bad84z

My car seems to be running rich. It get a black residue on the inside where the blades and stuff are like a carbon build up or something. When I clean it with carb cleaner it runs great, you can really tell a difference, but I should have to clean my carb that often should I. How do I lean it out a little. I have an edelbrock 1407 750cfm carb. Any advice.

305sbc

iTrader: (3)

That's not from running rich, it's from PCV and EGR.

bad84z

My car is non computer controlled, and the pcv is less than a year old. I don't even think it has an egr being non computer controlled does it.

305sbc

iTrader: (3)

You sound very confused. I'd suggest doing a lot of learning up about what you've got before you think about rejetting your carburetor.
I think you'd know if you had EGR or not because you would see the valve. As far as I know a non-vortech RPM manifold doesn't have EGR.
You did say you have PCV though and that can make a mess of things as well. You can clean up your PCV a lot by running a fuel filter inline with the PCV.
If you have a high overlap cam, then reversion will be letting exhaust gas back up into your intake at idle. This has the same dirting up effect as EGR.

Rejetting the carb is simple to do, but it will have no effect on dirt build up on the carb. Since you spend most time driving on the primaries, then start with that side. A metering rod change is better to start out with than a jet change. To go leaner you look for a metering rod with the same power step (small end) that you have now and a bigger cruise step. This will lean down the primaries except at WOT.
Even before that you might try increasing your low RPM spark advance by using lighter springs or adjusting your vacuum advance. This will have the same effect as leaning the primaries.

The only way to get rid of cam overlap is to swap cams. You could reduce reversion at idle a little bit by raising idle speed but it won't completely cure the problem.

bad84z

I know it doesn't have an EGR, but yah, I am not a master at carbs. I definatly need to learn. But what you are saying is that the dirtying up the carb is pretty normal for me having a 480 lift comp cam. I did raise my idle to about 750 and that helped out alot at idle. Just wish I could find a good place in md to give me a carb tune and let me watch.

F-BIRD'88

305 has pretty well hit the nail on the head.

The carb may only be slightly rich.

The overlap of your .480" lift cam will reduce manifold vacuum at idle. You want to change the power step up springs that control the primary metering rods to compensate.

Use blue step up springs. (3" ) { orange is stock} change the metering rod from the stock 7147 to a leaner cruising 7347 rod.
this rod change will not affect the WOT calibration,, just the cruise.

The cam you have needs lots of initial advance at idle.
Give it as much as it wants.

Like 20deg initial. Once you determine how much initial advance it wants at idle you can recurve your distributor to obtain this while maintaining the same 32/36deg mechanical at High speed.

This involves limiting the travel of the mechanical advance .....

Just for grins: You may even want to try locking out the mechanical advance altogether and run 32/36deg at idle and 32/36 at high speed.
Its easy to do this on an HEI. Just remove the weights and springs and tiewrap the mechanism fully advanced. Then reset the ignition timing to 32/36 at idle w/ vac adv disconnected.
ten reconnect the vac adv.

other wise use moderatly ligher than stock advance springs in the distributor or a combo of one light and one med spring.
The super lightest springs are too unstable at idle.

Then use ported vacuum advance for efficient cruising.

Take 305s advice and install a common inline fuel filter in the PCV hose . This will stop or reduce any oil from traveling throu the PCV into the manifold.

All third gen Fbodys suffer from exessive under hood heat.

Edelbrock carbs tend to be sensitive to exessive under hood heat. { "Hot soak"}this heat makes the fuel vapourize-- too well. This results in fuel perculation, vapour lock overrich idle, and fuel odour while idleing. The way to reduce this is to isulate the carb from the manifold with a wooden carb spacer. Wood is a good heat insulator.
Even a thin wood carb spacer is better than nothing.
Edelbrock sells wooden carb spacers.

Hooking up a cold air induction for your carb will help too.

www.ramairbox.com

Recurving the distributor for more initial advance or locked advance should help your car accelerate too.
Just curious,,, have you gotten a timeslip on that car?

bad84z

Thanks for the response fbird. No I havn't gotten any time slips with it yet, but I would like to got to the track soon. I am going to install the inline filter on my pcv and see if that helps. As far as timing goes, I thought my calibrator on the block was wrong because it showed like 18, I set it down some, but it just didn't seem right, so I set it back up to where it was. I am going to have to look at the edelbrock chart to see which are pimaries and everything, the only springs I have looked at is the ones right on top of the carb that come out when you loosen the torq screws. Are these the ones you are talking about, or am I in the complete wrong area. I am installing a 3" harwood cowl hood and an open element filter on my car this weekend, do you think that will help with the heatsoak on the carb you were talking about???

F-BIRD'88

Yes the power step up springs are accessd from the top of the carb. Loosen the torqx screws and rotate the covers out of the way so the rod and pistons can pop up.

The stock spring is orange 5" either the blue or yellow
will be better.

Now that you have the hood clearance you can put a
wooden divided carb spacer to good use to help keep the carb cool.
Edelbrock sells different wooden carb spacers. The divided plenum one is right for the RPM intake.
If your wood tool friendly you can even build your self one.

The cool air hood will help too, no doubt.
You can even build a carb box to seal the carb to the hood when its closed.

Seems it likes 18 deg initial advance or so.
But the total advance will likely be too high with the typical stock timing curve in most distributors. They are typically set up for a stock motor. You want to limit the travel of the mechanical advance so you have 18/22 initial advance and 32/36 total. + 10/15 deg if vacuum advance at cruise.