My Lord, Not the Carburetor Again !!!

[ski4funn]

Help me out here. My '77 240 OMC GM 350 with an Edelbrock 1413 four bbl. carb is acting up again. Took the boat out this morning (air temp 49 degree -brrr) and put it in the water to see if it did the same as yesterday (which it did). Ran the boat about 1 hour with absolutely no problems. Then I stopped in the middle of the lake and let it idle for about 45 seconds. Punched the throttle and you have never heard such a racket... It seems the carb. is getting flooded and just sputter and chugs along - slowly picking up speed but still sputtering. After letting it sit idle for about 4 minutes running, it clears up to a certain degree. Now I didn't start having this problem until after I replaced the fuel pump....Gas is fairly fresh and clean w/new filter, timing is good... What am I missing?? Spark plugs, wires, rotor, cap, points all replace in spring and I haven't run but about 40 hours since then... The engine and carb is about 2 years old. Could it be the carb going bad??? Any advise taken...

 

[BarryCF]

Taking a stab at it, fuel inlet valve leaking. OK when you are running from higher fuel use, then floods from to much fuel when you idle down. Heat may be playing a factor. The fuel inlet valve may be OK when cold, not so good when hot.

 

[fc3]

It seems the carb. is getting flooded and just sputter and chugs along - slowly picking up speed but still sputtering.


Now I didn't start having this problem until after I replaced the fuel pump

Correct fuel pump? Check the pressure. If the pressure is too high, fuel will force the float valve off the seat, flooding the bowl and therefore the engine.

Best regards.
Frank

 

[sprink56]

Correct fuel pump? Check the pressure. If the pressure is too high, fuel will force the float valve off the seat, flooding the bowl and therefore the engine.

Best regards.
Frank

This is a possibility but my money is on a worn out needle valve and seat. I think your carb has 2...get a kit and re-build it. It's no big deal really.:thumbsup:

 

[KRB64]

Like fc3 said, the problems started after the new pump so maybe the pump is wrong pressure?

If not the pump then I'd lean (no pun intended) towards a bad float needle/seat like sprink56. Maybe the parts are worn and the old pump was weak enough to not force fuel by but a fresh pump found the next weakest link? Something is not shutting the fuel off and allowing it to flood. Not a good idea in an enclosed space...

You're sure its flooding and not a hesitation like a bad accelerator pump right? Does it die?

 

[tdappleman]

The fuel pressure is easy to check and can certainly cause the problems you are seeing. I just went through this on my Weber 9600 which is almost the exact same as the 1409 on my other engine. Edelbrocks like the fuel pressure to be between 5 and 5.5 psi - any more and it can force fuel past the valve seats. The interesting thing on mine is when I did my rebuild the replacement valve and seat were not sealing and I went back to the originals.

One thing to keep in mind is to make sure the floats are adjusted properly - 7/16" is the appropriate float level and 15/16" is the appropriate float drop. One thing to try is with the bowl off the carb - and the valve seats closed by the floats - blow through the fuel inlet - if you hear any air coming through then you know the valve seats are not sealing.

 

[BarryCF]

Frank makes a good point about the fuel pump pressure. Since the problem started after changing the pump, it is a likely culprit. Check your pressure. The weight of the float is what closes the valve. Over pressure can lift the needle valve up, allowing to much fuel to enter.

 

[BonBini]

Just workin with your symtoms description: Boat fires up and runs ok for an hour. It idles ok in the middle of lake for 45 secs or so. You punch it and it makes a hel of a racket, sputtering and chugging along. You idle it for 4 mins or so and then it runs ok.

Dont sound to me like the carb is flooding via over filling the float bowl. Otherwise it would be spilling fuel over the top vents at idle and you would have to keep the throttle opened up just to keep it running. Also black smoke would be pouring from the transom area. This is how fires start.

Does sound like it may be backfiring up through the carb when you open up the secondaries. This is how fires start too. Be carefull and prepared. I dont know a lot about Edlebrocks, but I do know Hollys, Quadrajets and FoMoCos. On a Quad; if the choke pull of isn't right, the secondaries will come in too quick at too low an rpm a the stumbling and backfireing will begin. If you can run it and watch whats going on, you may see what the problem is. ...Ron

 

[ski4funn]

Thanks for all the advise gents. Where do I purchase a fuel pressure gauge and where do I install - between the fuel pump and carb?? Secondly, if the pressure is too high, is there an in-line regulator that I can purchase to bring it back down to normal operating pressure or do I have to adjust the carb to handle the current pressure??
Thanks again for advise. All taken into consideration for investigation... I thought I was headed towards spending $300 - $500 for a new carb. Maybe the current one is ok, just too much fuel.. The boat doesn't seem like it's backfired just sputtering heavy...

 

[tdappleman]

You can get a vacuum/fuel pressure gauge at almost any autoparts store. It will most likely come with a couple of adapters to allow you to unhook the fuel line and plug it into the gauge. Not sure if you have an electric pump - if electric turn the key on and check the gauge. If you have a mechanical pump then you will need to crank the engine over to get the pressure to build.

If your pressure is too high then you can install a fuel pressure regulator. Not sure if you need a specific marine part or not - but Edelbrock (and others) sells an adjustable one which may make you have to change some fuel lines around to get it installed.

http://www.jegs.com/i/Edelbrock/350/8190/10002/-1

 

[83searay]

I think its the change of the weather, but like I do is rebuild the carb every year, its easy... do it yourself if you own a boat you should be able to maintain it by yourself that's me.

 

[ski4funn]

Well, I finally got my new gasket for the carb and reinstalled. I have also got a fuel pressure gauge for the fuel line. I am running @ 5 - 5.5 psi on fuel. Like I had explained, the fuel pump is brand new and the carb is only 2 years old (probally on has 30-40 hrs on it). Runs like a dream cold and also runs good for the first hour. Then when you back off the throttle after running at about 1/2 throttle for an hours or so, and come to an idle, push the throttle down, it starts choking out as explained at the beginning... What would be my next option?? Looks like the needles may be sticking??

 

[BonBini]

If it were me: I would physically look down the throat of the carb when she's running ok and when she's acting up. This may identify the problem as being fuel delivery or not.

A interesting story: One of my first rebuilds on a small block in the late 70's. I used the wrong intake gaskets. Too much exhaust crossed over through the intake manifold and would boil the fuel over in the Quadra jet. Ran super cold, when warmed up would flood like a btch. ...Ron

 

[sprink56]

Well, I finally got my new gasket for the carb and reinstalled. I have also got a fuel pressure gauge for the fuel line. I am running @ 5 - 5.5 psi on fuel. Like I had explained, the fuel pump is brand new and the carb is only 2 years old (probally on has 30-40 hrs on it). Runs like a dream cold and also runs good for the first hour. Then when you back off the throttle after running at about 1/2 throttle for an hours or so, and come to an idle, push the throttle down, it starts choking out as explained at the beginning... What would be my next option?? Looks like the needles may be sticking??

Sounds to me like something is cutting off fuel supply in the main fuel circuit. What you are describing is the classic symptom for a bad accelerator pump. Since it works fine when it's cold...then the problem is not the accelerator pump.

Here are some possibilities:

• The fuel is "perculating" . This is a long shot but might be getting heated due to a heat source (like a coolant hose) touching the fuel line and heating it up.
• The gasket that controls the flow of exhaust gasses through a passage beneath the carburetor may be compromised allowing too much heat to accumulate beneath the carb, this would cause it to heat up. Fell the carb when yo have the problem. It should not be hot...maybe just warm to the touch.
• There may be trash or gum moving around the idle/main circuit of the carb stopping up a passage to the accelerator pump.
• Most likely...water/moisture in the fuel or you have ethanol fuel that has broken down over time that is causing this problem.

This ethanol fuel deal is causing a lot of problems all over the country in the marine industry. From what I read, it can start separating in as soon as 30 days.

I hope this helps you in your diagnosis. This type of problem is very frustrating to sort out.

 

[KRB64]

That is frustrating. Is it at least consistant? Fine when cold, then starts misbehaving when warm?

If so then the warmed up part is a clue. Something changes to affect performance. I can't see it being fuel quality, unless warmed ethanol acts differently. Nor the accel pump or float.