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Holley Street Avenger 670 won’t idle, runs very rich.


FBBO Gold Member
FBBO Gold Member
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2:32 PM
Jan 28, 2012
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Not on a Mopar but on a friends old Mustang 289 hi-po. I’ve had this carb apart 3 times now and we can’t get it to run. A mechanic tried his luck first on the carb but he left it in pretty bad shape and then I got to work on it. It won’t idle. It runs on the accelerator pump and on the main circuit given enough throttle. It looks like a steam engine running under throttle it puts out so much fuel smoke. Black, carbon-fouled gas is seeping out the left header flange. Plugs are wet with gas. Feels like it’s missing. I’ve cleaned, rodded out every passage, blown everything out, installed a complete new kit in it, adjusted everything, checked PV, checked for warpage, checked floats - nothing has worked so far. He has a pretty aggressive cam in it so I cracked the secondaries open a bit more so the primaries should sit about right on the transition slot. No help. Idle screws don’t seem to have much affect as it won’t idle at all. It’s clean as can be inside. For a couple days after the first time I cleaned it, it had a bunch of crap in it - some dried fuel deposits and some sort of red fuel residue that got in his fuel (?) - it actually ran right and idled, was smooth, and responsive. And then the next time he started it it was back to its possessed mayhem. New plugs, new points, new condenser, new cap/rotor, new fuel filter, new fuel pump, wires seem to be good, adjusted valves - just to eliminate those possibilities. Tried another Holley on it that he borrowed last weekend and it ran and idled perfect. He browsed the internet and found a lot of chatter that these carbs have a bad history and once they go bad a rebuild seldom helps. The Holley tech line says it must be pulling excess gas from somewhere - brilliant!

Anyone have any experience trying to get one of these Street Avengers running right? A Catholic priest is about all we can think of.
Also drained & flushed entire fuel system. Fuel bowl levels set just below sight hole. Fuel dripping off of boosters when throttle held open. After putting rebuild kit in the fuel off the boosters was finer drops but still not a fine spray. All the air bleeds are wide open - rodded out with wire, sprayed out, blown out - all pass air just fine.
What is the fuel pump pressure to the carburetor? Maybe too high and pushing fuel past the seats? If so, that will need to be resolved. I would also try lowering the floats settings to see what effect it has on the engine operation.
That’s actually one thing I haven’t checked. But we haven’t seen any sign of high pressure. It seems Holleys are not quite as finicky about fuel pressure as Carters but I’ll take a gage over next time to check it. I’ve pulled the bowl screws out right after running and it’s below the bottom. No fuel seems to be entering except the accelerator pump and the boosters. Not sure what’s going on with the idle/transition circuit - hard to believe it’s so rich it kills the engine and can’t be leaned down with the mixture screws - so I assume it’s not flowing. But fuel path from bowl to metering plate to carb body and bleeds are all open.
Have you considered this?
I've run the Avenger 670 on a 4.6 (281 cubic inch) DOHC w carb adapter quite a few times and never rich right out the box. I usually get the Holley refurbished ones. Have done about 8 of those conversions, all w refurbed carbs. There's a reason they were sent back to Holley n refurbed.
Carefully remove carb & place in a box. Place box on the shelf marked 'junk'.

Get an Edel 600 AFB or AVS.

Carters [ & Edel ] carbs are NOT finicky about fuel pressure, will handle up to 10 psi despite much BS that says otherwise.