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post #1 of (permalink) Old 04-03-2008, 08:13 PM Thread Starter
 
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Carburetor flooding problem

Hello all;

I've been kicking myself for a week now and I wonder if any of you has had this problem. First the vehicle: 1979 CJ-7 258 T-150 . I am having great difficulty trying to get my CJ to run lean enough. I rebuilt the original Carter carb after replacing the fuel tank, fill tubes, fuel sending unit, fuel lines, and all rubber hoses. I finally started the jeep only to watch fuel feeding out of the primary jets. No adjustment would properly stop the excessive fuel and I mistakenly thought my problem lay in the carb itself. Based on the overwhelming opinion on this site I found and ordered a Ford MC1200 card and installed that one. I found the Jeep runs better but I can tell it is still flooding and I need to hold the air blade open to lean it out enough to keep it running. This is the same problem I had with the Carter so I figured maybe the fuel return line was clogged in the short metal section just after the fuel filter ( the only orig. piece of fuel hose ) so I blew air throught the line and found it is not clogged. I now suspect the fuel pump is pushing too much fuel but I have to find my gauge to measure fuel pressure. The fuel pump was replaced prior to my purchase of the Jeep. Have any of you had a similar problem and if so what did you do to correct the problem?

Thanks for taking the time to read this post.

Dave
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post #2 of (permalink) Old 04-03-2008, 08:50 PM
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First, excessive pressure is almost an impossibility. The pump works by spring pressure. With time it can get weaker, but it's not likely to get stronger. There isn't too much pressure, even if the return line is completely blocked - the carb should be able to handle full pump pressure with no problems.

What caught my interest is your statement "I need to hold the air blade open to lean it out enough to keep it running." My guess is that you're talking about the choke plate, which should be open except during a cold start and the first few minutes of operation. If it doesn't open fully by itself in three to five minutes, it's a problem. On older Jeeps the choke is opened by air heated in a tube that passes through the exhaust manifold into a fitting in the choke housing. Later Jeeps used an electric heating element that is turned on when the engine starts. I have no idea about when they changed over. In either case, the heat warms a bi-metal coil that opens the choke as it warms.

If you have neither the wires or the heat tube the choke will never open and so the engine will be rich all the time. To fix it you can either put it back to stock, with wiring or tube, or you can remove the automatic choke and go to an old fashioned manual choke with a knob on the dash.

If it's not the choke, there might be a problem with the carb itself. Did you rebuild it before installation? What did it come off of? What size are the venturis?

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Last edited by Jim_Lou; 04-03-2008 at 08:53 PM.
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post #3 of (permalink) Old 04-03-2008, 09:09 PM Thread Starter
 
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Couldn't remember choke plate.... killing myself. I am unfortunately in a hurry to get the jeep running and therefore did not rebuild the carb as I wanted to prior to installation. In NJ you have to inspect your vehicle within 2 weeks of registration which gives me another 2 days. I figured I'd get to rebuilding when it was a little less pressing. I realize the choke plate will stay closed until the coil warms up, I have not hooked up the choke yet ( electronic ) and maybe I should hook up a temporary lead to eliminate that as a possibility. With the choke plate wide open I should not see fuel coming out of the upper venturi and that is what led me to believe I may have excessive pressure. I am going to take a trip outside and see if I can determine venturi size and also hook up the choke to see if that leans me out at all.

Thanks,
Dave
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post #4 of (permalink) Old 04-03-2008, 09:30 PM Thread Starter
 
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Well it seems as if I was sold a 520cfm carb, I imagine this is not helping any as I am over-carbing the motor.

I may have to resell this unit and purchase another if I cannot correct this issue I suppose. Not there yet though.

Thanks,
Dave
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post #5 of (permalink) Old 04-04-2008, 07:45 PM
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You want the one with the 1.08" venturis. It will be stsamped on the side somewhere.

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post #6 of (permalink) Old 04-04-2008, 10:02 PM Thread Starter
 
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Yes ,thanks.. I'll be picking through junkyards and this one will be rebuilt prior to installation.
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post #7 of (permalink) Old 04-05-2008, 02:36 AM
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"""""With the choke plate wide open I should not see fuel coming out of the upper venturi and that is what led me to believe I may have excessive pressure."""""

Sounds normal to me. If fuel didn't come out the dump tubes (when running) it wouldn't run!
It shouldn't when stopped, but when running that's how it gets fuel in the engine. You saw it on the last carb, on this one, and will see it on the next 1000 carbs you try too.

When the choke blade is closed it pulls even more fuel out (creates even more vacuum in the venturi to pull it out - normal!) When the engine is cold it needs that extra fuel to run better. Once warm, it doesn't need it any longer.

The faster the engine runs, it also pulls more out - normal. The total volume of air is greater, so to maintain the right A/F ratio is needs more fuel.

Sounds like it sure needs that choke blade wired open - unless you get the choke working properly.

BTW - Using a carb that's too big, like you did, it should still run fine, it just won't get quite as good a mileage (venturi velocity is slower, mixing isn't as good) and it won't "feel" quite as "crispy" a throttle response. But it will run smooth and work fine throughout the entire RPM range.

Wire that blade open or get the choke working right. Easy way - use an electric choke - wire it to the ignition switch - not the coil.

Last edited by RRich; 04-05-2008 at 02:47 AM.
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post #8 of (permalink) Old 04-06-2008, 09:40 AM Thread Starter
 
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RRich: Thank you for chiming in but with all due respect, the idle circuit in a carb feeds the carb at the throttle plates, not the main venturi just under the choke plate. I agree with you regarding the too-large carb still working fine but being less crisp except I have not been able to get it running properly at low idle and maybe lean enough which makes me wonder about the health of the carb. The float seems fine and the needle seems to be shutting the fuel off properly but I now have to wonder if my problems may involve other issues so my next step will be to take compression readings from the motor to see if I have an underlying problem.

Thanks..

Dave
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post #9 of (permalink) Old 04-06-2008, 10:40 AM
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Somewhat true - the majority of the fuel gets in at the base, but some comes through the dump tubes normally. Have a look at any carb while running! At sub idle speeds, like 300 RPM, there's not enough airflow to pull it from the dump tubes, so it's like you said.
Remember the float level is just a teeny bit below the tubes, so it doesn't take much venturi airflow to get the toilet effect working.

Did you get that choke blade wired open? If not, no matter what else you do, it's going to be too rich.

But then, How do you know it's rich?

2 different type carbs in a row doing the same thing?

Wondering - if your old carb had been flooding over and put lots of fuel in the crankcase, the PCV Valve may be pulling the fumes from the oil. That could be the source of the extra fuel.
Try pulling out the PCV Valve - leave it connected to the hose so it sucks fresh air instead of crankcase air. It should not make an appreciable difference in the way it idles. Don't just plug or pinch it off - the carb is counting on clean fairly fresh air coming in through the valve.

And - make sure there's a vent where clean fresh air can get into the crankcase, fresh air needs to circulate through the crankcase to keep it clean.

If you see a big improvement, simply change the oil and filter.

Compression - not likely it's affecting it - but - have a close look for what's called blowback.
Hold your hand or a piece of white paper - like notebook paper - over the carb top, about an inch above it - not restricting it - and rev it several times. And/or in a darkened area shine a strong narrow beamed flashlight across the top of the carb while reving it.

What you are looking for is tiny droplets or a mist above the carb. That indicates a leaking intake valve, or an exhaust valve not opening enough - like a worn cam lobe, bad lifter or rocker etc.

Usually a compression test will miss it since the compression test is at cranking speed!
It may or may not be severe enough to cause a rough running engine, but sure plays hell with how the carb works - it drives it nuts! The air is actually blowing UPWARDS in pulses (blowback.)

And of course you have disconnected the lines to and from the charcoal cannister? Sometimes the cannister gets full and causes problems. You said you replaced the hoses. The new hose may be sucking fuel out of it where the old one was leaking and wasn't purging the cannister.

Let us know.
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post #10 of (permalink) Old 04-06-2008, 07:45 PM Thread Starter
 
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Well I got sick of playing with the new carb and started thinking about where I could have gone wrong with the old carb. I checked the adjustment of the main needle assembly and vacuum piston and decided it was possible it was not set to the proper height which would have allowed fuel to come out of the main venturi. I also checked to be sure the idle pickup tubes were clear ( i drilled them with a #61 bit just to be sure..... I reinstalled and started the Jeep back up, seems to be running better but will not idle well at 700rpm. It has good power and I have no doubt it will run well down the road.

When I mentioned that I had replaced all hoses, I have not yet installed a charcoal canister yet. The previous owner had removed the air pump as well as the charcoal canister and bracket. I have been busy putting the Jeep back into reasonable shape. It hadn't been driven in 2 years and hadn't been legally driven in over 6 years. They left a number of important items out including the passenger side seat belt retractor. The Carter is much better but is running its best yet with both idle adjustment screws adjusted all the way in... I'll have to determine if the main jets or needles will require replacement. I have adjusted them as best as I know how. The chassis manual has also not enlightened me as to how better to adjust the problem out. I have made progress though.

I decided the Motorcraft had to go because there was no vacuum port for my vacuum advance and no port for my pcv. I will eventually get the charcoal canister back in but I will first need to install new screws in the bulkhead as the old ones were broken off.

I see no evidence of blowback.. on the contrary once the throttle is opened up a bit it has gobbs of power and still has decent vacuum. I'm going to test this carb on the road this week and take the Jeep back to the exhaust shop, they never properly seated the flange at the manifold and it is leaking there. Considering what I paid them It should be stainless.

Thanks
Dave
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