Portable tank vent ? Connector?

[BrianVT]

I have a metal 5 gal. tank that has a cap like a car's radiator and a quick connect fitting. When I have loosened the cap there can be a lot of pressure (or vacuum?) released. Is that normal? How are these tanks supposed to vent? Is it through the quick connect fitting?

I had cleaned the carbs. and replaced the diaphragms and float needles. I noticed the upper carb. is still dripping fuel. I took the carbs. off again and there was a lot of pressure pushing fuel out when I disconnected the fuel line from the carb. (I didn't think to release it before hand). I guess that means I don't have any air leaks.

I have the carbs. back on the bench but starting to wonder if I should move my attention to the fuel tank vent rather than tear the carbs. down again.

 

[GA_Boater]

I'm pretty sure most metal tanks have a physical vent - A knurled knob to open or close on the filler cap.

I think the smaller hole in the connector is for a guide pin so it doesn't twist.

 

[BrianVT]

No vent that I can tell. The cap is just like a car's radiator.

 

[GA_Boater]

No vent that I can tell. The cap is just like a car's radiator.

I think it is!

 

[BrianVT]

Are you saying that the cap is wrong for the tank?

 

[BrianVT]

I just noticed that the 2 small pins above the right pin release pressure from the tank when I press them in.
I guess maybe they aren't getting pushed in enough by the connector?

 

[BrianVT]

Bottom line...when I twist the tank cap there is usually pressure or vacuum released.
Would this be the cause of the engine to wanting to die above 1/4 throttle?
Should I replace the tank's quick connector or tear the carbs. down again or replace the fuel pump next?

 

[alldodge]

The older tanks are vented and the cap is where it vents. If its not venting then a vacuum will happen and starve fuel to the motor.

 

[roscoe]

I've got 2 of those OMC tanks as pictured above.
Circa 1984/1985.
Your cap is correct.
There is no vent in the cap.
The small pins on the fitting must be depressed by the fuel line connector.

Looks like your connector is a cheap aftermarket knock off.
The tab on the side of the connector is on the wrong side to depress the pins.

Here is an actual OMC connector, The square base is large enough to depress the pins.

 

[BrianVT]

Thanks for confirming the tank cap.
I confirmed that mine does depress the pins and does vent. I just had it in the water again. I loosened the cap just to rule that out. Still bogs/dies above 1/4 throttle. I had the carbs. apart again last night and didn’t find anything wrong. The floats were off just a bit so I adjusted them, fwiw. It idles great and the it revs as high as the fast idle goes. It just won’t rev. under way. I don’t even know what else to look at. Carbon clogged exhaust? Never had a lower end off before. It pumps water well but I guess I can throw some more $ into an impeller kit while I have it apart.
Any other ideas would be welcome

 

[roscoe]

You haven't told us what motor you are working on. ?
You told us you worked on the carbs.
But didn't mention the above 1/4 throttle issue until the 7th post in the thread.

Maybe you posted it in a different thread ?

So, what are you working on?
Is it a new to you motor?
New problem or did it just start acting up?

 

[BrianVT]

It’s a Classic 50 4 cyl. 2 carb. New to me. Won’t rev past 1/4 throttle. New plugs. New carb floats and needles. New diaphragms. 130 lbs. compression in the 3 cylinders I could test.
Starts, idles, and revs well with high idle but not in gear with main throttle.

 

[roscoe]

Most of acceleration/stalling issues are fixed with 3 procedures.

First, check the fuel flow to carbs, from the tank thru the fuel pump and then to the carbs.

Next, a thorough disassembling, cleaning, and adjusting of carbs, using new gaskets, compressed air and fine wires.

Last, perform a link 'n sync of the carbs and timing advance. Step by step following the detailed instructions in a service manual. There are instructions online, but nothing beats the details of a factory service manual for your specific motor. you can find a used manual on ebay most of the time.

 

[BrianVT]

Fuel flow seemed good when I forgot to depressurize before pulling the carb. hose and it flowed heavily until I disconnected from the tank.
I bought carb. kits. They looked very clean inside so I only replaced the floats, float needles, diaphragms, and gaskets. Jets were clean. I shot carb. cleaner where I could. Didn’t mess with any of the welch plugs as I fear I could do more harm than good.
I guess I’ll drop the bottom end next and hope for a clogged exhaust and do an impeller job while I have it apart. Can’t hurt.
How to rig a test for 3/8” spark jump?

 

[Poormansboating]

Did you change diaphragm in the fuel pump

 

[BrianVT]

Apparently the fuel pumps are in the carbs. so...yes?

 

[Poormansboating]

Sounds gas related issue to me. Are you running it on muffs or in a bucket

 

[Poormansboating]

If not gas related the linkages can cause alot of similar issues. Had a buddy that had issues with his and replaced alot of parts to only find that the linkages wasn't in sync right

 

[BrianVT]

Idles and revs fine with high idle lever with muffs. Won’t go past 1/4 throttle under way.

 

[roscoe]

How it revs on the muffs means nothing. There is no load on the engine, and no back pressure on the exhaust.

If your serial number was lower than A710280, pump would be in the carb, Your serial number is far above that, so you should have a separate fuel pump.

Look Here.

Classic 50 fuel pump?

Trying to figure out why this engine won’t rev. I suspect the fuel pump. But I don’t see one. Do these not have one or is it somehow located in the block under where the quick fuel connector comes into the lower cowl?

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