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Old 12-04-2006, 05:10 PM
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edelbrock carb trouble

I have a 1407 edelbrock 750 carb that I cant get to idle. I can run the idle mixture screws all the way in or take them out and it makes little difference. I can turn them all the way in and umplug the manafold port and the car will rev up just a little. Im running 15" of vac and Im running the 7.5" springs. Ive even tried every spring the jet kit has to offer. I also went down 1 and 2 jet sizes and tried every rod to just to see if I could make it better or worse. still nothing. I took the carb apart and cleaned it and even checked the floats and the needle and seats. All are good, no leaks, no vaccume leaks either. got me kinda stumped. with the 113 jets and 7347 rods. It revs great with awesome power. it just fluds at idle. anyone got any suggestions?
I also have a 1405 edelbrock 600 that has a bad bog I cant seem to get out of it. When the secondaries open it bogs just a sec and picks up no matter what RPM im at or what temp the engine is. it does just like a cold engine.
Thanks for the help.

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Old 12-04-2006, 08:01 PM
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Just guesses, but the 1407 sounds like a clogged jet. Take the air horn off and clean any passages you can get to and see if things change. Pull the idle jets out completely and squirt some carb cleaner in there.

The 1405 sounds like an accelerator pump thats on the wrong hole, or not providing enough squirt for the secondaries. In that case, less can be more. If you the rod further out on the accelerator pump, it will move less, saving some travel for when the secondaries open.
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Old 12-04-2006, 08:22 PM
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on the 1407 I took it all the way apart and soaked the whole thing in carb dip and blew compressed air through every jet, airhorn, crack and crevice to clean it out, but it didnt make any difference. I even checked to see if the floats had a leak or needed adjusting. nothing seems to be owrking. i was wondering if there is something Im not taking apart to clean in the metering system. there has to be something im missing. I took everything apart that was held in place by a screw and cleaned it.
on the 1405 I also set the accelerator pump on all three settings. believe it or not it actually does better with the smaller shot of fuel. but im afraid of jeting smaller because i dont want to run it lean. would it help to richen the secondaries? I didnt think on edelbrock you could accuratly jet the secondaries without having it on a dyno. as far as reading my plugs they look great. any other advice? would use a holley but these were freebies. plus i dont really know where to start on a holley. I can get one to run but i havent perfected it yet.
thanks for the help
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Old 12-04-2006, 09:04 PM
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What size engine do you have that 750 on? I think that your jets are way too big if its a sbc350. You said that the smaller the pump-shot the better...lean out your primaries. Better yet if its a 350, take your jets and metering rods out of the 600 and put them in the 750. Use the base calibration for the 600 and go from there. It is possible to actually run too rich and you will loose power.

As far as your bog with the 600, Im tuning with Innovate Motorsports wideband air fuel meter and I have a perfect stoich mixture in drive at idle, my WOT is 12.5-12.8 and cruise is as lean as 15.5 afr... sounds goood right? I have the same bog you describe and Im supercharged... its only there at 5-7 pounds of boost, more boost and the bog disappears. I have a theory that it has something to do with the air valve in the secondaries and when I get some time Im going to weigh the valve and take an ounce off at a time until the bog disapears. Ive heard that if you take the valve out completely you will bog because of a temp. lean condition that is caused by not having a shot of fuel into the secondaries... however if weight is trimmed it shouldn't uncover the secondaries too soon. A few people Ive talked to have done this modification with success...

I believe you have no control over your idle because your jets are too big, jet down the primaries and leave the secondaries alone for the time being. Try different rod combos as well to lean it out. When you get it so that you have some control over your idle mixture, hook up a vacuum gauge since you don't have a wide band and adjust the mixture screws to achieve the highest vacuum reading. If you lean it out too much two things will happen you'll get a lean backfire or you wont be able to accelerate past a certain point. Lean is bad and never good, however its not like your going to leave it lean, you wont hurt much at all. If you detonate, let out of the throttle immediately and pull over when safe and rejet or use a different rod. Work on just the primaries, adjust the pump shot to the middle hole and leave it there, once you get the primaries right then play with the pump-shot and last your secondaries.

This is rather lengthy, but hope it helps...

Regards,
-J
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Old 12-04-2006, 09:13 PM
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Check your fuel pressure. I had to high presure and it was acting the same way. That was my problem. Maybe it's yours too.

John
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Old 12-04-2006, 09:45 PM
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Projectjohn has a good point. Check your float level as well, its detailed on edelbrocks website if you lost your manual.

-J
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Old 12-04-2006, 10:05 PM
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on the 1407 when I went down to a 107 jet 7352 rod it started popping at 4500RPM. It may be fuel pressure. Im running the holley 7lb electric fuel pump. But I thought that was the recomended fuel pressure for an edelbrock. one thing I noticed about the 750 over the 600. the 750 doesnt have any hesitation at all. it just floods at idle.
the engine is a vortech 355 with a 276/282 comp hyd roller with a 10" 2400RPM stall in an 86 trans-am.
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Old 12-04-2006, 10:20 PM
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Did you try a richer (thinner) rod with that jet? Im running a .086 jet in my primaries with I think the 65/52 rod, orange spring and .098 jet in the secondaries and a 28 accel pump cluster. I can get a lean backfire with a .092 jet and their next to thickest rod. It has to do with the area of the jet and rod, so it doesn't exactly mean that what you tried is the lean point as far as jetting is concerned. It takes some time to figure things out especially doing it blind. You may be surprised at how much power you can make by leaning out the carb and as a bonus, better mpg. Yes... check your fuel pressure...and float level.
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Old 12-05-2006, 05:02 AM
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Check to see if any fuel is spraying/dripping from the primary boosters...There should be no fuel coming out of the boosters at idle. Like projectjohn already mentioned, check your fuel pressure. I have an Edelbrock 1405 that would drip fuel out of the boosters at idle. Fuel pressure was over six pounds, closer to seven...I believe Edelbrock instructions call for 5 to 6 psi max fuel pressure.

Hope this helps,

Steve
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Old 12-05-2006, 04:12 PM
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thanks for the help. I guess ill tinker with the carbs some more and see what i can get out of em.
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Old 12-05-2006, 04:46 PM
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RE Edelbrocg carb trouble

Hi, this is deno. install a new Holley 650 carb, and you might have to lower the jets by two #s. I have a Edelbrock 750 for sale because it was running lean. When I installed the Holley I had no problems. Is this a 350 engine ? Thanks deno---
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Old 12-05-2006, 05:08 PM
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Quote:
Originally Posted by Slimpikins
on the 1407 when I went down to a 107 jet 7352 rod it started popping at 4500RPM. It may be fuel pressure. Im running the holley 7lb electric fuel pump. But I thought that was the recomended fuel pressure for an edelbrock. one thing I noticed about the 750 over the 600. the 750 doesnt have any hesitation at all. it just floods at idle.
the engine is a vortech 355 with a 276/282 comp hyd roller with a 10" 2400RPM stall in an 86 trans-am.
the 1407 will alway flood at idle the carb is too rich for a smallblock from my experience it ran great but the 600 had better takeoff. your 1405 id move the accelerater pump rod down to the bottom hole. as far as your fuel pressure should be 6-7 psi and id use a mechanical pump i dont know on electric pumps
to get the carburetor to idle with the cam you have, drill air holes in the venturi's on the end that goes up when open, only on you primary's with a very small drill bit
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Old 12-06-2006, 09:59 AM
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You guy's need to read our manuals closer. Jet's, floats, needles, springs, secondary air valves, pump shot's, non of whick effec the idle circuit.

Bump up the ign. timing and lower the idle screw. the transfer slot aren't working properly.
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