayed with the #2 wire. I then swapped the output from the CDI box and the retested, this time I got constant light on #2 and flashing on #1 which leads me to believe that both coils are good, and it?s the CDI box or the pickup sensor. Today I?m going to retest it as well as try to run the motor and disconnect one plug at a time to see if the problem will show itself under real conditions. I will also be running through the test procedures listed to test the CDI box and pickup sensor.

 

[puddle jumper]

Re: 89 Force 50 Missing In Midrange

Keep us posted as you sound like you may be onto something.

 

[AGrayEngineering]

Re: 89 Force 50 Missing In Midrange

Update:

I received my new CDI pack last night. Was worth the 5 day wait, only cost $162.50 from Outboardparts.com where as the dealer wanted $450 for the same thing. Plus Don (owner) at Outboardparts.com was really helpful with tech advice. So after installing it I retested with the spark testers and got some results, though they were the opposite of what I would have expected.

Pre-Fix: #1 wire produced a constant light and #2 wire would flash. At first I dismissed it as the #1 cylinder was firing fast enough to keep the bulb lit constantly & #2 was bad.

Post-Fix: #1 & #2 wires produced a consistent flash. Motor seemed to run well through all rpm ranges.

Though I can?t its fixed until I get her out on the water and test it under load later in the week, however it looks good so far.

I?ll let everyone know how it goes after the testing.

Thanks again for everyone?s help.

 

[AGrayEngineering]

Re: 89 Force 50 Missing In Midrange

Final Update (Hopefully):

I took her out last night for full shakedown and everything went great, no missing, sputtering or anything. As a matter of fact it sounds better then it ever has.

Thanks again for everyone's help.

See ya on the water - Andy