89 Force 50 ... possible fuel vent issue?

[madhtr]

I am having an issue an 89 Force 50. about 20 mins into my run I experienced a rather sudden drop to quarter power at WOT issue. pumped the bulb, no dice. I Anchored, visually inspected fuel tank and the vent-cap. It was screwed open (counterclockwise to the stop) like I always did them. Then I read the small print on the cap that said 'Push to relieve pressure'. To my chagrin, I heard a whole lot of air being sucked into the tank when I pushed it WHILE it was screwed wide open, counterclockwise. I shook my head ruefully and thought OMG. The next time I take her out, I'm going to insure that there is ZERO vacuum in the tank, and see how that works. My initial thoughts are that possibly a 25 year old outboard is DESIGNED to work at zero vacuum? Is this a possibility? In any case, I can see no reason for a tank cap that maintains any vacuum at all. I'll post again after the next test float.

BTW The carb has been rebuilt and it has a new impeller. Back in the late 80s, I had a fuel tank that just had a simple zero pressure vent that worked fine with an old 7.5 hp outboard I ran on a 12ft aluminum john boat.

Here are the 'tech specs' on the cap ...
" ... Auto 'Self-Venting' pressure feature vents tank at 5 PSI (Min) when center popup vent is in open position"

Thanks!

<edit> I forgot to mention, I was anchored and unrunning for about 15 mins before I discovered the vacuum in the tank. after I released the vacuum, the motor started running normally again. but it was getting dark and I decided to recover before I could test further </edit>

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

Ok, I just performed a little test that I thought up (BTW, I have a new Moeller ultra-6 tank - plastic).

1) close the vent on the cap clockwise to stop
2) unscrew the entire fuel cap to insure airflow
3) STAND on the center of the tank to squash and compress it
4) while standing on the tank, screw the entire cap back on tight.
5) step off the fuel tank (unsquishing it) and listen for air (heard none, expect none)
6) open the vent on the cap counter-clockwise to stop and listen for air (heard none, EXPECTED some)
7) PUSH on the top of the vent (while in the full open counterclockwise position) and listen for air ...
Suprise ... the tank sucked air for a full 9 seconds until the vacuum was gone.

Vaccum on the tank with the vent in the open position confirmed.

 

[Jiggz]

Re: 89 Force 50 ... possible fuel vent issue?

That's not a good sign. If it was working perfectly before with the vent cap unscrewed (CCW) why would it not work now? What changed? check valve stuck?

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

That's not a good sign. If it was working perfectly before with the vent cap unscrewed (CCW) why would it not work now? What changed? check valve stuck?

thanx for the reply! ... I'm thinking an 'EPA regulation induced' design flaw. The 'self venting' fuel cap was slowly alowing the fuel pump to create a vacuum, even in the open position. Eventually the vacuum might have been too much for the fuel pump. When I pushed down on the vent (or just unscrewed and rescrewed the cap), the vacuum was released, and the motor ran again ... and might have stalled again after the vacuum built up again. I read that these new caps are the result of an EPA mandate in 2011. In any case, the tank definitely is maintaining a vacuum with the vent open (see my second post).

The cap appears to be actually designed so that only a certain PSI range will allow the cap to vent when its screwed all the way open. That range appears to be from a positive to a negative PSI. This was evidently mandated to keep too much gas vapor from entering the atmosphere for environmental reasons.

 

[jerryjerry05]

Re: 89 Force 50 ... possible fuel vent issue?

Never heard of the cap thingy???
Post a pic of the tank/cap?
Gotta go look at my tank.
I have a work tank from tempo.
Usually the fuel pump is so weak it can't suck with enough power to get the gas past a restriction.
Wonder why it suddenly started working?????

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

Thanx Jerry! here are pics of the cap:




Here is a link to a youtube video with what I hope is a better explanation.

Even if this turns out not to be my issue (or only a part of it), I still see no reason for an outboard fuel tank maintain any sort of vacuum with the cap vent open. Hopefully I'll get to test my theory on the river in a couople of days

 

[Jiggz]

Re: 89 Force 50 ... possible fuel vent issue?

My postable tanks have the same center vent screw. When the tank is not in use, it is screwed all the way in. When using the tank, I unscrew it half way. If I unscrew it out all the way it restricts venting or should I say it still allows venting but very restrictive. And depending on fuel consumption it can actually create a vacuum in the tank. Have you tried unscrewing it halfway?

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

My postable tanks have the same center vent screw. When the tank is not in use, it is screwed all the way in. When using the tank, I unscrew it half way. If I unscrew it out all the way it restricts venting or should I say it still allows venting but very restrictive. And depending on fuel consumption it can actually create a vacuum in the tank. Have you tried unscrewing it halfway?

Nope, havent tried that, I will, Thanks! However, the vaccum created by squasing the tank was not released by adjusting the valve from closed to wide open.

 

[jerryjerry05]

Re: 89 Force 50 ... possible fuel vent issue?

Looks like it's a vent while turning to open only.
Might have to open the cap a bit to vent???
Had trouble reading the cap upside down

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

Looks like it's a vent while turning to open only.
Might have to open the cap a bit to vent???
Had trouble reading the cap upside down

LOL sry bout the inverted pic

Yea, I'm going to try running on the river with the cap open hopefully tomorrow. If it fixes my ish, I will make an "adjustment" to the valve, heh

I'll let ya know how it goes!

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

Well, I wen out on the river today, left the fuel cap unscrewed, and it ran properly for about 40 mins instead of 15.

I wonder what this tells me? heh.

Also, I still barely get up on plane, and my top speed at WOT was 20mph. a good average was about 14-16.

Open to any suggestions, LOL

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

Well, time to quit blaming the EPA, heh (although I still think a portable tank that maintains a vaccum ain't right) ... Pulled the 'top' spark plug, and it looked like this:



pulled the bottom one, and it looked like this:



Black and oily is bad (AFIK) so I figure ignition issue on the top plug. I cleaned up both plugs, put them each back where they came from, and swapped the coils to see if the other cylinder would get a black, oily plug. went out and ran for about 30 mins, no 1/2T this time (My prop got foulded on someone's old jacket). But when I got home and checked the plugs, the top one was STILL black and oily. Next time, I'll swap the plugs, and see if it swaps the oil (mebbe a bad plug). If it comes back the same way, I think I can eliminate an ignition issue. That leaves me with the question, if the cylinder is getting good spark, why isnt it firing, and why is it black and oily? The only thing I've come up with so far is that mebbe it's getting flooded.

I'll keep uall posted

<edit>I did comfirm that each plug was sparking by the old pull it out and ground it to the block method ... Note to self: A pair of rubber gripped plyers ain't quite enough insulation, heh </edit>

 

[jerryjerry05]

Re: 89 Force 50 ... possible fuel vent issue?

Like the spark as it runs up the arm???
Do a comp test?

 

[madhtr]

Re: 89 Force 50 ... possible fuel vent issue?

Like the spark as it runs up the arm???
Do a comp test?

Yea, both cylinders were 120psi.

 

[foodfisher]

Re: 89 Force 50 ... possible fuel vent issue?

Bottom plug is too clean. Got water?

 

[emoney]

Re: 89 Force 50 ... possible fuel vent issue?

I got one of these new, post-2011, "pressurized portable fuel tanks" and they're a bit different for sure. I learned about it the hard way, of course, as the day I brought it back, she sat in the sun for about hour..ish (Which in Florida sun that equates to about 4 hours everywhere else) and that tank had swelled to almost twice it's size (exaggerating, but still). That did help me locate a leak in my connector (dealer used and OMC on the tank...sheesh) so I got a nice little puddle of gas that ran down the leg onto the driveway. Sure did release some serious fumes.