carburetor issues

[djburton]

Subject...the other big block, 460, Holley Brawler 750 carb, floats correct. At 750, 800 rpm idle, engine runs good but super rich. Pump gas deal, don't know the specs of the cam but fairly lopey, 8 inches vacuum at idle. The ported vacuum at idle was manifold vacuum, obviously drawing fuel from the mains. I opened the secondaries  to back off the primaries enough to zero out the ported. Still stinks up the place. The mixture screws have little to no effect. Power valve is 6.5. I was thinking of going to 4.5 but I understand it has no effect at idle. Jets are 72 primary, 82 secondary. Any help will be appreciated!

[My427stang]

I would likely do the following as the first steps

- If it backfired or if you see fuel looking down the venturi, I'd pull the PV and check it for a bad gasket, loose, or bad PV
- Check all the idle air bleeds and spray them or pin them to make sure they are clear
- Adjust the a/f to 3/4 from bottom to start for 4 corner idle, 1 1/8 from bottom for 2 corner and start there

If you haven't got a good run on it since balancing the throttle plates though, remember it could have dumped a lot of gas into the engine and may need a good run to clean out the exhaust stink

[djburton]

Thanks, Ross! I understand that it did backfire a few times when they were trying to start it. It is a new carb but have found machining trash in the bleeds before so definitely could be an issue. Haven't driven it yet as we're sorting out a couple other issues with the car.

[Drew Pojedinec]

If mixture has no effect you have an internal leak.

Fill carb with fuel and set it on a table. Look for leaks over time

[djburton]

Drew, been sitting for four days and no obvious leaks, fuel wise. I'll take it apart to see if anything looks wrong. Like I said, runs good, idles good, just gassy at idle, way more than acceptable in my opinion.

[1964Fastback]

What is the timing at idle?  If you can bump it up some, it would allow the throttle plates to be closed more, which might make the mixture screws more responsive.

Pat

[Stangman]

So you don’t have an AFR sensor?. Someone said bump timing a little so you can lower primaries. Do yo actually see black smoke coming out exhaust. Had a weird problem on a buddies car, it stunk and was burning eyes and it was to lean. I think Ross said start from scratch transfer slots and other basics so you know we’re you are. Get timing were it’s suppossed to be and add like 3 or 4 degrees.

[djburton]

Timing is 16, 17 advanced at idle, 36 total all in at 2900. MSD distributor set at factory specs for now. Haven't driven the car yet to see how that works. Haven't really noticed any black smoke but definitely eye watering. I could possibly advance timing some but would it be drivable on pump gas? Might have to go from ported to manifold vacuum advance and do some work on the total.

[1964Fastback]

Timing at 16-17 at idle sounds pretty good to me.  I was hoping you had it at 8-10, where you had room to increase it some.

On rich vs. lean, with it warmed up and choke fully open (and ideally with a vacuum gauge and tach hooked up so you can monitor), you could cup your hands over the choke housing some and see if it helps or hurts the idle, indicating which direction you need to go.

Pat

[cjshaker]

I don't know about others, and I imagine Drew has tons of experience with this, and maybe his reaction is different, but an obnoxious smell and burning eyes has always meant very lean to me. Rich has never caused my eyes to water, just smells bad, but not as noxious as lean.

Slowly closing the choke plate will definitely tell you if you're lean, by smoothing out when it reaches that fine line. It doesn't cure or figure out the problem of the idle jets not working, it's just an indicator of which direction it needs/wants.

[Drew Pojedinec]

I agree that normally lean does that Doug.
But a misfire is a misfire and 9:1 can make the same symptoms.

If he finds mixture does nothing tho that can’t be lean is my thinking.
If totally closed a lean mix will kill just about any engine.

[djburton]

Update...Definitely rich, I guess my eyes were watering too much to see the black smoke before. Removed the carb, took it apart, installed a 4.5 power valve, new gaskets. The 6.5 valve that was in it was still good. The carb is basically new and I didn't find any evidence of any drilling or any other mods. I noticed the primary and secondary transfer slots were fully exposed but was the only way to get it to idle. I adjusted the throttle plates so the transfer slots were right, drilled a 3/32 hole in all 4 throttle plates and stuck it back on. Runs a lot leaner than before but not close to good. Still little response from the mixture screws. They're sitting at 3/4 turn now. I'm at a loss! I guess I will keep drilling to get more air as it seemed to be in the right direction.  Thanks!!

[1964Fastback]

On my 3x2 setup (390 with bigish cam for that displacement), I couldn't get it to idle properly either.  One time it was better and I could adjust the idle with the screws, and then I discovered I'd left a vacuum cap off a 3/32" port.    So I capped the port and drilled a 1/16" hole in both primary carb throttle plates.  This is slightly less area, but I didn't want to go too big.  It worked out well for me.  I can get a good idle with 13-14 inches of vacuum and 850 RPM.  A side benefit is the neighbor lady that spends the summer working in her yard isn't complaining about the smell every time I take the Galaxie out.

Worst case I figure I can replace the throttle plates.

Pat

[Diogenes]

Just throwing this out there, but have you considered possible weak ignition?