that's cylinder 5

cylinder 6

Forgot to take #4's pic

That one was all tan with a little bit of greying just a little bit

All other spark plugs were all tan and looked good
This was with smaller jets ---62 ... Last night I put 65 back in

Regarding idle speed, if you have an aftermarket cam, the cam manufacturer may provide some idle speed recommendations.  With a more aggressive cam, vacuum and the engine's willingness to continue to run often drops off a cliff as you reduce idle speed.  With modern oil issues with flat tappet cams, a higher idle tends to improve spash lubrication to the cam lobes.  This may mean that with your torque converter the car will require some effort to keep it still at a stop light but preserving the cam and keeping your mixture optimized are usually more important.  It could be that what you have is OK but it is worth investigating.

And after re-reading your post - keep in mind that you can have a rich or lean bog.  I have found that with today's gas, it is hard to read plugs and if you idle for any period of time before you shut off, you are probably only seeing the idle mixture and you are not reading main jetting.

Last, for a lower RPM bog, you may also be able to improve this range by opening up the idle screws 1/8 or 1/4 turn on both sides.  You are balancing idle circuits and main circuits in this region so slight adjustments to one or both can help.  If you have to go too rich on idle to get past the bog (if it is indeed a lean bog) then you need to go to larger mains and back off on the idle, for example.

Hello Gaba, Robby 13 here. It sounds like you might have to big a carb. I've been through this. I have a 67 390 gt, and it came with a 600 Holley. I don't know what type of driving you do, it if you race etc., but for regular driving I would go smaller. Holley has a nice feature on their website, its a carb selector. You enter things like rpm operating range, vacuum secondary, or mechanical etc. They are spot on! I put a 600 on my 289 and had the same symptoms your explaining. Remember, with a carb, bigger is not always better! Check out the Holley site, very informative. Good luck.

The 600 can work - the throttle response may not be as snappy as a smaller carb but it is not so big that it can't work.  Remember that your best economy will come with close to the best A/F ratio so smaller jets can work against you.  If there is not stumble when you bumped up to the 65's you are on the right track.  The secondary spring discussion also works both ways.  If the spring is too stiff it can prevent or limit the opening of the secondaries leaving some horsepower bottled up.  Once you get it running well there is little you will have to do to the carb in the future.  If you decide to go for a new one, consider Quick Fuel - even their basic model has good tuning options, a better way to adjust the secondaries and a rear metering plate that uses jets instead of a fixed plate.  Not much more than a Holley.

It's not just about the size of the carb, but about how it's set up that matters.

A smaller carb often has better response, and atomization which can make for better economy - but not always.  If you are seriously under-carbed, your engine can run into another set of problems including but not limited to bad high-end performance.

The old Autolite 4100s (with the correct venturii) are just about the best 4V carb you could get back in the day for street use and some mild fun.  Some companies offer carbs that work as well, or better, now though.

If you want to drag race, your carburetor has to be set up in an entirely different way, since full-throttle performance is the thing that matters most.  Everything in a full-tilt racing carb is pretty much backward from what you'd choose for street use.

It's all a compromise, unless you go with fuel injection, pretty much.

Last edited by Technomancer (5/09/2014 3:19 PM)

This is from the holley website.

TUNING:

 

First, make some notes about carburetor performance as it is in stock condition. Does the engine falter or stumble at wide-open
throttle, anywhere in the rpm range? Can the secondary opening point be distinctly felt?

 

If there are no flat spots or stumbles, a lighter secondary spring should be installed. Try the accelerations again and if there are
still no flat spots, try a lighter spring yet. When a flat spot is felt, go back up to the next stiffer spring. If the carburetor bogs, out
of the box, note when it bogs. If it is an instantaneous off idle bog, the accelerator pump may be the real problem. A secondary
bog will usually occur in the 2000 to 3000 rpm range. If this is the case, install a heavier diaphragm spring.

 

The first thing many people do when they first disassemble the diaphragm assembly is throw out the small metal ball that is
contained in the vacuum passage in the lower housing, without really knowing why it is there. At first glance, it looks as if it
would block the flow of air, but a close inspection will reveal a small groove in the seat under the ball. This groove acts as a
restriction, so that the secondaries open in a slow controlled manner.

 

Removal of the ball will allow the secondaries to more or less flop open and may cause a bog, so unless your driving is
restricted to the track, leave the ball in place.

 

Some of the newer carburetors replace the ball and seat with a pressed-in brass restriction. Drilling out this restriction will have
the same effect as removing the ball.

 

In general, heavy cars require stiffer secondary diaphragm springs than light cars. Air cleaner configuration and restriction plays
an important part in spring selection, so be sure to use your air cleaner when evaluating your vehicle’s performance after each
change. An installation with an open element air cleaner will require a weaker spring than one with a restrictive snorkel-type air
cleaner.

 

Vacuum secondaries are designed to open when the engine is under load. “Winging” the throttle with the transmission in neutral
should result in no secondary movement. If they do open in neutral, the engine will almost surely bog under load. Do not clip a
spring in an effort to make a spring weaker, so the secondaries will open sooner. Strange as it seems, clipping springs actually
increases spring rate. While the spring load as installed will be lower, the spring’s resistance to change in height will be greater,
which means that the secondaries will start to open sooner, but will reach wide-open position later. Regardless of what you hear
do NOT leave the diaphragm spring completely out. Although the link on the left side of the carburetor will force the secondaries
to close, the diaphragm spring ensures complete return to idle giving the engine a consistent idle speed.

 

If the lightest spring is installed and the secondaries still do not open when all parts are functioning properly, the carburetor is
most likely too big for the engine and forcing the secondaries open by mechanical means will probably slow the car down.
 

You never did say what rpm range you'll be living in-that has a lot do with it. Keep us posted.

Wow tons of knowledge here .. I have been driving it in rain a lot and seeing the throttle response and stuff, I can say this it has been much crisper . Yes the 390 cfm mentioned above is something it will look into soon. But as far as the money and time I have , I have to keep the wife happy.. That's worth a million dollars lol . :D

I haven't made any changes after the 65 jets and the vaccum setting

Fuel needle is moving slower hahahah. It's no joke. I might be getting to a better A/F mixture

As far as timing. I got the total timing set to 36 mechanically, and then drive it without vaccum. It pinged so without to timing light (deliberately) this time I went with the white out method, and backed if a degree or so at a time till it got well in high rpm high load conditions with no ping. Now with the vaccum back on, I am "shaping" the vaccum advance curve by loosening the vaccum advance spring in the vaccum advance diaphram... And seeing where it'll hit that ping state in load and then I'll back it off. I am half way or may be two turns looser than half way now. That said. I do think after diligent work , ignition timing and curve is coming under control. thanks to people's advice here obviously. I do have a better understanding too

So.. That said now power valve. I'll check my vaccum again. Power valve was good when I was rejetting .. I checked it wasn't leaking, and holley on their website said if you close your idle screws and car doesn't die , means power valve is blown as the fuel is being supplied still. I checked all that, for sure the power valve is closed on idle no question about that. As far as the power valve vaccum rating. Yes if I have 11-11.5Hg vaccum on idle in gear with AC on ideling at 650rpm..  I need a 5.5 rather than a 6.5 (half) .. 6.5 will open sooner.

Ill look for a power valve after I recheck my vaccum. But just letting y'all know, I am heading in the right direction. Yes!!!! It's a bit bigger carb, but I am happy with it right now. (more like can't afford to spend a million bucks on it now .. Get it :D )

But please do not think , that your advice is not useful or absorbed. Please know that I am thankful for your responses and keep it coming

Last edited by Gaba (5/13/2014 7:50 PM)