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Unread 04-16-2013, 07:01 AM   #16
Matt1981CJ7
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A bypass filter has one nipple on the inlet side, which connects to the pump. It has two nipples on the outlet side. The middle nipple connects to the carb, the other returns to the fuel tank.

A bypass filter acts like a pressure regulator, and they were stock on all 304s, I believe. If you running a standard 2-nipple filter (1 inlet, 1 outlet), then it's likely you are getting too much fuel pressure to the carb.

You can take the guess work out of the fuel delivery by sticking a simple gauge somewhere between the filter and carb.

Hope this helps,

Matt

fuelgauge.jpg  
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Unread 04-16-2013, 07:04 AM   #17
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Quote:
Originally Posted by sean112280 View Post
I had problems with a Holley carb as well. My fix was a switch to an edelbrock and my SBC is running great now and it's easy to tune the carb now
There is no carb easier to tune than a Holley.


OP, you can install an inline fuel pressure regulator, pretty easy job.
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Unread 04-16-2013, 08:34 AM   #18
86cj74.2L
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Back in the day I thought a Holley would handle a carter hi pressure fuel pump. It didn't.

Try the bypass filter Matt shown if you still have a return line.

Have you tried lowering the float height a little with it off just to get it running. You can even pull float bowl and hold upside down to get it close.

Edit: go to a auto parts store or speed shop and get the clear sight plugs to put in place of the solid plug.

Post what power valve it came with.
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Unread 04-16-2013, 10:08 AM   #19
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Quote:
Originally Posted by Matt1981CJ7 View Post
From my reading on various carbs, Holleys are notorious for blowing power valves. That's their one fault that all the Rochester guys like to point to.

Fishhead, are you running a bypass fuel filter?

Matt
Matt,

This is taken from the Holley web site...

THE TRUTH ABOUT POWER VALVES USED WITH HOLLEY CARBURETORS

There still seems to be a lot of misconception about
Holley carburetors blowing power valves. Nothing
could be further from the truth. Holley performance
carburetors built since 1992 have utilized a power
valve check system that effectively eliminated this
infrequent problem. Consisting of a spring, brass
seat and check ball, the check ball system is 100%
effective protecting the power valve diaphragm
from damage due to engine backfire.

The power valve check ball is designed to be
normally open but quickly seals to close off the
internal vacuum passage when a backfire occurs.
Once closed, the check valve interrupts the pressure
wave generated by the backfire, thus protecting the
power valve diaphragm. There is no way that the
power valve’s diaphragm can rupture due to an
engine backfire!
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Unread 04-16-2013, 11:19 AM   #20
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Quote:
Originally Posted by Matt1981CJ7
A bypass filter has one nipple on the inlet side, which connects to the pump. It has two nipples on the outlet side. The middle nipple connects to the carb, the other returns to the fuel tank.

A bypass filter acts like a pressure regulator, and they were stock on all 304s, I believe. If you running a standard 2-nipple filter (1 inlet, 1 outlet), then it's likely you are getting too much fuel pressure to the carb.

You can take the guess work out of the fuel delivery by sticking a simple gauge somewhere between the filter and carb.

Hope this helps,

Matt
If the OP's intermediate CJ is like mine, it didn't come stock with a fuel filter with a return line.

Matt, do you know the pressure difference with and without the return line connected?

I have a Holley Truck Avenger 470 that seemed to run great on my first 70 mile test run a few days ago...no return fuel line.
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Unread 04-16-2013, 11:28 AM   #21
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He got a brand new carb. He needs to set float height and go from there.
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Unread 04-16-2013, 11:37 AM   #22
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Quote:
Originally Posted by 86cj74.2L
He got a brand new carb. He needs to set float height and go from there.
Yes
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Unread 04-16-2013, 11:37 AM   #23
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Steve,

Thanks, apparently the power valve problem was large enough for Holley to address it with a design change.

OleBlue, I suspect the pressure difference, with or without the return line, depends on the model and condition of the fuel pump. On my 360, a new OEM style mechanical pump produces 6-8 psi at the carb at idle without the return. With the return, the pressure is 3-4 psi at idle.

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Unread 04-20-2013, 06:38 PM   #24
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Finally had some time to tinker today. I swung by autozone and purchased a bypass filter. After bending up some tubing I was able to hook up the secondary port on the outlet side of the fuel filter to the return lines running back to the gas tank. I also ran an inline fuel PSI gauge just prior to entry into the carb. According to the gauge it's pushing 4.5-5 PSI.

I was hoping that this would solve by the problem by dropping the PSI. Nope, gas is still coming out. I think the issue is with the float valve adjustment but I don't have room to lower it much lower:



When I pull the inspection port screw off the side of the carburetor gas comes out, so it's obvious that the float level is too high. Like I posted earlier, I've aready pulled the brass adjustment piece out of the carb and cleaned it with carb cleaner and compressed air (even though it appeared clean when I pulled it). Since I'm out of adjustment on the float bowl adjustment I don't know where to go next.

Your thoughts?
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Unread 04-20-2013, 06:52 PM   #25
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Take the bowl off again. Turn it upside down. Loosen the float adjuster nut. Turn the float adjusted screw until the flat part of the float is parallel with the bottom surface of the bowl. Then reinstall the bowl and give it a try. Can't remember if you mentioned this but there should be an inlet screen where your fuel line attaches to the bowl. Make sure its clean.

Then if you get it running you can do the bowl adjustment from the outside. The engine must be hot to do this.
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Unread 04-20-2013, 09:28 PM   #26
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Take the bowl off again. Turn it upside down. Loosen the float adjuster nut. Turn the float adjusted screw until the flat part of the float is parallel with the bottom surface of the bowl. Then reinstall the bowl and give it a try. Can't remember if you mentioned this but there should be an inlet screen where your fuel line attaches to the bowl. Make sure its clean.

Then if you get it running you can do the bowl adjustment from the outside. The engine must be hot to do this.
I pulled the bowl off. It seemed like the bowl was stuck in the low posistion (on the "top" as I held the bowl inverted, but would be stuck in the low position/bottom of the bowl when the bowl was installed on the carb). With very light pressure the bowl became "unstuck" and seemed to move freely after that. Would this cause the issue of fuel continually pumping through and forcing it's way out of the top vent?

Although hard to see in the picture, the adjustment needle was set such that the float was slightly above parallel with the bottom lip of the inverted bowl assembly:



While I had everything apart I pulled the jets out and sprayed them with carb cleaner and compressed air. No issues to report there; everything was clean. While I have it apart to this stage, is there anything else I should clean/do?



Of note, the inside of the bowl had some kind of coating that was bubbled, cracked, and peeling inside of it:





What the hell is that stuff? In my mind that's just begging for crap to get inside the combustion chamber.

I also have the float bowl off my 4412-3 carb (a Holley model 2300 500 CFM variant) sitting on the bench. From what I'm reading, this is the correct initial setting, right? It appears to be identically sized. Perhaps more importantly it doesn't have whatever weird liner sprayed inside it. Will this float bowl work on the 7448 carb without causing any issues?

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Unread 04-20-2013, 09:43 PM   #27
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YES! The float hanging in the lowest condition is almost certainly your problem. If its stuck in that position, the valve stays wide open and your bowl overfills and comes out the top vent. You need to determine what's causing that float to stick. It should move freely every time you push it with the slightest force. And the valve should move with it. As to the coating, its hard to say from the pics but it could be the result of sitting for a long time with ethanol gas in it. Carb cleaner should take that out. Soak it in a pan for an hour and then spray, brush, blow it out. After you do that make sure all the holes, needle valves and the power valve are free and clear. And yes you should take that second plate off. If you that buildup in the bowl it will inside of that too. Use same procedure to clean it up. Make sure the last thing you do is clean out all the various holes and passageways. I use a welding tip cleaner. Let us know how you make out.
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Unread 04-20-2013, 10:12 PM   #28
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One thing to add: While the float is out, submerge it in water and look for bubbles. If it bubbles its leaking and won't float. Replace it. Otherwise you should be ok. I can't say if you second bowl will fit the other carb but it sure looks similar. If everything is identical give it a try.
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Unread 04-21-2013, 05:36 AM   #29
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To me it looks like the painting/coating that's on the outside of carb.

Those fuel bowls should be interchangeable. Only possible diff would be how fuel line gets attached.

Ethanol has never caused any problems on any carb I got.

That carb is brand new, correct?
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Unread 04-21-2013, 03:58 PM   #30
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Originally Posted by 86cj74.2L View Post
To me it looks like the painting/coating that's on the outside of carb.

Those fuel bowls should be interchangeable. Only possible diff would be how fuel line gets attached.

Ethanol has never caused any problems on any carb I got.

That carb is brand new, correct?
I agree, it looks like the coating is coming off, as oposed to varnish/contaminants from fuel sitting around.

I bought the carb off Craigslist and the guy tapdanced around and implied that it was only six months old by saying in both emails and the ad itself "I only had it for six months". It's clearly much older than that.

I opted to install the fuel bowl from my other Holley carb since it didn't have the funky coating.

It's still having issues. When I went to start it up it ran really rough. I blipped the throttle and it seemed to run a little healthier, but was idling really high. However, a few seconds later gas was venting out the top again.

I'm gettting REALLY frustrated here. I definitely had to tell myself that throwing the wrench against the wall of the garage wouldn't solve any problems and stepped out for a minute to cool off.

Next step?
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